A comparative study of hFIX expression mediated by rAAV8 and rAAV1 administrated intramuscularly

Recombinant adeno-associated virus vectors in the treatment of rare diseases

INTRODUCTION

An estimated 25 million Americans are living with rare diseases. Adeno-associated virus (AAV)-mediated gene therapy is an emerging therapeutic option for the more than 7,000 identified rare diseases. This paper highlights the benefits of AAV therapy compared to conventional small molecules, discusses current pre-clinical and clinical applications of AAV-mediated gene therapy, and offers insights into cutting edge research that will shape the future of AAV for broad therapeutic use.

AREAS COVERED

In this review the biology of AAV and our ability to generate disease-specific variants is summarized. Limitations of current therapy are reviewed, with an emphasis on immune detection of virus, viral tropism and tissue targeting, and limitations of gene expression. Information for this review was found using PubMed and clinicaltrials.gov.

EXPERT OPINION

Currently the scope of clinical trials of AAV gene therapy is concentrated in an array of phase I/II safety trials with less than two dozen rare diseases featured. Pre-clinical, translational studies are expanding in number as developments within the last decade have made generation of improved AAV vectors available to more researchers. Further, one bottleneck that is being overcome is the availability of disease models, which will allow for improved preclinical testing and advancement of AAV to more clinical applications.

Role of antigen-specific regulatory CD4+CD25+ T cells in tolerance induction after neonatal IP administration of AAV-hF.IX

Neonatal AAV8-mediated Factor IX (F.IX) gene delivery was applied as a model for exploring mechanisms of tolerance induction during immune ontogeny. Intraperitoneal delivery of AAV8/ Factor IX (hF.IX) during weeks 1–4 of life, over a 20-fold dose range, directed stable hF.IX expression, correction of coagulopathy in F.IX-null hemophilia B mice, and induction of tolerance to hF.IX; however, only primary injection at 1–2 days of life enabled increasing AAV8-mediated hF.IX expression after re-administration, due to the absence of anti-viral capsid antibodies. Adoptive splenocyte transfer from tolerized mice demonstrated induction of CD4⁺CD25⁺ T regulatory (T_reg) populations that specifically suppressed anti-hF.IX antibody responses, but not responses to third party antigen. Induction of hF.IX antibodies was only observed in tolerized mice after in vivo CD4⁺CD25⁺ cell depletion and hF.IX challenge. Thus, primary injection of AAV during a critical period in the first week of life does not elicit antiviral responses, enabling re-administration of AAV and augmentation of hF.IX levels. Expansion of hF.IX-specific CD4⁺CD25⁺ T_regs has a major role in tolerance induction early in immune ontogeny. Neonatal gene transfer provides a useful approach for defining the ontogeny of immune responses and may suggest approaches for inducing tolerance in the context of genetic therapies.

Induced liver allograft immunological tolerance in rats by intramuscular injection of recombinant adeno-associated virus-human cytotoxic T-lymphocyte-associated antigen-4 immunoglobulin (rAAV-hCTLA4Ig)

Induction of liver allograft immunological tolerance was performed in rats by intramuscular injection of recombinant adeno-associated virus-human cytotoxic T-lymphocyte-associated antigen-4 immunoglobulin (rAAV-hCTLA4Ig). Dark Agouti and Lewis rats were liver allograft donors and recipients, respectively, in four groups: (A) syngeneic control, (B) blank control, (C) rAAV-enhanced green fluorescent protein negative control, (D) rAAV-hCTLA4Ig. Gene transfers occurred 6 weeks before transplantation. Group D had a significantly longer liver graft survival time (> 100 days) than groups B (11.9 +/- 1.3 days) and C (11.6 +/- 1.1 days). Groups B and C showed severe rejection responses and large amounts of CD4(+) and CD8(+) T-lymphocyte infiltration, while only a mild response and few T-lymphocytes were observed in group D. There were no significant differences in interleukin-2 and interferon-gamma levels in liver grafts between groups D and C, but there were significant decreases in granzyme B and lymphotoxin beta levels in group D compared with group C. It is concluded that immunological tolerance to liver allograft could be achieved by gene transfer of rAAV-hCTLA4Ig through intramuscular injection.