There is no licenced vaccine against any human parasitic disease and Plasmodium falciparum malaria, a major cause of infectious mortality, presents a great challenge to vaccine developers. This has led to the assessment of a wide variety of approaches to malaria vaccine design and development, assisted by the availability of a safe challenge model for small-scale efficacy testing of vaccine candidates. Malaria vaccine development has been at the forefront of assessing many new vaccine technologies including novel adjuvants, vectored prime-boost regimes and the concept of community vaccination to block malaria transmission. Most current vaccine candidates target a single stage of the parasite's life cycle and vaccines against the early pre-erythrocytic stages have shown most success. A protein in adjuvant vaccine, working through antibodies against sporozoites, and viral vector vaccines targeting the intracellular liver-stage parasite with cellular immunity show partial efficacy in humans, and the anti-sporozoite vaccine is currently in phase III trials. However, a more effective malaria vaccine suitable for widespread cost-effective deployment is likely to require a multi-component vaccine targeting more than one life cycle stage. The most attractive near-term approach to develop such a product is to combine existing partially effective pre-erythrocytic vaccine candidates.
vaccines; parasite; malaria
Overcoming antigenic variation is one of the major challenges in the development of an effective vaccine against Plasmodium falciparum, a causative agent of human malaria. Inclusion of multiple antigen variants in subunit vaccine candidates is one strategy that has aimed to overcome this problem for the leading blood-stage malaria vaccine targets, merozoite surface protein 1 (MSP1) and apical membrane antigen 1 (AMA1). However previous studies, utilizing malaria antigens, have concluded that inclusion of multiple allelic variants, encoding altered peptide ligands (APL), in such a vaccine may be detrimental to both the priming and in vivo re-stimulation of antigen-experienced T cells. Here we analyze the T cell responses to two alleles of MSP1 and AMA1 induced by vaccination of malaria-naïve adult volunteers with bi-valent viral vectored vaccine candidates. We show a significant bias to the 3D7/MAD20 allele compared to the Wellcome allele for the 33kDa region of MSP1, but not for the 19kDa fragment or the AMA1 antigen. Whilst this bias could be caused by ‘immune interference’ at priming, the data don’t support a significant role for ‘immune antagonism’ during memory T cell re-stimulation, despite observation of the latter at a minimal epitope level in vitro. A lack of class I HLA epitopes in the Wellcome allele that are recognized by vaccinated volunteers may in fact contribute to the observed bias. We also show that controlled infection with 3D7 strain P. falciparum parasites neither boosts existing 3D7-specific T cell responses nor appears to ‘immune divert’ cellular responses towards the Wellcome allele.
An effective vaccine against P. falciparum malaria remains a global health priority. Blood-stage vaccines are an important component of this effort, with some indications of recent progress. However only a fraction of potential blood-stage antigens have been tested, highlighting a critical need for efficient down-selection strategies. Functional in vitro assays such as the growth/invasion inhibition assays (GIA) are widely used, but it is unclear whether GIA activity correlates with protection or predicts vaccine efficacy. While preliminary data in controlled human malaria infection (CHMI) studies indicate a possible association between in vitro and in vivo parasite growth rates, there have been conflicting results of immunoepidemiology studies, where associations with exposure rather than protection have been observed. In addition, GIA-interfering antibodies in vaccinated individuals from endemic regions may limit assay sensitivity in heavily malaria-exposed populations. More work is needed to establish the utility of GIA for blood-stage vaccine development.
GIA; Growth inhibition assay; Plasmodium falciparum; blood-stage; growth inhibition activity; malaria; parasite multiplication rate; vaccine
Rodent malaria species Plasmodium yoelii and P. chabaudi have been widely used to validate vaccine approaches targeting blood-stage merozoite antigens. However, increasing data suggest the P. berghei rodent malaria may be able to circumvent vaccine-induced anti-merozoite responses. Here we confirm a failure to protect against P. berghei, despite successful antibody induction against leading merozoite antigens using protein-in-adjuvant or viral vectored vaccine delivery. No subunit vaccine approach showed efficacy in mice following immunization and challenge with the wild-type P. berghei strains ANKA or NK65, or against a chimeric parasite line encoding a merozoite antigen from P. falciparum. Protection was not improved in knockout mice lacking the inhibitory Fc receptor CD32b, nor against a Δsmac
P. berghei parasite line with a non-sequestering phenotype. An improved understanding of the mechanisms responsible for protection, or failure of protection, against P. berghei merozoites could guide the development of an efficacious vaccine against P. falciparum.
