The possibility that vaccination with adenovirus (AdV) vectors increased mucosal T cell activation remains a central hypothesis to explain the potential enhancement of HIV acquisition within the Step trial. Modeling this within rhesus macaques is complicated because human adenoviruses, including human adenovirus type 5 (HAdV-5), are not endogenous to macaques. Here, we tested whether vaccination with a rhesus macaque-derived adenoviral vector (simian adenovirus 7 [SAdV-7]) enhances mucosal T cell activation within rhesus macaques. Following intramuscular SAdV-7 vaccination, we observed a pronounced increase in SAdV-7-specific CD4+ T cell responses in peripheral blood and, more dramatically, in rectal mucosa tissue. Vaccination also induced a significant increase in the frequency of activated memory CD4+ T cells in SAdV-7- and HAdV-5-vaccinated animals in the rectal mucosa but not in peripheral blood. These fluctuations within the rectal mucosa were also associated with a pronounced decrease in the relative frequency of naive resting CD4+ T cells. Together, these results indicate that peripheral vaccination with an AdV vector can increase the activation of mucosal CD4+ T cells, potentially providing an experimental model to further evaluate the role of host-vector interactions in increased HIV acquisition after AdV vector vaccination.
IMPORTANCE The possibility that vaccination with a human adenovirus 5 vector increased mucosal T cell activation remains a central hypothesis to explain the potential enhancement of human immunodeficiency virus (HIV) acquisition within the Step trial. In this study, we tested whether vaccination with a rhesus macaque-derived adenoviral vector in rhesus macaques enhances mucosal CD4+ T cell activation, the main cell target of simian immunodeficiency virus (SIV)/HIV. The results showed that vaccination with an adenoviral vector indeed increases activation of mucosal CD4+ T cells and potentially increases susceptibility to SIV infection.
Recombinant adeno-associated viral vectors based on serotype 8 (AAV8) transduce liver with superior tropism following intravenous (IV) administration. Previous studies conducted by our lab demonstrated that AAV8-mediated transfer of the human low-density lipoprotein receptor (LDLR) gene driven by a strong liver-specific promoter (thyroxin-binding globulin [TBG]) leads to high level and persistent gene expression in the liver. The approach proved efficacious in reducing plasma cholesterol levels and resulted in the regression of atherosclerotic lesions in a murine model of homozygous familial hypercholesterolemia (hoFH). Prior to advancing this vector, called AAV8.TBG.hLDLR, to the clinic, we set out to investigate vector biodistribution in an hoFH mouse model following IV vector administration to assess the safety profile of this investigational agent. Although AAV genomes were present in all organs at all time points tested (up to 180 days), vector genomes were sequestered mainly in the liver, which contained levels of vector 3 logs higher than that found in other organs. In both sexes, the level of AAV genomes gradually declined and appeared to stabilize 90 days post vector administration in most organs although vector genomes remained high in liver. Vector loads in the circulating blood were high and close to those in liver at the early time point (day 3) but rapidly decreased to a level close to the limit of quantification of the assay. The results of this vector biodistribution study further support a proposed clinical trial to evaluate AAV8 gene therapy for hoFH patients.
A 66-year-old woman heterozygous for a mutation in the ornithine transcarbamylase gene (Otc) participated in a phase I gene therapy trial for OTC deficiency. She received an adenovirus (Ad) vector expressing the functional OTC gene by intraportal perfusion. Fourteen years later she developed and subsequently died of hepatocellular carcinoma. A second subject, a 45-year-old woman, enrolled in the same trial presented with colon cancer 15 years later. We sought to investigate a possible association between the development of a tumor and prior adenoviral gene transfer in these two subjects. We developed and validated a sensitive nested polymerase chain reaction assay for recovering recombinant Ad sequences from host tissues. Using this method, we could not detect any Ad vector DNA in either tumor or normal tissue from the two patients. Our results are informative in ruling out the possibility that the adenoviral vector might have contributed to the development of cancer in those two subjects.
