Generation of two induced pluripotent stem cell lines (LVPEIi004-A and LVPEIi005-A) from probands with Leber Congenital Amaurosis 2 (LCA2) and harboring mutations in RPE65

Leber Congenital Amaurosis 2 is an early onset retinal dystrophy that occurs due to mutation in RPE65 gene. Here, we report the generation of two patient specific induced pluripotent stem cell lines harboring nonsense mutations in exon 7 (c.646A > T) and exon 9 (c.992G > A) of RPE65 gene, respectively, which leads to premature translational termination and formation of defective protein. These lines were generated by the reprogramming of human dermal fibroblast cells using integration-free, episomal constructs expressing stemness genes. The stable lines maintained a normal karyotype, expressed the key stemness factors, underwent trilineage differentiation, and maintained their genetic identity and genomic integrity.

Inducible caspase 9-mediated suicide gene therapy using AAV6 vectors in a murine model of breast cancer

Breast carcinoma has one of the highest incidence rates (11.7%), with significant clinical heterogeneity. Although conventional chemotherapy and surgical resection are the current standard of care, the resistance and recurrence, after these interventions, necessitate alternate therapeutic approaches. Cancer gene therapy for breast cancer with the suicide gene is an attractive option due to their directed delivery into the tumor. In this study, we have developed a novel treatment strategy against breast cancer with recombinant adeno-associated virus (AAV) serotype 6 vectors carrying a suicide gene, inducible Caspase 9 (iCasp9). Upon treatment with AAV6-iCasp9 vectors and the chemical inducer of dimerizer, AP20187, the viability of murine breast cancer cells (4T1) was significantly reduced to ∼40%-60% (mock control 100%). Following intratumoral delivery of AAV6-iCasp9 vectors in an orthotopic breast cancer mouse model, we observed a significant increase in iCasp9 transgene expression and a significant reduction in tumor growth rate. At the molecular level, immunohistochemical analysis demonstrated subsequent activation of the effector caspase 3 and cellular death. These data highlight the potential of AAV6-iCasp9-based suicide gene therapy for aggressive breast cancer in patients.

Targeted delivery of miR125a-5p and human Factor VIII attenuates molecular mediators of hemophilic arthropathy

Hemophilic arthropathy (HA) due to repeated bleeding into the joint cavity is a major cause of morbidity in patients with hemophilia. The molecular mechanisms contributing to this condition are not well characterized. MicroRNAs (miRs) are known to modulate the phenotype of multiple joint diseases such as osteoarthritis (OA) and rheumatoid arthritis (RA). Since miR125a is known to modulate disease progression in OA and RA, we performed a targeted screen of miR125a-5p and its target genes in a murine model of chronic HA. A digital PCR analysis demonstrated significant downregulation of miR125a-5p (2-fold vs control joint). Further molecular evaluation revealed elevated expression of the immunological markers STAT1 (7.6-fold vs control joint) and TRAF6 (10.6 fold vs control joint), which are direct targets of miR125a-5p. We then studied the impact of targeted overexpression of miR125a-5p using an Adeno-associated virus (AAV) vector in modulating the molecular mediators of HA. AAV5-miR125a vectors were administered intra-articularly either alone or in combination with a low dose of AAV8-based human factor 8 (F8) gene in a murine model of HA. We observed significantly increased expression of miR125a-5p in AAV5-miR125a administered mice (~12 fold vs injured joint) or in combination with AAV8-F8 vectors (~44 fold vs injured joint). The activity assay revealed ~17 %-20 % FVIII levels in mice that received low dose liver-directed F8 gene therapy. Further immunohistochemical analysis, demonstrated a decrease in inflammatory markers (STAT1 and TRAF6) and cartilage-degrading matrix metalloproteinases (MMPs) 3, 9, 13 in the joints of treated animals. These data highlight the crucial role of miR125a-5p in the development of HA.

Gene therapy for female infertility: A farfetched dream or reality?

A major cause of infertility in women is impaired ovulation or oogenesis. In this issue of Cell Reports Medicine, Kanatsu-Shinohara et al.1 demonstrate the potential of gene delivery with adeno-associated virus that can cross the blood-follicle barrier and restore oogenesis in congenitally infertile mice.

Vector engineering, strategies and targets in cancer gene therapy

Understanding the molecular basis of disease and the design of rationally designed molecular therapies has been the holy grail in the management of human cancers. Gene-based therapies are an important avenue for achieving a possible cure. Focused research in the last three decades has provided significant clues to optimize the potential of cancer gene therapy. The development of gene therapies with a high potential to kill the target cells at the lowest effective dose possible, the development of vectors with significant ability to target cancer-associated antigen, the application of adjunct therapies to target dysregulated microRNA, and embracing a hybrid strategy with a combination of gene therapy and low-dose chemotherapy in a disease-specific manner will be pivotal. This article outlines the advances and challenges in the field with emphasis on the biology and scope of vectors used for gene transfer, newer targets identified, and their outcome in preclinical and clinical studies.

Evaluation of the Anticancer Activity of pH-Sensitive Polyketal Nanoparticles for Acute Myeloid Leukemia

Polyketals are a class of acid-responsive polymers that have been relatively less explored for drug delivery applications compared to polyesters. The degradation of these polymers is accelerated in an acidic medium and does not result in acidic byproducts. Their biocompatibility depends on the diol used for the synthesis. The present work aims to synthesize, characterize, and fabricate nanospheres of an aliphatic polyketal for delivery of the nucleotide analogue cytarabine toward the treatment of acute myeloid leukemia (AML). The internalization mechanism of the nanospheres was probed, and its implication on the nuclear localization and escape from the endo-lysosomal compartments were studied. The drug-loaded polyketal nanoparticles reduced the cell viability to a greater extent compared with the free drug. The effect of the drug-loaded polyketal nanoparticles on the differential gene expression of leukemic cells was investigated for the first time to understand their therapeutic implications. It was found that treatment with drug-loaded polyketal nanoparticles downregulated AML-specific genes involved in cell proliferation and recurrence compared to the free drug. The protein expression studies were performed for selected genes obtained from gene expression analysis. Biodistribution studies showed that the poly(cyclohexane-1,4-diyl acetone dimethylene ketal) (PCADK) nanoparticles exhibit prolonged circulation time. Overall, our results suggest that polyketal-based delivery of cytarabine represents a more effective alternative strategy for AML therapy.

Gene Therapy: Contest between Adeno-Associated Virus and Host Cells and the Impact of UFMylation

Adeno-associated virus (AAV)-based gene therapy is currently limited by (1) decline in therapeutic gene expression over time, (2) immune cell activation and (3) neutralization by pre-existing antibodies. Hence, studying the interaction of AAV vectors with various cellular pathways during the production and transduction process is necessary to overcome such barriers. Post-translational modifications (PTM) of AAV vectors during the production and transduction process is known to limit its transduction efficiency and further evoke the immune response. Further, AAV vectors are known to trigger cellular stress, resulting in an upregulation of distinct arms of the unfolded protein response (UPR) pathway. Recognition of the AAV genome by Toll-like receptor-9 triggers the myeloid differentiation primary response signaling cascade for innate (IL-6, IFN-α, IFN-β) and adaptive (CD8+ T-cell, B-cell) immune response against the viral capsid and the transgene product. Herein, we highlight a potential intersection of the UPR, PTMs, and intracellular trafficking pathways, which could be fine-tuned to augment the outcome of AAV-based gene delivery.

