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Logo of nihpaAbout Author manuscriptsSubmit a manuscriptHHS Public Access; Author Manuscript; Accepted for publication in peer reviewed journal;
 
BioDrugs. Author manuscript; available in PMC 2010 August 2.
Published in final edited form as:
PMCID: PMC2913436
NIHMSID: NIHMS220542

Immunotherapy for Cervical Cancer: Research Status and Clinical Potential

Abstract

The high-risk types of human papillomavirus (HPV) have been found to be associated with most cervical cancers and play an essential role in the pathogenesis of the disease. Despite recent advances in preventive HPV vaccine development, such preventive vaccines are unlikely to reduce the prevalence of HPV infections within the next few years, due to their cost and limited availability in developing countries. Furthermore, preventive HPV vaccines may not be capable of treating established HPV infections and HPV-associated lesions, which account for high morbidity and mortality worldwide. Thus, it is important to develop therapeutic HPV vaccines for the control of existing HPV infection and associated malignancies. Therapeutic vaccines are quite different from preventive vaccines in that they require the generation of cell-mediated immunity, particularly T cell-mediated immunity, instead of the generation of neutralizing antibodies. The HPV-encoded early proteins, E6 and E7 oncoproteins, form ideal targets for therapeutic HPV vaccines since they are consistently expressed in HPV-associated cervical cancer and its precursor lesions and thus play crucial roles in the generation and maintenance of HPV-associated disease. Our review will cover the various therapeutic HPV vaccines for cervical cancer, including live vector-based, peptide or protein-based, nucleic acid-based, and cell-based vaccines targeting the HPV E6 and/or E7 antigens. Furthermore, we will review the studies using therapeutic HPV vaccines in combination with other therapeutic modalities and review the latest clinical trials on therapeutic HPV vaccines.

Keywords: HPV, therapeutic vaccine, HPV E6, HPV E7, cervical cancer, clinical trials

INTRODUCTION

Cervical cancer is the second most common cause of cancer in women worldwide, with approximately 510,000 new cases and 288,000 deaths reported annually (1). The high-risk types of human papillomavirus (HPV) have been found to be associated with the majority of cervical cancers and its precursor lesions (2). Two high-risk types, HPV-16 and 18, account for up to 75% of all cervical cancers. The identification of HPV as the etiological factor for cervical cancer provides an opportunity to control cervical cancer through vaccination against HPV. In order to develop effective therapeutic vaccines, it is essential to have a thorough understanding of the HPV biology and its role in the pathogenesis of cervical cancer.

HPV is a non-enveloped, double-stranded, circular DNA virus with unidirectional transcription. Its genome encodes six to seven early proteins (E1, E2, E4, E5, E6, E7 and E8), depending on the type of HPV, and two late (structural) proteins (L1, L2). The life cycle of HPV is closely associated with keratinocyte maturation. In order to establish an infection, the virus needs to infect the basal epithelial cells, which are capable of active replication and differentiation. As the keratinocytes undergo differentiation, the early gene products are expressed, and interact with cellular proteins to regulate viral DNA replication. In the terminally differentiated superficial cells, the late proteins are expressed and then assemble to form the structural components of the viral capsid. In some cases, the viral DNA is integrated into the host genome. The integration of viral DNA into the host genome often results in the deletion of several early (E2, E4, and E5) and late genes (L1 and L2), and is thought to be required for the transformation of epithelial cells by HPV. The two well-known HPV-encoded oncoproteins, E6 and E7, bind and complex with p53 and retinoblastoma (pRb) respectively. Since E2 is a transcriptional repressor of E6 and E7, the loss of E2 leads to upregulation of E6 and E7, thus contributing to malignant transformation (35). Through interaction with p53 and retinoblastoma (Rb) respectively, the uncontrolled expression of E6 and E7 may cause disruption of cell cycle regulation and lead to genomic instability (for review, see (6)).

For the prevention of HPV infection, it is necessary to elicit an antibody response that neutralizes HPV particles prior to their entry to epithelial cells. The L1 protein on the viral capsid represents an ideal target for neutralizing antibody generation, and therefore the development of preventive vaccines. It has been shown that expression of the recombinant major capsid protein L1 in various cell types led to the generation of virus-like particles (VLPs) that were morphologically and immunologically similar to native virions (79). Vaccination with HPV L1 VLPs has been shown to induce high titers of neutralizing antibodies in animal models and in humans (for review, see (10)). The newly licensed HPV preventive vaccines, Gardasil and Cervarix, represent a groundbreaking achievement in HPV vaccine development. Gardasil is a quadrivalent L1 virus-like particle (VLP) recombinant vaccine derived from HPV types 6, 11, 16, and 18, while Cervarix is an L1 VLP vaccine derived from HPV types 16 and 18. These vaccines generally offer type-restricted protection against cervical lesions associated with the specific types of HPV included in the vaccine, but also has some partial cross protection against other closely related types of HPV (1113). Since HPV-16 and 18 account for nearly 75% of all cervical cancers, Gardasil and Cervarix may protect up to 80% of all cervical cancers due to their cross-protection against closely related types such as HPV-31 and 45.

Despite the success of preventive HPV vaccines, its limited availability to developing countries, where there is a high prevalence of cervical cancer, may undermine the efforts made to reduce the incidence of the disease on a global scale. The high cost and the need for refrigeration of the currently available HPV vaccines may preclude the usage of these preventive HPV vaccines in the developing countries. Since most of the cervical cancers occur in the developing countries, we may not be able to see a significant difference in incidence and prevalence of cervical cancer worldwide in a short period (14). Another important issue in the control of cervical cancer is the treatment of established HPV infections and HPV-associated diseases. There is currently a significant burden of HPV-associated lesions worldwide, and existing preventive HPV vaccines, such as Gardasil and Cervarix, do not generate therapeutic effects against established HPV infection (15). Therefore, there is an urgent need to develop therapeutic HPV vaccines for the control of existing HPV infection and associated malignancies. In the following sections, we will discuss the various forms of therapeutic HPV vaccines.

THERAPEUTIC HPV VACCINES

Since infected basal epithelial cells and cervical cancer cells do not express an appreciable level of L1 and/or L2 antigens, it is unlikely that therapeutic HPV vaccines targeting the L1 or L2 antigens will generate therapeutic effects against established HPV infection and HPV-associated cancer. Thus, it is important to develop therapeutic HPV vaccines targeting antigens other than L1 and L2. The HPV E6 and E7 oncoproteins represent ideal targets for the development of therapeutic HPV vaccines. These early antigens are constantly expressed in HPV-associated cancers and contribute to the progression of HPV-associated malignancies (3). Furthermore, since HPV E6 and E7 are foreign proteins, they can circumvent the issue of immune tolerance against self-antigens, as in the case of many cancer vaccines targeting endogenous self-antigen. Therefore, in order to eradicate established HPV infections and HPV-associated cervical cancers, many investigators focused on HPV E6, E7 antigens for the development of therapeutic HPV vaccines.

Various forms of therapeutic HPV vaccines targeting HPV E6/E7 antigens have been tested in preclinical models and clinical trials. These approaches include live vector-based vaccines, protein-based vaccines, peptide-based vaccines, nucleic acid-based vaccines and whole cell-based vaccines (see Figure 1). Table 1 summarizes the advantages and disadvantages of each approach. The following sections will outline the principles of various forms of therapeutic HPV vaccine development, and the latest results from both preclinical studies and clinical trials. Table 2 summarizes the significant clinical trials that have been conducted using therapeutic HPV vaccines.

Figure 1
Therapeutic HPV Vaccination
Table 1
Advantages and Disadvantages of Current Therapeutic HPV Vaccines
Table 2
Selected Therapeutic HPV Vaccine Clinical Trials

Live vector-based vaccines

Live vector-based vaccines usually fall into two categories: 1) bacterial vectors and 2) viral vectors. One important advantage of using live vector-based vaccines is their high efficiency in delivering antigens or DNA encoding antigens of interests. Additionally, some live vectors can replicate and spread in the host, resulting in potent immune responses. Another advantage of live vector-based vaccines is the wide range of vectors to choose from; this makes it possible to find a desirable vector to deliver antigens. Although live vectors have many advantages, there are several drawbacks to its clinical applications. As with all live vectors, they may potentially have safety concerns to the host. In addition, the neutralizing antibodies generated against them upon vaccination may limit the efficacy of repeated immunizations with the same live vector. Recently, it has been demonstrated that COX-2 inhibitors, such as Celecoxib, can prevent the generation of neutralizing antibodies to vaccinia, allowing repeated administration without losing infectivity (16) and representing a potentially useful approach to boost the potency of viral vector-based vaccines.

Bacterial vectors

Various bacterial vectors including Listeria monocytogenes (17), Lactococcus lactis (18, 19), and Lactobacillus plantarum (20) have been tested in therapeutic HPV vaccines. Among the various bacterial vectors, Listeria-based vectors represent a potential promising vector for therapeutic HPV vaccine. Listeria is a gram-positive bacterium that usually infects macrophages. Unlike most intracellular pathogens, Listeria is able to evade phagosomal lysis by secreting a factor called listeriolysin O (LLO) and replicating in the cytoplasm of the host cell (for review, see (21)). Because Listeria is present in the cytoplasm and the endosomal compartments, peptides derived from L. monocytogenes can be presented via both major histocompatibility complex (MHC) class I and MHC class II pathways to induce potent antigen-specific T cell-mediated immune responses. Furthermore, live vector-based vaccines using Listeria as a bacterial vector have been proven to be able to break immune tolerance. Souders et al. have shown that in HPV-16 E6/E7 transgenic mice, Listeria-based vaccines targeting E7 can cause regression of implanted E6/E7 expression tumors (22). Furthermore, it has been reported that Listeria-based vaccines against E7 antigens can also limit growth of spontaneously arising HPV-16 E6/E7 expressing thyroid tumors in E6/E7 transgenic mice (17). Many strategies have been employed to enhance Listeria-based vaccine potency by fusing HPV antigen with Listeria protein, such as LLO (23) or ActA (24). Recently, Maciag et al. reported the first clinical use of a Listeria-based therapeutic HPV vaccine, using HPV-16 E7 antigen fused to a fragment of LLO (25). The vaccine was found to be well tolerated in end-stage cervical cancer patients who had failed prior chemotherapy, radiotherapy and/or surgery.

Lactococcus lactis (26) has also been used for therapeutic HPV vaccine development. This non-pathogenic, non-invasive and non-colonizing dairy microorganism allows for controlled and targeted administration of vaccine antigens to the mucosal immune system, which stimulates systemic immune responses and induces cytotoxic T-lymphocytes to clear infection. For example, intranasal vaccination with recombinant Lactococcus lactis expressing HPV-16 E7 antigen (LL-E7) and secreted form of interleukin-12 (LL-IL-12) induced an E7-specific response in mice and also demonstrated therapeutic antitumor effects against HPV-16 E7-expressing tumors (26). Furthermore, intranasal administration of LL-E7 was compared to Lactobacillus plantarum expressing HPV-16 E7 (LP-E7) for their ability to generate E7-specific T cell-mediated immune responses and antitumor effects against E7-expressing tumors (27). A greater efficacy of E7-specific immune response was observed for LP-E7 compared to LL-E7, suggesting that Lactobacillus plantarum fits as a better vector for mucosal immunotherapy against HPV-related tumors. Another vector, Lactobacillus casei expressing HPV-16 E7 antigen on its surface, has also been shown to greatly enhance E7-specific cell-mediated immune responses and antitumor effects in vaccinated mice (28).

Viral vectors

Recombinant viruses pose as attractive vaccine vectors for therapeutic HPV vaccination. Their high infection efficiency and excellent expression of antigens encoded by the virus in the infected cells make them an appealing choice for the delivery of HPV antigens (for review, see (29)). Many live viral vectors have been used for therapeutic HPV vaccine development, including adenoviruses (3032), adeno-associated viruses (33), fowlpox viruses (34), vaccinia viruses (3541), vesicular stomatitis viruses (VSV) (42), and alphaviruses (such as the Semliki Forest virus (4346), Venezuelan equine encephalitis (VEE) virus (47, 48), and Sindbis virus (49)). In the following sections, we will focus on adenovirus, vaccinia and alphavirus for further discussion of their applications in both preclinical models and clinical trials.

Adenoviruses have been used for therapeutic HPV vaccines in preclinical studies. Recent studies have shown that a replication-deficient adenovirus encoding fusion protein comprised of calreticulin fused to E7 antigen (CRT/E7) protects mice against E7-expressing tumor challenge and exerts therapeutic effects against established tumors (30). Adenovirus vaccine encoding chimeric hepatitis B virus surface antigen (HBsAg) fused to HPV-16 E7 protein is another alternative to induce good T cell responses. The HBsAg/E7 fusion protein assembles efficiently into virus-like particles, and evokes E7 antigen-specific cellular immune responses (31).

