Diverse germline-targeting HIV Env immunogens select for distinct mutations in the same knock-in mice B cell receptors.

VRC01-class HIV broadly neutralizing antibodies have been isolated from people living with HIV. Their unmutated (germline) forms do not bind Env and do not neutralize HIV. They acquire their broadly neutralizing potentials through the accumulation of specific somatic mutations. Here, we identify key modifications that allow Env-derived proteins from diverse HIV clades to effectively engage germline VRC01-class B cell receptors (BCRs) expressed by naive B cells. Noticeably, these germline-targeting Env proteins interact with VRC01-class BCRs differently depending on the specific Env background. When used as immunogens in a knock-in mouse model, all germline-targeting Envs successfully activate VRC01-class B cells. However, the resulting BCRs accumulate distinct mutations at key positions. Thus, while the same BCRs are initially activated, they follow different maturation pathways depending on the immunogen used. These findings have important implications not only for HIV vaccine design efforts but also for other immunogens aiming to direct specific BCR maturation pathways.