The magnitude of CD8 antitumor reactivity correlated with tumor regression. CD8 T cells were isolated from spleens and tumor draining lymph nodes 30 days after HSCT, from mice treated with naive T cell adoptive transfer and AGN2a-4P vaccination. The CD8 cells were assayed in IFN-γ ELISPOT assays with tumor cell stimulators to determine tumor-reactive IFN-γ–secreting cell frequencies. The experiment is representative of 2 independent experiments in which the CD8 T cells were pooled from 2 or 3 individual mice. ***P < .001; **P < .01 when mice with regressing tumors were compared with mice with progressing tumors.