Immune Responses to Viral Gene Therapy Vectors

Several viral vector-based gene therapy drugs have now received marketing approval. A much larger number of additional viral vectors are in various stages of clinical trials for the treatment of genetic and acquired diseases, with many more in pre-clinical testing. Efficiency of gene transfer and ability to provide long-term therapy make these vector systems very attractive. In fact, viral vector gene therapy has been able to treat or even cure diseases for which there had been no or only suboptimal treatments. However, innate and adaptive immune responses to these vectors and their transgene products constitute substantial hurdles to clinical development and wider use in patients. This review provides an overview of the type of immune responses that have been documented in animal models and in humans who received gene transfer with one of three widely tested vector systems, namely adenoviral, lentiviral, or adeno-associated viral vectors. Particular emphasis is given to mechanisms leading to immune responses, efforts to reduce vector immunogenicity, and potential solutions to the problems. At the same time, we point out gaps in our knowledge that should to be filled and problems that need to be addressed going forward

Modeling host interactions with hepatitis B virus using primary and induced pluripotent stem cell-derived hepatocellular systems

Hepatitis B virus (HBV) chronically infects 400 million people worldwide and is a leading driver of end-stage liver disease and liver cancer. Research into the biology and treatment of HBV requires an in vitro cell-culture system that supports the infection of human hepatocytes, and accurately recapitulates virus–host interactions. Here, we report that micropatterned cocultures of primary human hepatocytes with stromal cells (MPCCs) reliably support productive HBV infection, and infection can be enhanced by blocking elements of the hepatocyte innate immune response associated with the induction of IFN-stimulated genes. MPCCs maintain prolonged, productive infection and represent a facile platform for studying virus–host interactions and for developing antiviral interventions. Hepatocytes obtained from different human donors vary dramatically in their permissiveness to HBV infection, suggesting that factors—such as divergence in genetic susceptibility to infection—may influence infection in vitro. To establish a complementary, renewable system on an isogenic background in which candidate genetics can be interrogated, we show that inducible pluripotent stem cells differentiated into hepatocyte-like cells (iHeps) support HBV infection that can also be enhanced by blocking interferon-stimulated gene induction. Notably, the emergence of the capacity to support HBV transcriptional activity and initial permissiveness for infection are marked by distinct stages of iHep differentiation, suggesting that infection of iHeps can be used both to study HBV, and conversely to assess the degree of iHep differentiation. Our work demonstrates the utility of these infectious systems for studying HBV biology and the virus’ interactions with host hepatocyte genetics and physiology.Skolkovo Institute of Science and Technology (Grant 022423-003)National Institutes of Health (U.S.) (Grant UH2 EB017103)National Institutes of Health (U.S.) (Grant DK085713)National Cancer Institute (U.S.) (Koch Institute Support. Grant P30-CA14051)American Gastroenterological Association (Research Scholar Award)National Institutes of Health (U.S.) (Grant 1K08DK101754)Hertz Foundation (Fellowship)National Science Foundation (U.S.). Graduate Research Fellowship Progra

Dynamics of antigen presentation to transgene product-specific CD4+ T cells and of Treg induction upon hepatic AAV gene transfer

The tolerogenic hepatic microenvironment impedes clearance of viral infections but is an advantage in viral vector gene transfer, which often results in immune tolerance induction to transgene products. Although the underlying tolerance mechanism has been extensively studied, our understanding of antigen presentation to transgene product-specific CD4+ T cells remains limited. To address this, we administered hepatotropic adeno-associated virus (AAV8) vector expressing cytoplasmic ovalbumin (OVA) into wt mice followed by adoptive transfer of transgenic OVA-specific T cells. We find that that the liver-draining lymph nodes (celiac and portal) are the major sites of MHC II presentation of the virally encoded antigen, as judged by in vivo proliferation of DO11.10 CD4+ T cells (requiring professional antigen-presenting cells, e.g., macrophages) and CD4+CD25+FoxP3+ Treg induction. Antigen presentation in the liver itself contributes to activation of CD4+ T cells egressing from the liver. Hepatic-induced Treg rapidly disseminate through the systemic circulation. By contrast, a secreted OVA transgene product is presented in multiple organs, and OVA-specific Treg emerge in both the thymus and periphery. In summary, liver draining lymph nodes play an integral role in hepatic antigen presentation and peripheral Treg induction, which results in systemic regulation of the response to viral gene products

