112. Strong Transgene-Specific Immune Responses Can Be Elicited with Novel Adeno-Associated Virus Vectors in Mice

Abstract

Vectors based on recombinant adeno-associated virus (rAAV) have been widely appreciated for gene therapy application, in which the sustained expression of self-genes has been successfully achieved in a variety of animal models. However, the potential of rAAV vectors as vaccine carriers has only recently been recognized. We have isolated several novel AAV serotypes from primates i.e AAVs 7, 8, and 9. Therefore, it is of our interest to develop potential vaccines for human immunodeficiency virus type 1 (HIV-1) based on rAAV vectors of these new serotypes. We have constructed a panel of rAAV vectors based on different AAV serotypes (including AAV2/1, AAV2, AAV2/5, AAV2/7, AAV2/8, and AAV2/9), which all encoded HIV-1 gag p17 and p24 (designated as gagshort). BALB/c mice were i.m. immunized with this panel of AAVHIVgagshort vectors at the dose of E11 genome copies/mouse. 2, 3, and 4 weeks after immunization, splenocytes were harvested and stimulated with the H-2d restricted gag-specific CD8 T-cell epitope in intracellular IFN-g staining. Overall, AAV2/7 and AAV2/8 vaccine vectors elicited the highest levels of gag-specific CD8 T-cell responses; while AAV2/1 and AAV2/9 vaccine vectors were able to induce intermediate levels of gag-specific CD8 T-cell responses. Gag-specific CD8 T-cell responses induced with AAV2/5 and AAV2/2 vaccine vectors were barely detectable. In addition, serum samples from immunized mice were collected and total IgG responses to gag p24 were measured by ELISA. Overall, AAV2/7 and AAV2/9 vaccine vectors yielded the strongest IgG responses against p24; while AAV2/8, AAV2/1, and AAV2/5 vaccine vectors produced the intermediate IgG responses against p24. Surprisingly, there was no detectable p24-specific IgG response in serum samples from mice immunized with AAV2/2HIVgagshort vector, even though this vector yielded very high level of p24 expression in transduced cells in vitro. Interestingly, different patterns of p24-specific IgG1 vs IgG2a responses were observed in serum samples from mice immunized with HIVgagshort vaccine vectors based on different AAV serotypes. Furthermore, significant inflammation and infiltration in the mouse muscles injected with AAV2/7 and AAV2/8 vaccine vectors were observed at 4 weeks after i.m. injection by H/E staining. Taken together, these data suggested that strong transgene-specific immune responses can be elicited with novel rAAV vectors in mice. The immunogenicity of these vectors based on novel AAV serotypes will be examined in nonhuman primates.