Isotype modulates epitope specificity, affinity, and antiviral activities of anti-HIV-1 human broadly neutralizing 2F5 antibody

摘要

The constant heavy chain (CH1) domain affects antibody affinity and fine specificity, challenging the paradigm that only variable regions contribute to antigen binding. To investigate the role of the CH1 domain, we constructed lgA2 from the broadly neutralizing anti-HIV-1 2F5 lgG1, and compared 2F5 lgA2 and IgG binding affinity and functional activities. We found that 2F5 lgA2 bound to the gp41 membrane proximal external region with higher affinity than lgG1. Functionally, compared with lgG1, 2F5 lgA2 more efficiently blocked HIV-1 transcytosis across epithelial cells and CD4~+ cell infection by R5 HIV-1. The 2F5 lgG1 and lgA2 acted synergisti-cally to fully block HIV-1 transfer from Langerhans to autologous CD4~+ T cells and to inhibit CD4~+ T-cell infection. Epitope mapping performed by screening a random peptide library and in silico docking modeling suggested that along with the 2F5 IgG canonical ELDKWA epitope on gp41, the lgG1 recognized an additional 3D-conformational epitope on the gp41 C-helix. In contrast, the lgA2 epitope included a unique conformational motif on the gp41 N-helix. Overall, the CH1 region of 2F5 contributes to shape its epitope specificity, antibody affinity, and functional activities. In the context of sexually transmitted infections such as HIV-1/AIDS, raising a mucosal IgA-based vaccine response should complement an IgG-based vaccine response in blocking HIV-1 transmission.