A potent and broad CD4 binding site neutralizing antibody with strong ADCC activity from a Chinese HIV-1 elite neutralizer

The discovery of broadly neutralizing antibodies (bNAbs) that target conserved epitopes on the HIV-1 envelope glycoprotein (Env) has garnered significant attention for its potential in the development of effective therapeutic and vaccine strategies. In this study, we isolated and characterized a CD4 binding site (CD4bs) antibody, FD22, from an elite neutralizer in China who had been infected with a clade B virus through contaminated blood plasma for 23 years. The heavy chain of FD22 was derived from a rarely reported IGHV3-30 germline gene and exhibited an exceptionally high degree of somatic hypermutation (SHM) (37%), along with a long and unique CDRH3 loop of 20-amino acids. FD22 exhibited potent and broad neutralizing activity, comparable to that of the well-known bNAb VRC01. It effectively neutralized 82% of a panel of 145 diverse HIV-1 pseudoviruses, including the two major circulating strains in China, CRF01_AE and CRF07_BC. FD22 bound strongly to HIV-1-infected cell lines, efficiently engaged FcγRIIIa receptors, triggered NK cell degranulation and the release of key cytokines such as IFN-γ and β-chemokines, and robustly induced antibody-dependent cellular cytotoxicity (ADCC) against HIV-1-infected target cells. Structural prediction for FD22 and the HIV Env SOSIP trimer performed by AlphaFold3, site-mutagenesis, and autologous virus reverse mutation assays revealed that the epitope of FD22 spans key CD4 binding site, including Loop D, the CD4 binding loop (CD4 BLP), and the V5 Loop. The unique long CDRH3 loop of FD22 interacts with the CD4 binding site through its negatively charged residue R102, distinguishing it from other CD4bs antibodies. Our findings provide valuable insights into the mechanisms of FD22 in viral neutralization and ADCC. The dual functionality of FD22 enhances its potential as a promising therapeutic antibody and offers new avenues for designing CD4bs-targeting vaccines with enhanced ADCC capabilities.