Vaccinia virus is a promising candidate for virus-based vaccines due to its high efficiency of infection and large complete genome. Several strategies have been used in vaccinia virus based vaccine to facilitate the antigen processing in dendritic cells (DCs), such as fusing E7 with calreticulin (CRT) (35) or listeriolysin O (36), and they have been shown to elicit E7-specific immune responses in mice. In Phase I/II clinical trials, a recombinant vaccinia virus expressing HPV-16/18 E6/E7 fusion protein (TA-HPV) has been tested. TA-HPV has been shown to induce HPV antigen-specific T cell-mediated immune response and some therapeutic effects in patients with late-stage cervical cancer (38), Stage Ib or IIa cervical cancer (37), vulvar intraepithelial neoplasia (VIN) (39), and vaginal intraepithelial neoplasia (VAIN) (40). Furthermore, there is an ongoing Phase II trial in patients with Stage Ib or IIa cervical cancer to study the safety and immunological effects of vaccination with TA-HPV following surgery (41). Other vaccinia virus vector-based therapeutic HPV vaccine candidates being tested in clinical trials are MVA-E2 (5052) and MVA-HPV-IL2 (53).

Alphaviruses have also been employed for therapeutic HPV vaccines. Semliki Forest virus (SFV), an alphavirus, has been shown to induce potent antigen-specific immune responses and break immune tolerance in immune-tolerant E6/E7-transgenic mice (43). Recently, it has been reported that alphavirus vector-induced HPV-specific immune response is augmented by co-expression of IL-12 (45). Thus, viral vectors can be further modified to enhance their potency.

Peptide / Protein-based vaccines

Peptide-based vaccines

Vaccination with peptides derived from HPV antigenic proteins involve the uptake of the peptide antigen by DCs and presentation of the peptide antigen in association with MHC molecules. Peptide vaccines are generally stable, easy to produce compared to protein vaccine and safe compared to live-vector based vaccine. However, in order to develop peptide-based therapeutic HPV vaccines, it is generally necessary to identify the immunogenic epitope of HPV antigens. The polymorphic nature of major histocompatibility complex (MHC) molecules in the genetically outbred population makes it difficult to develop a “one size fits all” peptide-based vaccine. The potential solution for this issue is the employment of overlapping long peptide vaccine covering HPV E6/E7 antigens. Overlapping long peptide vaccines against HPV E6 and/or E7 antigens have been tested in preclinical models, including mice (54) and rabbit (55), and proven to be effective in generating antigen-specific T cell responses.

In general, peptide vaccines have poor immunogenicity, so use of adjuvants in peptide-based vaccine can circumvent this problem. Most studies on peptide-based vaccines have focused on enhancing vaccine potency by using adjuvants such as GM-CSF (54), 4-1BB ligand (56), mutant cholera toxin (57) and CpG oligodeoxynucleotides (CpG ODN) (58, 59) to enhance vaccine potency (for review, see (10)).

In early Phase I/II clinical trials, several peptide-based HPV vaccines have been found to be well tolerated (6063). Recently, Kenter et al. conducted a phase I trial involving an overlapping HPV-16 E6 and E7 long peptide vaccine with Montanide ISA 51 adjuvant in end-stage cervical cancer patients and showed that the vaccines are well tolerated, and elicited a broad IFN-γ-associated T cell response in patients (64). They also conducted a study involving the vaccination of 11 HPV-16+ vulvar intraepithelial neoplasia (VIN) grade III patients with the same long peptide vaccine and adjuvant, and a complete clinical immune response was seen in 4 out of 11 patients (65). Furthermore, the same vaccine regimen was also tested in stage 1B1 HPV-16+ cervical cancer patients. The result of the trial showed increased HPV-16-specific CD4+ and CD8+ T cell responses to a broad array of epitopes in all 6 patients (66). Recently, a Phase II trial to evaluate the effectiveness of a HPV-16 E6/E7 peptide-based vaccine in patients with metastatic or advanced cervical cancer is currently undergoing investigation (67). Overall, the results from these early phase clinical trials have generated a significant enthusiasm on therapeutic HPV E6/E7 long peptide vaccines.

Protein-based vaccines

Protein-based vaccines, like peptide vaccines, are safe compared to live-vector based vaccines. Furthermore, protein-based vaccines can circumvent the MHC specificity limitation associated with peptide vaccines. Since protein antigens can be processed in dendritic cells, which contain all the possible human leukocyte antigen (HLA) epitopes of an antigen, this approach precludes the need to determine the HLA haplotype of prospective patients. The low immunogenicity of protein-based vaccines is a major drawback to its development; thus, many strategies employing adjuvants and fusion with immunostimulatory molecules are often used to overcome this problem. Another concern for the development of protein-based vaccines is the limited efficacy of generating cytotoxic T lymphocyte (CTL) responses, since they are often administered exogenously.

Adjuvants and fusion of immunostimulatory proteins have been used to increase the immunogenicity and CTL responses of HPV protein-based vaccines. For example, adjuvants such as the liposome-polycationic-DNA (LPD) adjuvant (68) and saponin-based adjuvant ISCOMATRIX (69) have been shown to improve CTL responses of HPV protein-based vaccines. Furthermore, fusions of HPV antigen with molecules that can target the antigens to antigen-presenting cells (APCs) have been shown to increase the antigen uptake and presentation efficiency. Examples of such a strategy include fusion of HPV-16 E7 with Bordetella pertussis adenylyl cyclase (CyaA), a protein that targets APCs through specific interaction with integrin (70), or fusion of HPV-16 E7 with the truncated bacterial exotoxin Pseudomonas aeruginosa exotoxin A, which facilitates translocation of protein to enhance MHC class I presentation (71). Another important immunostimulatory molecule capable of enhancing CTL responses is heat shock protein (HSP) derived from Mycobacteria (72, 73).

Several HPV protein-based vaccines have been tested in clinical trials (7481). For example, a HPV fusion protein composed of HPV-6 L2 and E7 (TA-GW) has been tested in 42 healthy male volunteers (74) as well as 27 patients with genital warts (75). TA-GW has been shown to be well tolerated in these clinical trials and was effective in generating antigen-specific T cell responses in 19 patients and clearing HPV-associated genital warts in 5 patients. Another protein-based vaccine is TA-CIN, which utilizes a fusion protein comprised of HPV-16 L2, E6, and E7 antigens. It has been tested in 40 healthy volunteers and has shown no serious side effects. The vaccination with TA-CIN was also shown to induce antibody responses against L2 in all patients and T cell immunity against HPV-16 E6 and E7 oncoproteins in 8 out of 11 healthy patients receiving the highest dose (76). In another early phase clinical trial, a vaccine (PD-E7) created from mutated HPV-16 E7 fused with a fragment of Haemophilus influenzae protein D, formulated in an adjuvant system containing Monophosphoryl Lipid A, QS-21 saponin adjuvant and oil-in-water emulsion (GlaxoSmithKline AS02B adjuvant), was shown to induce significant E7-specific CD8+ T cell responses in patients with cervical intraepithelial neoplasia (CIN) 1 or CIN 3 lesions (77). Furthermore, a vaccine comprised of HPV-16 E6/E7 fusion protein mixed with ISCOMATRIX adjuvant was shown to be well-tolerated and immunogenic and showed significantly enhanced E6 and E7-specific CD8+ T cell responses in patients compared with those observed in placebo recipients (78). Additionally, a fusion protein vaccine comprising of HPV-16 E7 and M. bovis HSP65 (HSPE7) was well tolerated in patients with high-grade anal intraepithelial neoplasia (AIN) (79) as well as in patients with CIN 3 (80, 81). In a clinical study evaluating HSPE7 in patients with CIN 3, 13 out of 58 patients showed complete pathologic responses, and 32 out of 58 patients had partial responses, defined as colposcopic lesion regression of >50% in size (80). However, it is not clear whether the response was due to natural regression rather than treatment effects. Clinical trials are ongoing in patients with CIN 3 (82) and atypical squamous cells of undetermined significance (ASCUS)/low-grade squamous intraepithelial lesions (LSIL) (83). Recently, Nventa Biopharmaceuticals (bought by Akela Pharma) discovered upon further investigation that the potency of HSPE7 could be enhanced with the adjuvant Poly-ICLC and are subsequently pursuing Phase I clinical trials of HSPE7 adjuvanted with Poly-ICLC (84). More studies are needed to better define the clinical outcomes of the vaccine.

Nucleic acid-based vaccines

DNA-based vaccines

DNA vaccines are attractive candidates for therapeutic HPV vaccines. DNA-based vaccines are stable, easy to produce and can lead to sustained cellular gene expression compared to RNA or protein-based vaccines. Unlike the live vector-based vaccines, DNA vaccines do not lead to the generation of neutralizing antibodies and accordingly have the capacity for repeated administration. However, an important limitation of DNA vaccines is its limited potency since DNA vaccines lack the intrinsic ability to amplify and spread in vivo. Therefore, it is important to consider strategies to improve DNA vaccine potency.

Strategies to enhance DNA vaccine potency

It is now clear that dendritic cells (DCs) serves as a central player for DNA vaccine development because DCs are the most important professional antigen-presenting cells capable of priming naïve T cells. The following section will address the major directions and strategies used in enhancing DNA vaccine potency through modifications of DCs in vivo (for review, see (85, 86)). Table 3 summarizes the various strategies that have been developed to enhance the potency of therapeutic DNA vaccines for HPV.

Table 3
Strategies to Enhance the Potency of Therapeutic HPV DNA vaccines

Strategies to increase the number of antigen-expressing/loaded DCs

The identification of efficient methods to deliver DNA directly into DCs may increase the number of antigen-expressing DCs. Intradermal administration of DNA vaccine via gene gun represents a potentially efficient way of delivering DNA vaccines to DCs. DNA-coated gold particles delivered by gene gun can efficiently deliver DNA to Langerhans cells, which are immature DCs present in the epidermis of the skin. The DNA-transfected Langerhans cells express the antigens encoded by DNA vaccine and become mature. Then, the antigen-expressing DCs migrate to the draining lymph nodes, where they prime naive T cells. In a head-to-head comparison study of DNA vaccine administrated by different methods, gene gun requires the smallest dose to generate similar responses compared to other methods such as biojector and intramuscular injection with syringe (87). More recently, gene gun has also been shown to be able to deliver noncarrier naked DNA under a low-pressure system. Noncarrier naked therapeutic HPV DNA vaccination was shown to result in significantly less local skin damage than gold particle-coated DNA vaccination, enhanced HPV antigen-specific T cell immunity and antibody responses, and antitumor effects comparable to gold particle-coated therapeutic HPV DNA vaccination (88).

Another strategy to increase the number of antigen-loaded DCs is the employment of intramuscular injection using electroporation (EP). Usage of EP will significantly enhance the uptake of DNA vaccine by muscle cells, resulting in more muscle cells expressing the antigen encoded by DNA vaccine. With an increased amount of antigen released by muscle cells, more DCs may be able to uptake and process the released antigens to activate antigen-specific T cells. It has recently been reported that intramuscular injection of HPV DNA vaccine in conjunction with electroporation could elicit potent HPV antigen-specific CTL responses (89, 90).

Other strategies used to increase the population of antigen-bearing DCs include the fusion of HPV antigens with molecules that are capable of concentrating and targeting the antigens to the DCs. Such molecules include FMS-like tyrosine kinase 3 (flt3) ligands, which bind to with flt3 receptors on DCs (91) and heat shock proteins, which bind with scavenger receptors on DCs, such as CD91 (87, 92, 93).

DNA vaccine does not spread beyond cells that are initially transfected. Increasing the spread of antigen encoded by DNA vaccine can increase antigen loading by DCs. This has been done by linking antigen to proteins capable of intercellular transport. VP22 is a herpes simplex virus type 1 (HSV-1) microtubule binding protein. DNA encoding HPV-16 E7 fused to HSV-1 VP22 has been shown to enhance E7-specific CD8+ T cell immune responses in vivo and generate stronger antitumor immune responses (94). Strong antitumor responses have also been found using Marek’s disease virus type 1 VP22 (MVP22) (95). This strategy has also been applied to other nucleic acid-based vaccines and was found to generate significant antitumor effects (96). Taken together, efficacious administration routes, employment of molecules that target HPV antigen to DCs and molecules that increase the intercellular spread of antigen encoded by DNA vaccines, are strategies that have been shown in preclinical models to enhance antigen expression by DCs, resulting in improvement of therapeutic HPV vaccine potency.

Strategies to improve antigen expression, processing and presentation in DCs

One of the strategies to increase antigen expression in DCs is codon optimization, which eliminates codons not frequently used by the specific host and replaces them with more commonly recognized codons. This strategy can be used in both naturally occurring and recombinant gene sequences. Codon optimization has been shown to be effective in boosting the CTL response induced by HPV DNA vaccines (97100). Another strategy to increase antigen expression by DNA vaccine is the usage of demethylation agents. It is known that DNA methylation leads to silencing of the genes that would affect the expression of the encoded antigen in a DNA vaccine. Recently, Lu et al demonstrated that administration of CRT/E7 DNA vaccine combined with demethylating agent, 5-aza 2 deoxycytidine (DAC) leads to upregulation of CRT/E7 expression, thus enhancing DNA vaccine potency (101).