Zhong and colleagues use a nested PCR assay to examine whether adenoviral gene transfer led to the development of cancer in two clinical research subjects with ornithine transcarbamylase deficiency. Using this approach, they were unable to detect adenovirus vector genomes in normal or tumor tissues from the subjects more than a decade after vector infusion. These results suggest that adenoviral gene transfer was an unlikely contributor to the colon cancer or hepatocellular carcinoma observed in the two research subjects.
The ability to regulate both the timing and specificity of gene expression mediated by viral vectors will be important in maximizing its utility. We describe the development of an adeno-associated virus (AAV)-based vector with tissue-specific gene regulation, using the ARGENT dimerizer-inducible system. This two-vector system based on AAV serotype 9 consists of one vector encoding a combination of reporter genes from which expression is directed by a ubiquitous, inducible promoter and a second vector encoding transcription factor domains under the control of either a heart- or liver-specific promoter, which are activated with a small molecule. Administration of the vectors via either systemic or intrapericardial injection demonstrated that the vector system is capable of mediating gene expression that is tissue specific, regulatable, and reproducible over induction cycles. Somatic gene transfer in vivo is being considered in therapeutic applications, although its most substantial value will be in basic applications such as target validation and development of animal models.
Chen and colleagues describe the development of an AAV-based vector with tissue-specific gene regulation, using the ARGENT dimerizer-inducible system. They demonstrate that administration of these vectors via either systemic or intrapericardial injection leads to gene expression that is tissue specific, regulatable, and reproducible over induction cycles.
Intramuscular (IM) administration of adeno-associated viral (AAV) vectors has entered the early stages of clinical development with some success, including the first approved gene therapy product in the West called Glybera. In preparation for broader clinical development of IM AAV vector gene therapy, we conducted detailed pre-clinical studies in mice and macaques evaluating aspects of delivery that could affect performance. We found that following IM administration of AAV8 vectors in mice, a portion of the vector reached the liver and hepatic gene expression contributed significantly to total expression of secreted transgenes. The contribution from liver could be controlled by altering injection volume and by the use of traditional (promoter) and non-traditional (tissue-specific microRNA target sites) expression control elements. Hepatic distribution of vector following IM injection was also noted in rhesus macaques. These pre-clinical data on AAV delivery should inform safe and efficient development of future AAV products.
Bisulfite conversion of genomic DNA combined with next-generation sequencing (NGS) has become a very effective approach for mapping the whole-genome and sub-genome wide DNA methylation landscapes. However, whole methylome shotgun bisulfite sequencing is still expensive and not suitable for analyzing large numbers of human cancer specimens. Recent advances in the development of targeted bisulfite sequencing approaches offer several attractive alternatives. The characteristics and applications of these methods are discussed in this review article. In addition, the bioinformatic tools that can be used for sequence capture probe design as well as downstream sequence analyses are also addressed.
It is not known whether genetic variants in the cholesteryl-ester-transfer-protein (CETP) gene are associated with recurrent coronary heart disease events or mortality in secondary prevention patients. Among 3717 acute coronary syndrome (ACS) or coronary artery bypass grafting (CABG) patients enrolled in a prospective genetic registry; we evaluated whether CETP gene variants previously shown to be associated with reduced CETP activity and high-density-lipoprotein-cholesterol increase (“A” allele for both TaqIB [rs708272] and rs12149545) are associated with a reduction in recurrent myocardial infarction [MI], recurrent revascularization or death. At 4.5 years of follow-up; 439 recurrent MI, 698 recurrent revascularizations and 756 deaths occurred. Using an additive model of inheritance, the “A” allele for rs708272 was not associated with recurrent MI (HR 0.95, 95% CI 0.78-1.17 for AG; HR 0.89, 95% CI 0.67-1.19 for AA; compared with GG genotype), recurrent revascularization (HR 1.13, 95% CI 0.95-1.33 for AG; HR 1.05, 95% CI 0.84-1.32 for AA) or mortality (HR 1.02, 95% CI 0.86-1.19 for AG; HR 1.11, 95% CI 0.91-1.37 for AA) in the overall cohort. Similar results were seen for the “A” allele for rs12149545. In the CABG subgroup, AG genotype for rs708272 was associated with an increased mortality (HR 1.38, 95% CI 1.06-1.79) compared to GG genotype. Results remained consistent using dominant model of inheritance. In conclusion, genetic CETP variants were not associated with recurrent MI or recurrent revascularization in overall cohort with a possible mortality increase in CABG patients.
