Neutralization of HIV by antibodies

HIV gp120 H375 is unique to HIV-1 subtype CRF01_AE and confers strong resistance to the entry inhibitor BMS-599793, a candidate microbicide drug

BMS-599793 is a small molecule entry inhibitor that binds to human immunodeficiency virus type 1 (HIV-1) gp120, resulting in the inhibition of CD4-dependent entry into cells. Since BMS-599793 is currently considered a candidate microbicide drug, we evaluated its efficacy against a number of primary patient HIV isolates from different subtypes and circulating recombinant forms (CRFs) and showed that activity varied between ∼3 ρM and 7 μM at 50% effective concentrations (EC(50)s). Interestingly, CRF01_AE HIV-1 isolates consistently demonstrated natural resistance against this compound. Genotypic analysis of >1,600 sequences (Los Alamos HIV sequence database) indicated that a single amino acid polymorphism in Env, H375, may account for the observed BMS-599793 resistance in CRF01_AE HIV-1. Results of site-directed mutagenesis experiments confirmed this hypothesis, and in silico drug docking simulations identified a drug resistance mechanism at the molecular level. In addition, CRF01_AE viruses were shown to be resistant to multiple broadly neutralizing monoclonal antibodies. Thus, our results not only provide insight into how Env polymorphisms may contribute to entry inhibitor resistance but also may help to elucidate how HIV can evade some broadly neutralizing antibodies. Furthermore, the high frequency of H375 in CRF01_AE HIV-1, and its apparent nonoccurrence in other subtypes, could serve as a means for rapid identification of CRF01_AE infections.

New virologic reagents for neutralizing antibody assays

PURPOSE OF REVIEW

This review summarizes current and novel virologic reagents employed for the development and application of in-vitro assays that assess neutralizing activity of antibodies against HIV-1. Characteristics of several virologic approaches are placed in context with various cellular targets and assay read-outs intended to determine potency and breadth of neutralization in patient cohorts and clinical vaccine trials.

RECENT FINDINGS

New molecular virologic reagents developed for in-vitro primary cell-based assays promise to facilitate rigorous and standardized assessment of anti-HIV-1-neutralizing antibody responses elicited by vaccine immunogens.

SUMMARY

Comprehensive assessment of anti-HIV-1 antibody potency and breadth is essential for evaluating vaccine immunogens, the advancement of vaccine candidates into clinical trials, and ultimately the development of effective vaccine strategies. Env-pseudovirion and recombinant reporter cell line neutralization assays are important tools for rapid and standardized measurement of neutralizing antibody activity. However, recent studies indicate that reporter cell lines fail to detect neutralization activity of certain antibodies observed when analyzed in peripheral blood mononuclear cells and may yield results on neutralizing antibody breadth that are discordant with peripheral blood mononuclear cell assays. Importantly, it remains unknown whether current in-vitro assays may be predictive of a protective neutralizing antibody response elicited by vaccine immunogens. This situation underscores the significance of standardizing existing, complementary methods as well as developing new assay concepts that assess neutralization in primary cells. Thus, this chapter focuses on new virologic reagents that promise to facilitate reaching this goal.