► Current influenza vaccines do not generate heterologous protection. ► Targeting internal influenza antigens may confer cross protection. ► We tested Adenovirus and MVA vectored NP and M1 in chickens. ► Heterologous prime-boost resulted in earlier cessation of viral shedding.
Current vaccines targeting surface proteins can drive antigenic variation resulting either in the emergence of more highly pathogenic viruses or of antigenically distinct viruses that escape control by vaccination and thereby persist in the host population. Influenza vaccines typically target the highly mutable surface proteins and do not provide protection against heterologous challenge. Vaccines which induce immune responses against conserved influenza epitopes may confer protection against heterologous challenge. We report here the results of vaccination with recombinant modified Vaccinia virus Ankara (MVA) and Adenovirus (Ad) expressing a fusion construct of nucleoprotein and matrix protein (NP + M1). Prime and boost vaccination regimes were trialled in different ages of chicken and were found to be safe and immunogenic. Interferon-γ (IFN-γ) ELISpot was used to assess the cellular immune response post secondary vaccination. In ovo Ad prime followed by a 4 week post hatch MVA boost was identified as the most immunogenic regime in one outbred and two inbred lines of chicken. Following vaccination, one inbred line (C15I) was challenged with low pathogenic avian influenza (LPAI) H7N7 (A/Turkey/England/1977). Birds receiving a primary vaccination with Ad-NP + M1 and a secondary vaccination with MVA-NP + M1 exhibited reduced cloacal shedding as measured by plaque assay at 7 days post infection compared with birds vaccinated with recombinant viruses containing irrelevant antigen. This preliminary indication of efficacy demonstrates proof of concept in birds; induction of T cell responses in chickens by viral vectors containing internal influenza antigens may be a productive strategy for the development of vaccines to induce heterologous protection against influenza in poultry.
AI, avian influenza; NP + M1, fusion construct of influenza nucleoprotein and matrix protein; SFU, spot-forming units; dpb, days post boost; dpi, days post infection; wph, weeks post hatch; SPF, specific pathogen free; Influenza; LPAI; Vaccine; Chicken; MVA; Adenovirus
Current vaccine strategies against the asexual blood-stage of Plasmodium falciparum are mostly focused on well-studied merozoite antigens which induce immune responses after natural exposure, but have yet to induce robust protection in any clinical trial. Here we compare human-compatible viral vectored vaccines targeting ten different blood-stage antigens. We show that the full-length P. falciparum reticulocyte-binding protein homologue 5 (PfRH5) is highly susceptible to cross-strain neutralizing vaccine-induced antibodies, out-performing all other antigens delivered by the same vaccine platform. We find that despite being susceptible to antibody, PfRH5 is unlikely to be under substantial immune selection pressure; there is minimal acquisition of anti-PfRH5 IgG antibodies in malaria-exposed Kenyans. These data challenge the widespread beliefs that any merozoite antigen that is highly susceptible to immune attack would be subject to significant levels of antigenic polymorphism, and that erythrocyte invasion by P. falciparum is a degenerate process involving a series of parallel redundant pathways.
Apical membrane antigen 1 (AMA1) is one of the leading candidate antigens for inclusion in a subunit vaccine against blood-stage malaria. However, the efficacy of antibody-inducing recombinant AMA1 protein vaccines in Phase IIa/b clinical trials to date remains disappointing. Here we describe the development of recombinant human adenovirus serotype 5 (AdHu5) and modified vaccinia virus Ankara (MVA) vectors encoding AMA1 from the Plasmodium chabaudi chabaudi strain AS (PccAS). These vectors, when used in a heterologous prime-boost regime in BALB/c mice, are capable of inducing strong transgene-specific humoral as well as cellular immune responses. We show that this vaccination regime is protective against a non-lethal PccAS blood-stage challenge, resulting in reduced peak parasitemias. The role of vaccine-induced, AMA1-specific antibodies and T cells in mediating anti-parasite effect was investigated by in vivo depletion of CD4+ T cells and adoptive transfer studies into naive and immunodeficient mice. Depletion of CD4+ T cells led to a loss of vaccine-induced protection. Adoptive transfer studies confirmed that efficacy is mediated by both CD4+ T cells and antibodies functioning in the context of an intact immune system. Unlike previous studies, these results confirm that antigen-specific CD4+ T cells, induced by a clinically relevant vaccine delivery platform, can make a significant contribution to vaccine blood-stage efficacy in the P. chabaudi model. Given cell-mediated immunity may also contribute to parasite control in human malaria, these data support the clinical development of viral vectored vaccines that induce both T cell and antibodies against P. falciparum blood-stage malaria antigens like AMA1.