Dendritic cells must efficiently process the antigens and present them through the MHC class I pathway to generate antigen-specific CD8+ T cell responses. Researchers have also attempted to link HPV E7 antigens with molecules that target the endoplasmic reticulum (102) or facilitate proteasome degradation (103). For example, DNA vaccines encoding E6/E7 antigen linked to various MHC class I-targeting proteins and protein domains, includes M. tuberculosis HSP70 (104), HSP60 (105), calreticulin (CRT) (106108), Gp96 (109), γ-tubulin (110), extracellular domain of Flt3-ligand (91), and the translocation domain of Pseudomonas aeruginosa exotoxin A (111). These strategies have been shown to significantly improve MHC class I presentation of E6/E7 antigens and result in potent E6/E7 antigen-specific CTL responses generated by therapeutic HPV DNA vaccines.

Another strategy to enhance the antigen presentation by DCs involves the generation of DNA construct encoding a fusion protein that links an antigenic peptide to the β2-microglobulin and MHC class I heavy chain, called single chain trimer (SCT) technology (112, 113). The expression of the encoded fusion protein by the DNA-transfected DCs will lead to a constant presentation of the antigenic peptide by MHC class I molecule. It has been shown that vaccination of DNA construct encoding a SCT composing of HPV-16 E6 antigenic peptide fused with β2-microglobulin and H-2Kb MHC class I heavy chain could generate significantly increased E6-specific CD8+ T cell response compared to mice vaccinated with DNA encoding HPV-16 E6 antigen (112).

Significant endeavors have been made to improve the MHC class II presentation of antigens by using DNA encoding antigen fused with intracellular targeting protein. It has been shown that linkage of E7 antigen to a signal peptide for the endoplasmic reticulum (Sig) and the sorting signal of the lysosomal-associated membrane protein 1 (LAMP-1) can change the location of E7 from cytoplasm/nucleus to endosomal/lysosomal compartments, an important location for MHC class II presentation, and result in the enhancement of MHC class II presentation of E7 to CD4+ helper T cells (114). Vaccination of the DNA encoding the chimeric Sig/E7/LAMP-1 protein has led to increased E7-specific CD4+ T cell responses and antitumor effects against E7-expressing tumor in vaccinated mice (115).

The MHC class II-associated invariant chain (Ii) has also been employed to improve antigen presentation through MHC class II pathway to enhance DNA vaccine potency. By substituting the Class II-associated invariant chain peptide (CLIP) region of the Ii with T helper (TH) epitope such as Pan-DR T helper epitope (PADRE) (Ii-PADRE), the epitope can thus be presented by the MHC class II pathway efficiently. Mice vaccinated with a DNA vaccine encoding Ii-PADRE can generate significant PADRE-specific CD4+ T cell responses. Furthermore, co-administration of DNA encoding E7 and DNA encoding Ii-PADRE was shown to elicit potent E7-specific CD8+ T cell responses (116). The activated PADRE-specific CD4+ T helper cells, which can secret IL-2, enhances the E7-specific CD8+ T-cell immune responses generated by DNA vaccination (117).

Strategies to enhance DC function and interaction with T cell

In order to improve DC interaction with T cells, it is important to consider the following: (1) prolonging the life of DCs, (2) preventing apoptosis of activated T cells and (3) increasing expression of cytokines by DCs.

DNA vaccines employing strategies to prolong DC life were shown to further improve antigen-specific CTL responses (118, 119). DNA encoding anti-apoptotic proteins can be co-delivered with the vaccine to increase DC resistance to CTL-mediated killing. In previous studies, co-delivery of E7 DNA with DNA encoding BCL-xL, BCL-2, XIAP, or dominant-negative caspases have been shown to enhance E7-specific CD8+ T cell responses in mice (120). However, the introduction of anti-apoptotic proteins might raise the concern for oncogenicity. An alternative solution to the problem is to apply the RNA interference technology to knockdown the pro-apoptotic proteins. For example, Kim et al. have demonstrated that the co-administration of E7 DNA vaccines with small interfering RNA (siRNA) targeting Bak and Bax was effective in enhancing DC resistance to apoptosis and enhance E7 specific CD8+ T cell immune responses in the vaccinated mice (121). Recently, connective tissue growth factor (CTGF), important for cell survival, has also been used to prolong DC life. It has been shown that DNA encoding CTGF linked to E7 antigen can prolong the survival of DCs and generate potent antitumor responses (122).

Another strategy to improve DCs and T cells interaction is to prevent the apoptosis of activated T cells. Fas ligand (FasL) is a key pro-apoptotic signaling protein expressed on the surface of DCs and can bind to its cognate ligand, Fas, on T cells. The binding of Fas on T cells to Fas ligand on DCs can lead to T cell apoptosis. Recently, Huang et al. have shown that co-administration of E7 DNA and DNA encoding small hairpin RNA (shRNA) targeting FasL can generate significant E7-specific CTL responses (123). The downregulation of the FasL on DCs by RNA interference (RNAi) may improve the survival of the activated T cells and result in increased antigen-specific CTL responses.

Another approach to improve the interaction between T cells and DCs is to enhance the expression of relevant cytokines by DCs. Co-administration of DNA vaccines encoding HPV antigens with DNA encoding GM-CSF (124), IL-2 (125), or IL-12 (126) have been shown to improve HPV antigen-specific immune responses. Moreover, HPV 16 E7-based DNA vaccine with DNA encoding sequence-optimized adjuvants such as IL-2 and IL-12 has also been shown to enhance E7-specific CTL responses (127). Furthermore, HPV DNA vaccine encoding E7 linked to IL-6 has been shown to increase E7-specific T-cell immunities, anti-E7 antibody responses, and antitumor effects against E7-expressing tumors (128).

Several DNA vaccines for HPV have been investigated in clinical trials. A microencapsulated DNA vaccine encoding multiple HLA-A2-restricted HPV-16 E7 epitopes (ZYC-101) has been tested in patients with CIN-2/3 (129) and in patients with high-grade anal intraepithelial neoplasia (130). The vaccine was well tolerated in both trials and shown to enhance E7-specific immune responses in some of the patients. A newer version of the DNA vaccine, ZYC-101a, which encodes HPV-16 and HPV-18 E6- and E7-derived epitopes has been used in phase II clinical trial in patients with CIN 2/3 lesions. This DNA vaccine has been shown to promote the resolution of CIN 2/3 in most (70%) of the patients younger than 25 years compared to the placebo group of the same age (131). A Phase II/III trial is currently ongoing to evaluate the vaccine in patients with CIN 2/3 (132). At the Johns Hopkins Hospital, a Phase I trial using a DNA vaccine encoding modified HPV-16 E7 DNA (with abolished Rb-binding site) linked with M. tuberculosis HSP70 (Sig/E7(detox)/HSP70) was tested in patients with CIN-2/3 lesions. The results of the trial showed that the vaccine was well tolerated by all the patients, and among the patients who received the maximum dosage of vaccine, some showed detectable E7-specific CD8+ T cell immune response. In addition, complete histological regression of the lesions was observed in 3 of 9 individuals in highest-dose cohort (133). The same DNA vaccine (Sig/E7(detox)/HSP70) has also been tested in HPV-16+ patients with advanced head and neck squamous cell carcinoma (Gillison and Wu, personal communication). The same investigators also plan to initiate a Phase I trial with a DNA vaccine encoding the modified HPV-16 E7 linked to CRT (CRT/E7(detox)) in patients with high grade intraepithelial cervical lesion using a clinical-grade gene gun device (Trimble, Huh and Wu, personal communication). More recently, a phase I clinical trial using DNA vaccine encoding HPV-16 and −18 modified E6 and E7 antigens (VGX-3100) via electroporation in patients with CIN 2 or 3 lesion is in progression (134).

Naked RNA replicon vaccines

Naked RNA replicons for therapeutic HPV vaccine development have been tested in preclinical models. RNA replicons are RNA molecules that can replicate in a self-limiting fashion within the transfected cell. They may be derived from alphavirus, such as Semliki Forest virus (135, 136), Sindbis virus (137, 138), or Venezuelan Equine Encephalitis (48, 139). The RNA replicon vaccine can be administered in the form of RNA or DNA, which transcribes into the RNA replicons. One obvious advantage of the RNA replicon vaccine is its ability to self-replicate in a variety of cells, which can help sustain the cellular antigen expression, and thus enable them to produce more protein of interests than conventional DNA vaccines. Since most RNA replicon vectors have been modified to lack the viral structural genes, they do not form viral particles. Thus, RNA replicon vaccines may be repeatedly administered in patients without the generation of neutralizing antibodies against viral capsid protein. In addition, RNA replicons can bypass the possibility of chromosomal integration and cellular transformation that is associated with DNA vaccines. However, RNA is generally less stable than DNA, and is easily degraded in the injected host.

Attempts have been made to combine the benefits of RNA replicons and DNA vaccine by making a DNA-launched RNA replicon vaccine, so called ‘suicidal’ DNA. This suicidal DNA can be transcribed into RNA replicons and provide a stable way to express encoded antigens. The suicidal DNA is more stable and easier to prepare compared to naked RNA replicons. Because the cells uptaking the suicidal DNA vector will eventually lead to apoptosis, there are no concerns of integration or transformation in the transfected cells. The suicidal DNA vector has been used for therapeutic HPV vaccine developments in preclinical models and generates significant HPV antigen-specific CD8+ T cell mediated immune responses and antitumor effects (140). Because the delivery of suicidal DNA vector by gene gun will make transfected cells such DCs undergo apoptosis, leading to poor immunogenicity, Kim et al. have generated a suicidal DNA vector, pSCA1, encoding E7 fused with BCL-xL, an antiapoptotic protein of the BCL-2 family, to enhance the survival of antigen-presenting cells. These vaccines have shown to generate higher E7-specific CD8+ T cell immune responses and better antitumor effects than suicidal DNA vector encoding wild type E7 alone in preclinical models (141).

Another strategy to alleviate the concern of apoptosis associated with RNA replicon system involves the use of a flavivirus called Kunjin (KUN) to deliver antigens of interests to the cells. The key advantage of the KUN replicon vector is that it does not induce apoptosis in the transfected cells, thus enabling a more prolonged antigen presentation time by the transfected DCs compared to other RNA replicon vectors (142). Vaccination of mice with DNA-launched KUN replicons encoding HPV-16 E7 epitopes generated E7-specific T cell responses and protected vaccinated mice against tumor challenge of E7-expressing murine tumor (143). Despite the general success of naked RNA replicon vaccines in preclinical models, they have not been tested in clinical trials yet.

Whole cell vaccines

Dendritic cell-based vaccines

The increasing understanding of dendritic cell biology as well as the improved methods for preparing DCs ex vivo has paved the way for DC-based vaccines. DCs can serve as natural adjuvants in antigen-specific cancer immunotherapy (for review, see (144)). A recent phase III clinical trial study using the DC-based cell vaccine (PROVENGE) in patients with advanced prostate cancer has shown encouraging results with improving overall patient survivals compared to placebo (145). The result has generated great enthusiasm for DC-based vaccines.

Although dendritic cell-based vaccines may seem promising, there are several serious limitations. The use of autologous DCs for individualized therapy will limit the large-scale production of the vaccine and will be technically demanding. Since culturing techniques will also affect the quality of the vaccines generated, it will be challenging to establish standard criteria for the preparation of DC-based vaccine. Furthermore, the route of administration is critical for the success of the vaccination, because it is essential for the DCs to target the T cells in the lymphoid organs to generate an effective immune response.

Nevertheless, DC-based vaccines have been used for HPV therapeutic vaccine development, and various methods have been used to prepare DCs for therapeutic HPV vaccines, including the usage of vectors (146, 147), pulsing DCs with protein (148)/peptide (149, 150)/tumor cell lysates (151), or transfecting DCs with DNA (152)/RNA (153). Several strategies have been used to improve the DC-based vaccine. For example, one approach is to transfect DCs with siRNAs targeting key pro-apoptotic molecules such as Bak, Bax and Bim to avoid T-cell mediated apoptosis of DCs. The prolonged life of DC will lead to improved DC and T cell interaction, and result in enhancement of T cell priming. Vaccination with E7-loaded DCs transfected with siRNA targeting Bak and Bax has been shown to generate improved E7-specific immune responses and antitumor effects in mice (149). More recently, vaccination with E7-presenting DCs transfected with siRNA targeting Bim was capable of generating a strong E7-specific CTL response and a marked therapeutic effect in vaccinated mice (150).

Dendritic cell-based vaccines have been tested in patients with HPV-associated cervical cancer. In a case report, a patient with advanced metastatic cervical cancer was treated with DCs loaded with HPV-18 E7 antigens. Although the vaccine did not induce complete remission in the patient, no significant side effects were observed (154). In another clinical study, autologous DCs pulsed with HPV-16 or HPV-18 E7 recombinant protein were tested in 15 patients with late stage cervical cancer. The result showed no local or systemic side effects, and E7-specific T cell responses were observed in 4 out of 11 patients (155). Another clinical study using DCs pulsed with HPV-16 or HPV-18 E7 proteins was performed in 4 patients with advanced refractory cervical cancers. Elevated E7-specific CD4+ T cell immune responses were observed in 2 out of 4 patients, and E7-specific CD8+ T cell immune responses were detected in all 4 patients (156). In another clinical study, vaccination using autologous DCs pulsed with recombinant HPV-16/18 E7 antigens and keyhole limpet hemocyanin (KLH), an immunological tracer molecule, was shown to be well tolerated in Stage IB or IIA cervical cancer patients and generated E7-specific CD8+ T cell immune responses in 8 out of 10 patients and CD4+ T cell and antibody responses in all patients (157). A pilot study using DC-based vaccine (HPV-16 E7 peptide-pulsed autologous DCs) for patients with recurrent cervical cancer is currently underway (158).