Cholesteryl-ester-transfer-protein; TaqIB; recurrent events; mortality
Bryant and colleagues follow the development of Glybera (alipogene tiparvovec), the first gene therapy product approved in the European Union, from early preclinical studies through the approval process. They review key data from human and animal studies with an emphasis on issues that will be critical to other gene therapy products. The article concludes with an analysis of the complex review process that eventually led to Glybera's approval.
Cystic fibrosis (CF) is one of the most common autosomal recessive lethal disorders affecting white populations of northern European ancestry. To date there is no cure for CF. Life-long treatments for CF are being developed and include gene therapy and the use of small-molecule drugs designed to target specific cystic fibrosis transmembrane conductance regulator (CFTR) gene mutations. Irrespective of the type of molecular therapy for CF, which may include gene replacement, exon skipping, nonsense suppression, or molecular correctors, because all of these modulate gene expression there is an inherent risk of activation of T cells against the wild-type version of CFTR. Here we report the validation of the human interferon-γ enzyme-linked immunospot assay and its application for the analysis of CFTR-specific T cell responses in patients with CF and in non-CF subjects. We found non-CF subjects with low levels of self-reactive CFTR-specific T cells in the United States and several patients with CF with low to high levels of self-reactive CFTR-specific T cells in both the United States and the United Kingdom.
Calcedo and colleagues develop and validate a sensitive interferon-γ enzyme-linked immunospot assay for detection of human T cells specific to the cystic fibrosis (CF) transmembrane conductance regulator (CFTR) protein. They detect CFTR reactive T cells in a significant portion of CF patients. Remarkably, T cells recognizing CFTR are also identified in non-CF subjects. These data have important implications for measuring and interpreting transgene-specific immune responses in gene therapy trials.
Avoiding activation of immunity to vector-encoded proteins is critical to the safe and effective use of adeno-associated viral (AAV) vectors for gene therapy. While commonly used serotypes, such as AAV serotypes 1, 2, 7, 8, and 9, are often associated with minimal and/or dysfunctional CD8+ T cell responses in mice, the threshold for immune activation appears to be lower in higher-order species. We have modeled this discrepancy within the mouse by identifying two capsid variants with differential immune activation profiles: AAV serotype 8 (AAV8) and a hybrid between natural rhesus isolates AAVrh32 and AAVrh33 (AAVrh32.33). Here, we aimed to characterize the structural determinants of the AAVrh32.33 capsid that augment cellular immunity to vector-encoded proteins or those of AAV8 that may induce tolerance. We hypothesized that the structural domain responsible for differential immune activation could be mapped to surface-exposed regions of the capsid, such as hypervariable regions (HVRs) I to IX of VP3. To test this, a series of hybrid AAV capsids was constructed by swapping domains between AAV8 and AAVrh32.33. By comparing their ability to generate transgene-specific T cells in vivo versus the stability of transgene expression in the muscle, we confirmed that the functional domain lies within the VP3 portion of the capsid. Our studies were able to exclude the regions of VP3 which are not sufficient for augmenting the cellular immune response, notably, HVRs I, II, and V. We have also identified HVR IV as a region of interest in conferring the efficiency and stability of muscle transduction to AAVrh32.33.