MicroRNA-based recombinant AAV vector assembly improves efficiency of suicide gene transfer in a murine model of lymphoma

Recent success in clinical trials with recombinant Adeno-associated virus (AAV)-based gene therapy has redirected efforts in optimizing AAV assembly and production, to improve its potency. We reasoned that inclusion of a small RNA during vector assembly, which specifically alters the phosphorylation status of the packaging cells may be beneficial. We thus employed microRNAs (miR-431, miR-636) identified by their ability to bind AAV genome and also dysregulate Mitogen-activated protein kinase (MAPK) signaling during vector production, by a global transcriptome study in producer cells. A modified vector assembly protocol incorporating a plasmid encoding these microRNAs was developed. AAV2 vectors packaged in the presence of microRNA demonstrated an improved gene transfer potency by 3.7-fold, in vitro. Furthermore, AAV6 serotype vectors encoding an inducible caspase 9 suicide gene, packaged in the presence of miR-636, showed a significant tumor regression (~2.2-fold, P < .01) in a syngeneic murine model of T-cell lymphoma. Taken together, we have demonstrated a simple but effective microRNA-based approach to improve the assembly and potency of suicide gene therapy with AAV vectors.

Exosome-associated SUMOylation mutant AAV demonstrates improved ocular gene transfer efficiency in vivo

Exosome associated Adeno-associated virus (AAV) vectors have emerged as a promising tool in gene therapy. Recently, we elucidated the role of SUMOylation post-translational modification in AAV2 capsid and demonstrated that capsid modifications at SUMOylation sites, enhance vector transduction. The present study was designed to study the combinatorial effect of exosome delivery of a SUMOylation site modified AAV2, during ocular gene therapy. In the first set of experiments, we investigated the in vitro gene transfer potential of exo-some-associated SUMOylation mutant AAV2 (Exo-K105Q-EGFP) in human retinal pigmental epithelial (ARPE19) cells. Our data showed that, Exo-K105Q vectors had a significantly higher transduction potential in ARPE19 cells when compared to exosomes derived from wildtype AAV2 (Exo-AAV2-EGFP) vector packaging. Subsequently, an intravitreal administration of exosome associated mutant AAV2 vectors in C57BL6/J mice, demonstrated a significant increase reporter gene (EFGP) expression 4 weeks after gene transfer. Further immunostaining, revealed that these exosome-based vectors also had a better permeation across the retinal layers. These data highlight the translational potential of exosome associated SUMOylation mutant AAV for ocular gene therapy.

AAV6 Vexosomes Mediate Robust Suicide Gene Delivery in a Murine Model of Hepatocellular Carcinoma

During recombinant Adeno-associated virus (AAV) production, a proportionately large amount of vectors is released in the culture supernatant, which is often discarded. It has been shown that these vectors often associate with vesiculated structures, such as exosomes. Exosome-associated AAV (vexosomes) represent an additional gene-delivery platform. The efficiency of such vexosomes in suicide gene therapy is unexplored. In the present study, we have generated AAV serotype 6 vexosomes containing an inducible caspase 9 (iCasp9) suicide gene by a differential ultracentrifugation-based protocol. We further tested the cytotoxic potential of these vexosomes in a human hepatocellular carcinoma (HCC) model in vitro and in vivo. The AAV6-iCasp9 containing vexosomes, when primed with a pro-drug (AP20187), demonstrated a significant loss in cell viability (57% ± 8% versus 100% ± 4.8%, p < 0.001) in comparison to mock-treated Huh7 cells. An intratumoral administration of AAV6-iCasp9 vexosomes and AP20187 in a murine xenograft model revealed a 2.3-fold increase in tumor regression in comparison to untreated animals. These findings were further corroborated by histological analysis and apoptosis assays. In conclusion, our data demonstrate the therapeutic potential of AAV6 vexosomes in a xenotransplantation model of HCC. Furthermore, the simplicity in production and isolation of vexosomes should further facilitate its application in other malignancies.

Rational Engineering and Preclinical Evaluation of Neddylation and SUMOylation Site Modified Adeno-Associated Virus Vectors in Murine Models of Hemophilia B and Leber Congenital Amaurosis

Synthetic engineering of viral vectors such as adeno-associated virus (AAV) is crucial to overcome host transduction barriers observed during clinical gene therapy. We reasoned that exploring the role of cellular ubiquitin-like modifiers (UBLs) such as Neddylation or SUMOylation during AAV transduction could be beneficial. Using a combination of in silico biochemical and molecular engineering strategies, we have studied the impact of these UBLs during AAV2 infection and further developed Neddylation or SUMOylation site–modified AAV vectors and validated them in multiple disease models in vitro and in vivo. Hepatic gene transfer of two novel vectors developed, K105Q (SUMOylation-site mutant) and K665Q (Neddylation-site mutant), demonstrated a significantly improved human coagulation factor (F) IX expression (up to two-fold) in a murine model of hemophilia B. Furthermore, subretinal gene transfer of AAV2-K105Q vector expressing RPE65 gene demonstrated visual correction in a murine model of a retinal degenerative disease (rd12 mice). These vectors did not have any adverse immunogenic events in vivo. Taken together, we demonstrate that gene delivery vectors specifically engineered at UBLs can improve the therapeutic outcome during AAV-mediated ocular or hepatic gene therapy.

Molecular Engineering of Adeno-Associated Virus Capsid Improves Its Therapeutic Gene Transfer in Murine Models of Hemophilia and Retinal Degeneration

Recombinant adeno-associated virus (AAV)-based gene therapy has been promising, but several host-related transduction or immune challenges remain. For this mode of therapy to be widely applicable, it is crucial to develop high transduction and permeating vectors that infect the target at significantly low doses. Because glycosylation of capsid proteins is known to be rate limiting in the life cycle of many viruses, we reasoned that perturbation of glycosylation sites in AAV2 capsid will enhance gene delivery. In our first set experiments, pharmacological modulation of the glycosylation status in host cells, modestly decreased (1-fold) AAV2 packaging efficacy while it improved their gene expression (∼74%) in vitro. We then generated 24 mutant AAV2 vectors modified to potentially create or disrupt a glycosylation site in its capsid. Three of them demonstrated a 1.3-2.5-fold increase in transgene expression in multiple cell lines (HeLa, Huh7, and ARPE-19). Hepatic gene transfer of these vectors in hemophilia B mice, resulted in a 2-fold increase in human coagulation factor (F)IX levels, while its T/B-cell immunogenic response was unaltered. Subsequently, intravitreal gene transfer of glycosylation site-modified vectors in C57BL6/J mice demonstrated an increase in green fluorescence protein expression (∼2- to 4-fold) and enhanced permeation across retina. Subretinal administration of these modified vectors containing RPE65 gene further rescued the photoreceptor response in a murine model of Leber congenital amarousis. Our studies highlight the translational potential of glycosylation site-modified AAV2 vectors for hepatic and ocular gene therapy applications.

