PROJECT SUMMARY/ABSTRACT: The development of an effective HIV vaccine has proven to be a daunting challenge. Previous strategies for HIV vaccine design aimed to elicit protective T cell responses, non-neutralizing antibodies, broadly neutralizing antibodies (bnAbs), or some combination of the three. All three approaches have thus far failed to consistently protect nonhuman primates (NHPs) or humans from infection. This grant aims to elicit bnAbs by means of a novel strategy that combines – for the first time – germline-targeting, immunofocusing and molecularly guided affinity maturation. This study design evolves from a growing consensus that critical elements to a successful bnAb-based vaccine will be its ability to efficiently bind and activate rare naïve B cell germline precursors of bnAbs; to immunofocus these B cell responses to canonical, conserved bnAb epitopes on the HIV Env trimer and away from off-target strain specific or trimer base epitopes; and to mature or “polish” this bnAb lineage response by a process of molecularly guided Env-Ab coevolution. The study design proposed in this application addresses each of these three essential requirements as it aims to elicit bnAbs targeting the highly conserved HIV-1 V2-apex site. The principal investigators (Andrabi and Shaw) have assembled a talented collaborating research team with a strong track record of scientific discovery, bioengineering and molecular tool development, including the discovery of V2-apex bnAbs (Burton), development of germline targeted V2 apex immunogens (Andrabi), bioengineering of phosphoserine-linked alum nanoparticle antigen displays (Irvine), discovery of V2- apex immunofocusing chimpanzee simian immunodeficiency viruses (Hahn), creation of CRISPRCas9 knock-in mice (Batista), development of next-generation “designer” SHIVs (Shaw) and preclinical-clinical translation (Dey). The project consists of four aims: Aim #1 will isolate HIV envelope V2-apex targeted bnAbs from SHIV infected rhesus macaques, identify their UCA’s, and generate UCA-expressing knock-in mouse models for vaccine evaluation. Aim #2 will design novel V2-apex germline-targeted and immunofocused SOSIP Env trimer immunogens and by mammalian display saturation mutagenesis and structure-guided design present them as soluble proteins or alum-based nanoparticles for enhanced B cell responses. Aim #3 will optimize germline- targeting and B cell immunofocusing boost strategies in V2-apex bnAb UCA-expressing KI-mice and outbred RMs, and will identify in SOSIP Env primed and SHIV infected RMs, Env “immunotypes” that can drive neutralization breadth. Aim #4 will design and test, first in KI mice and then in a pivotal preclinical trial in RMs, an all-SOSIP Env vaccination regimen designed to prime, boost and affinity-mature bnAb responses in a majority of animals. If successful, this would be the first example of a vaccine regimen that consistently elicits bnAbs in an outbred animal model, and it would represent...