Lewis, V. R. | Search bioRxiv

bioRxiv2026

HIV broadly neutralizing antibody precursor maturation induced by mRNA vaccination in nonhuman primates

The induction of broadly neutralizing antibodies (bnAbs) is a principal goal of prophylactic HIV vaccines. For many bnAbs, priming ultrarare precursors from the naive B cell repertoire is the first major immunological hurdle. Previous studies have shown that the germline-targeting (GT) priming immunogen N332-GT5 delivered as adjuvanted protein to non-human primates (NHPs) activates bnAb precursor B cells for the human bnAb BG18 targeting the V3-glycan supersite on the HIV envelope (Env) glycoprotein. Here, we engineered N332-GT6 to improve binding affinity to diverse BG18-class precursor naive B cells by 9-fold. mRNA-LNP vaccines expressing N332-GT5 or N332-GT6 as membrane-bound (gp151) trimers were evaluated for their ability to prime BG18-class precursor B cells in NHPs across three related studies. Although N332-GT5 gp151 mRNA-LNP priming induced BG18-class precursor B cells in most animals after two vaccinations, the higher-affinity N332-GT6 gp151 induced responses more consistently after only one immunization. Sequential vaccination with two heterologous mRNA-LNP booster immunizations drove affinity maturation and induced BG18-class memory B cells capable of binding wildtype HIV Env. Together, these findings demonstrate that mRNA immunization can achieve GT priming, boosting, and early maturation of ultrarare bnAb-class B cells in NHPs.

immunology↗

bioRxiv2024

Diverse priming outcomes under conditions of very rare precursor B cells

Rare B cells can have special pathogen-recognition features giving them the potential to make outsized contributions to protective immunity. However, rare naive B cells infrequently participate in immune responses. We investigated how germline-targeting vaccine antigen delivery and adjuvant selection affect priming of exceptionally rare BG18-like HIV broadly neutralizing antibody-precursor B cells (~1 in 50 million) in non-human primates. Only escalating dose (ED) priming immunization using the saponin adjuvant SMNP elicited detectable BG18-like cells in germinal centers (GCs). All groups had strong GC responses, but only ED+SMNP and bolus+SMNP induced BG18-like memory B cells in >50% of animals. One group had vaccine-specific GC responses equivalent to ED+SMNP, but BG18-like memory B cells were rarely detected. Following homologous boosting, BG18-like memory B cells were more frequent in a bolus priming group, but had lower somatic hypermutation and affinities. This outcome was inversely associated with post-prime antibody titers, suggesting antibody feedback can significantly influence rare precursor B cell responses.

immunology↗