Adaptive immune responses to Adeno-Associated Virus (AAV) vector-mediated gene transfer

Adeno-Associated Virus (AAV) vectors are promising gene transfer vehicles that have been tested extensively in preclinical animal models and human clinical trials. However, immune responses to the AAV vectors remain a concern for safety and for sustained therapeutic transgene expression. This thesis attempts to investigate adaptive immune responses to the transgene product as well as the capsid of different DNA configurations of AAV vectors: self-complementary AAV vectors, single-stranded AAV vectors, and empty AAV vectors. The results show that self-complementary AAV vectors induce elevated CD8+ T and B cell responses to the transgene product compared to single-stranded AAV vectors, across multiple serotypes including AAV2, 7 and 8. T cell responses to the transgene product carried by self-complementary AAV vectors demonstrate impaired functionality as well as gradual loss of functions with upregulation of PD-1 expression, indicative of T cell exhaustion. The B cell response to the transgene product from self-complementary AAV vectors shows immunoglobulin isotype switching, whereas single-stranded AAV vectors, predominantly induced antibodies of the IgM isotype. In clinical trials, patients with point mutations so far showed cellular immune responses to the AAV capsid rather than the transgene product, which have in some cases limited sustained gene expression upon AAV-mediated gene transfer. The results from the thesis show that proliferative CD8+ T cell immune responses to capsids of single-stranded AAV vectors are more pronounced and of longer duration compared to self-complementary AAV vectors. The serotype affected the magnitude of responses. Capsid-specific T cell responses to genome-empty AAV vectors, which are by-products of recombinant AAV production, are poor. In all, the data from the thesis illustrates a comprehensive analysis of the adaptive immune responses generated during AAV-mediated gene transfer and paves way for the future use of transient immune suppression regimen for AAV gene therapy in humans