In vivo evolution of env in SHIV-AD8EO-infected rhesus macaques after AAV-vectored delivery of eCD4-Ig.

eCD4-Ig is an entry inhibitor of the human immunodeficiency virus (HIV) that mimics the engagement of both CD4 and CCR5 with the HIV Envelope (Env) protein, a property which imbues it with remarkable potency and breadth. However, env is exceptionally genetically malleable and can evolve to escape a wide variety of entry inhibitors. Here we document the evolution of partial eCD4-Ig resistance in simian-HIV (SHIV)-AD8_EO-infected rhesus macaques (RMs) treated with adeno-associated vectors (AAV) encoding eCD4-Ig. In one RM, setpoint viremia plateaued at 1,000 vRNA copies/ml, despite concomitant serum concentrations of eCD4-Ig in the 60-110 μg/ml range, implying that the virus had gained partial eCD4-Ig resistance. Env mutations occurring prominently in this animal were cloned and further characterized. Three of these mutations (R315G, A436T, G471E) were sufficient to confer substantial resistance to eCD4-Ig-mediated neutralization onto the parental Env, accompanied by a marked loss of viral fitness. This resistance was not driven by decreased CD4 affinity, subverted sulfopeptide mimicry, changes to coreceptor tropism, or by a gain of CD4 independence. Rather, our data argue that the Env evolving in this animal attained eCD4-Ig resistance by decreasing triggerability, stabilizing state-2, and changing the nature of its relationship to the host CD4.