Tumor cell-based vaccines

Tumor cell-based vaccines are another approach to whole cell vaccines. Tumor cells can be isolated and manipulated to express immunomodulatory proteins ex vivo to enhance their immunogenicity. Cytokine genes such as IL-2 (159), IL-12 (160, 161), and GM-CSF (161, 162) have been used in HPV-transformed tumor cell-based vaccines.

Some tumor cell-based vaccines have been tested in preclinical studies. Vaccination of mice with GM-CSF-expressing E7-positive tumor cells has been shown to lead to increased E7-specific CTL response and potent antitumor immune response against E7-expressing tumors in mice (162). Although tumor cell-based vaccines have been used in clinical trials for colorectal carcinoma, renal cell carcinoma, and melanoma, they have not been tested in HPV-associated malignancies in patients (for review, see (163)). One potential concern with using tumor cell-based vaccines is the possibility of introducing new cancers to the patient. On the other hand, the key advantage of using tumor cell-based vaccines is the convenience that tumor antigens do not have to be well defined. In addition, potentially more tumor antigens may be covered with this approach. Because cervical cancer has well-known tumor-specific antigens, E6 and E7, most studies have been focused on HPV antigen-specific cancer immunotherapy.

COMBINATIONAL APPROACHES

Prime-boost regimen for therapeutic HPV vaccines

The availability of different forms of therapeutic HPV vaccines creates opportunities for prime-boost regimens to further enhance therapeutic HPV vaccine potency. For example, previous studies have shown that priming with a HPV-16 E6/E7 DNA vaccine followed by boosting with recombinant vaccinia (164) or adenovirus (165) or with the HPV-16 E6/E7 expressing tumor cell-based vaccine (166) elicited greater HPV antigen-specific CD8+ T cell immune responses in vaccinated mice compared to vaccination with DNA vaccine, viral vector vaccine or tumor cell-based vaccine alone. In another prime-boost study, mice first primed with a Sindbis virus RNA replicon containing HPV-16 E7 linked to M. tuberculosis HSP70 (E7/HSP70) were boosted with a recombinant vaccinia virus encoding E7/HSP70. Significantly increased E7-specific CTL responses were observed in vaccinated mice (167). Also, prime-boost regimen has been proven successful in HPV-16 E7 protein prime and vaccinia boost regimen (168). More recently, it was demonstrated that a prime boost regimen of heterologous vaccination of Venezuelan equine encephalitis virus replicon particles (VRP) encoding HPV E6/E7 antigen and recombinant vesicular stomatitis virus (VSV) encoding HPV E6/E7 antigen was dramatically more immunogenic than homologous vaccination with either vector alone in both mouse and monkey models (169).

Some of the prime-boost regimens have been evaluated in therapeutic HPV vaccines clinical trials (170172). For example, in a phase II clinical trial, HPV protein based vaccine, TA-CIN (HPV-16 L2/E6/E7 fusion protein), was used for priming and a recombinant vaccinia virus encoding HPV-16/18, E6/E7 fusion protein (TA-HPV) was used for boosting in 29 patients with anogenital intraepithelial neoplasia. No serious adverse effects were observed in all patients; in addition, 5 out of 29 patients showed increased HPV-16-specific T cell mediated immune responses. However, the result doesn’t show significant advantage over single TA-HPV vaccination (171). In another prime-boost regimen, ten patients with HPV-16+ high-grade vulvar intraepithelial neoplasia were primed with TA-HPV and boosted with TA-CIN. Among all the patients, 9 patients developed HPV-16-specific T cell responses, and 3 showed significant reduction in the size of the lesion. However, the result doesn’t show direct correlation between clinical and immunological responses (172). More recently, a clinical trial using pNGVL4a/Sig/E7(detox)/HSP70 DNA prime followed by TA-HPV boost is currently underway in patients with CIN 2/3 lesions, evaluating whether or not the topical application of imiquimod can further enhance prime-boost administration (173).

Combination of therapeutic HPV vaccines with immunomodulatory agents

It is now clear that an effective immune therapy should consider modulation of the tumor microenvironment. There are many factors within tumor microenvironment that may hinder the success of effective immune therapies. For example, T regulatory cells can release immune suppressive cytokines such as IL-10 (174) and TGF-β (175), which can paralyze T cell function. The depletion of T regulatory cells in the tumor microenvironment has been shown to significantly enhance therapeutic HPV vaccine potency (176). Other factors contributing to tumor immune suppression in tumor microenvironment include B7 homolog-1 (B7-H1) (177), signal transducer and activator of transcription 3 (STAT3) (for review, see (178)) and MHC class I polypeptide-related sequence (MIC)-A and B (179), indoleamine 2,3-dioxygenase (IDO) enzyme (180), and galectin-1 (181). These factors may serve as potential targets for immune modulation to enhance therapeutic HPV vaccine potency (for review, see (182)).

Combination of therapeutic HPV vaccines with other therapeutic modalities

Therapeutic HPV vaccines may potentially be combined with other therapeutic modalities, such as chemotherapy, radiation therapy, or other therapeutic agents to augment the therapeutic vaccine effects (101, 183188). Several chemotherapies and radiotherapies have been shown to enhance the potency of therapeutic HPV vaccines. For example, Chuang et al. showed that combination of apigenin, a chemotherapeutic agent that is abundantly present in common fruits and vegetables and possesses anti-carcinogenic properties (for review, see (189)), with therapeutic HPV DNA vaccine could improve therapeutic HPV vaccine potency. Treatment with apigenin led to apoptotic tumor cell death in vitro in a dose-dependent manner and rendered the E7-expressing tumor cells more susceptible to lysis by E7-specific cytotoxic CD8+ T cells. Furthermore, E7-expressing tumor-bearing mice treated with apigenin combined with therapeutic HPV DNA vaccine generate enhanced E7-specific CD8+ T cell responses, leading to potent therapeutic antitumor effects against E7-expressing tumors (188). Likewise, death receptor (DR5)-specific antibodies (190) or proteasome inhibitor, bortezomib (186), have also been shown to improve therapeutic HPV DNA vaccine potency.

More recently, low-dose radiotherapy has been combined with therapeutic HPV DNA vaccine for the control of E7-expressing tumor in a preclinical model (187). Treatment with low-dose radiotherapy rendered the TC-1 tumor cells more susceptible to lysis by E7-specific CTLs, and significantly enhanced therapeutic antitumor effects generated by HPV DNA vaccine (187).

CONCLUDING REMARKS

Although preventive HPV vaccines are now commercially available, it is expected that it will take decades before the preventive HPV vaccines can generate impact on the incidence of cervical cancer. Thus, it is important to continuously develop effective and safe therapeutic HPV vaccines in order to accelerate the control of cervical cancer. The impressive preclinical data for therapeutic HPV vaccine development have led to several early phase clinical trials.

The control of advanced cervical cancer will most likely require the combination of therapeutic HPV vaccine with other therapeutic modalities. With the increasing discovery of new drugs (i.e. targeted therapeutic agents and chemotherapeutic agents), as well as the better understanding of tumor biology, we will have greater opportunities to combine these therapeutic modalities with therapeutic HPV vaccines in order to improve therapeutic effects against HPV-associated cervical cancer.

Acknowledgements

This review is not intended to be an encyclopedic one, and the authors apologize to those not cited. We gratefully acknowledge Dr. Richard Roden for his critical review of the manuscript. The work is supported by the NCI SPORE in Cervical Cancer P50 CA098252 and NCI 1RO1 CA114425-01.

