P10.11 Background: The human immune system generates diverse antibodies against the binding site for the CD4 receptor in response to infection or vaccination. Two classes of antibodies that effectively neutralize HIV-1 through CD4 mimicry have been described, including those derived from VH1-2 germline, which include the well-characterized VRC01 class of antibodies, and those derived from VH1-46. Methods: We defined structural modes of recognition of three VH1-46 germline-derived antibodies from 2 donors by crystallizing antigen-binding fragments in complex with extended core version of the HIV-1 gp120. We used surface plasmon resonance and biolayer interferometry to determine antigen-binding properties, tested neutralization in a representative panel of 192 viruses, and performed cross-donor phylogenetic analyses to study antibody evolution. Results: VH1-46 derived antibodies show a structural mode of CD4 mimicry distinct from that of the VH1-2 derived antibodies. The altered mode of heavy chain recognition allows the VH1-46 derived antibodies to accommodate light chain CDR3s of different lengths. Cross-donor phylogenetic analysis showed that the VH1-46 derived antibodies from 2 donors evolved similarly and indicated that the VH1-46 antibodies form a class. Conclusions: Our studies show how antibodies of the VH1-46 class achieve CD4 mimicry, expand the range of known structural solutions that permit such heavy-chain mimicry, and reveal how small differences in germline (e.g. between VH1-2 and VH1-46) can impact mature antibody recognition.