A CD33 Antigen-Targeted AAV6 Vector Expressing an Inducible Caspase-9 Suicide Gene Is Therapeutic in a Xenotransplantation Model of Acute Myeloid Leukemia

Current chemotherapeutic regimens for acute myeloid leukemia (AML) have been modestly effective in patients and are associated with poor long-term survival (<30% at 5 years). Viral vector-based suicide gene therapy is an attractive option, if these vectors can target the AML cells with high specificity and efficiency. In this study, we have developed a receptor-specific adeno-associated virus (AAV) based vector to target the CD33 antigen which is overexpressed in leukemic cells. A targeting peptide was rationally designed from the antigen-binding regions of a CD33 monoclonal antibody. This peptide was further expressed on the capsid of the AAV6 vector, since this serotype was most efficient among AAV1-rh10 vectors to infect the pro-monocytic, human myeloid leukemia cells (U937). AAV6-CD33 vectors expressing a suicide gene, the inducible caspase 9 (iCasp9), and its prodrug AP20187 significantly reduced (∼59%) the viability of U937 cells. To further test its efficacy and specificity in vivo, AAV6-CD33 vectors were administered into a xenotransplantation model of AML in zebrafish through systemic delivery. We observed a significant antileukemic effect with AAV6-CD33 vectors, with a markedly higher survival (100% for AAV6-CD33 vectors vs 15% for mock-treated) and a higher number of TUNEL positive apoptotic cells after systemic vector delivery. Taken together, our work demonstrates the efficacy and translational potential of CD33-targeted AAV6 vectors for cytotoxic gene therapy in AML.

Molecular characterization of novel Adeno-associated virus variants infecting human tissues

Despite the many advantages with Adeno-associated virus (AAV) based vectors for gene therapy, certain barriers related to host permissivity and immune response precludes their widespread application in humans. A comprehensive study of the distribution and complexity of naturally occurring AAV in human tissues should facilitate their optimal utilization for gene therapy and tissue targeting in humans. A total of 205 samples, comprising 198 tissue samples from individuals of Indian origin and 7 different cell lines were investigated. A panel of 8 primate samples was used as controls. DNA from these samples was screened for the AAV capsid specific signature regions by a modified PCR and DNA sequencing approach. Further, we generated a single point mutation (S224A) in AAV3 vector, analogous to the mutation identified in a novel AAV3 sequence variant isolated from a peripheral blood stem cell (PBSC) sample. We further studied the infectivity of these vectors in HeLa and HS5 cells in vitro. Of the 205 samples analyzed, an AAV specific signature DNA sequence was detected in 92 samples (45%), including 85 out of 198 human tissues and in all the 7 human cell lines investigated. DNA sequencing analysis showed that AAV6(34%) was the most common serotype and identified predominantly in PBSCs. Interestingly, a comparative genotypic analysis in primate samples identified AAV3 specific DNA in most of the bone marrow or liver tissue analyzed (n = 7/8) suggesting species-specific differences in AAV infectivity. Further characterization of an AAV3 serotype variant isolated from the PBSCs was non-infectious in vitro, possibly due to altered receptor affinity. Our data outlines the genetic diversity and the distribution of AAV serotypes infecting humans and provides a basis for their further characterization to generate efficient gene delivery vectors.

Post-translational modifications in capsid proteins of recombinant adeno-associated virus (AAV) 1-rh10 serotypes

Post‐translational modifications in viral capsids are known to fine‐tune and regulate several aspects of the infective life cycle of several viruses in the host. Recombinant viruses that are generated in a specific producer cell line are likely to inherit unique post‐translational modifications during intra‐cellular maturation of its capsid proteins. Data on such post‐translational modifications in the capsid of recombinant adeno‐associated virus serotypes (AAV1‐rh10) is limited. We have employed liquid chromatography and mass spectrometry analysis to characterize post‐translational modifications in AAV1‐rh10 capsid protein. Our analysis revealed a total of 52 post‐translational modifications in AAV2‐AAVrh10 capsids, including ubiquitination (17%), glycosylation (36%), phosphorylation (21%), SUMOylation (13%) and acetylation (11%). While AAV1 had no detectable post‐translational modification, at least four AAV serotypes had >7 post‐translational modifications in their capsid protein. About 82% of these post‐translational modifications are novel. A limited validation of AAV2 capsids by MALDI‐TOF and western blot analysis demonstrated minimal glycosylation and ubiquitination of AAV2 capsids. To further validate this, we disrupted a glycosylation site identified in AAV2 capsid (AAV2‐N253Q), which severely compromised its packaging efficiency (~ 100‐fold vs. AAV2 wild‐type vectors). In order to confirm other post‐translational modifications detected such as SUMOylation, mutagenesis of a SUMOylation site(K258Q) in AAV2 was performed. This mutant vector demonstrated reduced levels of SUMO‐1/2/3 proteins and negligible transduction, 2 weeks after ocular gene transfer. Our study underscores the heterogeneity of post‐translational modifications in AAV vectors. The data presented here, should facilitate further studies to understand the biological relevance of post‐translational modifications in AAV life cycle and the development of novel bioengineered AAV vectors for gene therapy applications.

Enzymes

Trypsin, EC 3.4.21.4

Visualization of Retinal Morphology in rd12 Mice by Scanning Electron Microscopy

We have evaluated the retinal morphological changes in normal C57BL6/J mice and a retinal degenerative disease (rd12 mice) model using scanning electron microscopy. A method of sample preparation for electron microscopy was developed and the cryosectioned retina was used to study the retinal thickness. Our data demonstrate variation in the neural retina texture between rd12 mice and C57BL6/J mice.

Combination Suicide Gene Delivery with an Adeno-Associated Virus Vector Encoding Inducible Caspase-9 and a Chemical Inducer of Dimerization Is Effective in a Xenotransplantation Model of Hepatocellular Carcinoma

Current treatment approaches for hepatocellular carcinoma (HCC) have a narrow therapeutic index and alternate modes of treatment are thus required. We have utilized a gene delivery vector containing inducible caspase 9 (iCasp9) gene, which is a synthetic analogue based on the mammalian caspase 9 and fused to a human FK506 binding protein that allows its conditional dimerization to a synthetic, small molecule [chemical inducer of dimerization, AP20187] and results in target cell apoptosis. In our studies, we have tested these synthetic vectors based on an adeno-associated virus platform for their potential anti-tumorigenic effect in human HCC cells in vitro and in a HCC tumor model developed in nude mice. Our data demonstrates that the iCasp9-AP20187 bioconjugate is able to trigger terminal effectors of cellular apoptosis and presents a viable approach for the potential treatment of HCC.