REFERENCES

1. Parkin DM, Bray F, Ferlay J, Pisani P. Global cancer statistics, 2002. CA Cancer J Clin. 2005 Mar-Apr;55(2):74–108. [PubMed]
2. Munoz N, Bosch FX, de Sanjose S, Herrero R, Castellsague X, Shah KV, et al. Epidemiologic classification of human papillomavirus types associated with cervical cancer. N Engl J Med. 2003 Feb 6;348(6):518–527. [PubMed]
3. Howley PM, Munger K, Romanczuk H, Scheffner M, Huibregtse JM. Cellular targets of the oncoproteins encoded by the cancer associated human papillomaviruses. Princess Takamatsu Symp. 1991;22:239–248. [PubMed]
4. Romanczuk HHP. Disruption of either the E1 or the E2 regulatory gene of human papillomavirus type 16 increases viral immortalization capacity. 1992 [PubMed]
5. Jabbar SF, Abrams L, Glick A, Lambert PF. Persistence of high-grade cervical dysplasia and cervical cancer requires the continuous expression of the human papillomavirus type 16 E7 oncogene. Cancer Res. 2009 May 15;69(10):4407–4414. [PMC free article] [PubMed]
6. zur Hausen H. Papillomaviruses and cancer: from basic studies to clinical application. Nat Rev Cancer. 2002 May;2(5):342–350. [PubMed]
7. Kirnbauer R, Booy F, Cheng N, Lowy DR, Schiller JT. Papillomavirus L1 major capsid protein self-assembles into virus-like particles that are highly immunogenic Proc Natl Acad Sci U S A 1992. Dec 15;892412180–12184.12184 [PubMed]
8. Kirnbauer R, Taub J, Greenstone H, Roden R, Durst M, Gissmann L, et al. Efficient self-assembly of human papillomavirus type 16 L1 and L1-L2 into virus-like particles. J Virol. 1993 Dec;67(12):6929–6936. [PMC free article] [PubMed]
9. Hagensee ME, Yaegashi N, Galloway DA. Self-assembly of human papillomavirus type 1 capsids by expression of the L1 protein alone or by coexpression of the L1 and L2 capsid proteins. J Virol. 1993 Jan;67(1):315–322. [PMC free article] [PubMed]
10. Roden RB, Monie A, Wu TC. Opportunities to improve the prevention and treatment of cervical cancer. Curr Mol Med. 2007 Aug;7(5):490–503. [PubMed]
11. Harper DM, Franco EL, Wheeler C, Ferris DG, Jenkins D, Schuind A, et al. Efficacy of a bivalent L1 virus-like particle vaccine in prevention of infection with human papillomavirus types 16 and 18 in young women: a randomised controlled trial. Lancet. 2004 Nov 13–19;364(9447):1757–1765. [PubMed]
12. Villa LL, Costa RL, Petta CA, Andrade RP, Ault KA, Giuliano AR, et al. Prophylactic quadrivalent human papillomavirus (types 6, 11, 16, and 18) L1 virus-like particle vaccine in young women: a randomised double-blind placebo-controlled multicentre phase II efficacy trial. Lancet Oncol. 2005 May;6(5):271–278. [PubMed]
13. Harper DM, Franco EL, Wheeler CM, Moscicki AB, Romanowski B, Roteli-Martins CM, et al. Sustained efficacy up to 4.5 years of a bivalent L1 virus-like particle vaccine against human papillomavirus types 16 and 18: follow-up from a randomised control trial. Lancet. 2006 Apr 15;367(9518):1247–1255. [PubMed]
14. Shank-Retzlaff MLZQ, Anderson C. Evaluation of the thermal stability of Gardasil. 2006 [PubMed]
15. Schiller JT, Castellsague X, Villa LL, Hildesheim A. An update of prophylactic human papillomavirus L1 virus-like particle vaccine clinical trial results. Vaccine. 2008 Aug 19;26 Suppl 10:K53–K61. [PMC free article] [PubMed]
16. Chang CL, Ma B, Pang X, Wu TC, Hung CF. Treatment with cyclooxygenase-2 inhibitors enables repeated administration of vaccinia virus for control of ovarian cancer. Mol Ther. 2009 Aug;17(8):1365–1372. [PubMed]
17. Sewell DA, Pan ZK, Paterson Y. Listeria-based HPV-16 E7 vaccines limit autochthonous tumor growth in a transgenic mouse model for HPV-16 transformed tumors. Vaccine. 2008 Aug 1; [PMC free article] [PubMed]
18. Bermudez-Humaran LG, Langella P, Miyoshi A, Gruss A, Guerra RT, Montes de Oca-Luna R, et al. Production of human papillomavirus type 16 E7 protein in Lactococcus lactis. Appl Environ Microbiol. 2002 Feb;68(2):917–922. [PMC free article] [PubMed]
19. Bermudez-Humaran LG, Cortes-Perez NG, Le Loir Y, Alcocer-Gonzalez JM, Tamez-Guerra RS, de Oca-Luna RM, et al. An inducible surface presentation system improves cellular immunity against human papillomavirus type 16 E7 antigen in mice after nasal administration with recombinant lactococci. J Med Microbiol. 2004 May 53;(Pt5):427–433. [PubMed]
20. Cortes-Perez NG, Azevedo V, Alcocer-Gonzalez JM, Rodriguez-Padilla C, Tamez-Guerra RS, Corthier G, et al. Cell-surface display of E7 antigen from human papillomavirus type-16 in Lactococcus lactis and in Lactobacillus plantarum using a new cell-wall anchor from lactobacilli. J Drug Target. 2005 Feb;13(2):89–98. [PubMed]
21. Schnupf P, Portnoy DA. Listeriolysin O: a phagosome-specific lysin. Microbes Infect. 2007 Aug;9(10):1176–1187. [PubMed]
22. Souders NC, Sewell DA, Pan ZK, Hussain SF, Rodriguez A, Wallecha A, et al. Listeria-based vaccines can overcome tolerance by expanding low avidity CD8+ T cells capable of eradicating a solid tumor in a transgenic mouse model of cancer. Cancer Immun. 2007;7:2 [PMC free article] [PubMed]
23. Sewell DA, Shahabi V, Gunn GR, 3rd, Pan ZK, Dominiecki ME, Paterson Y. Recombinant Listeria vaccines containing PEST sequences are potent immune adjuvants for the tumor-associated antigen human papillomavirus-16 E7. Cancer Res. 2004 Dec 15;64(24):8821–8825. [PubMed]
24. Sewell DA, Douven D, Pan ZK, Rodriguez A, Paterson Y. Regression of HPV-positive tumors treated with a new Listeria monocytogenes vaccine. Arch Otolaryngol Head Neck Surg. 2004 Jan;130(1):92–97. [PubMed]
25. Maciag PC, Radulovic S, Rothman J. The first clinical use of a live-attenuated Listeria monocytogenes vaccine: a Phase I safety study of Lm-LLO-E7 in patients with advanced carcinoma of the cervix. Vaccine. 2009 Jun 19;27(30):3975–3983. [PubMed]
26. Bermudez-Humaran LG, Cortes-Perez NG, Lefevre F, Guimaraes V, Rabot S, Alcocer-Gonzalez JM, et al. A novel mucosal vaccine based on live Lactococci expressing E7 antigen and IL-12 induces systemic and mucosal immune responses and protects mice against human papillomavirus type 16-induced tumors. J Immunol. 2005 Dec 1;175(11):7297–7302. [PubMed]
27. Cortes-Perez NG, Lefevre F, Corthier G, Adel-Patient K, Langella P, Bermudez-Humaran LG. Influence of the route of immunization and the nature of the bacterial vector on immunogenicity of mucosal vaccines based on lactic acid bacteria. Vaccine. 2007 Sep 4;25(36):6581–6588. [PubMed]
28. Poo H, Pyo HM, Lee TY, Yoon SW, Lee JS, Kim CJ, et al. Oral administration of human papillomavirus type 16 E7 displayed on Lactobacillus casei induces E7-specific antitumor effects in C57/BL6 mice. Int J Cancer. 2006 Oct 1;119(7):1702–1709. [PubMed]
29. Hung CF, Ma B, Monie A, Tsen SW, Wu TC. Therapeutic human papillomavirus vaccines: current clinical trials and future directions. Expert Opin Biol Ther. 2008 Apr;8(4):421–439. [PMC free article] [PubMed]
30. Gomez-Gutierrez JG, Elpek KG, Montes de Oca-Luna R, Shirwan H, Sam Zhou H, McMasters KM. Vaccination with an adenoviral vector expressing calreticulin-human papillomavirus 16 E7 fusion protein eradicates E7 expressing established tumors in mice. Cancer Immunol Immunother. 2007 Jul;56(7):997–1007. [PubMed]
31. Baez-Astua A, Herraez-Hernandez E, Garbi N, Pasolli HA, Juarez V, Zur Hausen H, et al. Low-dose adenovirus vaccine encoding chimeric hepatitis B virus surface antigen-human papillomavirus type 16 E7 proteins induces enhanced E7-specific antibody and cytotoxic T-cell responses. J Virol. 2005 Oct;79(20):12807–12817. [PMC free article] [PubMed]
32. Jin HS, Park EK, Lee JM, NamKoong SE, Kim DG, Lee YJ, et al. Immunization with adenoviral vectors carrying recombinant IL-12 and E7 enhanced the antitumor immunity to human papillomavirus 16-associated tumor. Gynecol Oncol. 2005 May;97(2):559–567. [PubMed]
33. Liu DW, Tsao YP, Kung JT, Ding YA, Sytwu HK, Xiao X, et al. Recombinant adeno-associated virus expressing human papillomavirus type 16 E7 peptide DNA fused with heat shock protein DNA as a potential vaccine for cervical cancer. J Virol. 2000 Mar;74(6):2888–2894. [PMC free article] [PubMed]
34. Pozzi E, Basavecchia V, Zanotto C, Pacchioni S, Morghen Cde G, Radaelli A. Construction and characterization of recombinant fowlpox viruses expressing human papilloma virus E6 and E7 oncoproteins. J Virol Methods. 2009 Jun;158(1–2):184–189. [PubMed]
35. Hsieh CJ, Kim TW, Hung CF, Juang J, Moniz M, Boyd DA, et al. Enhancement of vaccinia vaccine potency by linkage of tumor antigen gene to gene encoding calreticulin. Vaccine. 2004 Sep 28;22(29–30):3993–4001. [PubMed]
36. Lamikanra A, Pan ZK, Isaacs SN, Wu TC, Paterson Y. Regression of established human papillomavirus type 16 (HPV-16) immortalized tumors in vivo by vaccinia viruses expressing different forms of HPV-16 E7 correlates with enhanced CD8(+) T-cell responses that home to the tumor site. J Virol. 2001 Oct;75(20):9654–9664. [PMC free article] [PubMed]
37. Borysiewicz LK, Fiander A, Nimako M, Man S, Wilkinson GW, Westmoreland D, et al. A recombinant vaccinia virus encoding human papillomavirus types 16 and 18, E6 and E7 proteins as immunotherapy for cervical cancer. Lancet. 1996 Jun 1;347(9014):1523–1527. [PubMed]
38. Kaufmann AM, Stern PL, Rankin EM, Sommer H, Nuessler V, Schneider A, et al. Safety and immunogenicity of TA-HPV, a recombinant vaccinia virus expressing modified human papillomavirus (HPV)-16 and HPV-18 E6 and E7 genes, in women with progressive cervical cancer. Clin Cancer Res. 2002 Dec;8(12):3676–3685. [PubMed]
39. Davidson EJ, Boswell CM, Sehr P, Pawlita M, Tomlinson AE, McVey RJ, et al. Immunological and clinical responses in women with vulval intraepithelial neoplasia vaccinated with a vaccinia virus encoding human papillomavirus 16/18 oncoproteins. Cancer Res. 2003 Sep 15;63(18):6032–6041. [PubMed]
40. Baldwin PJ, van der Burg SH, Boswell CM, Offringa R, Hickling JK, Dobson J, et al. Vaccinia-expressed human papillomavirus 16 and 18 e6 and e7 as a therapeutic vaccination for vulval and vaginal intraepithelial neoplasia. Clin Cancer Res. 2003 Nov 1;9(14):5205–5213. [PubMed]
41. European Organization for Research and Treatment of Cancer. Surgery and Vaccine Therapy in Treating Patients With Early Cervical Cancer. [Accessed 2009 June 26]. [ClinicalTrials.gov identifier NCT00002916]. US National Institutes of Health, ClinicalTrials.gov [online]. Available from URL: http://www.clinicaltrials.gov.
42. Liao JB, Publicover J, Rose JK, DiMaio D. Single-dose, therapeutic vaccination of mice with vesicular stomatitis virus expressing human papillomavirus type 16 E7 protein. Clin Vaccine Immunol. 2008 May;15(5):817–824. [PMC free article] [PubMed]
43. Riezebos-Brilman A, Regts J, Freyschmidt EJ, Dontje B, Wilschut J, Daemen T. Induction of human papilloma virus E6/E7-specific cytotoxic T-lymphocyte activity in immune-tolerant, E6/E7-transgenic mice. Gene Ther. 2005 Sep;12(18):1410–1414. [PubMed]
44. Daemen T, Riezebos-Brilman A, Regts J, Dontje B, van der Zee A, Wilschut J. Superior therapeutic efficacy of alphavirus-mediated immunization against human papilloma virus type 16 antigens in a murine tumour model: effects of the route of immunization. Antivir Ther. 2004 Oct;9(5):733–742. [PubMed]
45. Riezebos-Brilman A, Regts J, Chen M, Wilschut J, Daemen T. Augmentation of alphavirus vector-induced human papilloma virus-specific immune and anti-tumour responses by co-expression of interleukin-12. Vaccine. 2009 Jan 29;27(5):701–707. [PubMed]
46. Riezebos-Brilman A, Walczak M, Regts J, Rots MG, Kamps G, Dontje B, et al. A comparative study on the immunotherapeutic efficacy of recombinant Semliki Forest virus and adenovirus vector systems in a murine model for cervical cancer. Gene Ther. 2007 Dec;14(24):1695–1704. [PubMed]
47. Velders MP, McElhiney S, Cassetti MC, Eiben GL, Higgins T, Kovacs GR, et al. Eradication of established tumors by vaccination with Venezuelan equine encephalitis virus replicon particles delivering human papillomavirus 16 E7 RNA. Cancer Res. 2001 Nov 1;61(21):7861–7867. [PubMed]
