Correlates of Relative Resistance Against Low-dose Rectal Simian Immunodeficiency Virus Challenges in Peripheral Blood Mononuclear Cells of Vaccinated Rhesus Macaques

In this study, we compared the immunogenicity and protection from repeated low-dose intrarectal SIVmac251 challenge in two groups of vaccinated RMs. Animals were immunized with live SIVmac239, which had been attenuated by a deletion of the nef sequence, or they were vaccinated twice with an E1-deleted AdHu5, expressing SIVmac239gag. The vaccinated animals and a cohort of unvaccinated control animals were then challenged 10 times in weekly intervals with low doses of SIVmac251 given rectally. Our results confirm previous studies showing that whereas SIVΔnef provides some degree of protection against viral acquisition after repeated low-dose rectal SIVmac251 challenges, vaccination with an AdHu5gag vaccine designed to induce only antiviral T cell responses is ineffective. As immunological analyses of prechallenge, vaccine-induced T and B cell responses failed to reveal correlates of protection that distinguished the more susceptible from the more resistant vaccinated animals, we carried out RNA-Seq studies of paired pre- and postvaccination samples to identify transcriptional patterns that correlated with the differences in response. We show that gene expression signatures associated with the delayed SIV infection seen in some AdHu5gag recipients were largely present in prevaccination samples of those animals. In contrast, the responding SIVΔnef-immunized animals showed a predominance of vaccine-induced changes, thus enabling us to define inherited and vaccine-induced gene expression signatures and their associated pathways that may play a role in preventing SIV acquisition.