Characterizing the therapeutic efficacy of CD8 T cell responses induced by the IL-15 superagonist ALT-803

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PROJECT SUMMARY We do not have a vaccine or a cure for HIV. CD8 T cells are necessary for initial control of HIV viremia, but attempts to design a CD8 T cell based HIV vaccine have been met with challenges. These include (1) eliciting cellular immune responses against the most immunogenic regions of HIV and (2) enhancing the function of antiviral immune responses at the right location to contain virus replication. This proposal is a renewal of our original R01 testing the hypothesis that CD8 T cells targeting invariant epitopes are unable to detect and destroy virally-infected cells. Based on the data generated during the grant period, we published 4 manuscripts, presented 4 oral abstracts, presented 7 poster abstracts, and delivered 8 seminars. We found that SIV control was delayed and incomplete in the absence of CD8 T cells targeting the most immunogenic regions of SIV. Without detecting effective CD8 T cells to suppress SIV replication in animals with non-protective MHC alleles, our study raises questions over the feasibility of designing a universal vaccine to elicit CD8 T cells targeting invariant epitopes. During the last grant period and using funds from the previous R01, we also made the remarkable observation that the immunomodulatory IL-15 superagonist ALT-803 could boost CD8 T cell function to promote virus suppression in macaques that received prior vaccination, but not in vaccine-naïve animals. The data gathered from these studies has laid the foundation for us to test the hypothesis that that ALT-803 treatment enhances the antiviral function of vaccine-elicited memory CD8 T cells by recruiting IL-15 responsive antigen-specific CD8 T cells to lymph nodes to kill infected target cells. We will test this hypothesis by comparing ALT-803 mediated suppression of SIV in vaccine- naïve and vaccinated macaques. We also propose to characterize the responding CD8 T cell population to determine if ALT-803 enhanced memory CD8 T cells in the vaccinated animals exhibit increased antiviral function that is associated with transcription signatures indicative of increased IL-15 signaling through the JAK/STAT pathway. Together these data will help identify the features of functionally relevant antiviral CD8 T cells in animals with non-protective MHC alleles. Our study is relevant because ALT-803 is being used in clinical trials as an anti-tumor and anti-viral agent. We want to maximize the effect of ALT-803 so that it is used most effectively in these settings. Certain studies of ALT-803 cannot be performed in humans, including the one that we have proposed. We will specifically evaluate whether vaccination BEFORE SIV infection is necessary for ALT-803 to elicit functionally active CD8 T cells AFTER SIV infection. This is a paradigm shifting approach for vaccine research, because it places a value on prophylactic vaccination of immunocompetent individuals so that interventions are effective in HIV+ immunocomprimised individuals.