Intrarectal Immunization for a Barrier to Mucosal HIV Infection

Abstract The impressive amount of data generated by experimental but mostly unsuccessful HIV/SIV vaccines has led to the realization that protection will most likely requires 2 levels of barriers, the initial one at the mucosal port of entry and if breached, a second set of systemic defenses. The capacity of humoral and cellular immune responses in mucosal tissues to block or contain replication at the initial stage of virus transmission may have a profound impact on the ability of a vaccinated host to resist infection, even when virus progresses beyond the port of entry, allowing the systemic response more time to control or eradicate the incoming pathogen. We hypothesized that there are two features necessary for a successful vaccine: 1) A prolonged if not life-long stimulation of the immune system with viral antigens to maintain “alert” immune responses; and 2) a targeted immune response at the site of primary HIV replication. A vaccine approach that simultaneously addresses these two issues would have the potential to achieve solid, long-term active protection. To fulfill these requirements, we have developed an original strategy that successfully delivers a vaccine to mucosal sites, providing antigen stimuli at recurrent intervals and elicit protective mucosal and systemic immune responses. Our strategy leverages epithelial stem cells as permanent but non-expressing source of viral antigen while their short-lived differentiated offspring express and present antigen to the local immune system, along the mucosal surfaces of viral entry. Using a single cycle replicative-deficient SIV (SIVsc) approach, which has been shown to be safe compared to traditional attenuated vaccines, we have cloned the SIVsc genome under the control of the involucrin promoter (pINV-SIVsc), a terminally differentiated keratinocyte specific promoter. When administered, the vaccine targets and transduces basal epithelial stem cells from colorectal tissues. These cells then proliferate and differentiate into mature epithelial cells, triggering SIV antigen expression via the promoter and leading to both direct and cross priming. For this project, we propose: 1) To confirm and further improve the efficacy and safety profile of the pINV-SIVsc vaccine via the colorectal route; 2) To visualize and optimize vaccine delivery, and investigate the mechanisms of action underlying protection; and 3) Using our best optimized vaccine strategy, demonstrate protection from virus acquisition and/or viral replication in vivo and determine the correlates of protection or control against repeated low-dose intrarectal challenges with heterologous SIV.