An efficient method to generate xenograft tumor models of acute myeloid leukemia and hepatocellular carcinoma in adult zebrafish

Zebrafish is emerging as a promising model for the study of human cancers. Several xenograft models of zebrafish have been developed, particularly in larval stages (<48 h post fertilization) when the immune system of fish is not developed. However, xenografting in adult zebrafish requires laborious and transient methods of immune suppression (γ- irradiation or dexamethasone) that limits engraftment and survival of the tumor or fail to recapitulate specific characteristics of malignancies. Thus, the availability of a simple protocol to successfully engraft adult zebrafish, remains a challenge. The current study addresses this limitation and describes a robust method of xenografting in adult zebrafish. We describe a protocol that involves pre-conditioning of Casper, a pigmentation mutant of zebrafish with busulfan that led to a higher rate of engraftment of hepatocellular carcinoma and acute myeloid leukemia cells. To further ascertain the homing characteristics of the injected cancer cells, we transplanted adult zebrafish by two routes of administration and then studied their compartmentalization. This model presents a valuable alternative to rodents to study the biology of these cancers and also a cost-effective platform for evaluation of potential anti-cancer agents.

Infectivity of adeno-associated virus serotypes in mouse testis

Background

Recombinant adeno-associated viruses (AAVs) are emerging as favoured transgene delivery vectors for both research applications and gene therapy. In this context, a thorough investigation of the potential of various AAV serotypes to transduce specific cell types is valuable. Here, we rigorously tested the infectivity of a number of AAV serotypes in murine testis by direct testicular injection.

Results

We report the tropism of serotypes AAV2, 5, 8, 9 and AAVrh10 in mouse testis. We reveal unique infectivity of AAV2 and AAV9, which preferentially target intertubular testosterone-producing Leydig cells. Remarkably, AAV2 TM, a mutant for capsid designed to increase transduction, displayed a dramatic alteration in tropism; it infiltrated seminiferous tubules unlike wildtype AAV2 and transduced Sertoli cells. However, none of the AAVs tested infected spermatogonial cells.

Conclusions

In spite of direct testicular injection, none of the tested AAVs appeared to infect sperm progenitors as assayed by reporter expression. This lends support to the current view that AAVs are safe gene-therapy vehicles. However, testing the presence of rAAV genomic DNA in germ cells is necessary to assess the risk of individual serotypes.

Electronic supplementary material

The online version of this article (10.1186/s12896-018-0479-1) contains supplementary material, which is available to authorized users.

Mutations in coagulation factor XIII A gene in eight unrelated Indians

Factor XIII deficiency is a rare autosomal (1:2,000,000) recessive disorder of blood coagulation usually attributed to mutations in the coagulation factor XIII (FXIII) A gene. We have studied the molecular basis of FXIII deficiency in eight unrelated South Indian patients. Their diagnosis was based on clinical history, normal plasma clotting times and increased solubility of fibrin clot in5 mol/l urea. Genomic DNA was screened for FXIII A gene defects by a novel PCR and CSGE strategy. Mutations were identified in all these patients. Five of these were novel mutations occurring in four patients. These included a novel c.210T>G transversion in homozygosity in exon 3 predicting a Tyr69X in the beta-sandwich domain in one patient. Another patient was compound heterozygote for a novel c.791C>T transition predicting a Ser263Phe in the core domain and a novel c.2045–1G>A transition at the acceptor splice junction of in tron 14. Two novel frame shifts were also identified in two patients in a homozygous condition. One of them resulted from a single base ‘G’ duplication (c.892_895dupG) at codons Ser290/Ala291fs affecting the core domain and the other was due to a single base ‘A’ duplication (c.1642_1644dupA) and at codonTyr547fs affecting barrel-1 domain. The remaining four patients had the previously reported Arg260His, Ser413Leu, and Val414Phe (n = 2) missense mutations in the core domain. The novel mutations identified were considered to be disease causative by studying the nature of mutation, the degree of conservation of the mutated aminoacid among transglutaminases of different species and by molecular modeling. Apart from describing a significant number of novel mutations, this report is the first study from Southern India to describe FXIII A gene mutations.

Optimized AAV rh.10 Vectors That Partially Evade Neutralizing Antibodies during Hepatic Gene Transfer

Of the 12 common serotypes used for gene delivery applications, Adeno-associated virus (AAV)rh.10 serotype has shown sustained hepatic transduction and has the lowest seropositivity in humans. We have evaluated if further modifications to AAVrh.10 at its phosphodegron like regions or predicted immunogenic epitopes could improve its hepatic gene transfer and immune evasion potential. Mutant AAVrh.10 vectors were generated by site directed mutagenesis of the predicted targets. These mutant vectors were first tested for their transduction efficiency in HeLa and HEK293T cells. The optimal vector was further evaluated for their cellular uptake, entry, and intracellular trafficking by quantitative PCR and time-lapse confocal microscopy. To evaluate their potential during hepatic gene therapy, C57BL/6 mice were administered with wild-type or optimal mutant AAVrh.10 and the luciferase transgene expression was documented by serial bioluminescence imaging at 14, 30, 45, and 72 days post-gene transfer. Their hepatic transduction was further verified by a quantitative PCR analysis of AAV copy number in the liver tissue. The optimal AAVrh.10 vector was further evaluated for their immune escape potential, in animals pre-immunized with human intravenous immunoglobulin. Our results demonstrate that a modified AAVrh.10 S671A vector had enhanced cellular entry (3.6 fold), migrate rapidly to the perinuclear region (1 vs. >2 h for wild type vectors) in vitro, which further translates to modest increase in hepatic gene transfer efficiency in vivo. More importantly, the mutant AAVrh.10 vector was able to partially evade neutralizing antibodies (~27–64 fold) in pre-immunized animals. The development of an AAV vector system that can escape the circulating neutralizing antibodies in the host will substantially widen the scope of gene therapy applications in humans.

MicroRNA-15b Modulates Molecular Mediators of Blood Induced Arthropathy in Hemophilia Mice

The development of arthropathy is a major co-morbidity in patients with hemophilia. The present study was designed to study the role of a microRNA biomarker (miR-15b) in the development of joint disease. To investigate the expression profile of miR-15b during the development of arthropathy, we first isolated and studied small RNA from the acute and chronic hemarthrosis model of hemophilia A mice. We observed that miR-15b was consistently repressed (~1- to 4-fold) from the onset of joint bleeding (1, 3, 7 and 24 h) until six bleeding episodes (up to 90 days). To test if reconstitution of miR-15b modulates biomarkers of joint damage in a chronic hemarthrosis model, we administered an adeno-associated virus (AAV) 5-miR-15b vector intra-articularly alone or in combination with systemic administration of AAV2-factor VIII. miR-15b overexpression downregulated markers of angiogenesis and hypoxia (vascular epithelial growth factor α (VEGF-α) and hypoxia inducing factor 2α (HIF-2α), ~70% and ~34%, respectively) in the affected joints. In addition, the co-administration of miR-15b and factor VIII vectors reduced the levels of the chondrodegenerative matrix-metalloproteinases (MMPs) 1, 3, 9 and 14 (~14% to 60%) in the injured joints. These data demonstrate for the first time the role of a miR-15b in the development of hemophilic arthropathy and has implications in development of miR based therapies for joint disease.

