Characterization Of A Broadly Neutralizing Human Fab Antibody Against HIV-1

Neutralizing antibodies (NAbs) are natural defense mechanism against virus infections, and are the basis of efficient vaccines. In the case of HIV-1, NAbs are believed to play an important role in immunity against virus infection and are therefore considered an essential component of a vaccine-elicited immune response. Induction of an antibody response capable of neutralizing diverse HIV-1isolates is a critical goal for vaccines that protect against HIV-1infection. Thus, extensive efforts have been made to isolate monoclonal broadly cross-reactive HlV-neutralizing antibodies. However, HIV-1has evolved many strategies to evade the host humoral immune response. Consequently, the neutralizing antibody response during HIV-1infection is weak and narrow, and only a limited number of monoclonal antibodies are with broad neutralization breadth, including2F5,4E10,2G12, b12, VRC01, PG9, PG16, X5, and17b et al (reviewed in reference). More recently, a considerably more broad and potent antibody has been discovered which targets the membrane-proximal external region (MPER) on gp41, named10E8, which neutralizes98%of tested viruses.However, it’s worth noting that the enormous sequence diversity of the viral envelope has led to HIV-1variants into the most complicated clades or subtypes, and this genetic makeup of HIV-1in China is more complex. HIV-1strains circulating in China can be broadly classified into three major groups:those clustering closely with circulating recombinant form (CRF)01_AE, subtype B’, or subtype C/CRF07_BC/CRF08_BC/B’C (C/07/08/BC), many of which are resistant to neutralization by the NAbs mentioned above. Obviously, this increased genetic complexity has posed greater challenges to human immune system and vaccine development in China. Furthermore, NAb response data derived from naturally HIV-1-infected cohorts in the USA, South Africa, Europe, Kenya, and India provide useful information for vaccine development. However, there has been no equally comprehensive study of NAbs responses to HIV-1among subjects in China. Recently, Hu et al measured NAbs responses using a panel of25Env-pseudotyped viruses, including clade B, C, A, CRF07_BC and CRF01_AE strains, against plasma samples from103subjects in a former plasma donor cohort in central China, who were infected with HIV-1clade B’ for at least10years and were elite controllers without any antiretroviral therapy at the time of sampling. They found that29%of plasma samples (n=30) neutralized80%of the viral strains tested. Strikingly, plasma sample F524neutralized all of the viruses tested, indicating the presence of broadly reactive NAbs in this patients.Here we describe the identification of a new broad and potent anti-HIV human monoclonal Fab antibody, A16, which was isolated from F524. A16exhibited highly cross-clade neutralizing activity against clade A, B, C, B’, CRF_AG, CRF07_BC, and CRF01_AE HIV-1strains. Competition studies suggested that A16targets the CD4-binding site (CD4bs) of gp120. Interestingly, A16could well neutralize multiple unrelated subtypes BC and B’HIV-1variants which were even resistant to the most potent CD4bs antibodies b12and VRC01. By selecting mimotopes fron a random peptide library in combination with computational algorithms and site-directed mutagenesis, the epitope of A16was mapped to the structurally conserved sites of loop D, residues of W96,1109, R480and residue N425of (320-21hairpin within the CD4bs of gp120. Sequence analysis identified that A16has a relatively long CDR3for both heavy (VH) and light (VL) chains and possesses very low level of somatic hypermutations as compared to other HIV-neutralizing antibodies.In summary, the ability of A16to broadly and potently neutralize representative isolates from different HIV-1clades, particularly from clades BC and B’of china, suggests its potential use in combination with other antibodies for the treatment of HIV-1infected individuals. Furthermore, our results imply that specific epitopes, distinct from the CD4binding loop, can be recognized by the immune system and elicit broadly HIV-1-neutralizing antibodies. Our study may point to further efforts regarding the development of HIV-1vaccines to induce broadly cross-reactive antibodies based on its gp120epitope.