In the present study, a novel adeno-associated virus (AAV) vector-mediated gene delivery approach was taken to improve the reconstitution of functional CD8+ T cells in humanized mice, thereby mimicking the human immune system (HIS). Human genes encoding HLA-A2 and selected human cytokines (A2/hucytokines) were introduced to an immune-deficient mouse model [NOD/SCID/IL2rγnull (NSG) mice] using AAV serotype 9 (AAV9) vectors, followed by transplantation of human hematopoietic stem cells. NSG mice transduced with AAV9 encoding A2/hucytokines resulted in higher levels of reconstitution of human CD45+ cells compared to NSG mice transduced with AAV9 encoding HLA-A2 alone or HLA-A2-transgenic NSG mice. Furthermore, this group of HIS mice also mounted the highest level of antigen-specific A2-restricted human CD8+ T-cell response upon vaccination with recombinant adenoviruses expressing human malaria and HIV antigens. Finally, the human CD8+ T-cell response induced in human malaria vaccine-immunized HIS mice was shown to be functional by displaying cytotoxic activity against hepatocytes that express the human malaria antigen in the context of A2 molecules. Taken together, our data show that AAV vector-mediated gene delivery is a simple and efficient method to transfer multiple human genes to immune-deficient mice, thus facilitating successful reconstitution of HIS in mice. The HIS mice generated in this study should ultimately allow us to swiftly evaluate the T-cell immunogenicity of various human vaccine candidates in a pre-clinical setting.
Familial hypercholesterolemia (FH) is a life-threatening genetic disease caused by mutations in the gene encoding low-density lipoprotein receptor (LDLR). As a bridge to clinical trials, we generated a “humanized” mouse model lacking LDLR and apolipoprotein B (ApoB) mRNA editing catalytic polypeptide-1 (APOBEC-1) expression and expressing a human ApoB100 transgene in order to permit more authentic simulation of in vivo interactions between the clinical transgene product, human LDLR (hLDLR), and its endogenous ligand, human ApoB100. On a chow diet, the humanized LDLR-deficient mice have substantial hypercholesterolemia and a lipoprotein phenotype more closely resembling human homozygous FH (hoFH) than in previous mouse models of FH. On injection of an adeno-associated virus serotype 8 (AAV8) vector encoding the human LDLR cDNA, significant correction of hypercholesterolemia was realized at doses as low as 1.5×1011 genome copies (GC)/kg. Given that some patients with heterozygous FH (heFH) cannot be adequately treated with current therapy, we then extended our studies to similarly “humanized” mice that were heterozygous for LDLR deficiency, and that have a lipoprotein phenotype resembling heterozygous FH. Injection of AAV8-hLDLR brought about significant reduction in total and LDL cholesterol at doses as low as 5×1011 GC/kg. Collectively, these data demonstrate the safety and efficacy of the liver-specific AAV8-hLDLR vector in the treatment of humanized mice modeling both hoFH and heFH.
Kassim and colleagues demonstrate that injection of an adeno-associated virus serotype 8 (AAV8) vector encoding the human low-density lipoprotein receptor (LDLR) cDNA results in significant correction of hypercholesterolemia in humanized mouse models of homozygous and heterozygous familial hypercholesterolemia (FH).
Recombinant adeno-associated virus (rAAV) vectors have shown promise for the treatment of several diseases; however, immune-mediated elimination of transduced cells has been suggested to limit and account for a loss of efficacy. To determine whether rAAV vector expression can persist long term, we administered rAAV vectors expressing normal, M-type α-1 antitrypsin (M-AAT) to AAT-deficient subjects at various doses by multiple i.m. injections. M-specific AAT expression was observed in all subjects in a dose-dependent manner and was sustained for more than 1 year in the absence of immune suppression. Muscle biopsies at 1 year had sustained AAT expression and a reduction of inflammatory cells compared with 3 month biopsies. Deep sequencing of the TCR Vβ region from muscle biopsies demonstrated a limited number of T cell clones that emerged at 3 months after vector administration and persisted for 1 year. In situ immunophenotyping revealed a substantial Treg population in muscle biopsy samples containing AAT-expressing myofibers. Approximately 10% of all T cells in muscle were natural Tregs, which were activated in response to AAV capsid. These results suggest that i.m. delivery of rAAV type 1–AAT (rAAV1-AAT) induces a T regulatory response that allows ongoing transgene expression and indicates that immunomodulatory treatments may not be necessary for rAAV-mediated gene therapy.