Intracellular Trafficking of AAV5 Vectors

The present study was designed to visualize the cellular trafficking of adeno-associated virus (AAV) vectors in general and AAV5 serotype vectors in particular. We fluorescently labeled AAV5 wild-type and a mutant (S652A) virus and studied their infection process by live cell imaging and confocal microscopy. Our data demonstrate considerable difference in the ability of these vectors to reach the nuclear compartment within the first 6 hr after infection.

Synergistic inhibition of PARP-1 and NF-κB signaling downregulates immune response against recombinant AAV2 vectors during hepatic gene therapy

Host immune response remains a key obstacle to widespread application of adeno-associated virus (AAV) based gene therapy. Thus, targeted inhibition of the signaling pathways that trigger such immune responses will be beneficial. Previous studies have reported that DNA damage response proteins such as poly(ADP-ribose) polymerase-1 (PARP-1) negatively affect the integration of AAV in the host genome. However, the role of PARP-1 in regulating AAV transduction and the immune response against these vectors has not been elucidated. In this study, we demonstrate that repression of PARP-1 improves the transduction of single-stranded AAV vectors both in vitro (∼174%) and in vivo (two- to 3.4-fold). Inhibition of PARP-1, also significantly downregulated the expression of several proinflammatory and cytokine markers such as TLRs, ILs, NF-κB subunit proteins associated with the host innate response against self-complementary AAV2 vectors. The suppression of the inflammatory response targeted against these vectors was more effective upon combined inhibition of PARP-1 and NF-κB signaling. This strategy also effectively attenuated the AAV capsid-specific cytotoxic T-cell response, with minimal effect on vector transduction, as demonstrated in normal C57BL/6 and hemophilia B mice. These data suggest that targeting specific host cellular proteins could be useful to attenuate the immune barriers to AAV-mediated gene therapy.

Basic biology of adeno-associated virus (AAV) vectors used in gene therapy

Adeno-associated virus (AAV) based vectors have emerged as important tools for gene therapy in humans. The recent successes seen in Phase I/II clinical trials have also highlighted the issues related to the host and vector-related immune response that preclude the universal application of this promising vector system. A fundamental insight into the biological mechanisms by which AAV infects the host cell and a thorough understanding of the immediate and long-lived cellular responses to AAV infection is likely to offer clues and help design better intervention strategies to improve the therapeutic efficiency of AAV vectors. This article reviews the biology of AAV-host cellular interactions and outlines their application in the development of novel and improved AAV vector systems.

Cellular unfolded protein response against viruses used in gene therapy

Viruses are excellent vehicles for gene therapy due to their natural ability to infect and deliver the cargo to specific tissues with high efficiency. Although such vectors are usually "gutted" and are replication defective, they are subjected to clearance by the host cells by immune recognition and destruction. Unfolded protein response (UPR) is a naturally evolved cyto-protective signaling pathway which is triggered due to endoplasmic reticulum (ER) stress caused by accumulation of unfolded/misfolded proteins in its lumen. The UPR signaling consists of three signaling pathways, namely PKR-like ER kinase, activating transcription factor 6, and inositol-requiring protein-1. Once activated, UPR triggers the production of ER molecular chaperones and stress response proteins to help reduce the protein load within the ER. This occurs by degradation of the misfolded proteins and ensues in the arrest of protein translation machinery. If the burden of protein load in ER is beyond its processing capacity, UPR can activate pro-apoptotic pathways or autophagy leading to cell death. Viruses are naturally evolved in hijacking the host cellular translation machinery to generate a large amount of proteins. This phenomenon disrupts ER homeostasis and leads to ER stress. Alternatively, in the case of gutted vectors used in gene therapy, the excess load of recombinant vectors administered and encountered by the cell can trigger UPR. Thus, in the context of gene therapy, UPR becomes a major roadblock that can potentially trigger inflammatory responses against the vectors and reduce the efficiency of gene transfer.

Diffuse large B cell lymphoma in wiskott-Aldrich syndrome: a case report and review of literature

Wiskott-Aldrich syndrome (WAS) is an X linked rare primary immunodeficiency syndrome with an increased propensity for infection, autoimmunity and malignancy. Here we report a male child, who was diagnosed with WAS at 1 year of age following evaluation for symptomatic thrombocytopenia and eczematous skin lesions. He presented later with lymphadenopathy, which was consistent with diffuse large B cell lymphoma on histopathology. He received 6 cycles of R-CHOP chemotherapy for the same and is presently in remission after 6 months. We review the major publications of lymphoma in WAS and discuss the pathological findings, treatment and prognosis of lymphoma in WAS.

Optimizing the transduction efficiency of capsid-modified AAV6 serotype vectors in primary human hematopoietic stem cells in vitro and in a xenograft mouse model in vivo

BACKGROUND AIMS

Although recombinant adeno-associated virus serotype 2 (AAV2) vectors have gained attention because of their safety and efficacy in numerous phase I/II clinical trials, their transduction efficiency in hematopoietic stem cells (HSCs) has been reported to be low. Only a few additional AAV serotype vectors have been evaluated, and comparative analyses of their transduction efficiency in HSCs from different species have not been performed.

METHODS

We evaluated the transduction efficiency of all available AAV serotype vectors (AAV1 through AAV10) in primary mouse, cynomolgus monkey and human HSCs. The transduction efficiency of the optimized AAV vectors was also evaluated in human HSCs in a murine xenograft model in vivo.

RESULTS

We observed that although there are only six amino acid differences between AAV1 and AAV6, AAV1, but not AAV6, transduced mouse HSCs well, whereas AAV6, but not AAV1, transduced human HSCs well. None of the 10 serotypes transduced cynomolgus monkey HSCs in vitro. We also evaluated the transduction efficiency of AAV6 vectors containing mutations in surface-exposed tyrosine residues. We observed that tyrosine (Y) to phenylalanine (F) point mutations in residues 445, 705 and 731 led to a significant increase in transgene expression in human HSCs in vitro and in a mouse xenograft model in vivo.

CONCLUSIONS

These studies suggest that the tyrosine-mutant AAV6 serotype vectors are the most promising vectors for transducing human HSCs and that it is possible to increase further the transduction efficiency of these vectors for their potential use in HSC-based gene therapy in humans.

