Adaptation of Subtype A Human Immunodeficiency Virus Type 1 Envelope to Pig-Tailed Macaque Cells

Abstract

The relevance of simian/human immunodeficiency virus (SHIV) infection of macaques to HIV-1 infection in humans depends on how closely SHIVs mimic HIV-1 transmission, pathogenesis, and diversity. Circulating HIV-1 strains are predominantly subtypes C and A and overwhelmingly require CCR5 for entry, yet most SHIVs incorporate CXCR4-using subtype B envelopes (Envs). While pathogenic subtype C-based SHIVs have been constructed, the subtype A-based SHIVs (SHIV-As) constructed to date have been unable to replicate in macaque cells. To understand the barriers to SHIV-A replication in macaque cells, HIVA(Q23)/SIV(vif) was constructed by engineering a CCR5-tropic subtype A provirus to express SIV vif, which counters the macaque APOBEC3G restriction. HIVA(Q23)/SIV(vif) replicated poorly in pig-tailed macaque (Ptm) lymphocytes, but viruses were adapted to Ptm lymphocytes. Two independent mutations in gp120, G312V (V3 loop) and A204E (C2 region), were identified that increased peak virus levels by >100-fold. Introduction of G312V and A204E to multiple subtype A Envs and substitution of G312 and A204 with other residues increased entry into Ptm cells by 10- to 100-fold. G312V and A204E Env variants continued to require CCR5 for entry but were up to 50- and 200-fold more sensitive to neutralization by IgG1b12 and soluble CD4 and had a 5- to 50-fold increase in their ability to utilize Ptm CD4 compared to their wild-type counterparts. These findings identify the inefficient use of Ptm CD4 as an unappreciated restriction to subtype A HIV-1 replication in Ptm cells and reveal amino acid changes to gp120 that can overcome this barrier.