(= 6) vs. increase surface expression of the encoded protein (13, 14). The codon usage of these expression cassettes was modified to reflect the codon usage of RRV glycoprotein to allow adequate expression in the monkeys (15). For the trial, 1 mL of a mixture of the five strains was administered i.v. to each of six Indian-origin rhesus macaques. Each rRRV vector strain was present at 1.0 1010 vector genomes per inoculum. A second dose of the same rRRV constructs was administered i.v. and orally at week 25. Following vaccine administration, all six monkeys seroconverted to the SIV envelope glycoproteins gp120 and gp140 (Fig. 1 and for 19 wk (Fig. 1and for 19 wk is shown as a horizontal dashed line. The ID50 titer of an animal chronically infected with SIVmac239 Rabbit Polyclonal to STAT5A/B is shown as a horizontal dashed-dotted line. The value SIRT-IN-1 was determined by the Wilcoxon matched-pairs signed-rank test. We performed intracellular cytokine staining (ICS) assays to monitor SIV-specific T cell responses in all six animals throughout the vaccine phase. These assays included pools of peptides spanning all SIRT-IN-1 nine SIV proteins. At week 4 after rRRV vaccination, low to modest levels of SIV-specific CD8+ T cell responses against all nine SIV proteins were detected, although not necessarily in the same animal (Fig. 2and and ((gene contained a 6-bp deletion corresponding to Nef amino acids 239C240 to abrogate down-regulation of MHC-I (16). The gene also encoded a L35Q substitution to inactivate the immunodominant Mamu-A*01Crestricted Tat28C35SL8 epitope (17). Because subdominant CD8+ T cell responses can be actively suppressed by dominant CD8+ T SIRT-IN-1 cell responses in the context of rDNA immunization (18), the rationale for the Tat L35Q change in the rDNA-SIVnfl vector was to broaden the repertoire of vaccine-induced SIV-specific CD8+ T cells in the vaccinees in the present study. A total of four EP rDNA immunizations were delivered at 3-wk intervals. At 1 day after the third and fourth EP rDNA boosters, the vaccinated macaques were treated with 3 mg/kg body weight of an mAb that blocks the immune checkpoint (IC) receptor cytotoxic T lymphocyte antigen-4 (CTLA-4). CTLA-4 is up-regulated on T cells shortly after activation and suppresses immune responses by interfering with CD28 signaling, a prerequisite for proper T cell activation (19). Consequently, blocking CTLA-4 during antigen exposure can amplify the ensuing effector immune response. The EP rDNA immunizations resulted in repeated boosting of the SIRT-IN-1 anti-SIV antibody levels (Fig. 1= 0.03). The median of this range was only slightly less than the ID50 titer of 1 1:29,600 present in serum from a monkey infected with SIVmac239for 19 wk (Fig. 1= 0.05, log-rank test). The rRRV/EP rDNA vaccine regimen also resulted in a 79% reduction in the per-exposure probability of infection compared with the contemporaneous control group (= 0.04, Fishers exact test). Since we had historical controls that received the same dose of the same challenge stock with the same regimen through six challenges that could be included in the analysis, we also compared the rate of acquisition between vaccinees and contemporaneous (= 6) plus historical (= 10) controls (Fig. 3= 0.003, log-rank test; = 0.002, Fishers exact test). Of note, there was no significant difference in the per-exposure probability of.