Antibody Guided Exploration of V3 Exposure on Subtype C HIV

The limited neutralizing activity of V3 antibodies is typically attributed to V3 masking. While relatively much effort has been devoted to exploring V3 accessibility on subtype B viruses, V3 exposure and mechanism(s) that might restrict V3 exposure on non-subtype B viruses have yet to be understood. I have focused on exploring the significance of the conserved V3 tip motifs GPGR and GPGQ of subtype B and nonsubtype B viruses for antibody recognition. Position 315 in representative subtype B and subtype C viruses was mutated to Gln and Arg respectively to assess the effect of the conserved Arg/Gln at position 315 on V3-specific neutralization. The Q315R subtype C viruses became sensitive to anti-V3 mAb B4e8 neutralization whereas the R315Q switched subtype B virus became resistant to V3 neutralization, even to V3 antibodies that do no contact the residue at position 315. These observations suggest that at least the tip of V3 is antibody accessible on the surface of some non-B viruses but it is the presence of Gln315 residue that modulates V3 antibody recognition. As such, engineering V3 tip antibodies to make high affinity interactions with a Gln315 residue could broaden V3 neutralization of non-subtype B viruses. To attempt to improve B4e8’s neutralizing activity, targeted mutagenesis of B4e8 complementarity determining region residues was done to generate antibody libraries using yeast and phage display. The libraries were subjected to multiple rounds of selection on subtype C gp120s, however B4e8 variants with enhanced affinity for subtype C gp120 were not recovered after the final rounds of selection. This suggests that the residues targeted here were not sufficient for enhancing B4e8 affinity for non-subtype B HIV.