Figure 3.

CD8⁺ T cell response and tumor protection induced by Ms-TRP vaccine. C57BL/6J mice were immunized in (a) with 1, 10, or 30 μg TRP peptide entrapped in Ms archaeosomes on days 0 and 21. At 5 weeks, representative mice (n = 2 per group) were euthanized, the spleen cells were stimulated with IL-2 (0.1 ng/mL) and peptide (5 μg/mL) for 48 h, and the frequency of IFN-gamma secreting cells was enumerated by ELISPOT. Mean ± SD (n = 3) of IFN-gamma secreting cells per 10⁶ spleen cells is indicated. Spleen cells from mice immunized with 10 μg TRP-peptide per injection were also cultured for 5 days with antigen to generate CTL effectors. The ability of effectors to kill peptide specific (EL-4-TRP) versus nonspecific (EL-4) targets was evaluated in an in-vitro CTL assay (b). Mean killing ± SD of 2 mice per group at different effector : target ratio is indicated for Naïve, PBS-TRP, and Ms-TRP vaccinated mice (b). In another group of representative mice vaccinated with 20 μg Ms-TRP, in vivo CTL response was evaluated on day 7 and day 28. Mean ± SD of n = 4 mice per group is indicated (c). Finally, groups of naïve (n = 12), Ms-TRP vaccinated (n = 12), and TRP-PBS (n = 4) vaccinated mice were challenged with B16 tumors at 6 weeks. Survival was monitored based on a maximum tumor size of 300 mm². Tumor survival data are presented as an aggregate from 3 different experiments conducted, and TRP dose was 15–30 μg/injection. Loading was 19 μg peptide/mg lipid, and average archaeosome size was 99 nm. Survival with Ms-TRP is significantly different (P < .001) by log-rank test relative to naïve group.