48. Cassetti MC, McElhiney SP, Shahabi V, Pullen JK, Le Poole IC, Eiben GL, et al. Antitumor efficacy of Venezuelan equine encephalitis virus replicon particles encoding mutated HPV16 E6 and E7 genes. Vaccine. 2004 Jan 2;22(3–4):520–527. [PubMed]
49. Cheng WF, Lee CN, Su YN, Chai CY, Chang MC, Polo JM, et al. Sindbis virus replicon particles encoding calreticulin linked to a tumor antigen generate long-term tumor-specific immunity. Cancer Gene Ther. 2006 Sep;13(9):873–885. [PubMed]
50. Corona Gutierrez CM, Tinoco A, Navarro T, Contreras ML, Cortes RR, Calzado P, et al. Therapeutic vaccination with MVA E2 can eliminate precancerous lesions (CIN 1, CIN 2, and CIN 3) associated with infection by oncogenic human papillomavirus. Hum Gene Ther. 2004 May;15(5):421–431. [PubMed]
51. Garcia-Hernandez E, Gonzalez-Sanchez JL, Andrade-Manzano A, Contreras ML, Padilla S, Guzman CC, et al. Regression of papilloma high-grade lesions (CIN 2 and CIN 3) is stimulated by therapeutic vaccination with MVA E2 recombinant vaccine Cancer Gene Ther 2006. Jun;136592–597.597 [PubMed]
52. Albarran YCA, de laGarza A, Cruz Quiroz BJ, Vazquez Zea E, Diaz Estrada I, Mendez Fuentez E, et al. MVA E2 recombinant vaccine in the treatment of human papillomavirus infection in men presenting intraurethral flat condyloma: a phase I/II study. BioDrugs. 2007;21(1):47–59. [PubMed]
53. Transgene. Transgene and Roche Modify the Clinical Development Programme for Their HPV Targeted Immunotherapy TG4001/R3484. 2008. Aug 28, Available from: http://www.transgene.fr/us/pdf/communique_presse/communiques_divers_2008/PR-US-Roche-Transgene-28-08-2008.pdf.
54. Zwaveling S, Ferreira Mota SC, Nouta J, Johnson M, Lipford GB, Offringa R, et al. Established human papillomavirus type 16-expressing tumors are effectively eradicated following vaccination with long peptides. J Immunol. 2002 Jul 1;169(1):350–358. [PubMed]
55. Vambutas A, DeVoti J, Nouri M, Drijfhout JW, Lipford GB, Bonagura VR, et al. Therapeutic vaccination with papillomavirus E6 and E7 long peptides results in the control of both established virus-induced lesions and latently infected sites in a pre-clinical cottontail rabbit papillomavirus model. Vaccine. 2005 Nov 1;23(45):5271–5280. [PubMed]
56. Sharma RK, Elpek KG, Yolcu ES, Schabowsky RH, Zhao H, Bandura-Morgan L, et al. Costimulation as a platform for the development of vaccines: a peptide-based vaccine containing a novel form of 4-1BB ligand eradicates established tumors. Cancer Res. 2009 May 15;69(10):4319–4326. [PMC free article] [PubMed]
57. Manuri PR, Nehete B, Nehete PN, Reisenauer R, Wardell S, Courtney AN, et al. Intranasal immunization with synthetic peptides corresponding to the E6 and E7 oncoproteins of human papillomavirus type 16 induces systemic and mucosal cellular immune responses and tumor protection. Vaccine. 2007 Apr 30;25(17):3302–3310. [PMC free article] [PubMed]
58. Chen YF, Lin CW, Tsao YP, Chen SL. Cytotoxic-T-lymphocyte human papillomavirus type 16 E5 peptide with CpG-oligodeoxynucleotide can eliminate tumor growth in C57BL/6 mice. J Virol. 2004 Feb;78(3):1333–1343. [PMC free article] [PubMed]
59. Daftarian P, Mansour M, Benoit AC, Pohajdak B, Hoskin DW, Brown RG, et al. Eradication of established HPV 16-expressing tumors by a single administration of a vaccine composed of a liposome-encapsulated CTL-T helper fusion peptide in a water-in-oil emulsion. Vaccine. 2006 Jun 12;24(24):5235–5244. [PubMed]
60. Steller MA, Gurski KJ, Murakami M, Daniel RW, Shah KV, Celis E, et al. Cell-mediated immunological responses in cervical and vaginal cancer patients immunized with a lipidated epitope of human papillomavirus type 16 E7. Clin Cancer Res. 1998 Sep;4(9):2103–2109. [PubMed]
61. van Driel WJ, Ressing ME, Kenter GG, Brandt RM, Krul EJ, van Rossum AB, et al. Vaccination with HPV16 peptides of patients with advanced cervical carcinoma: clinical evaluation of a phase I-II trial. Eur J Cancer. 1999 Jun;35(6):946–952. [PubMed]
62. Ressing ME, van Driel WJ, Brandt RM, Kenter GG, de Jong JH, Bauknecht T, et al. Detection of T helper responses, but not of human papillomavirus-specific cytotoxic T lymphocyte responses, after peptide vaccination of patients with cervical carcinoma J Immunother 2000. Mar-Apr;232255–266.266 [PubMed]
63. Muderspach L, Wilczynski S, Roman L, Bade L, Felix J, Small LA, et al. A phase I trial of a human papillomavirus (HPV) peptide vaccine for women with high-grade cervical and vulvar intraepithelial neoplasia who are HPV 16 positive. Clin Cancer Res. 2000 Sep;6(9):3406–3416. [PubMed]
64. Kenter GG, Welters MJ, Valentijn AR, Lowik MJ, Berends-van der Meer DM, Vloon AP, et al. Phase I immunotherapeutic trial with long peptides spanning the E6 and E7 sequences of high-risk human papillomavirus 16 in end-stage cervical cancer patients shows low toxicity and robust immunogenicity. Clin Cancer Res. 2008 Jan 1;14(1):169–177. [PubMed]
65. Melief CJ, Welters MJ, Lowik MJ, Vloon AP, Kenter GG. Long peptide vaccine-induced migration of HPV16-specific type 1 and 2 T cells into the lesions of VIN III patients associated with complete clinical responses. Cancer Immun. 2007;7 Suppl.1
66. Welters MJ, Kenter GG, Piersma SJ, Vloon AP, Lowik MJ, Berends-van der Meer DM, et al. Induction of tumor-specific CD4+ and CD8+ T-cell immunity in cervical cancer patients by a human papillomavirus type 16 E6 and E7 long peptides vaccine. Clin Cancer Res. 2008 Jan 1;14(1):178–187. [PubMed]
67. NCI. Vaccine Therapy in Treating Patients With Advanced or Recurrent Cancer. [Accessed 2009 June 28]. [ClinicalTrials.gov identifier NCT00019110]. US National Institutes of Health, ClinicalTrials.gov [online]. Available from URL: http://www.clinicaltrials.gov.
68. Cui Z, Huang L. Liposome-polycation-DNA (LPD) particle as a carrier and adjuvant for protein-based vaccines: therapeutic effect against cervical cancer. Cancer Immunol Immunother. 2005 Dec;54(12):1180–1190. [PubMed]
69. Stewart TJ, Drane D, Malliaros J, Elmer H, Malcolm KM, Cox JC, et al. ISCOMATRIX adjuvant: an adjuvant suitable for use in anticancer vaccines. Vaccine. 2004 Sep 9;22(27–28):3738–3743. [PubMed]
70. Preville X, Ladant D, Timmerman B, Leclerc C. Eradication of established tumors by vaccination with recombinant Bordetella pertussis adenylate cyclase carrying the human papillomavirus 16 E7 oncoprotein. Cancer Res. 2005 Jan 15;65(2):641–649. [PubMed]
71. Liao CW, Chen CA, Lee CN, Su YN, Chang MC, Syu MH, et al. Fusion protein vaccine by domains of bacterial exotoxin linked with a tumor antigen generates potent immunologic responses and antitumor effects. Cancer Res. 2005 Oct 1;65(19):9089–9098. [PubMed]
72. Chu NR, Wu HB, Wu T, Boux LJ, Siegel MI, Mizzen LA. Immunotherapy of a human papillomavirus (HPV) type 16 E7-expressing tumour by administration of fusion protein comprising Mycobacterium bovis bacille Calmette-Guerin (BCG) hsp65 and HPV16 E7. Clin Exp Immunol. 2000 Aug;121(2):216–225. [PubMed]
73. Liu B, Ye D, Song X, Zhao X, Yi L, Song J, et al. A novel therapeutic fusion protein vaccine by two different families of heat shock proteins linked with HPV16 E7 generates potent antitumor immunity and antiangiogenesis. Vaccine. 2008 Mar 4;26(10):1387–1396. [PubMed]
74. Thompson HS, Davies ML, Holding FP, Fallon RE, Mann AE, O'Neill T, et al. Phase I safety and antigenicity of TA-GW: a recombinant HPV6 L2E7 vaccine for the treatment of genital warts. Vaccine. 1999 Jan;17(1):40–49. [PubMed]
75. Lacey CJ, Thompson HS, Monteiro EF, O'Neill T, Davies ML, Holding FP, et al. Phase IIa safety and immunogenicity of a therapeutic vaccine, TA-GW, in persons with genital warts. J Infect Dis. 1999 Mar;179(3):612–618. [PubMed]
76. de Jong A, O'Neill T, Khan AY, Kwappenberg KM, Chisholm SE, Whittle NR, et al. Enhancement of human papillomavirus (HPV) type 16 E6 and E7-specific T-cell immunity in healthy volunteers through vaccination with TA-CIN, an HPV16 L2E7E6 fusion protein vaccine. Vaccine. 2002 Oct 4;20(29–30):3456–3464. [PubMed]
77. Hallez S, Simon P, Maudoux F, Doyen J, Noel JC, Beliard A, et al. Phase I/II trial of immunogenicity of a human papillomavirus (HPV) type 16 E7 protein-based vaccine in women with oncogenic HPV-positive cervical intraepithelial neoplasia. Cancer Immunol Immunother. 2004 Jul;53(7):642–650. [PubMed]
78. Frazer IH, Quinn M, Nicklin JL, Tan J, Perrin LC, Ng P, et al. Phase 1 study of HPV16-specific immunotherapy with E6E7 fusion protein and ISCOMATRIX adjuvant in women with cervical intraepithelial neoplasia. Vaccine. 2004 Nov 25;23(2):172–181. [PubMed]
79. Palefsky JM, Berry JM, Jay N, Krogstad M, Da Costa M, Darragh TM, et al. A trial of SGN-00101 (HspE7) to treat high-grade anal intraepithelial neoplasia in HIV-positive individuals. AIDS. 2006 May 12;20(8):1151–1155. [PubMed]
80. Einstein MH, Kadish AS, Burk RD, Kim MY, Wadler S, Streicher H, et al. Heat shock fusion protein-based immunotherapy for treatment of cervical intraepithelial neoplasia III. Gynecol Oncol. 2007 Sep;106(3):453–460. [PMC free article] [PubMed]
81. Roman LD, Wilczynski S, Muderspach LI, Burnett AF, O'Meara A, Brinkman JA, et al. A phase II study of Hsp-7 (SGN-00101) in women with high-grade cervical intraepithelial neoplasia. Gynecol Oncol. 2007 Sep;106(3):558–566. [PubMed]
82. Gynecologic Oncology Group. Vaccine Therapy in Preventing Cervical Cancer in Patients with Cervical Intraepithelial Neoplasia. [Accessed 2009 June 8]. [ClinicalTrials.gov identifier NCT00054041]. US National Institutes of Health, ClinicalTrials.gov [online]. Available from URL: http://www.clinicaltrials.gov.
83. Chao Family Comprehensive Cancer Center. SGN-00101 Vaccine in Treating Human Papillomavirus in Patients Who Have Abnormal Cervical Cells. [Accessed 2009 July 1]. [ClinicalTrials.gov identifier NCT00091130]. US National Institutes of Health, ClinicalTrials.gov [online]. Available from URL: http://www.clinicaltrials.gov.
84. Nventa Biopharmaceuticals Corporation. Safety Study to Test the Safety of HspE7 and Poly-ICLC Given in Patients with Cervical Intraepithelial Neoplasia. [Accessed 2009 November 25]. [ClinicalTrials.gov identifier NCT00493545]. United States Food and Drug Administration. ClinicalTrials.gov [online]. Available from URL: http://www.clinicaltrials.gov.
85. Hung CF, Wu TC. Improving DNA vaccine potency via modification of professional antigen presenting cells. Curr Opin Mol Ther. 2003 Feb;5(1):20–24. [PubMed]
86. Tsen SW, Paik AH, Hung CF, Wu TC. Enhancing DNA vaccine potency by modifying the properties of antigen-presenting cells. Expert Rev Vaccines. 2007 Apr;6(2):227–239. [PMC free article] [PubMed]
87. Trimble C, Lin CT, Hung CF, Pai S, Juang J, He L, et al. Comparison of the CD8+ T cell responses and antitumor effects generated by DNA vaccine administered through gene gun, biojector, and syringe. Vaccine. 2003 Sep 8;21(25–26):4036–4042. [PubMed]
88. Chen CA, Chang MC, Sun WZ, Chen YL, Chiang YC, Hsieh CY, et al. Noncarrier naked antigen-specific DNA vaccine generates potent antigen-specific immunologic responses and antitumor effects. Gene Ther. 2009 Jun;16(6):776–787. [PubMed]
89. Yan J, Harris K, Khan AS, Draghia-Akli R, Sewell D, Weiner DB. Cellular immunity induced by a novel HPV18 DNA vaccine encoding an E6/E7 fusion consensus protein in mice and rhesus macaques. Vaccine. 2008 Apr 14; [PubMed]
90. Best SR, Peng S, Juang CM, Hung CF, Hannaman D, Saunders JR, et al. Administration of HPV DNA vaccine via electroporation elicits the strongest CD8+ T cell immune responses compared to intramuscular injection and intradermal gene gun delivery. Vaccine. 2009 Jul 18; [PMC free article] [PubMed]
91. Hung CF, Hsu KF, Cheng WF, Chai CY, He L, Ling M, et al. Enhancement of DNA vaccine potency by linkage of antigen gene to a gene encoding the extracellular domain of Fms-like tyrosine kinase 3-ligand. Cancer Res. 2001 Feb 1;61(3):1080–1088. [PubMed]
92. Hauser H, Chen SY. Augmentation of DNA vaccine potency through secretory heat shock protein-mediated antigen targeting. Methods. 2003 Nov;31(3):225–231. [PubMed]