Vaccines have made a major contribution to global health in recent decades but they could do much more. In November 2011, a Royal Society discussion meeting, ‘New vaccines for global health’, was held in London to discuss the past contribution of vaccines to global health and to consider what more could be expected in the future. Papers presented at the meeting reviewed recent successes in the deployment of vaccines against major infections of childhood and the challenges faced in developing vaccines against some of the world's remaining major infectious diseases such as human immunodeficiency virus (HIV), malaria and tuberculosis. The important contribution that development of more effective veterinary vaccines could make to global health was also addressed. Some of the social and financial challenges to the development and deployment of new vaccines were reviewed. The latter issues were also discussed at a subsequent satellite meeting, ‘Accelerating vaccine development’, held at the Kavli Royal Society International Centre. Delegates at this meeting considered challenges to the more rapid development and deployment of both human and veterinary vaccines and how these might be addressed. Papers based on presentations at the discussion meeting and a summary of the main conclusions of the satellite meeting are included in this issue of Philosophical Transactions of the Royal Society B.
global health; vaccine introduction; new vaccines
The rate of decay of antibody concentration following serogroup C meningococcal (MenC) polysaccharide-protein conjugate vaccination varies between individuals. This depends partly on vaccination age but may be influenced by human genetics. We studied 721 single nucleotide polymorphisms (SNPs) across 131 candidate genes in a first cohort of 905 Caucasians (11 to 21 years old; mean time after vaccination, 4.9 years) and 30 SNPs across 17 genes in a replication study using 155 children, aged 6 to 12 years (mean time after vaccination, 6.7 years), and 196 infants (1 year old; mean time after vaccination, 8 months). Individuals were classified as responders or nonresponders for total MenC IgG concentration and MenC serum bactericidal antibody (SBA) measurements. Associated genes were examined further for quantitative outcome measures. Fifty-nine SNPs in 37 genes were associated with IgG persistence (adjusted for age at measurement), and 56 SNPs in 36 genes were associated with SBA persistence (adjusted for age at measurement and vaccine used). Three SNPs each within the Toll-like receptor 3 (TLR3) (rs3775291, rs3775292, and rs5743312) and CD44 (rs11033013, rs353644, and rs996076) genes were associated with IgG (adjusted for age at measurement) or SBA (adjusted for age at measurement and vaccine used) persistence in the initial genetic study (P, 0.02 to 0.04). Single SNPs within the TLR3 (rs7657186) (P = 0.004 [unadjusted]) and CD44 (rs12419062) (P = 0.01 [unadjusted]) genes were associated with IgG persistence in the replication study. These results suggest that genetic polymorphisms in the TLR3 and CD44 genes are associated with the persistence of the immune response to MenC vaccines 1 to 6 years after vaccination.
► We compared 3 doses of a the candidate TB vaccine MVA85A. ► All doses of the vaccine were safe and induced a Th1 type immune response. ► The strongest and most sustained response was seen with the highest dose of MVA85A. ► A high dose of 1 × 108 PFU of MVA85A is safe and induces sustained immunity.
A non-randomised, open-label, Phase I safety and immunogenicity dose-finding study to assess the safety and immunogenicity of the candidate TB vaccine Modified Vaccinia virus Ankara expressing Antigen 85A (MVA85A) from Mycobacterium tuberculosis (MTB) in healthy adult volunteers previously vaccinated with BCG.
Healthy BCG-vaccinated volunteers were vaccinated with either 1 × 107 or 1 × 108 PFU of MVA85A. All adverse events were documented and antigen specific T cell responses were measured using an ex vivo IFN-γ ELISPOT assay. Safety and immunogenicity were compared between the 2 dose groups and with a previous trial in which a dose of 5 × 107 PFU MVA85A had been administered.
