Innate protection against intrarectal SIV acquisition by a live Simian HIV vaccine

Identifying immune correlates of protection is a major challenge in AIDS vaccine development. Anti-Envelope antibodies have been considered critical against SIV/HIV acquisition. Here, we evaluated the efficacy of a SHIV vaccine against SIVmac251 challenge, where the role of antibody was excluded as there was no cross-reactivity between SIV and SHIV Envelope antibodies. After eight low-dose rectal challenges with SIVmac251, 12 SHIV-vaccinated animals demonstrated 83% efficacy, compared to six naïve controls, suggesting protection could be achieved in the absence of anti-Envelope antibodies. Interestingly, CD8+ T cells (and some NK cells) were not essential for the preventing viral acquisition, as none of the CD8-depleted macaques was infected by SIVmac251 challenges. Initial investigation of protective innate immunity revealed that protected animals had elevated pathways related to platelet aggregation/activation, and reduced pathways related to interferon and responses to virus. Moreover, higher expression of platelet factor 4 (PF4) on circulating platelet-leukocyte aggregates was associated with reduced viral acquisition. Our data highlighted the importance of innate immunity and may provide new opportunities for novel HIV vaccines or therapeutic strategy development. We then performed gene expression profiling analysis using data obtained from RNA-seq of macaque PBMC samples from three different groups: Naïve-infected group, SHIV vaccinated-infected group and SHIV-vaccinated-protected group.