Improved adeno-associated virus (AAV) serotype 1 and 5 vectors for gene therapy

Despite significant advancements with recombinant AAV2 or AAV8 vectors for liver directed gene therapy in humans, it is well-recognized that host and vector-related immune challenges need to be overcome for long-term gene transfer. To overcome these limitations, alternate AAV serotypes (1–10) are being rigorously evaluated. AAV5 is the most divergent (55% similarity vs. other serotypes) and like AAV1 vector is known to transduce liver efficiently. AAV1 and AAV5 vectors are also immunologically distinct by virtue of their low seroprevalence and minimal cross reactivity against pre-existing AAV2 neutralizing antibodies. Here, we demonstrate that targeted bio-engineering of these vectors, augment their gene expression in murine hepatocytes in vivo (up to 16-fold). These studies demonstrate the feasibility of the use of these novel AAV1 and AAV5 vectors for potential gene therapy of diseases like hemophilia.

Targeted modifications in adeno-associated virus serotype 8 capsid improves its hepatic gene transfer efficiency in vivo

Recombinant adeno-associated virus vectors based on serotype 8 (AAV8) have shown significant promise for liver-directed gene therapy. However, to overcome the vector dose dependent immunotoxicity seen with AAV8 vectors, it is important to develop better AAV8 vectors that provide enhanced gene expression at significantly low vector doses. Since it is known that AAV vectors during intracellular trafficking are targeted for destruction in the cytoplasm by the host-cellular kinase/ubiquitination/proteasomal machinery, we modified specific serine/threonine kinase or ubiquitination targets on the AAV8 capsid to augment its transduction efficiency. Point mutations at specific serine (S)/threonine (T)/lysine (K) residues were introduced in the AAV8 capsid at the positions equivalent to that of the effective AAV2 mutants, generated successfully earlier. Extensive structure analysis was carried out subsequently to evaluate the structural equivalence between the two serotypes. scAAV8 vectors with the wild-type (WT) and each one of the S/T→Alanine (A) or K-Arginine (R) mutant capsids were evaluated for their liver transduction efficiency in C57BL/6 mice in vivo. Two of the AAV8-S→A mutants (S279A and S671A), and a K137R mutant vector, demonstrated significantly higher enhanced green fluorescent protein (EGFP) transcript levels (~9- to 46-fold) in the liver compared to animals that received WT-AAV8 vectors alone. The best performing AAV8 mutant (K137R) vector also had significantly reduced ubiquitination of the viral capsid, reduced activation of markers of innate immune response, and a concomitant two-fold reduction in the levels of neutralizing antibody formation in comparison to WT-AAV8 vectors. Vector biodistribution studies revealed that the K137R mutant had a significantly higher and preferential transduction of the liver (106 vs. 7.7 vector copies/mouse diploid genome) when compared to WT-AAV8 vectors. To further study the utility of the K137R-AAV8 mutant in therapeutic gene transfer, we delivered human coagulation factor IX (h.FIX) under the control of liver-specific promoters (LP1 or hAAT) into C57BL/6 mice. The circulating levels of h.FIX:Ag were higher in all the K137R-AAV8 treated groups up to 8 weeks post-hepatic gene transfer. These studies demonstrate the feasibility of the use of this novel AAV8 vectors for potential gene therapy of hemophilia B.

Bioengineering of AAV2 capsid at specific serine, threonine, or lysine residues improves its transduction efficiency in vitro and in vivo

We hypothesized that the AAV2 vector is targeted for destruction in the cytoplasm by the host cellular kinase/ubiquitination/proteasomal machinery and that modification of their targets on AAV2 capsid may improve its transduction efficiency. In vitro analysis with pharmacological inhibitors of cellular serine/threonine kinases (protein kinase A, protein kinase C, casein kinase II) showed an increase (20-90%) on AAV2-mediated gene expression. The three-dimensional structure of AAV2 capsid was then analyzed to predict the sites of ubiquitination and phosphorylation. Three phosphodegrons, which are the phosphorylation sites recognized as degradation signals by ubiquitin ligases, were identified. Mutation targets comprising eight serine (S) or seven threonine (T) or nine lysine (K) residues were selected in and around phosphodegrons on the basis of their solvent accessibility, overlap with the receptor binding regions, overlap with interaction interfaces of capsid proteins, and their evolutionary conservation across AAV serotypes. AAV2-EGFP vectors with the wild-type (WT) capsid or mutant capsids (15 S/T→alanine [A] or 9 K→arginine [R] single mutant or 2 double K→R mutants) were then evaluated in vitro. The transduction efficiencies of 11 S/T→A and 7 K→R vectors were significantly higher (~63-90%) than the AAV2-WT vectors (~30-40%). Further, hepatic gene transfer of these mutant vectors in vivo resulted in higher vector copy numbers (up to 4.9-fold) and transgene expression (up to 14-fold) than observed from the AAV2-WT vector. One of the mutant vectors, S489A, generated ~8-fold fewer antibodies that could be cross-neutralized by AAV2-WT. This study thus demonstrates the feasibility of the use of these novel AAV2 capsid mutant vectors in hepatic gene therapy.

High-efficiency transduction of primary human hematopoietic stem cells and erythroid lineage-restricted expression by optimized AAV6 serotype vectors in vitro and in a murine xenograft model in vivo

We have observed that of the 10 AAV serotypes, AAV6 is the most efficient in transducing primary human hematopoietic stem cells (HSCs), and that the transduction efficiency can be further increased by specifically mutating single surface-exposed tyrosine (Y) residues on AAV6 capsids. In the present studies, we combined the two mutations to generate a tyrosine double-mutant (Y705+731F) AAV6 vector, with which >70% of CD34⁺ cells could be transduced. With the long-term objective of developing recombinant AAV vectors for the potential gene therapy of human hemoglobinopathies, we generated the wild-type (WT) and tyrosine-mutant AAV6 vectors containing the following erythroid cell-specific promoters: β-globin promoter (βp) with the upstream hyper-sensitive site 2 (HS2) enhancer from the β-globin locus control region (HS2-βbp), and the human parvovirus B19 promoter at map unit 6 (B19p6). Transgene expression from the B19p6 was significantly higher than that from the HS2-βp, and increased up to 30-fold and up to 20-fold, respectively, following erythropoietin (Epo)-induced differentiation of CD34⁺ cells in vitro. Transgene expression from the B19p6 or the HS2-βp was also evaluated in an immuno-deficient xenograft mouse model in vivo. Whereas low levels of expression were detected from the B19p6 in the WT AAV6 capsid, and that from the HS2-βp in the Y705+731F AAV6 capsid, transgene expression from the B19p6 promoter in the Y705+731F AAV6 capsid was significantly higher than that from the HS2-βp, and was detectable up to 12 weeks post-transplantation in primary recipients, and up to 6 additional weeks in secondary transplanted animals. These data demonstrate the feasibility of the use of the novel Y705+731F AAV6-B19p6 vectors for high-efficiency transduction of HSCs as well as expression of the b-globin gene in erythroid progenitor cells for the potential gene therapy of human hemoglobinopathies such as β-thalassemia and sickle cell disease.

