Immunogenicity of co-administered recombinant VSV vectors expressing GM-CSF and HIV-1 Gag in mice (47.25)

Abstract Highly attenuated recombinant vesicular stomatitis virus (rVSV) vectors expressing HIV-1 Gag have been shown to be immunogenic in preclinical animal models. Here we explored the potential to enhance immunogenicity through co-delivery of either replication-competent (rVSV-N3CT9) or non-propagating (rVSV-Gstem) vectors expressing GM-CSF. A construct expressing both antigen and cytokine, Gstem-Gag1-GMCSF6, was also generated. BALB/c mice were injected i.m. with Indiana rVSV vectors and boosted 8 weeks later with New Jersey glycoprotein-exchange vectors. Co-delivery of 105pfu of N3CT9-GMCSF5 and 105 pfu of N4CT9-Gag1 resulted in Gag specific IFN-g responses that were approximately two-fold higher than responses elicited by 105pfu of N4CT9-Gag1 alone. These results were confirmed by CBA analysis of supernatants from peptide-restimulated cells. Interestingly, MHC-pentamer staining revealed no significant difference in the frequency of Gag specific CD8+ cells between the two immunization groups. Similar observations were made in tests of the Gstem vector, where 106pfu of Gstem-Gag1-GMCSF6 elicited a more robust IFN-g response after boost than 106pfu of Gstem-Gag1, while the percentage of Gag specific CD8+ cells remained equivalent. In conclusion, GM-CSF exerted immunomodulatory effects in vivo, distinguished here by the enhanced functional differentiation of vaccine elicited effector cells. This work was supported by NIH contract NO1-AI-25458