There were no serious adverse events recorded following administration of either 1 × 107 or 1 × 108 PFU of MVA85A. Systemic adverse events were more frequently reported following administration of 1 × 108 PFU of MVA85A when compared to either 5 × 107 or 1 × 107 PFU of MVA85A but were mild or moderate in severity and resolved completely within 7 days of immunisation. Antigen specific T cell responses as measured by the IFN-γ ELISPOT were significantly higher following immunisation in adults receiving 1 × 108 PFU compared to the 5 × 107 and 1 × 107 doses. Additionally, a broader range of Ag85A epitopes are detected following 1 × 108 PFU of MVA85A.
A higher dose of 1 × 108 PFU of MVA85A is well-tolerated, increases the frequency of IFN-γ secreting T cells detected following immunisation and broadens the range of Ag85A epitopes detected.
Tuberculosis; Vaccine; BCG; MVA
Signal transduction pathways activated by Toll-like Receptors and the IL-1 family of cytokines are fundamental to mounting an innate immune response and thus to clearing pathogens and promoting wound healing. Whilst mechanistic understanding of the regulation of innate signalling pathways has advanced considerably in recent years, there are still a number of critical controllers to be discovered. In order to characterise novel regulators of macrophage inflammation, we have carried out an extensive, cDNA-based forward genetic screen and identified 34 novel activators, based on their ability to induce the expression of cxcl2. Many are physiologically expressed in macrophages, although the majority of genes uncovered in our screen have not previously been linked to innate immunity. We show that expression of particular activators has profound but distinct impacts on LPS-induced inflammatory gene expression, including switch-type, amplifier and sensitiser behaviours. Furthermore, the novel genes identified here interact with the canonical inflammatory signalling network via specific mechanisms, as demonstrated by the use of dominant negative forms of IL1/TLR signalling mediators.
Recombinant adenoviruses are among the most promising tools for vaccine antigen delivery. Recently, the development of new vectors has focused on serotypes to which the human population is less exposed in order to circumvent pre-existing anti vector immunity. This study describes the derivation of a new vaccine vector based on a chimpanzee adenovirus, Y25, together with a comparative assessment of its potential to elicit transgene product specific immune responses in mice. The vector was constructed in a bacterial artificial chromosome to facilitate genetic manipulation of genomic clones. In order to conduct a fair head-to-head immunological comparison of multiple adenoviral vectors, we optimised a method for accurate determination of infectious titre, since this parameter exhibits profound natural variability and can confound immunogenicity studies when doses are based on viral particle estimation. Cellular immunogenicity of recombinant E1 E3-deleted vector ChAdY25 was comparable to that of other species E derived chimpanzee adenovirus vectors including ChAd63, the first simian adenovirus vector to enter clinical trials in humans. Furthermore, the prevalence of virus neutralizing antibodies (titre >1∶200) against ChAdY25 in serum samples collected from two human populations in the UK and Gambia was particularly low compared to published data for other chimpanzee adenoviruses. These findings support the continued development of new chimpanzee adenovirus vectors, including ChAdY25, for clinical use.
Replication-deficient adenovirus and modified vaccinia virus Ankara (MVA) vectors expressing single pre-erythrocytic or blood-stage Plasmodium falciparum antigens have entered clinical testing using a heterologous prime-boost immunization approach. Here we investigated the utility of the same immunization regime when combining viral vectored vaccines expressing the 42kDa C-terminus of the blood-stage antigen merozoite surface protein 1 (MSP142) and the pre-erythrocytic antigen circumsporozoite protein (CSP) in the P. yoelii mouse model. We find that vaccine co-administration leads to maintained antibody responses and efficacy against blood-stage infection, but reduced secondary CD8+ T cell responses against both antigens and efficacy against liver-stage infection. CD8+ T cell interference can be minimized by co-administering the MVA vaccines at separate sites, resulting in enhanced liver-stage efficacy in mice immunized against both antigens compared to just one. CD8+ T cell interference (following MVA co-administration as a mixture) may partly be caused by a lack of physiological space for high magnitude responses against multiple antigens, but is not caused by competition for presentation of antigen on MHC class I molecules, nor is it due to restricted T cell access to APCs presenting both antigens. Instead, enhanced killing of peptide-pulsed cells is observed in mice possessing pre-existing T cells against two antigens, in comparison to just one, suggesting priming against multiple antigens may in part reduce the potency of multi-antigen MVA vectors to stimulate secondary CD8+ T cell responses. These data have important implications for the development of a multi-stage or multi-component viral vectored malaria vaccine for use in humans.
