Abstract/Project Summary HIV-1 envelope glycoprotein (Env) is the sole target for development of antibody-mediated immune response. Studies of patients infected with HIV have led to the isolation of antibodies against different epitopes on the Env surface, capable of neutralizing a broad range of circulating HIV strains and providing passive protection against repeated viral challenges in non-human primates (NHPs). The current goal of HIV vaccine research is to create immunogens capable of eliciting similar antibody responses in naïve individuals. Structure- based engineering of the soluble ectodomain of Env trimer is in the core of most of the current approaches. One major complicating factor with this approach comes from the large antigenic surface on the Env, where many off-target and competing epitopes are available to the immune system. The induction of immune responses against “distracting” epitopes leads to attenuated and inconsistent response against the targeted bnAb epitopes of interest. NHPs are an important model for this work, because wildtype mice do not make Ab responses to major Env nAb epitopes observed in humans. Analysis of the polyclonal Ab response in NHP immunizations where soluble Env ectodomain trimers were used, revealed a set of highly immunogenic epitopes with low potential for the development of protective heterologous, and in some cases even autologous, responses. These epitopes include the base of the Env trimer ectodomain, N241/N289 glycan hole and variable loops (V1-V5). To address this shortcoming we have developed a rational approach to consistently elicit antibodies against the conserved fusion peptide (FP) epitope, for which there are several examples of human bnAbs. We have used our designer trimers and continuous antigen release program to generate preliminary results verifying success of this concept in NHPs. The reproducibility of the epitope targeting is the most impressive preliminary result presented here, and it indicates that reproducible elicitation of FP nAbs in humans may be readily achievable. Here we propose to conduct a series of experiments designed to further optimize this immunization strategy by minimizing the accessibility of immuno-distracting, off-target epitopes, and ultimately verify if protective, FP-targeting, bnAbs can be reproducibly elicited in NHPs. We intend to also immunize some animals in parallel with a SARS-CoV2 RBD immunogen we have designed. The RBD immunizations will be at a different site (deltoid) and will not interfere with the Env fusion peptide targeted immunizations. This dual use immunization approach is generally valuable for future HIV vaccine studies, and we will perform a pilot study to show this type of dual use immunization strategy is informative, which will be of value to use in our future HIV vaccine studies. The SARS-CoV2 RBD will also serve as a negative control for immunological parameters compared to the HIV candidate vaccine, which is of additional val...