2A). However, the number of antigen-specific cells recovered at day 5 was not different between CpG-treated and control mice. Co-injection
of poly(I:C), LPS, or imiquimod did not modify the number of tetramer+ cells recovered from the spleens or LN at these early time points compared with mice immunized with peptide alone (data not shown), demonstrating a selective potency of CpG to enhance the early expansion of CD8+ T cells in response to soluble peptide in vivo. Consistent with the increased clonal population size at day 3 post-immunization, tetramer+ cells recovered from mice treated with CpG displayed a more robust proliferation profile compared with control mice that received peptide alone, as indicated by CFSE dilution (Fig. 2B). The effects of CpG were not as striking PLX4032 mouse in the spleen, though similar trends were observed. By day 5, however, there was no accumulation of CFSElo cells regardless of CpG treatment, with proliferation profiles similar to those observed previously at day 5 in all groups (data not shown). Further, the numbers of tetramer+ cells recovered from the spleens of immunized mice 10 days post-immunization were
not changed by treatment with any TLR, including CpG (Fig. 2C). Thus, in spite of inducing more robust early proliferative activity, CpG treatment could not modify the widespread cell death observed after peptide immunization. Addition of MHC class II-restricted peptides to the Daporinad concentration inoculum to elicit help from CD4+ T cells did not enhance the survival of the peptide-stimulated CD8+ T cells, even in the presence of CpG (Supporting Information Fig. 2). In mice that were immunized with peptide alone, we could not detect antigen-specific T cells by ELISPOT, suggesting that they were unable
to produce IFN-γ (Fig. 2D). However, antigen-specific Parvulin cells from the dLN of mice treated with CpG and peptide were readily detected by IFN-γ ELISPOT. These differences were not merely due to differences in frequency, as there was a ten-fold increase in tetramer+ cells measured by FACS, but there were greater than 300-fold differences in the number of IFN-γ-producing cells. Curiously, antigen-specific IFN-γ secreting T cells were not detected in the spleen when immunizing mice with either peptide alone or CpG with peptide. CpG clearly modulates the CD8+ T-cell response to soluble peptide by promoting cell division and clonal expansion, as well as supporting IFN-γ production. However, CpG could not induce T-cell survival, as there was no significant increase in the final magnitude of the CD8+ T cell after the contraction phase. Since CpG has been shown to have many effects on the immune system 21 that may change over time, we modified the timing of the CpG administration relative to the peptide to investigate whether there were temporal effects of the CpG that could enhance T-cell survival.