4A). Interestingly, the majority of mice vaccinated with the subdominant GP283 epitope survived the LCMV infection as did the control mice vaccinated with the control P. berghei CS252 epitope. As previously observed,

the majority of mice vaccinated with the dominant NP118 epitope succumbed to the LCMV infection (Fig. 4B and 1E). Importantly, the NP118- and the GP283-specific memory CD8+ T cells exhibited similar memory phenotype and function (CD127hi, KLRG-1lo, CD27hi, CD43lo, and high frequencies of these cells Y 27632 produce IL-2 and TNF upon specific peptide restimulation) at the time of LCMV infection (Fig. 4C) suggesting the difference in outcome was not an issue of memory quality. However, a statistically significant difference

(p = 0.03) in total number of NP118- and GP283-specific memory CD8+ T cells in the spleen of vaccinated PKO mice prior to LCMV challenge was observed (Fig. 4D). To determine if the difference in the starting number of memory CD8+ T cells of different Ag-specificity controls the difference in susceptibility to the LCMV challenge, groups of naïve PKO mice were immunized with different numbers of peptide-coated DC to equalize the number of memory CD8+ T cells. At day 124 following DC immunization, the frequency of GP283-specific memory CD8+ T cells was approximately equal to that of NP118-specific memory CD8+ selleck screening library T cells (Fig. 4E). More importantly, the magnitude of expansion was also similar between GP283- and NP118-specific CD8+ T cells at days 5 and Acyl CoA dehydrogenase 7 after LCMV infection (Fig. 4E). However, we observed 100% mortality in DC-NP118-vaccinated mice but 0% mortality in DC-GP283- or DC-CS252- vaccinated groups of mice (Fig. 4F). Thus, PKO mice containing memory CD8+ T cells against a dominant epitope, but not a subdominant epitope, are predisposed to LCMV-induced mortality, under conditions where the starting number and magnitude of expansion of memory CD8+ T cells are similar. These results suggested that the epitope specificity dictates vaccination-induced mortality in BALB/c-PKO mice following LCMV challenge. Since

vaccination of naïve PKO with the subdominant epitope did not result in mortality following LCMV challenge, we also sought to determine whether these vaccinated mice showed enhanced resistance against LCMV infection. Similar to the DC-NP118-vaccinated PKO mice, the DC-GP283-vaccinated mice had significantly reduced viral load at day 5 post-LCMV infection compared with the nonimmunized mice. However, the viral load reduction was not sustained by day 7 post-LCMV (Fig. 5). Thus, although CD8+ T-cell-mediated LCMV-induced mortality can be avoided by vaccination of PKO mice with the subdominant instead of the dominant epitope, this immunization did not provide sustained virus control. In general, CD8+ T cells exhibit tight regulation of cytokine production and do not produce IFN-γ directly ex vivo unless they receive Ag-stimulation.