The earliest events following mucosal HIV-1 infection, prior to measurable viremia, remain poorly understood. Here we show by detailed necropsy studies that the virus can disseminate rapidly following mucosal SIV infection of rhesus monkeys and trigger components of the inflammasome, both at the site of inoculation and at early sites of distal virus spread. By 24 hours following inoculation, a proinflammatory signature that lacked antiviral restriction factors was observed in viral RNA positive tissues. The early innate response included expression of NLRX1, which inhibits antiviral responses, and activation of the TGF-β pathway, which negatively regulates adaptive immune responses. These data suggest a model in which the virus triggers specific host mechanisms that suppress the generation of antiviral innate and adaptive immune responses in the first few days of infection, thus facilitating its own replication. These findings have important implications for the development of vaccines and other strategies to prevent infection.

Previous studies have established that strain 68-1–derived rhesus cytomegalovirus (RhCMV) vectors expressing simian immunodeficiency virus (SIV) proteins (RhCMV/SIV) are able to elicit and maintain cellular immune responses that provide protection against mucosal challenge of highly pathogenic SIV in rhesus monkeys (RMs). However, these efficacious RhCMV/SIV vectors were replication and spread competent and therefore have the potential to cause disease in immunocompromised subjects. To develop a safer CMV-based vaccine for clinical use, we attenuated 68-1 RhCMV/SIV vectors by deletion of the Rh110 gene encoding the pp71 tegument protein (ΔRh110), allowing for suppression of lytic gene expression. ΔRh110 RhCMV/SIV vectors are highly spread deficient in vivo (~1000-fold compared to the parent vector) yet are still able to superinfect RhCMV+ RMs and generate high-frequency effector-memory–biased T cell responses. Here, we demonstrate that ΔRh110 68-1 RhCMV/SIV–expressing homologous or heterologous SIV antigens are highly efficacious against intravaginal (IVag) SIVmac239 challenge, providing control and progressive clearance of SIV infection in 59% of vaccinated RMs. Moreover, among 12 ΔRh110 RhCMV/SIV–vaccinated RMs that controlled and progressively cleared an initial SIV challenge, 9 were able to stringently control a second SIV challenge ~3 years after last vaccination, demonstrating the durability of this vaccine. Thus, ΔRh110 RhCMV/SIV vectors have a safety and efficacy profile that warrants adaptation and clinical evaluation of corresponding HCMV vectors as a prophylactic HIV/AIDS vaccine.

HIV-1-specific broadly neutralizing antibodies (bNAbs) can protect rhesus monkeys against simian-human immunodeficiency virus (SHIV) challenge. However, the site of antibody interception of virus and the mechanism of antibody-mediated protection remain unclear. We administered a fully protective dose of the bNAb PGT121 to rhesus monkeys and challenged them intravaginally with SHIV-SF162P3. In PGT121 treated animals, we detected low levels of viral RNA and viral DNA in distal tissues for several days following challenge. Viral RNA positive tissues showed transcriptomic changes indicative of innate immune activation, and cells from these tissues initiated infection following adoptive transfer into naïve hosts. These data demonstrate that bNAb mediated protection against a mucosal virus challenge can involve clearance of infectious virus in distal tissues.

Simian immunodeficiency virus (SIV) insert–expressing, 68-1 rhesus cytomegalovirus (RhCMV/SIV) vectors elicit major histocompatibility complex E (MHC-E)– and MHC-II–restricted, SIV-specific CD8+ T cell responses, but the basis of these unconventional responses and their contribution to demonstrated vaccine efficacy against SIV challenge in the rhesus monkeys (RMs) have not been characterized. We show that these unconventional responses resulted from a chance genetic rearrangement in 68-1 RhCMV that abrogated the function of eight distinct immunomodulatory gene products encoded in two RhCMV genomic regions (Rh157.5/Rh157.4 and Rh158-161), revealing three patterns of unconventional response inhibition. Differential repair of these genes with either RhCMV-derived or orthologous human CMV (HCMV)–derived sequences (UL128/UL130; UL146/UL147) leads to either of two distinct CD8+ T cell response types—MHC-Ia–restricted only or a mix of MHC-II– and MHC-Ia–restricted CD8+ T cells. Response magnitude and functional differentiation are similar to RhCMV 68-1, but neither alternative response type mediated protection against SIV challenge. These findings implicate MHC-E–restricted CD8+ T cell responses as mediators of anti-SIV efficacy and indicate that translation of RhCMV/SIV vector efficacy to humans will likely require deletion of all genes that inhibit these responses from the HCMV/HIV vector.