Nuclear factor (NF)-κB and its associated pathways are major molecular regulators of blood-induced joint damage in a murine model of hemophilia

BACKGROUND

The present study was designed to investigate the molecular signaling events from onset of bleeding through the development of arthropathy in a murine model of hemophilia A.

METHODS AND RESULTS

A sharp-injury model of hemarthrosis was used. A global gene expression array on joint-specific RNA isolated 3 h post-injury revealed nuclear factor-kappa B (NF-κB) as the major transcription factor triggering inflammation. As a number of genes encoding the cytokines, growth factors and hypoxia regulating factors are known to be activated by NF-κB and many of these are part of the pathogenesis of various joint diseases, we reasoned that NF-κB-associated pathways may play a crucial role in blood-induced joint damage. To further understand its role, we screened NF-κB-associated pathways between 1 h to 90 days after injury. After a single articular bleed, distinct members of the NF-κB family (NF-κB1/NF-κB2/RelA/RelB) and their responsive pro-inflammatory cytokines (IL-1β/IL-6/IFNγ/TNFα) were significantly up-regulated (> 2 fold, P < 0.05) in injured vs. control joints at the various time-points analyzed (1 h/3 h/7 h/24 h). After multiple bleeds (days 30/60/75/90), there was increased expression of NF-κB-associated factors that contribute to hypoxia (HIF-1α, 3.3-6.5 fold), angiogenesis (VEGF-α, 2.5-4.4 fold) and chondrocyte damage (matrix metalloproteinase-13, 2.8-3.8 fold) in the injured joints. Micro RNAs (miR) that are known to regulate NF-κB activation (miRs-9 and 155), inflammation (miRs-16, 155 and 182) and apoptosis (miRs-19a, 155 and 186) were also differentially expressed (-4 to +13-fold) after joint bleeding, indicating that the small RNAs could modulate the arthropathy phenotype.

CONCLUSIONS

These data suggest that NF-κB-associated signaling pathways are involved in the development of hemophilic arthropathy.

Activation of the cellular unfolded protein response by recombinant adeno-associated virus vectors

The unfolded protein response (UPR) is a stress-induced cyto-protective mechanism elicited towards an influx of large amount of proteins in the endoplasmic reticulum (ER). In the present study, we evaluated if AAV manipulates the UPR pathways during its infection. We first examined the role of the three major UPR axes, namely, endoribonuclease inositol-requiring enzyme-1 (IRE1α), activating transcription factor 6 (ATF6) and PKR-like ER kinase (PERK) in AAV infected cells. Total RNA from mock or AAV infected HeLa cells were used to determine the levels of 8 different ER-stress responsive transcripts from these pathways. We observed a significant up-regulation of IRE1α (up to 11 fold) and PERK (up to 8 fold) genes 12–48 hours after infection with self-complementary (sc)AAV2 but less prominent with single-stranded (ss)AAV2 vectors. Further studies demonstrated that scAAV1 and scAAV6 also induce cellular UPR in vitro, with AAV1 vectors activating the PERK pathway (3 fold) while AAV6 vectors induced a significant increase on all the three major UPR pathways [6–16 fold]. These data suggest that the type and strength of UPR activation is dependent on the viral capsid. We then examined if transient inhibition of UPR pathways by RNA interference has an effect on AAV transduction. siRNA mediated silencing of PERK and IRE1α had a modest effect on AAV2 and AAV6 mediated gene expression (∼1.5–2 fold) in vitro. Furthermore, hepatic gene transfer of scAAV2 vectors in vivo, strongly elevated IRE1α and PERK pathways (2 and 3.5 fold, respectively). However, when animals were pre-treated with a pharmacological UPR inhibitor (metformin) during scAAV2 gene transfer, the UPR signalling and its subsequent inflammatory response was attenuated concomitant to a modest 2.8 fold increase in transgene expression. Collectively, these data suggest that AAV vectors activate the cellular UPR pathways and their selective inhibition may be beneficial during AAV mediated gene transfer.

Development of Novel Recombinant AAV Vectors and Strategies for the Potential Gene Therapy of Hemophilia

Recombinant vectors based on a non-pathogenic human parvovirus, the adeno-associated virus (AAV), have gained attention as a potentially safe and useful alternative to the more commonly used retroviral and adenoviral vectors. AAV vectors are currently in use in Phase I/II clinical trials for gene therapy of a number of diseases such as cystic fibrosis, α-1 antitrypsin deficiency, muscular dystrophy, Batten's disease, and Parkinson's disease, and have shown efficacy in patients with Leber's congenital amaurosis, and hemophilia B. For patients with hemophilia B, however, relatively large vector doses are needed to achieve therapeutic benefits. Large vector doses also trigger an immune response as significant fraction of the vectors fails to traffic efficiently to the nucleus, and is targeted for degradation by the host cell proteasome machinery. With a better understanding of the various steps in the life cycle of AAV vectors, strategies leading to the development of novel AAV vectors that are capable of high-efficiency transduction at lower doses are needed. In this review, we summarize our strategies to develop novel AAV vectors for the potential gene therapy of both hemophilia B and hemophilia A, based on our recent studies on the basic molecular biology of AAV. These strategies, including the development of novel AAV vectors by site-directed mutagenesis of critical surface-exposed tyrosine residues on AAV2 capsids to circumvent the ubiquitination step and the use of different AAV serotypes and self-complementary (sc) AAV2 vectors, and their use as helper vectors to circumvent the obstacles of second-strand DNA synthesis of single-stranded (ss) AAV, should dramatically accelerate the progress towards the potential gene therapy of both hemophilia A and hemophilia B.

Innate Immune Responses to AAV Vectors

Gene replacement therapy by in vivo delivery of adeno-associated virus (AAV) is attractive as a potential treatment for a variety of genetic disorders. However, while AAV has been used successfully in many models, other experiments in clinical trials and in animal models have been hampered by undesired responses from the immune system. Recent studies of AAV immunology have focused on the elimination of transgene-expressing cells by the adaptive immune system, yet the innate immune system also has a critical role, both in the initial response to the vector and in prompting a deleterious adaptive immune response. Responses to AAV vectors are primarily mediated by the TLR9–MyD88 pathway, which induces the production of pro-inflammatory cytokines by activating the NF-κB pathways and inducing type I IFN production; self-complementary AAV vectors enhance these inflammatory processes. Additionally, the alternative NF-κB pathway influences transgene expression in cells transduced by AAV. This review highlights these recent discoveries regarding innate immune responses to AAV and discusses strategies to ablate these potentially detrimental signaling pathways.

A simple method to increase the transduction efficiency of single-stranded adeno-associated virus vectors in vitro and in vivo

We have recently shown that co-administration of conventional single-stranded adeno-associated virus 2 (ssAAV2) vectors with self-complementary (sc) AAV2-protein phosphatase 5 (PP5) vectors leads to a significant increase in the transduction efficiency of ssAAV2 vectors in human cells in vitro as well as in murine hepatocytes in vivo. In the present study, this strategy has been further optimized by generating a mixed population of ssAAV2-EGFP and scAAV2-PP5 vectors at a 10:1 ratio to achieve enhanced green fluorescent protein (EGFP) transgene expression at approximately 5- to 10-fold higher efficiency, both in vitro and in vivo. This simple coproduction method should be adaptable to any ssAAV serotype vector containing transgene cassettes that are too large to be encapsidated in scAAV vectors.

