Evaluating the ability of receptor binding site antibody combinations to restrict HIV escape

About This Grant

PROJECT SUMMARY Broadly neutralizing antibodies (bNAbs) are a promising immunotherapy for the treatment and cure of HIV-1. Clinical trials passively infusing bNAbs have proven their ability to significantly reduce viral loads but pre- existing and de novo resistance remains the limiting factor to their success. Rationally designing improved bNAb combinations that impose stronger constraints on viral resistance is required to achieve bNAb control of HIV. As with antiretroviral therapy (ART), successful bNAb strategies will likely require combinations where resistance can only emerge through multiple mutations that incur a high fitness cost. Targeting Env epitopes less tolerant of mutations is central to achieving this goal. Broadly neutralizing antibodies against the CD4bs function by directly blocking viral binding to cellular CD4 receptors on its primary target, CD4 T cells. Since these bNAbs mimic CD4 interactions, CD4bs bNAbs are advantageous in that escape mutations can carry a fitness cost by impairing viral CD4 receptor binding. Additionally, these bNAbs take longer to escape from than antibodies targeting other Env epitopes. Focusing bNAb strategies on the CD4bs therefore shows promise for increasing the difficulty of viral escape. Importantly, recent data has shown that CD4bs bNAbs can have different, non-overlapping resistance mutations, which indicates that a CD4bs bNAb combination could put distinct selection pressures on the CD4 binding site. Thus, we hypothesize that two CD4bs bNAbs together will exert strong selection pressure on the receptor binding site inducing multiple resistance mutations that either delay escape or severely reduce replication. We will test this hypothesis with 2 specific aims: AIM 1. Quantify the ease of virus escape from multiple CD4bs bNAbs and AIM 2. Identify selection pressures imposed by CD4bs bNAb combinations. First, to identify the bNAb pairing with the least overlap in resistance, we will assess neutralization patterns of 3 clinically relevant bNAbs VRC07-523, 1-18, and N49-P9.6 against CD4bs bNAb resistant viruses. We will quantify the resistance overlap between every bNAb pairing and define an optimal combination. To understand if CD4bs bNAbs with distinct resistance phenotypes can indeed delay or prevent the emergence of viral escape, time to escape from this combination will be quantitated in an in vitro CD4 T cell assay. Finally, to get a mechanistic understanding of viral escape from multiple CD4bs bNAbs, we will map mutational escape pathways from the CD4bs bNAb combinations and quantify the impact of each mutation on viral fitness. These findings will reveal if independent resistance mutations arose in response to each bNAb, as well as if gaining resistance exerts a fitness cost. Successful completion of these aims will reveal if including multiple CD4bs bNAbs in combination regimes is advantageous and greatly expand our understanding of CD4bs bNAb neutralization mechanisms. These findings will directly inform new bNAb combination strategies for the treatment and cure of HIV.