(See the editorial commentary by Dockrell, on pages 1029–31.)
Background. There is currently no safe human challenge model of Mycobacterium tuberculosis infection to enable proof-of-concept efficacy evaluation of candidate vaccines against tuberculosis. In vivo antimycobacterial immunity could be assessed using intradermal Mycobacterium bovis bacille Calmette-Guérin (BCG) vaccination as a surrogate for M. tuberculosis infection.
Methods. Healthy BCG-naive and BCG-vaccinated volunteers were challenged with intradermal BCG. BCG load was quantified from skin biopsy specimens by polymerase chain reaction (PCR) and culture colony-forming units. Cellular infiltrate was isolated by suction blisters and examined by flow cytometry. Prechallenge immune readouts were correlated with BCG load after challenge.
Results. In BCG-naive volunteers, live BCG was detected at the challenge site for up to 4 weeks and peaked at 2 weeks. Infiltration of mainly CD15+ neutrophils was observed in blister fluid. In previously BCG-vaccinated individuals, PCR analysis of skin biopsy specimens reflected a degree of mycobacterial immunity. There was no significant correlation between BCG load after challenge and mycobacterial-specific memory T cells measured before challenge by cultured enzyme-linked immunospot assay.
Conclusions. This novel experimental human challenge model provides a platform for the identification of correlates of antimycobacterial immunity and will greatly facilitate the rational down-selection of candidate tuberculosis vaccines. Further evaluation of this model with BCG and new vaccine candidates is warranted.
Infectious pathogens have long been recognized as potentially powerful agents impacting on the evolution of human genetic diversity. Analysis of large-scale case–control studies provides one of the most direct means of identifying human genetic variants that currently impact on susceptibility to particular infectious diseases. For over 50 years candidate gene studies have been used to identify loci for many major causes of human infectious mortality, including malaria, tuberculosis, human immunodeficiency virus/acquired immunodeficiency syndrome, bacterial pneumonia and hepatitis. But with the advent of genome-wide approaches, many new loci have been identified in diverse populations. Genome-wide linkage studies identified a few loci, but genome-wide association studies are proving more successful, and both exome and whole-genome sequencing now offer a revolutionary increase in power. Opinions differ on the extent to which the genetic component to common disease susceptibility is encoded by multiple high frequency or rare variants, and the heretical view that most infectious diseases might even be monogenic has been advocated recently. Review of findings to date suggests that the genetic architecture of infectious disease susceptibility may be importantly different from that of non-infectious diseases, and it is suggested that natural selection may be the driving force underlying this difference.
susceptibility; genomics; pathogen-driven selection; evolution; diversity; exome
A central goal in vaccinology is the induction of high and sustained antibody responses. Protein-in-adjuvant formulations are commonly used to achieve such responses. However, their clinical development can be limited by the reactogenicity of some of the most potent pre-clinical adjuvants and the cost and complexity of licensing new adjuvants for human use. Also, few adjuvants induce strong cellular immunity which is important for protection against many diseases, such as malaria. We compared classical adjuvants such as alum to new pre-clinical adjuvants and adjuvants in clinical development such as Abisco®100, CoVaccine HT™, Montanide®ISA720 and SE-GLA, for their ability to induce high and sustained antibody responses and T cell responses. These adjuvants induced a broad range of antibody responses when used in a three-shot protein-in-adjuvant regime using the model antigen ovalbumin and leading blood-stage malaria vaccine candidate antigens. Surprisingly, this range of antibody immunogenicity was greatly reduced when a protein-in-adjuvant vaccine was used to boost antibody responses primed by a human adenovirus serotype 5 (AdHu5) vaccine recombinant for the same antigen. This AdHu5-protein regime also induced a more cytophilic antibody response and demonstrated improved efficacy of merozoite surface protein-1 (MSP-1) protein vaccines against a Plasmodium yoelii blood-stage challenge. This indicates that the differential immunogenicity of protein vaccine adjuvants may be largely overcome by prior immunization with recombinant adenovirus, especially for adjuvants that are traditionally considered poorly immunogenic in the context of subunit vaccination, and may circumvent the need for more potent chemical adjuvants.