The best method of identifying regions within pancreatic tumours that might benefit from an increased radiotherapy dose is not known. We investigated the utility of pre-treatment FDG-PET in predicting the spatial distribution of residual metabolic activity following chemoradiotherapy (CRT) in locally advanced pancreatic cancer (LAPC).
17 patients had FDG-PET/CT scans at baseline and six weeks post-CRT. Tumour segmentation was performed at 40% and 50% of SUVmax at baseline and 60%, 70%, 80% and 90% post-CRT. FDG-PET scans were non-rigidly registered to the radiotherapy planning CT using the CT component of the FDG-PET/CT. Percentage overlap of the post-CRT volumes with the pre-CRT volumes with one another and the gross tumour volume (GTV) was calculated.
SUVmax decreased during CRT (median pre- 8.0 and post- 3.6, p < 0.0001). For spatial correlation analysis, 9 pairs of scans were included (Four were excluded following complete metabolic response, one patient had a non-FDG avid tumour, one had no post-CRT imaging, one had diffuse FDG uptake that could not be separated from normal tissues and one had an elevated blood glucose). The Pre40% and 50% of SUVmax volumes covered a mean of 50.8% and 30.3% of the GTV respectively. The mean% overlap of the 90%, 80%, 70%, 60% of SUVmax post-CRT with the Pre40% and Pre50% volumes were 83.3%, 84.0%, 83.7%, 77.9% and 77.8%, 69.9%, 74.5%, 64.8% respectively.
Regions of residual metabolic activity following CRT can be predicted from the baseline FDG-PET and could aid definition of a biological target volume for non-uniform dose prescriptions.
Pancreatic cancer; PET-CT; Residual metabolic activity; Intra-tumour heterogeneity; Biological target volume
Our aim was to investigate serotype-specific cell and tissue-transduction tropisms, transgene expression levels and longevity, and immunogenicity of candidate rAAV serotypes in rat osteochondral cells, tissues, and stifle joints. In vitro, we used six rAAV serotypes and two promoters to transduce synoviocytes and chondrocytes. Serotypes rAAV2/5 and 2/2 yielded the highest transduction efficiency 4 days after transduction. No differences were detected between cytomegalovirus and chicken β-actin promoters. In vivo, intra-articular injection was used to introduce four rAAV serotypes into 4-month-old rats in the left stifle joint. Eleven months later, serotype 2/5 vector, diluted with saline or surfactant, was injected into the right stifle joint of the same rats. Rats were analyzed up to 12 months after initial injection. Bioluminescence was detected at 7 days and all serotypes tested displayed bioluminescence above controls after 1 year in the left stifle. Gene expression was detected in the right stifle joints of all rats with the exception of rats previously injected with serotype 2/5. We observed no difference irrespective of whether the luciferin was injected subcutaneously or intraperitoneally. However, surfactant-diluted vectors led to increased gene expression compared with saline-diluted vectors. Cell- and tissue-specific transduction was observed in rat stifles injected with an nLacZ-containing rAAV. Transduction was greatest in stromal tissues and mesenchymal cell types. Exposure to a specific serotype did not inhibit subsequent transduction with a different serotype at a second vector injection. Including surfactant as a vector diluent increased gene expression within the stifle joint and should be considered for in vivo gene therapy applications.