Experimental variables that affect human hepatocyte MV transduction in liver chimeric mice

Adeno-associated virus (AAV) vector serotypes vary in their ability to transduce hepatocytes from different species. Chimeric mouse models harboring human hepatocytes have shown translational promise for liver-directed gene therapies. However, many variables that influence human hepatocyte transduction and transgene expression in such models remain poorly defined. Here, we aimed to test whether three experimental conditions influence AAV transgene expression in immunodeficient, fumaryl-acetoactetate-hydrolase-deficient (Fah(-/-)) chimeric mice repopulated with primary human hepatocytes. We examined the effects of the murine liver injury cycle, human donor variability, and vector doses on hepatocyte transduction with various AAV serotypes expressing a green fluorescent protein (GFP). We determined that the timing of AAV vector challenge in the liver injury cycle resulted in up to 7-fold differences in the percentage of GFP expressing human hepatocytes. The GFP+ hepatocyte frequency varied 7-fold between human donors without, however, changing the relative transduction efficiency between serotypes for an individual donor. There was also a clear relationship between AAV vector doses and human hepatocyte transduction and transgene expression. We conclude that several experimental variables substantially affect human hepatocyte transduction in the Fah(-/-) chimera model, attention to which may improve reproducibility between findings from different laboratories

Engineering and In Vitro Selection of a Novel AAV3B Variant with High Hepatocyte Tropism and Reduced Seroreactivity

Limitations to successful gene therapy with adeno-associated virus (AAV) can comprise pre-existing neutralizing antibodies to the vector capsid that can block cellular entry, or inefficient transduction of target cells that can lead to sub-optimal expression of the therapeutic transgene. Recombinant serotype 3 AAV (AAV3) is an emerging candidate for liver-directed gene therapy. In this study, we integrated rational design by using a combinatorial library derived from AAV3B capsids with directed evolution by in vitro selection for liver-targeted AAV variants. The AAV3B-DE5 variant described herein was undetectable in the original viral library but gained a selective advantage upon in vitro passaging in human hepatocarcinoma spheroid cultures. AAV3B-DE5 contains 24 capsid amino acid substitutions compared with AAV3B, distributed among all five variable regions, with strong selective pressure on VR-IV, VR-V, and VR-VII. In vivo, AAV3B-DE5 demonstrated improved human hepatocyte tropism in a liver chimeric mouse model. Importantly, this variant exhibited reduced seroreactivity to human intravenous immunoglobulin (i.v. Ig), as well as individual serum samples from 100 healthy human donors. Therefore, molecular evolution using a combinatorial library platform generated a viral capsid with high hepatocyte tropism and enhanced evasion of pre-existing AAV neutralizing antibodies

Broadly neutralizing antibodies abrogate established hepatitis C virus infection

In most exposed individuals, hepatitis C virus (HCV) establishes a chronic infection; this long-term infection in turn contributes to the development of liver diseases such as cirrhosis and hepatocellular carcinoma. The role of antibodies directed against HCV in disease progression is poorly understood. Neutralizing antibodies (nAbs) can prevent HCV infection in vitro and in animal models. However, the effects of nAbs on an established HCV infection are unclear. We demonstrate that three broadly nAbs—AR3A, AR3B, and AR4A—delivered with adeno-associated viral vectors can confer protection against viral challenge in humanized mice. Furthermore, we provide evidence that nAbs can abrogate an ongoing HCV infection in primary hepatocyte cultures and in a human liver chimeric mouse model. These results showcase a therapeutic approach to interfere with HCV infection by exploiting a previously unappreciated need for HCV to continuously infect new hepatocytes to sustain a chronic infection

HCV animal models and liver disease

SummaryThe development and evaluation of effective therapies and vaccines for the hepatitis C virus (HCV) and the study of its interactions with the mammalian host have been hindered for a long time by the absence of suitable small animal models. Due to the narrow host tropism of HCV, the development of mice that can be robustly engrafted with human hepatocytes was a major breakthrough since they recapitulate the complete HCV life cycle. This model has been useful to investigate many aspects of the HCV life cycle, including antiviral interventions. However, studies of cellular immunity, immunopathogenesis and resulting liver diseases have been hampered by the lack of a small animal model with a functional immune system. In this review, we summarize the evolution of in vivo models for the study of HCV