93. Hauser H, Shen L, Gu QL, Krueger S, Chen SY. Secretory heat-shock protein as a dendritic cell-targeting molecule: a new strategy to enhance the potency of genetic vaccines. Gene Ther. 2004 Jun;11(11):924–932. [PubMed]
94. Hung CF, Cheng WF, Chai CY, Hsu KF, He L, Ling M, et al. Improving vaccine potency through intercellular spreading and enhanced MHC class I presentation of antigen. J Immunol. 2001 May 1;166(9):5733–5740. [PubMed]
95. Hung CF, He L, Juang J, Lin TJ, Ling M, Wu TC. Improving DNA vaccine potency by linking Marek's disease virus type 1 VP22 to an antigen. J Virol. 2002 Mar;76(6):2676–2682. [PMC free article] [PubMed]
96. Cheng WF, Hung CF, Lee CN, Su YN, Chang MC, He L, et al. Naked RNA vaccine controls tumors with down-regulated MHC class I expression through NK cells and perforin-dependent pathways. Eur J Immunol. 2004 Jul;34(7):1892–1900. [PubMed]
97. Cheung YK, Cheng SC, Sin FW, Xie Y. Plasmid encoding papillomavirus Type 16 (HPV16) DNA constructed with codon optimization improved the immunogenicity against HPV infection. Vaccine. 2004 Dec 16;23(5):629–638. [PubMed]
98. Liu WJ, Gao F, Zhao KN, Zhao W, Fernando GJ, Thomas R, et al. Codon modified human papillomavirus type 16 E7 DNA vaccine enhances cytotoxic T-lymphocyte induction and anti-tumour activity. Virology. 2002 Sep 15;301(1):43–52. [PubMed]
99. Lin CT, Tsai YC, He L, Calizo R, Chou HH, Chang TC, et al. A DNA vaccine encoding a codon-optimized human papillomavirus type 16 E6 gene enhances CTL response and anti-tumor activity. J Biomed Sci. 2006 Jul;13(4):481–488. [PubMed]
100. Yan J, Reichenbach DK, Corbitt N, Hokey DA, Ramanathan MP, McKinney KA, et al. Induction of antitumor immunity in vivo following delivery of a novel HPV-16 DNA vaccine encoding an E6/E7 fusion antigen. Vaccine. 2009 Jan 14;27(3):431–440. [PubMed]
101. Lu D, Hoory T, Monie A, Wu A, Wang MC, Hung CF. Treatment with demethylating agent, 5-aza-2'-deoxycytidine enhances therapeutic HPV DNA vaccine potency. Vaccine. 2009 Jul 9;27(32):4363–4369. [PMC free article] [PubMed]
102. Smahel M, Polakova I, Pokorna D, Ludvikova V, Duskova M, Vlasak J. Enhancement of T cell-mediated and humoral immunity of beta-glucuronidase-based DNA vaccines against HPV16 E7 oncoprotein. Int J Oncol. 2008 Jul;33(1):93–101. [PubMed]
103. Massa S, Simeone P, Muller A, Benvenuto E, Venuti A, Franconi R. Antitumor activity of DNA vaccines based on the human papillomavirus-16 E7 protein genetically fused to a plant virus coat protein. Hum Gene Ther. 2008 Apr;19(4):354–364. [PubMed]
104. Chen CH, Wang TL, Hung CF, Yang Y, Young RA, Pardoll DM, et al. Enhancement of DNA vaccine potency by linkage of antigen gene to an HSP70 gene. Cancer Res. 2000 Feb 15;60(4):1035–1042. [PubMed]
105. Huang CY, Chen CA, Lee CN, Chang MC, Su YN, Lin YC, et al. DNA vaccine encoding heat shock protein 60 co-linked to HPV16 E6 and E7 tumor antigens generates more potent immunotherapeutic effects than respective E6 or E7 tumor antigens. Gynecol Oncol. 2007 Dec;107(3):404–412. [PubMed]
106. Cheng WF, Hung CF, Chai CY, Hsu KF, He L, Ling M, et al. Tumor-specific immunity and antiangiogenesis generated by a DNA vaccine encoding calreticulin linked to a tumor antigen. J Clin Invest. 2001 Sep;108(5):669–678. [PMC free article] [PubMed]
107. Kim JW, Hung CF, Juang J, He L, Kim TW, Armstrong DK, et al. Comparison of HPV DNA vaccines employing intracellular targeting strategies. Gene Ther. 2004 Jun;11(12):1011–1018. [PubMed]
108. Peng S, Ji H, Trimble C, He L, Tsai YC, Yeatermeyer J, et al. Development of a DNA vaccine targeting human papillomavirus type 16 oncoprotein E6. J Virol. 2004 Aug;78(16):8468–8476. [PMC free article] [PubMed]
109. Bolhassani A, Zahedifard F, Taghikhani M, Rafati S. Enhanced immunogenicity of HPV16E7 accompanied by Gp96 as an adjuvant in two vaccination strategies. Vaccine. 2008 Jun 19;26(26):3362–3370. [PubMed]
110. Hung CF, Cheng WF, He L, Ling M, Juang J, Lin CT, et al. Enhancing major histocompatibility complex class I antigen presentation by targeting antigen to centrosomes. Cancer Res. 2003 May 15;63(10):2393–2398. [PubMed]
111. Hung CF, Cheng WF, Hsu KF, Chai CY, He L, Ling M, et al. Cancer immunotherapy using a DNA vaccine encoding the translocation domain of a bacterial toxin linked to a tumor antigen. Cancer Res. 2001 May 1;61(9):3698–3703. [PubMed]
112. Huang CH, Peng S, He L, Tsai YC, Boyd DA, Hansen TH, et al. Cancer immunotherapy using a DNA vaccine encoding a single-chain trimer of MHC class I linked to an HPV-16 E6 immunodominant CTL epitope. Gene Ther. 2005 Aug;12(15):1180–1186. [PMC free article] [PubMed]
113. Huang B, Mao CP, Peng S, He L, Hung CF, Wu TC. Intradermal administration of DNA vaccines combining a strategy to bypass antigen processing with a strategy to prolong dendritic cell survival enhances DNA vaccine potency. Vaccine. 2007 Nov 7;25(45):7824–7831. [PMC free article] [PubMed]
114. Wu TC, Guarnieri FG, Staveley-O'Carroll KF, Viscidi RP, Levitsky HI, Hedrick L, et al. Engineering an intracellular pathway for major histocompatibility complex class II presentation of antigens. Proc Natl Acad Sci U S A. 1995 Dec 5;92(25):11671–11675. [PubMed]
115. Ji H, Wang TL, Chen CH, Pai SI, Hung CF, Lin KY, et al. Targeting human papillomavirus type 16 E7 to the endosomal/lysosomal compartment enhances the antitumor immunity of DNA vaccines against murine human papillomavirus type 16 E7-expressing tumors. Hum Gene Ther. 1999 Nov 20;10(17):2727–2740. [PubMed]
116. Hung CF, Tsai YC, He L, Wu TC. DNA vaccines encoding Ii-PADRE generates potent PADRE-specific CD4+ T-cell immune responses and enhances vaccine potency. Mol Ther. 2007 Jun;15(6):1211–1219. [PMC free article] [PubMed]
117. Kim D, Monie A, He L, Tsai YC, Hung CF, Wu TC. Role of IL-2 secreted by PADRE-specific CD4+ T cells in enhancing E7-specific CD8+ T-cell immune responses. Gene Ther. 2008 May;15(9):677–687. [PMC free article] [PubMed]
118. Kim TW, Hung CF, Boyd D, Juang J, He L, Kim JW, et al. Enhancing DNA vaccine potency by combining a strategy to prolong dendritic cell life with intracellular targeting strategies. J Immunol. 2003 Sep 15;171(6):2970–2976. [PubMed]
119. Kim TW, Hung CF, Zheng M, Boyd DA, He L, Pai SI, et al. A DNA vaccine co-expressing antigen and an anti-apoptotic molecule further enhances the antigen-specific CD8+ T-cell immune response. J Biomed Sci. 2004 Jul-Aug;11(4):493–499. [PubMed]
120. Kim TW, Hung CF, Ling M, Juang J, He L, Hardwick JM, et al. Enhancing DNA vaccine potency by coadministration of DNA encoding antiapoptotic proteins. J Clin Invest. 2003 Jul;112(1):109–117. [PMC free article] [PubMed]
121. Kim TW, Lee JH, He L, Boyd DA, Hardwick JM, Hung CF, et al. Modification of professional antigen-presenting cells with small interfering RNA in vivo to enhance cancer vaccine potency. Cancer Res. 2005 Jan 1;65(1):309–316. [PubMed]
122. Cheng WF, Chang MC, Sun WZ, Lee CN, Lin HW, Su YN, et al. Connective tissue growth factor linked to the E7 tumor antigen generates potent antitumor immune responses mediated by an antiapoptotic mechanism. Gene Ther. 2008 Jul;15(13):1007–1016. [PubMed]
123. Huang B, Mao CP, Peng S, Hung CF, Wu TC. RNA interference-mediated in vivo silencing of fas ligand as a strategy for the enhancement of DNA vaccine potency. Hum Gene Ther. 2008 Aug;19(8):763–773. [PubMed]
124. Leachman SA, Tigelaar RE, Shlyankevich M, Slade MD, Irwin M, Chang E, et al. Granulocyte-macrophage colony-stimulating factor priming plus papillomavirus E6 DNA vaccination: effects on papilloma formation and regression in the cottontail rabbit papillomavirus--rabbit model. J Virol. 2000 Sep;74(18):8700–8708. [PMC free article] [PubMed]
125. Chen CH, Wu TC. Experimental vaccine strategies for cancer immunotherapy. J Biomed Sci. 1998 Jul-Aug;5(4):231–252. [PubMed]
126. Kim MS, Sin JI. Both antigen optimization and lysosomal targeting are required for enhanced anti-tumour protective immunity in a human papillomavirus E7-expressing animal tumour model. Immunology. 2005 Oct;116(2):255–266. [PubMed]
127. Ohlschlager P, Quetting M, Alvarez G, Durst M, Gissmann L, Kaufmann AM. Enhancement of immunogenicity of a therapeutic cervical cancer DNA-based vaccine by co-application of sequence-optimized genetic adjuvants. Int J Cancer. 2009 Jul 1;125(1):189–198. [PubMed]
128. Hsieh CY, Chen CA, Huang CY, Chang MC, Lee CN, Su YN, et al. IL-6-encoding tumor antigen generates potent cancer immunotherapy through antigen processing and anti-apoptotic pathways. Mol Ther. 2007 Oct;15(10):1890–1897. [PubMed]
129. Sheets EE, Urban RG, Crum CP, Hedley ML, Politch JA, Gold MA, et al. Immunotherapy of human cervical high-grade cervical intraepithelial neoplasia with microparticle-delivered human papillomavirus 16 E7 plasmid DNA. Am J Obstet Gynecol. 2003 Apr;188(4):916–926. [PubMed]
130. Klencke B, Matijevic M, Urban RG, Lathey JL, Hedley ML, Berry M, et al. Encapsulated plasmid DNA treatment for human papillomavirus 16-associated anal dysplasia: a Phase I study of ZYC101. Clin Cancer Res. 2002 May;8(5):1028–1037. [PubMed]
131. Garcia F, Petry KU, Muderspach L, Gold MA, Braly P, Crum CP, et al. ZYC101a for treatment of high-grade cervical intraepithelial neoplasia: a randomized controlled trial. Obstet Gynecol. 2004 Feb;103(2):317–326. [PubMed]
132. Eisai Inc. A Study of Amolimogene (ZYC101a) in Patients with High Grade Cervical Intraepithelial Lesions of the Uterine Cervix. [Accessed 2009 November 13]. [ClinicalTrials.gov identifier NCT00264732]. US Food and Drug Administration, ClinicalTrials.gov [online]. Available from URL: http://clinicaltrials.gov.
133. Trimble CL, Peng S, Kos F, Gravitt P, Viscidi R, Sugar E, et al. A phase I trial of a human papillomavirus DNA vaccine for HPV16+ cervical intraepithelial neoplasia 2/3. Clin Cancer Res. 2009 Jan 1;15(1):361–367. [PMC free article] [PubMed]
134. VGX Pharmaceuticals, Inc. Phase I of Human Papillomavirus (HPV) DNA Plasmid (VGX-3100) + Electroporation for CIN 2 or 3. [Accessed 2009 July 13]. [ClinicalTrials.gov identifier NCT00685412]. US National Institutes of Health, ClinicalTrials.gov [online]. Available from URL: http://www.clinicaltrials.gov.
135. Berglund P, Quesada-Rolander M, Putkonen P, Biberfeld G, Thorstensson R, Liljestrom P. Outcome of immunization of cynomolgus monkeys with recombinant Semliki Forest virus encoding human immunodeficiency virus type 1 envelope protein and challenge with a high dose of SHIV-4 virus. AIDS Res Hum Retroviruses. 1997 Nov 20;13(17):1487–1495. [PubMed]
136. Berglund P, Smerdou C, Fleeton MN, Tubulekas I, Liljestrom P. Enhancing immune responses using suicidal DNA vaccines. Nat Biotechnol. 1998 Jun;16(6):562–565. [PubMed]
137. Hariharan MJ, Driver DA, Townsend K, Brumm D, Polo JM, Belli BA, et al. DNA immunization against herpes simplex virus: enhanced efficacy using a Sindbis virus-based vector. J Virol. 1998 Feb;72(2):950–958. [PMC free article] [PubMed]
138. Cheng WF, Hung CF, Hsu KF, Chai CY, He L, Polo JM, et al. Cancer immunotherapy using Sindbis virus replicon particles encoding a VP22-antigen fusion. Hum Gene Ther. 2002 Mar 1;13(4):553–568. [PubMed]
139. Pushko P, Parker M, Ludwig GV, Davis NL, Johnston RE, Smith JF. Replicon-helper systems from attenuated Venezuelan equine encephalitis virus: expression of heterologous genes in vitro and immunization against heterologous pathogens in vivo. Virology. 1997 Dec 22;239(2):389–401. [PubMed]
140. Hsu KF, Hung CF, Cheng WF, He L, Slater LA, Ling M, et al. Enhancement of suicidal DNA vaccine potency by linking Mycobacterium tuberculosis heat shock protein 70 to an antigen. Gene Ther. 2001 Mar;8(5):376–383. [PubMed]
141. Kim TW, Hung CF, Juang J, He L, Hardwick JM, Wu TC. Enhancement of suicidal DNA vaccine potency by delaying suicidal DNA-induced cell death. Gene Ther. 2004 Feb;11(3):336–342. [PubMed]