Mason and colleagues investigate serotype-specific cell and tissue transduction tropisms, transgene expression levels, and longevity, as well as immunogenicity of candidate recombinant adenoassociated virus vectors (rAAV) in rat osteochondral cells, tissues, and stifle joints. Transduction was greatest in stromal tissues and mesenchymal cell types. Exposure to a specific serotype did not inhibit subsequent transduction with a different serotype. Including surfactant as a vector diluent increased gene expression within the stifle joint.
At sites of inflammation, certain regulatory T cells (Treg cells) can undergo rapid reprogramming into helper-like cells, without loss of the transcription factor Foxp3. We show that reprogramming is controlled by down-regulation of the transcription factor Eos (Ikzf4), an obligate co-repressor for Foxp3. Reprogramming was restricted to a specific subset of “Eoslabile” Treg cells which were present in the thymus and identifiable by characteristic surface markers and DNA methylation. Mice made deficient in this subset became impaired in their ability to provide help for presentation of new antigens to naive T cells. Down-regulation of Eos required the pro-inflammatory cytokine IL-6, and mice lacking IL-6 had impaired development and function of the Eos-labile subset. Conversely, the immunoregulatory enzyme IDO blocked loss of Eos, and prevented the Eos-labile Treg cells from reprogramming. Thus, the Foxp3+ lineage contains a committed subset of Treg cells capable of rapid conversion into biologically important helper cells.
Recombinant adeno-associated viruses (rAAVs) have been tested in humans and other large mammals without adverse events. However, one study of mucopolysaccharidosis VII correction in mice showed repeated integration of rAAV in cells from hepatocellular carcinoma (HCC) in the Dlk1–Dio3 locus, suggesting possible insertional mutagenesis. In contrast, another study found no association of rAAV integration with HCC, raising questions about the generality of associations between liver transformation and integration at Dlk1–Dio3. Here we report that in rAAV-treated ornithine transcarbamylase (Otc)–deficient mice, four examples of integration sites in Dlk1–Dio3 could be detected in specimens from liver nodule/tumors, confirming previous studies of rAAV integration in the Dlk1–Dio3 locus in the setting of another murine model of metabolic disease. In one case, the integrated vector was verified to be present at about one copy per cell, consistent with clonal expansion. Another verified integration site in liver nodule/tumor tissue near the Tax1bp1 gene was also detected at about one copy per cell. The Dlk1–Dio3 region has also been implicated in human HCC and so warrants careful monitoring in ongoing human clinical trials with rAAV vectors.
Zhong and colleagues use deep sequencing to examine the distribution of integrated AAV genomes in nodules/tumors from the livers of ornithine transcarbamylace (Otc) deficient mice. Using this approach, they report four examples of integration sites in the Dlk1-Dio3 locus; this site has previously been implicated in human hepatocellular carcinoma and may warrant careful monitoring in human clinical trials using AAV vectors.
Several small-molecule CDK inhibitors have been identified, but none have been approved for clinical use in the past few years. A new series of 4-[(3-hydroxybenzylamino)-methylene]-4H-isoquinoline-1,3-diones were reported as highly potent and selective CDK4 inhibitors. In order to find more potent CDK4 inhibitors, the interactions between these novel isoquinoline-1,3-diones and cyclin-dependent kinase 4 was explored via in silico methodologies such as 3D-QSAR and docking on eighty-one compounds displaying potent selective activities against cyclin-dependent kinase 4. Internal and external cross-validation techniques were investigated as well as region focusing, bootstraping and leave-group-out. A training set of 66 compounds gave the satisfactory CoMFA model (q2 = 0.695, r2 = 0.947) and CoMSIA model (q2 = 0.641, r2 = 0.933). The remaining 15 compounds as a test set also gave good external predictive abilities with r2pred values of 0.875 and 0.769 for CoMFA and CoMSIA, respectively. The 3D-QSAR models generated here predicted that all five parameters are important for activity toward CDK4. Surflex-dock results, coincident with CoMFA/CoMSIA contour maps, gave the path for binding mode exploration between the inhibitors and CDK4 protein. Based on the QSAR and docking models, twenty new potent molecules have been designed and predicted better than the most active compound 12 in the literatures. The QSAR, docking and interactions analysis expand the structure-activity relationships of constrained isoquinoline-1,3-diones and contribute towards the development of more active CDK4 subtype-selective inhibitors.