Molecular basis of Bernard-Soulier syndrome in 27 patients from India

BACKGROUND

Bernard-Soulier syndrome (BSS) is an extremely rare (1:1 million) bleeding disorder of platelet adhesion, caused by defects in the glycoprotein (GP)Ib/IX/V complex.

PATIENTS AND METHODS

The diagnosis in 27 patients was based on low platelet count, presence of giant platelets and aggregometry studies. Flow cytometry to assess the surface GPIb/IX/V complex showed reduced (7.7-57%) expression. gDNA was screened for mutations in the GPIBA, GPIBB, GP9 genes using PCR-conformation sensitive gel electrophoresis (CSGE).

RESULTS

Thirteen different disease-causing mutations, including missense (54%), frameshifts (38%) and nonsense (8%) mutations, were identified in 27 patients. Eleven of them were novel including five novel frameshifts (GPIbα: p.Gln97_98fsX113, p.Pro402_403fsX52; GPIbβ: p.Arg17fsX14; GPIX: p.Gly24fsX43, p. Pro130fs, a nonsense mutation (GPIX, p.94, Gln>X) and five novel missense mutations (GPIbα: p.492, Tyr>His; GPIbβ: p.65, Pro>Arg, p.129, Gln>His, p.132, Leu>Pro; GPIX: p.55, Phe>Cys). Interestingly, four common mutations, Cys8Arg (n = 6) and Phe55Ser (n = 2), Phe55Cys (n = 2) in GPIX and a novel 22-bp deletion in the GPIBB gene predicting p.Arg17fsX 14 (n = 10) were seen in 20 patients.

CONCLUSION

The molecular data presented here is the largest series of BSS patients to be reported so far, adding significantly to the mutation database of this condition and also useful for its genetic diagnosis in India.

Human hepatocyte growth factor receptor is a cellular coreceptor for adeno-associated virus serotype 3

Adeno-associated viruses (AAVs) use a variety of cellular receptors/coreceptors to gain entry into cells. A number of AAV serotypes are now available, and the cognate receptors/coreceptors for only a handful of those have been identified thus far. Of the 10 commonly used AAV serotypes, AAV3 is by far the least efficient in transducing cells in general. However, in our more recent studies, we observed that AAV3 vectors transduced human liver cancer cells remarkably well, which led to the hypothesis that AAV3 uses hepatocyte growth factor receptor (HGFR) as a cellular coreceptor for viral entry. AAV3 infection of human liver cancer cell lines was strongly inhibited by hepatocyte growth factor, HGFR-specific small interfering RNA, and anti-HGFR antibody, which corroborated this hypothesis. However, AAV3 vectors failed to transduce murine hepatocytes, both in vitro and in vivo, suggesting that AAV3 specifically uses human HGFR, but not murine HGFR, as a cellular coreceptor for transduction. AAV3 may prove to be a useful vector for targeting human liver cancers for the potential gene therapy.

Adeno-associated virus serotype 6 capsid tyrosine-to-phenylalanine mutations improve gene transfer to skeletal muscle

Adeno-associated viral (AAV) vectors are the most efficient in vivo gene transfer tools for gene therapy applications. Efforts have been made to translate encouraging results in small animal models to human patients. However, the need for large quantities of vector for clinical application remains a great challenge. Developing novel AAV vectors with enhanced infectivity may reduce the high vector dose requirement for many applications such as gene therapy for muscular dystrophy. Selective mutation of AAV capsid surface-exposed tyrosine (Y) is a novel strategy to improve transduction efficiency. AAV6 has been considered one of the most robust muscle gene delivery vehicles. Here, we hypothesize that AAV6 transduction efficiency can be further enhanced by mutating surface Y to phenylalanine (F). We found that mutants AAV6-Y445F and AAV6-Y731F, especially the former, achieved more efficient gene transfer than the original AAV6 after intramuscular administration to mice. Expression of both firefly luciferase and alkaline phosphatase reporter genes increased up to 8-fold and DNA copy numbers in muscle increased up to 6-fold. Our results suggest that tyrosine-mutant AAV6 vectors may represent powerful tools for testing muscle gene therapy in animal models and potentially in humans.

Novel properties of tyrosine-mutant AAV2 vectors in the mouse retina

Vectors based on adeno-associated virus serotype 2 (AAV2) have been used extensively in many gene-delivery applications, including several successful clinical trials for one type of Leber congenital amaurosis in the retina. Many studies have focused on improving AAV2 transduction efficiency and cellular specificity by genetically engineering its capsid. We have previously shown that vectors-containing single-point mutations of capsid surface tyrosines in serotypes AAV2, AAV8, and AAV9 displayed significantly increased transduction efficiency in the retina compared with their wild-type counterparts. In the present study, we evaluated the transduction characteristics of AAV2 vectors containing combinations of multiple tyrosine to phenylalanine mutations in seven highly conserved surface-exposed capsid tyrosine residues following subretinal or intravitreal delivery in adult mice. The multiply mutated vectors exhibited different in vivo transduction properties, with some having a unique ability of transgene expression in all retinal layers. Such novel vectors may be useful in developing valuable new therapeutic strategies for the treatment of many genetic diseases.

High-efficiency transduction of fibroblasts and mesenchymal stem cells by tyrosine-mutant AAV2 vectors for their potential use in cellular therapy

Adeno-associated virus 2 (AAV2) vectors transduce fibroblasts and mesenchymal stem cells (MSCs) inefficiently, which limits their potential widespread applicability in combinatorial gene and cell therapy. We have reported that AAV2 vectors fail to traffic efficiently to the nucleus in murine fibroblasts. We have also reported that site-directed mutagenesis of surface-exposed tyrosine residues on viral capsids leads to improved intracellular trafficking of the mutant vectors, and the transduction efficiency of the single tyrosine-mutant vectors is ∼10-fold higher in human cells. In the current studies, we evaluated the transduction efficiency of single as well as multiple tyrosine-mutant AAV2 vectors in murine fibroblasts. Our results indicate that the Y444F mutant vectors transduce these cells most efficiently among the seven single-mutant vectors, with >30-fold increase in transgene expression compared with the wild-type vectors. When the Y444F mutation is combined with additional mutations (Y500F and Y730F), the transduction efficiency of the triple-mutant vectors is increased by ∼130-fold and the viral intracellular trafficking is also significant improved. Similarly, the triple-mutant vectors are capable of transducing up to 80-90% of bone marrow-derived primary murine as well as human MSCs. Thus, high-efficiency transduction of fibroblasts with reprogramming genes to generate induced pluripotent stem cells, and the MSCs for delivering therapeutic genes, should now be feasible with the tyrosine-mutant AAV vectors.