Neutralizing antibodies are likely to be required for an effective HIV-1 vaccine. However, few candidate vaccines efficiently elicit broadly neutralizing antibodies (bNAbs) following vaccination. Recently, the VRC working group has elicited fusion peptide-directed bNAbs in guinea pigs and non-human primates (NHPs). Similarly, we recently elicited bNAbs in rabbits following heterologous NFL (uncleaved) trimer-liposome prime:boosting at Scripps where we activated B cell responses with targeted N-glycan deletions in the priming immunizations (Dubrovskaya et al, Immunity 2019). We isolated two rabbit bNAbs that recapitulate the serum activity. These bNAbs are directed against two distinct sites of Env vulnerability. The elicitation of neutralizing responses was enhanced by targeted N-glycan deletion, high-density liposomal array and heterologous trimer restorative boosting Env. In independent experiments in guinea pigs, we have elicited bNAbs in multiple animals also using a N-glycan deletion, heterologous Env NFL prime:boost approach. These recent outcomes are encouraging inroads toward the successful solution of a 3-decade-long problem. The new era of near-native trimeric spike mimics, coupled with particulate array, structure-informed design and high-resolution analysis of Env-specific B cell and lymph node responses, afford new opportunities to more efficiently elicit bNAbs. We propose an integrated, multi-faceted approach blending the expertise of world leaders in HIV Env trimer design, analysis of B cell responses and Abs following vaccination, NHP immune tissue analysis and EM-based analysis of ongoing immune responses and high-resolution Ab:trimer interactions. We will use well-ordered trimer prime:boosting that elicited bNAbs in rabbits and guinea pigs to elicit such responses in NHPs, translating success in small animals to NHPs using novel immunogen design and presentation in Project 1 (Wyatt) and immunization of NFL trimers into NHPs via Core B (Silvestri). We will use ?real-time? serum Fab-to-trimer binding evaluated by EM polyclonal IgG epitope mapping (EMPEM) in Core C (Ward) in complement with rapid mAb NGS-based mAb cloning, sequencing and functional expression in Project 2 (Karlsson Hedestam). In collaboration with the VRC (Mascola) we will define either non-neutralizing mAbs to mask unwanted non-neutralizing epitopes or to better display the epitopes of cross-neutralizing mAbs. We will compare NFL trimer-liposomes to cell surface NFL trimer array expressed from the exciting mRNA lipid encapsulation technology. We will assess if immunization in the juvenile NHP B cell repertoire compared to adult macaques will better generate bNAbs as is observed during human infection. To follow our discovery of a tier 2 CD4bs-directed bNAb following trimer-liposome vaccination, termed E70, we will target the CD4bs by directed NFL trimer deglycosylation in the NHPs. Based on our recent discovery of the very broadly neutralizing vaccine-induced mAb, 1C2, we will also focus on the gp41:120 trimer interface. Leveraging these initial leads, we will undertake a multifaceted, cross-component integrated approach to guide the elicitation of bNAbs in NHPs following vaccination with near-native, uncleaved NFL Env trimers.
The major goals of the Overview are to build upon the leads using cleavage-independent, NFL trimer-liposomes and heterologous prime:boosting that generated bNAbs in a subset of rabbits to translate this remarkable progress at multiple sites of HIV Env vulnerability into non-human primates (NHPs). We propose to use negative stain EM Polyclonal Fab:trimer Epitope Mapping (EMPEM) to better guide boost selection in NHPs from both trimer-liposomes and lipid particle encapsulated mRNA expressing membrane-bound trimers (Projects 1 and Core C, Core B and Projects2) followed by structural analysis of cross-neutralizing antibodies in complex with trimer (Core C), administered by Core A in a multi-faceted approach. The efficient elicitation of tier 2 cross- antibodies in either adult or juvenile NHPs would be a significant step forward toward the goal of generating an effective HIV-1 vaccine to have a substantial impact on improving human public health.
