CD4+ T-cell loss and delayed expression of modulators of immune responses at mucosal sites of vaccinated macaques following SIVmac251 infection

Systemic immunization of macaques with a combination of DNA-poxvirus-based vaccines confers protection from high level of both systemic and mucosal viral replication following rectal exposure to the pathogenic SIVmac251. Here we investigated early post-infection events in rectal and vaginal tissues, and found that the loss of CCR5(+) CD4(+) T cells was equivalent in vaccinated and control macaques, despite a three logs reduction at mucosal sites of simian immunodeficiency virus (SIV) RNA in the vaccinated group. Even though a normal CD4(+) T cell number is not reconstituted at mucosal sites in either group, vaccination appeared to confer a better preservation of the CD4(+) CCR5(+) T cells that replenish these sites. Analysis of rectal tissues RNA following challenge exposure demonstrated a decreased expression in vaccinated macaques of transforming growth factor-beta, cytotoxic T lymphocyte antigen-4, FoxP3, and indoleamine 2,3-dioxygenase, an immune suppressive enzyme expressed by dendritic cells that converts tryptophan to kynurenine and limits T-cell responses. Accordingly, the ratio of kynurenine and tryptophan in the plasma was significantly reduced in the vaccinated animals respect to the controls. Thus, preexisting adaptive immune responses induced by these vaccine modalities, although they do not protect from CD4(+) T-cell depletion, nevertheless, they contain SIVmac251 replication and delay expression of markers of T-cell activation and/or suppression at mucosal sites.