New SHIVs and Improved Design Strategy for Modeling HIV-1 Transmission, Immunopathogenesis, Prevention and Cure
Simian-human immunodeficiency virus (SHIV) chimeras contain the HIV-1 envelope (env) gene embedded within an SIVmac proviral backbone. Previously, we showed that substitution of Env residue 375-Ser by bulky aromatic residues enhances Env binding to rhesus CD4 and enables primary or transmitted/founder (T/F) HIV-1 Envs to support efficient SHIV replication in rhesus macaques (RMs). Here, we test this design strategy more broadly by constructing and analyzing SHIVs containing ten strategically selected primary or T/F HIV-1 Envs corresponding to subtypes A, B, C, AE and AG, each with six allelic variants at position 375. All ten SHIVs bearing wildtype Env375 residues replicated efficiently in human CD4+ T cells, but only one of these replicated efficiently in rhesus CD4+ T cells. This was a SHIV whose subtype AE Env naturally contained a bulky aromatic His residue at position 375. Replacement of wildtype Env375 residues by Trp, Tyr, Phe or His in the other nine SHIVs uniformly led to efficient replication in rhesus CD4+ T in vitro and in RMs in vivo. Env375-Trp - the residue found most frequently among SIV strains infecting Old World monkeys - was favored for SHIV replication in RMs, although some SHIVs preferred Env375-Tyr, -His or -Phe. Nine SHIVs containing optimized Env375 alleles were grown large scale in primary activated rhesus CD4+ T cells to serve as challenge stocks in preclinical prevention trials. These virus stocks were genetically homogeneous, native-like in Env antigenicity and tier-2 neutralization sensitivity, transmissible by rectal, vaginal, penile, oral or intravenous inoculation routes, and exhibited acute and early replication kinetics that were indistinguishable from HIV-1 infection in humans. Finally, to expedite future SHIV constructions and eliminate short redundant elements in tat1 and env gp41 that were spontaneously deleted in chronically infected monkeys, we engineered a simplified second-generation SHIV design scheme and validated it in RMs. Overall, our findings demonstrate that SHIVs bearing primary or T/F Envs with bulky aromatic amino acid substitutions at position Env375 consistently replicate in RMs, recapitulating many features of HIV-1 infection in humans. We further show that SHIV challenge stocks grown in primary rhesus CD4+ T cells are efficiently transmitted by mucosal routes common to HIV-1 infection and can be used effectively to test for vaccine efficacy in preclinical monkey trials.