Functional Activity of HIV-1 bNAbs Across Diverse Strains is Driven by Binding Site and Can be Enhanced Through Fc Engineering.

Broadly neutralizing antibodies (bNAbs) are promising tools for HIV-1 treatment and prevention, due to their ability to mediate both Fab-dependent neutralization and Fc-dependent effector functions. While antibody-dependent cellular cytotoxicity (ADCC) and antibody-dependent cellular phagocytosis (ADCP) have been implicated in antiviral activity, the extent to which these functions vary across bNAb epitopes, viral strains, and Fc region remains unclear. Here, we systematically evaluated twenty bNAbs targeting five distinct Env epitopes against a diverse panel of nine HIV-1 strains. We found that epitope specificity and Env sequence both critically influenced bNAb effector functions. CD4 binding site (CD4bs)- and V3 glycan-targeting bNAbs mediated the broadest and most potent ADCC and ADCP, while V1/V2 apex-directed bNAbs preferentially induced ADCP. In contrast, MPER-targeting bNAbs triggered ADCC more selectively, and gp120/gp41 interface-targeting bNAbs showed limited activity. Irrespective of binding epitope, different strains exhibited a broad range of effector function sensitivities. To investigate the impact of Fc modifications on this variability, we subclass-switched and introduced previously identified Fc mutations known to change Fcγ receptor affinity. Some of these mutations significantly boosted ADCC, while IgG3 subclass switching dramatically enhanced ADCP, even against highly resistant strains. Collectively, these results demonstrate that effector function is shaped by both antibody specificity and viral Env context and that rational Fc modification has the potential to improve antibody-based therapeutics against HIV.