Development of a novel mucosal CTL-based HIV vaccine. - Abstract Despite extensive efforts, the development of an effective HIV vaccine that prevents HIV infections remains a significant challenge. The high degree of sequence variation in the HIV Env protein poses a hurdle in developing vaccines generating broadly neutralizing antibodies against diverse HIV strains. Vaccines inducing HIV-specific T cell responses did not show efficacy in clinical trials, they even increased the risk of infection. It is speculated that the HIV-specific CD4+ T cells, induced in vaccinated individuals, are activated to proliferate upon exposure to HIV, the proliferative T cells support HIV replication leading to elevated viremia levels. Thus, a vaccine strategy avoiding induction of HIV-specific CD4+ T cells may prevent the vaccine-enhanced infection. Ample evidence suggests that CD8+ cytotoxic T cells (CTLs) play critical roles in controlling early HIV infection. Furthermore, a vaccine based on a rhesus cytomegalovirus vector expressing SIV Gag antigen induced complete arrest of pathogenic SIV replication and subsequent clearance of the initial infection in 50-60% of vaccinated rhesus macaques, which was mediated by MHC-E(Ib)-restricted CTLs. Based on these findings, we hypothesize that an HIV vaccine capable of exclusively inducing HIV-specific CD8+ CTLs, restricted by MHC class Ia and MHC E, without eliciting HIV-specific CD4+ T cells, can confer protection against HIV. Additionally, about 90% of all new HIV infections globally occur through mucosal contact. As systemic immunization typically induces limited CTL responses at mucosal sites, a mucosal vector is imperative for the development of an HIV vaccine to elicit effective HIV-specific CTL responses in both local and distal mucosal compartments. Furthermore, tissue- resident memory CTLs can provide immediate protection against viral infections. In this proposal, we plan to use bovine papillomavirus-like particles (BPV VLPs) as a mucosal vector and IL-7/IL-15/CD70 to increase memory CTL precursors and promote memory CTL generation for the development of the mucosal HIV vaccine that can elicit robust systemic and mucosal tissue-resident memory CTL responses, while avoiding the induction of HIV- specific CD4+ T cells. Before we test our hypothesis in rhesus macaques for viral challenge experiments, we will perform proof of principle studies in mice. In Aim 1, we will construct plasmids with ubiquitin gene-tagged HIV clade B Gag/Env minigenes encoding CTL epitopes, package them with BPV VLPs to make a pseudovirus (PsV) vaccine, immunize mice with it orally, and determine if HIV-specific MHC class Ia-restricted CTLs but not CD4+ T cells are induced in mucosal and systemic lymphoid tissues. In Aim 2, we will construct a plasmid with UL40 gene-tagged HIV clade B Gag minigenes, package it with BPV VLPs to make a PsV vaccine, immunize mice with it orally, determine if mucosal and systemic HIV-specific MHC-E-restricted CTLs are induced. In Aim 3, we will construct a plasmid expressing IL-7/IL-15 and CD70, package it with BPV VLPs to make a PsV adjuvant, immunize mice orally with the PsV vaccines with or without the PsV adjuvant, and determine if strong and durable systemic/mucosal HIV-specific memory CTL responses are generated.