142. Varnavski AN, Young PR, Khromykh AA. Stable high-level expression of heterologous genes in vitro and in vivo by noncytopathic DNA-based Kunjin virus replicon vectors. J Virol. 2000 May;74(9):4394–4403. [PMC free article] [PubMed]
143. Herd KA, Harvey T, Khromykh AA, Tindle RW. Recombinant Kunjin virus replicon vaccines induce protective T-cell immunity against human papillomavirus 16 E7-expressing tumour. Virology. 2004 Feb 20;319(2):237–248. [PubMed]
144. Santin AD, Bellone S, Roman JJ, Burnett A, Cannon MJ, Pecorelli S. Therapeutic vaccines for cervical cancer: dendritic cell-based immunotherapy. Curr Pharm Des. 2005;11(27):3485–3500. [PubMed]
145. Williams JC. Dendreon Corporation. Data Presented at AUA Demonstrate PROVENGE Significantly Prolongs Survival for Men with Advanced Prostate Cancer in Pivotal Phase 3 IMPACT Study [online] [Accessed 2009 Apr 30]. Available from URL: http://investor.dendreon.com/releasedetail.cfm?ReleaseID=380042.
146. Tillman BW, Hayes TL, DeGruijl TD, Douglas JT, Curiel DT. Adenoviral vectors targeted to CD40 enhance the efficacy of dendritic cell-based vaccination against human papillomavirus 16-induced tumor cells in a murine model. Cancer Res. 2000 Oct 1;60(19):5456–5463. [PubMed]
147. Mackova J, Kutinova L, Hainz P, Krystofova J, Sroller V, Otahal P, et al. Adjuvant effect of dendritic cells transduced with recombinant vaccinia virus expressing HPV16-E7 is inhibited by co-expression of IL12. Int J Oncol. 2004 Jun;24(6):1581–1588. [PubMed]
148. Murakami M, Gurski KJ, Marincola FM, Ackland J, Steller MA. Induction of specific CD8+ T-lymphocyte responses using a human papillomavirus-16 E6/E7 fusion protein and autologous dendritic cells. Cancer Res. 1999 Mar 15;59(6):1184–1187. [PubMed]
149. Peng S, Kim TW, Lee JH, Yang M, He L, Hung CF, et al. Vaccination with dendritic cells transfected with BAK and BAX siRNA enhances antigen-specific immune responses by prolonging dendritic cell life. Hum Gene Ther. 2005 May;16(5):584–593. [PMC free article] [PubMed]
150. Kim JH, Kang TH, Noh KH, Bae HC, Kim SH, Yoo YD, et al. Enhancement of dendritic cell-based vaccine potency by anti-apoptotic siRNAs targeting key pro-apoptotic proteins in cytotoxic CD8(+) T cell-mediated cell death. Immunol Lett. 2009 Jan 29;122(1):58–67. [PubMed]
151. Adams M, Navabi H, Jasani B, Man S, Fiander A, Evans AS, et al. Dendritic cell (DC) based therapy for cervical cancer: use of DC pulsed with tumour lysate and matured with a novel synthetic clinically non-toxic double stranded RNA analogue poly [I]:poly [C(12)U] (Ampligen R) Vaccine. 2003 Jan 30;21(7–8):787–790. [PubMed]
152. Wang TL, Ling M, Shih IM, Pham T, Pai SI, Lu Z, et al. Intramuscular administration of E7-transfected dendritic cells generates the most potent E7-specific anti-tumor immunity. Gene Ther. 2000 May;7(9):726–733. [PubMed]
153. Benencia F, Courreges MC, Coukos G. Whole tumor antigen vaccination using dendritic cells: comparison of RNA electroporation and pulsing with UV-irradiated tumor cells. J Transl Med. 2008;6:21 [PMC free article] [PubMed]
154. Santin AD, Bellone S, Gokden M, Cannon MJ, Parham GP. Vaccination with HPV-18 E7-pulsed dendritic cells in a patient with metastatic cervical cancer. N Engl J Med. 2002 May 30;346(22):1752–1753. [PubMed]
155. Ferrara A, Nonn M, Sehr P, Schreckenberger C, Pawlita M, Durst M, et al. Dendritic cell-based tumor vaccine for cervical cancer II: results of a clinical pilot study in 15 individual patients. J Cancer Res Clin Oncol. 2003 Sep;129(9):521–530. [PubMed]
156. Santin AD, Bellone S, Palmieri M, Ravaggi A, Romani C, Tassi R, et al. HPV16/18 E7-pulsed dendritic cell vaccination in cervical cancer patients with recurrent disease refractory to standard treatment modalities. Gynecol Oncol. 2006 Mar;100(3):469–478. [PubMed]
157. Santin AD, Bellone S, Palmieri M, Zanolini A, Ravaggi A, Siegel ER, et al. Human papillomavirus type 16 and 18 E7-pulsed dendritic cell vaccination of stage IB or IIA cervical cancer patients: a phase I escalating-dose trial. J Virol. 2008 Feb;82(4):1968–1979. [PMC free article] [PubMed]
158. National Taiwan University Hospital. Immunotherapy of Recurrent Cervical Cancers Using Dendritic Cells (DCs) [Accessed 2009 June 22]. [ClinicalTrials.gov identifier NCT00155766]. US National Institutes of Health, ClinicalTrials.gov [online]. Available from URL: http://www.clinicaltrials.gov.
159. Bubenik J, Simova J, Hajkova R, Sobota V, Jandlova T, Smahel M, et al. Interleukin 2 gene therapy of residual disease in mice carrying tumours induced by HPV 16. Int J Oncol. 1999 Mar;14(3):593–597. [PubMed]
160. Hallez S, Detremmerie O, Giannouli C, Thielemans K, Gajewski TF, Burny A, et al. Interleukin-12-secreting human papillomavirus type 16-transformed cells provide a potent cancer vaccine that generates E7-directed immunity. Int J Cancer. 1999 May 5;81(3):428–437. [PubMed]
161. Mikyskova R, Indrova M, Simova J, Jandlova T, Bieblova J, Jinoch P, et al. Treatment of minimal residual disease after surgery or chemotherapy in mice carrying HPV16-associated tumours: Cytokine and gene therapy with IL-2 and GM-CSF. Int J Oncol. 2004 Jan;24(1):161–167. [PubMed]
162. Chang EY, Chen CH, Ji H, Wang TL, Hung K, Lee BP, et al. Antigen-specific cancer immunotherapy using a GM-CSF secreting allogeneic tumor cell-based vaccine. Int J Cancer. 2000 Jun 1;86(5):725–730. [PubMed]
163. de Gruijl TD, van den Eertwegh AJ, Pinedo HM, Scheper RJ. Whole-cell cancer vaccination: from autologous to allogeneic tumor- and dendritic cell-based vaccines. Cancer Immunol Immunother. 2008 Oct;57(10):1569–1577. [PMC free article] [PubMed]
164. Chen CH, Wang TL, Hung CF, Pardoll DM, Wu TC. Boosting with recombinant vaccinia increases HPV-16 E7-specific T cell precursor frequencies of HPV-16 E7-expressing DNA vaccines. Vaccine. 2000 Apr 3;18(19):2015–2022. [PubMed]
165. Wlazlo AP, Deng H, Giles-Davis W, Ertl HC. DNA vaccines against the human papillomavirus type 16 E6 or E7 oncoproteins. Cancer Gene Ther. 2004 Jun;11(6):457–464. [PubMed]
166. Rittich S, Duskova M, Mackova J, Pokorna D, Jinoch P, Smahel M. Combined immunization with DNA and transduced tumor cells expressing mouse GM-CSF or IL-2. Oncol Rep. 2005 Feb;13(2):311–317. [PubMed]
167. Lin CT, Hung CF, Juang J, He L, Lin KY, Kim TW, et al. Boosting with recombinant vaccinia increases HPV-16 E7-Specific T cell precursor frequencies and antitumor effects of HPV-16 E7-expressing Sindbis virus replicon particles. Mol Ther. 2003 Oct;8(4):559–566. [PubMed]
168. Mackova J, Stasikova J, Kutinova L, Masin J, Hainz P, Simsova M, et al. Prime/boost immunotherapy of HPV16-induced tumors with E7 protein delivered by Bordetella adenylate cyclase and modified vaccinia virus Ankara. Cancer Immunol Immunother. 2006 Jan;55(1):39–46. [PubMed]
169. Kast WM. VEEV Replicon-Based Vaccines Used in Heterologous Prime Boost Strategies Induce Lifelong Protection againt Cancer and Therapy of Cervical Cancer in Mice and Robust Cell-mediated Immunity in Rhesus macques. Vaccine Technology II. 2008:P09.
170. Smyth LJ, Van Poelgeest MI, Davidson EJ, Kwappenberg KM, Burt D, Sehr P, et al. Immunological responses in women with human papillomavirus type 16 (HPV-16)-associated anogenital intraepithelial neoplasia induced by heterologous prime-boost HPV-16 oncogene vaccination. Clin Cancer Res. 2004 May 1;10(9):2954–2961. [PubMed]
171. Fiander AN, Tristram AJ, Davidson EJ, Tomlinson AE, Man S, Baldwin PJ, et al. Prime-boost vaccination strategy in women with high-grade, noncervical anogenital intraepithelial neoplasia: clinical results from a multicenter phase II trial. Int J Gynecol Cancer. 2006 May-Jun;16(3):1075–1081. [PubMed]
172. Davidson EJ, Faulkner RL, Sehr P, Pawlita M, Smyth LJ, Burt DJ, et al. Effect of TA-CIN (HPV 16 L2E6E7) booster immunisation in vulval intraepithelial neoplasia patients previously vaccinated with TA-HPV (vaccinia virus encoding HPV 16/18 E6E7) Vaccine. 2004 Jul 29;22(21–22):2722–2729. [PubMed]
173. Johns Hopkins University. Vaccine Therapy With or Without Imiquimod in Treating Patients With Grade 3 Cervical Intraepithelial Neoplasia. [Accessed 2009 June 4]. [ClinicalTrials.gov identifier NCT00788164]. US National Institutes of Health, ClinicalTrials.gov [online]. Available from URL: http://wwwclinicaltrials.gov.
174. Yue FY, Dummer R, Geertsen R, Hofbauer G, Laine E, Manolio S, et al. Interleukin-10 is a growth factor for human melanoma cells and down-regulates HLA class-I, HLA class-II and ICAM-1 molecules. Int J Cancer. 1997 May 16;71(4):630–637. [PubMed]
175. Gorelik L, Flavell RA. Immune-mediated eradication of tumors through the blockade of transforming growth factor-beta signaling in T cells. Nat Med. 2001 Oct;7(10):1118–1122. [PubMed]
176. Chuang CM, Hoory T, Monie A, Wu A, Wang MC, Hung CF. Enhancing therapeutic HPV DNA vaccine potency through depletion of CD4+CD25+ T regulatory cells. Vaccine. 2009 Jan 29;27(5):684–689. [PMC free article] [PubMed]
177. Goldberg MV, Maris CH, Hipkiss EL, Flies AS, Zhen L, Tuder RM, et al. Role of PD-1 and its ligand, B7-H1, in early fate decisions of CD8 T cells. Blood. 2007 Jul 1;110(1):186–192. [PubMed]
178. Yu H, Kortylewski M, Pardoll D. Crosstalk between cancer and immune cells: role of STAT3 in the tumour microenvironment. Nat Rev Immunol. 2007 Jan;7(1):41–51. [PubMed]
179. Groh V, Wu J, Yee C, Spies T. Tumour-derived soluble MIC ligands impair expression of NKG2D and T-cell activation. Nature. 2002 Oct 17;419(6908):734–738. [PubMed]
180. Munn DH, Mellor AL. IDO and tolerance to tumors. Trends Mol Med. 2004 Jan;10(1):15–18. [PubMed]
181. Rubinstein N, Alvarez M, Zwirner NW, Toscano MA, Ilarregui JM, Bravo A, et al. Targeted inhibition of galectin-1 gene expression in tumor cells results in heightened T cell-mediated rejection; A potential mechanism of tumor-immune privilege. Cancer Cell. 2004 Mar;5(3):241–251. [PubMed]
182. Kim R, Emi M, Tanabe K, Arihiro K. Tumor-driven evolution of immunosuppressive networks during malignant progression. Cancer Res. 2006 Jun 1;66(11):5527–5536. [PubMed]
183. Kang TH, Lee JH, Song CK, Han HD, Shin BC, Pai SI, et al. Epigallocatechin-3-gallate enhances CD8+ T cell-mediated antitumor immunity induced by DNA vaccination. Cancer Res. 2007 Jan 15;67(2):802–811. [PMC free article] [PubMed]
184. Bae SH, Park YJ, Park JB, Choi YS, Kim MS, Sin JI. Therapeutic synergy of human papillomavirus E7 subunit vaccines plus cisplatin in an animal tumor model: causal involvement of increased sensitivity of cisplatin-treated tumors to CTL-mediated killing in therapeutic synergy. Clin Cancer Res. 2007 Jan 1;13(1):341–349. [PubMed]
185. Ye GW, Park JB, Park YJ, Choi YS, Sin JI. Increased sensitivity of radiated murine cervical cancer tumors to E7 subunit vaccine-driven CTL-mediated killing induces synergistic anti-tumor activity. Mol Ther. 2007 Aug;15(8):1564–1570. [PubMed]
186. Tseng CW, Monie A, Wu CY, Huang B, Wang MC, Hung CF, et al. Treatment with proteasome inhibitor bortezomib enhances antigen-specific CD8+ T-cell-mediated antitumor immunity induced by DNA vaccination. J Mol Med. 2008 Aug;86(8):899–908. [PMC free article] [PubMed]
187. Tseng CW, Trimble C, Zeng Q, Monie A, Alvarez RD, Huh WK, et al. Low-dose radiation enhances therapeutic HPV DNA vaccination in tumor-bearing hosts. Cancer Immunol Immunother. 2009 May;58(5):737–748. [PMC free article] [PubMed]
188. Chuang CM, Monie A, Wu A, Hung CF. Combination of apigenin treatment with therapeutic HPV DNA vaccination generates enhanced therapeutic antitumor effects. J Biomed Sci. 2009 May 27;16(1):49. [PMC free article] [PubMed]
189. Patel D, Shukla S, Gupta S. Apigenin and cancer chemoprevention: progress, potential and promise (review) Int J Oncol. 2007 Jan;30(1):233–245. [PubMed]
190. Tseng CW, Monie A, Trimble C, Alvarez RD, Huh WK, Buchsbaum DJ, et al. Combination of treatment with death receptor 5-specific antibody with therapeutic HPV DNA vaccination generates enhanced therapeutic anti-tumor effects. Vaccine. 2008 Aug 12;26(34):4314–4319. [PMC free article] [PubMed]