Anti-tumor T cell response and protective immunity in mice that received sublethal irradiation and immune reconstitution.

To test whether homeostasis-driven T cell proliferation in reconstituted lymphodepleted hosts would improve the therapeutic efficacy of tumor vaccines, normal mice and reconstituted lymphopenic mice (RLM; C57BL/6 mice rendered lymphopenic with sublethal total-body irradiation and reconstituted with naive splenocytes) were used in the vaccination and challenge experiments with weakly immunogenic F10 melanoma cells. Only limited protection was observed in vaccinated normal mice (16.7%), whereas significantly greater protection was induced in vaccinated RLM (63.2%). Protective immunity in RLM depended on CD8 T cells. Following vaccination, a significant increase in the percentage of CD44(hi)CD62L(lo) T cells was detected in the tumor vaccine-draining lymph node (TVDLN) of vaccinated RLM compared to that of vaccinated normal mice. After in vitro stimulation, effector T cells generated from TVDLN of vaccinated RLM produced more IFN-gamma than T cells from vaccinated normal mice, and contained more melanoma-specific T cells, as assessed by ELISA and intracellular cytokine staining. This study suggests that vaccination of reconstituted lymphopenic hosts could elicit superior anti-tumor immunity compared to normal hosts, highlighting the potential clinical benefit of performing tumor vaccination during immune reconstitution.