New SHIVs and Improved Design Strategy for Modeling HIV-1 Transmission, Immunopathogenesis, Prevention and Cure

Abstract

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.

A germline-targeting chimpanzee SIV envelope glycoprotein elicits a new class of V2-apex directed cross-neutralizing antibodies

“…To test the bNAb induction potential of the CAM13K Env in the context of a productive viral infection, we cloned its ectodomain (Fig. 3A) into an SIVmac766 vector previously optimized for SHIV construction ( 21 ). Since the amino acid residue at position 375 of the HIV-1 Env determines how efficiently the corresponding SHIV replicates in rhesus CD4+ T cells ( 21, 49 ), we created isogenic mutants of SCIV.CAM13K by changing the wildtype methionine (375M) to serine (375S), tyrosine (375Y), histidine (375H), tryptophan (375W) or phenylalanine (375F) residues.…”

“…SHIVs express HIV-1 Envs as functional trimers on the surface of infected cells and virions. Moreover, SHIVs replicate continuously over the course of the infection, resulting in an evolving viral quasispecies that can drive antibody somatic hypermutation and maturation ( 12, 21 ). Indeed, the patterns of envelope-antibody (Env-Ab) co-evolution in SHIV-infected RMs are remarkably similar to those observed in HIV-1 infected humans, indicating similar mechanisms of epitope recognition and neutralizing antibody escape ( 12 ).…”

“…Indeed, the patterns of envelope-antibody (Env-Ab) co-evolution in SHIV-infected RMs are remarkably similar to those observed in HIV-1 infected humans, indicating similar mechanisms of epitope recognition and neutralizing antibody escape ( 12 ). Finally, SHIVs expressing V2-apex bNAb sensitive Envs commonly induce V2-directed neutralization breadth in RMs ( 12, 21 ). Thus, SHIV infection of RMs recapitulates V2-apex and other bNAb development in an animal model that closely approximates HIV-1 infected humans.…”

Anti-viral efficacy of a next-generation CD4-binding site bNAb in SHIV-infected animals in the absence of anti-drug antibody responses

“…In brief, animals were inoculated intrarectally with one milliliter of a 1:8 dilution of challenge stock. This corresponds to an animal infectious dose of approximately 5 based on the reported AID 50 titer which was 1 mL of 1:120 dilution of the challenge stock ( Li et al., 2021 ). The animals were infected for a period of 1–4 years and then used in this study.…”

Broadly Neutralizing Antibodies for HIV-1 Prevention

“…Despite these potential drawbacks, NHP remain the best available animal model for bnAb protection studies. Recent advances in the development of genetically diverse panels of SHIVs that recapitulate many features of HIV-1 infection will certainly allow for more rigorous assessment of protection afforded by bnAbs and bnAb combinations (44)(45)(46)(47). Together, both the humanized mouse and NHP models have been critical for accelerating the translation of bnAb passive immunity into human clinical trials.…”