Due to their efficient transduction potential, adeno-associated virus (AAV) vectors are leading candidates for gene therapy in skeletal muscle diseases. However, immune responses toward the vector or transgene product have been observed in preclinical and clinical studies. TLR9 has been implicated in promoting AAV-directed immune responses, but vectors have not been developed to circumvent this barrier. To assess the requirement of TLR9 in promoting immunity toward AAV-associated antigens following skeletal muscle gene transfer in mice, we compared immunological responses in WT and Tlr9-deficient mice that received an AAV vector with an immunogenic capsid, AAVrh32.33. In Tlr9-deficient mice, IFN-γ T cell responses toward capsid and transgene antigen were suppressed, resulting in minimal cellular infiltrate and stable transgene expression in target muscles. These findings suggest that AAV-directed immune responses may be circumvented by depleting the ligand for TLR9 (CpG sequences) from the vector genome. Indeed, we found that CpG-depleted AAVrh32.33 vectors could establish persistent transgene expression, evade immunity, and minimize infiltration of effector cells. Thus, CpG-depleted AAV vectors could improve outcome of clinical trials of gene therapy for skeletal muscle disease.
Gene therapy has shown clinical efficacy for several rare diseases, using different approaches and vectors. The Gene Therapy for Rare Diseases workshop, sponsored by the National Institutes of Health (NIH) Office of Biotechnology Activities and Office of Rare Diseases Research, brought together investigators from different disciplines to discuss the challenges and opportunities for advancing the field including means for enhancing data sharing for preclinical and clinical studies, development and utilization of available NIH resources, and interactions with the U.S. Food and Drug Administration.
Translational research is a lengthy, complex, and necessary endeavor in order to bring basic science discoveries to clinical fruition. The NIH offers several programs to support translational research including an important resource established specifically for gene therapy researchers—the National Heart, Lung, and Blood Institute (NHLBI) Gene Therapy Resource Program (GTRP). This paper reviews the core components of the GTRP and describes how the GTRP provides researchers with resources that are critical to advancing investigational gene therapy products into clinical testing.
For genetic diseases that manifest at a young age with irreversible consequences, early treatment is critical and essential. Neonatal gene therapy has the advantages of achieving therapeutic effects before disease manifestation, a low vector requirement and high vector-to-cell ratio, and a relatively immature immune system. Therapeutic effects or long-term rescue of neonatal lethality have been demonstrated in several animal models. However, vigorous cell proliferation in the newborn stage is a significant challenge for nonintegrating vectors, such as adeno-associated viral (AAV) vector. Slightly delaying the injection age, and readministration at a later time, are two of the alternative strategies to solve this problem. In this study, we demonstrated robust and efficient hepatic gene transfer by self-complementary AAV8 vector in neonatal mice. However, transduction quickly decreased over a few weeks because of vector dilution caused by fast proliferation. Delaying the injection age improved sustained expression, although it also increased neutralizing antibody (NAb) responses to AAV capsid. This approach can be used to treat genetic diseases with slow progression. For genetic diseases with early onset and severe consequences, early treatment is essential. A second injection of vector of a different serotype at a later time may overcome preexisting NAb and achieve sustained therapeutic effects.
Wang and colleagues conduct a series of preclinical animal studies examining the kinetics of AAV gene transfer. They demonstrate that self-complementary AAV8 results in robust and efficient hepatic gene transfer in neonatal mice. Yet, this transduction quickly decreases over a few weeks because of vector dilution caused by rapid cell proliferation in the liver of growing young mice.