Guiding the maturation of anti-CD4-BS bnAbs through sequential heterologous Env immunization

PROJECT SUMMARY / ABSTRACT An effective HIV-1 vaccine will be one that elicits diverse anti-viral immune responses, including broadly neutralizing antibodies (bnAbs). Here, we focus on eliciting anti-CD4-binding site (CD4-BS) bnAbs, including VRC01-class bnAbs, through a guided immunization approach with specifically designed Env-derived immunogens. We previously reported on the design of a clade C Env-derived immunogen that activates naïve B cells expressing the bnAb precursors of VRC01-class antibodies in vivo. We also reported on the design of a second immunogen, derived from a clade B Env, that when administered as a 1st boost, increases the maturation of the emerging VRC01 B cells. Our proposal is based on our recent identification of two additional Env immunogens that complete the maturation of VRC01-class antibody responses towards their cross- neutralizing forms. Thus, after 4 Env immunizations of knock-in mice expressing elements of human VRC01 BCRs, we isolate VRC01-class antibodies that neutralize ~33% of heterologous tier 2 viruses. Here, our efforts focus on optimizing this immunization schema to improve the neutralizing breadth of the elicited VRC01-class antibodies. An important aspect of our proposal is that we will not limit our work to well-controlled knock-in mice, but transgenic mice that express diverse human VH/VL genes, as well. Because the B cell repertoire of these mice better reflects that of humans, we expect that our optimized immunization schema will not only lead to the generation of VRC01-class antibodies, as it does in the knock-in mice, but that additional classes of anti- CD4-BS antibody responses will also be elicited. A second important aspect of our proposal is that we will examine whether mRNA-based immunogen-delivery platforms accelerate the development of cross- neutralizing CD4-BS antibody responses.