Functional screening for potent broadly neutralizing HIV-1 human monoclonal antibodies and identification of dominant ADCC epitopes on HIV-1 envelope glycoprotein

Abstract

HIV/AIDS has become a global pandemic. Development of an effective HIV-1 vaccine eliciting broadly neutralizing monoclonal antibodies (bnmAbs) remains a big challenge. Novel approaches for prevention and treatment of HIV-1 infection may alleviate the burden caused by the pandemic. About 20% HIV-1-infected individuals can develop strong B cell response within 3-5 months after infection, and 3-5% HIV-1-infected individuals can generate high titers of bnAbs within 1-2 years during chronic infection. Many bnAbs have been isolated against different epitopes, including 2G12, 2F5, 4E10, m43, b12, x5, VRC01 like antibodies, PG9, PG16, PGT121-128 and 10E8. Most of these antibodies were isolated based on binding affinities. However, binding affinity does not necessarily correlate with neutralizing abilities. For the purpose of facilitating the bnmAbs screening, a novel methodology for isolating HIV-1 bnmAbs directly based on antibody neutralization activity has been developed. Immune recombinant full length IgGs libraries were displayed on target cell surface followed by sorting the cells by antibody neutralization ability. After several rounds of sorting, a panel of human cell-associated mAbs has been isolated that can neutralize various isolates from different Chinese clades when displayed on the surface of mammalian cells. Several isolated antibodies have been converted into soluble version for purification and characterization. Three mAbs (FS1416, FS1476 and FS1482) were identified to be able to neutralize several Chinese circulating viruses. These antibodies showed the complementary neutralizing profiles to existing antibody b12 which allows for a broadly neutralizing of 50% virus isolates from Africa and American. Our results indicate the discovery of novel antibodies which may have the application to use jointly with other existing antibodies to largely extend the current neutralizing spectrum.

Antibody-dependent cell-mediated cytotoxicity (ADCC) has been observed associated with the reduced risk of HIV acquisition in RV144 vaccine trial. And an increasing number of evidences shows that ADCC activity correlates with enhanced HIV-1 control, retards the progression of disease, strongly suggesting the importance of antibody effector functions in immune protection against HIV-1. HIV-1 envelope glycoprotein gp160 has been shown to be highly immunogenic and thus is considered as the most important target for immune protection. Although a few neutralizing epitopes which are targeted by human potent broadly neutralizing antibodies have been studied there was no study about ADCC epitopes on HIV-1. Here, this issue has been addressed by yeast display based epitope mapping of serum purified IgG from HIV-1 infected long term non progressors with different ADCC activities in China. As a result, four dominant ADCC epitopes were identified on HIV-1 HXB2 gp160. They were designated D1 (aa 72 to 133), D2 (aa 196-226), and D3 (254-275), which are located in gp120, and D4 (742-824) that is located in gp41. This study would provide a useful information in vaccine design to elicit both potent neutralizing and strong ADCC activity antibodies, which could be used for protection against HIV-1 infection.

In summary, this novel methodology generated for functional screening of broadly neutralizing antibodies and potential vaccination epitopes characterized here may help in applications for treatment and prevention of HIV-1 infection.