Abstract
HIV-1 vaccines need to induce broadly neutralizing antibodies (bnAb) against conserved epitopes in the envelope glycoprotein (Env) to protect against diverse HIV-1 clades. To achieve this, we need to understand how different amino acids affect the Env trimer structure to find a common strategy to readily produce Env vaccines of different subtypes. Previously, using a saturation mutagenesis strategy we identified single Env substitutions that open the CD4bs without modifying the trimer apex. One of these substitutions was a tryptophan residue introduced at position 375. Here, we introduced 375W into a large panel of 27 T/F, acute stage, chronic infection, and AIDS M-tropic, and non-M-tropic primary isolates from clades A, B, C, D and G, and circulating recombinant forms (CRFs) (CRF02_AG, and CRF01_AE), and a complex (cpx) (CRF13_cpx). To understand the effect of 375W mutation on Env trimer structure and tropism, we evaluated soluble (sCD4) and monoclonal antibody (mAb) neutralization (b6, 17b, b12, VCR01, 3BNC117, PGT128, 10-1074, PGT145, PG9 and PG16), as well as macrophage infection using wt and mutant Env+ pseudovirions. Broadly neutralizing Abs (bnAbs) such VCR01, and 3BNC117 neutralized almost all the primary isolates tested while the other bnAbs neutralized many but not all of our panel. B12 and VCR01 showed some tendencies to neutralize 375W macrophage-tropic (mac-tropic) and intermediate mac-tropic mutants more efficiently compared with non-mac-tropic mutants. In general, 375W did not impair neutralization of bnAbs. Envs that infected macrophages more efficiently than non-mac-tropic variants but did not reach the levels of highly macrophage-tropic brain reference Envs were classified as intermediate mac-tropic variants. Surprisingly, we observed intermediate mac-tropic primary isolates from clade C, D and G wt Envs that were not derived from the central nervous system (CNS). 375W substitution increased the affinity for sCD4 in all Envs of our panel and macrophage infection in Envs tested including a CRF01_AE X4 variant with the exception of one intermediate and mac-tropic variants. Increased sCD4 sensitivity and enhanced macrophage infection provide strong evidence that 375W confers exposure of the CD4bs across Envs from different clades/CRF/cpx and disease stages. Enhanced exposure of the CD4bs by 375W had little or no effect on exposure and sensitivity of CD4bs epitopes targeted by bnAbs. 375W is an ideal substitution for inclusion into HIV vaccines constructed from different subtype Envs, with aim to elicit neutralizing antibodies that target the CD4bs while maintaining exposure of other Env neutralization sites.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
Dr. Paul Clapham has been added as an author.