Endotoxin tolerance is characterized by the suppression of further TNF release upon recurrent exposure to LPS. This phenomenon is proposed to act as a homeostatic mechanism preventing uncontrolled cytokine release such as that observed in bacterial sepsis. The regulatory mechanisms and inter-individual variation of endotoxin tolerance induction in man remain poorly characterized. Here we describe a genetic association study of variation in endotoxin tolerance amongst healthy individuals. We identify a common promoter haplotype in TNFRSF1B (encoding TNFR2) to be strongly associated with reduced tolerance to LPS (P = 5.82×10−6). This identified haplotype is associated with increased expression of TNFR2 (P = 4.9 ×10−5) and we find basal expression of TNFR2, irrespective of genotype and unlike TNFR1, is associated with secondary TNF release (P <0.0001). Functional studies demonstrate a positive feedback loop via TNFR2 of LPS induced TNF release, confirming this previously unrecognized role for TNFR2 in the modulation of LPS response.
The lack of an effective TB vaccine hinders current efforts in combating the TB pandemic. One theory as to why BCG is less protective in tropical countries is that exposure to non-tuberculous mycobacteria (NTM) reduces BCG efficacy. There are currently several new TB vaccines in clinical trials, and NTM exposure may also be relevant in this context. NTM exposure cannot be accurately evaluated in the absence of specific antigens; those which are known to be present in NTM and absent from M. tuberculosis and BCG. We therefore used a bioinformatic pipeline to define proteins which are present in common NTM and absent from the M. tuberculosis complex, using protein BLAST, TBLASTN and a short sequence protein BLAST to ensure the specificity of this process. We then assessed immune responses to these proteins, in healthy South Africans and in patients from the United Kingdom and United States with documented exposure to NTM. Low level responses were detected to a cluster of proteins from the mammalian cell entry family, and to a cluster of hypothetical proteins, using ex vivo ELISpot and a 6 day proliferation assay. These early findings may provide a basis for characterising exposure to NTM at a population level, which has applications in the field of TB vaccine design as well as in the development of diagnostic tests.
The Royal Society convened a meeting on the 17th and 18th November 2010 to review the current ways in which vaccines are developed and deployed, and to make recommendations as to how each of these processes might be accelerated. The meeting brought together academics, industry representatives, research sponsors, regulators, government advisors and representatives of international public health agencies from a broad geographical background. Discussions were held under Chatham House rules. High-throughput screening of new vaccine antigens and candidates was seen as a driving force for vaccine discovery. Multi-stakeholder, small-scale manufacturing facilities capable of rapid production of clinical grade vaccines are currently too few and need to be expanded. In both the human and veterinary areas, there is a need for tiered regulatory standards, differentially tailored for experimental and commercial vaccines, to allow accelerated vaccine efficacy testing. Improved cross-fertilization of knowledge between industry and academia, and between human and veterinary vaccine developers, could lead to more rapid application of promising approaches and technologies to new product development. Identification of best-practices and development of checklists for product development plans and implementation programmes were seen as low-cost opportunities to shorten the timeline for vaccine progression from the laboratory bench to the people who need it.
human vaccines; veterinary vaccines; vaccine development; vaccine implementation
We examined the safety, immunogenicity and efficacy of a prime-boost vaccination regime involving two poxvirus malaria subunit vaccines, FP9-PP and MVA-PP, expressing the same polyprotein consisting of six pre-erythrocytic antigens from Plasmodium falciparum.
Following safety assessment of single doses, 15 volunteers received a heterologous prime-boost vaccination regime and underwent malaria sporozoite challenge. The vaccines were safe but interferon-γ ELISPOT responses were low compared to other poxvirus vectors, despite targeting multiple antigens. There was no vaccine efficacy as measured by delay in time to parasitaemia. A number of possible explanations are discussed, including the very large insert size of the polyprotein transgene.
Malaria; Vaccine; Heterologous prime-boost