There is increasing evidence that the effect of chemotherapy on tumor rejection is not cell autonomous but relies on the immune system. Indeed, several reports have shown that human and murine tumors respond to chemotherapeutic agents more efficiently when the host immune system is intact. In particular, we have shown that cyclophosphamide treatment of DBA/2 mice bearing P815 mastocytoma induces rejection and long term protection in a CD4- and CD8-dependent manner. We used this tumor model, as it is poorly immunogenic, expresses tumor-associated P1A and tumor-specific P1E antigens, encoded by germline and mutated genes, respectively, and allows the identification of some tumor-specific CD8+ T cells.We have previously reported that tumor regression correlates with selective infiltration of CD8+ T cells specific for P1E/H-2Kd antigen in tumor bed upon cyclophosphamide treatment. Unexpectedly, the proportion of CD8+ T cells specific for the tumor-associated antigen P1A in the context of H-2Ld decreases concomitantly, indicating that cyclophosphamide alters the repertoire of CD8+ T cells recognizing tumor antigens. Using P1A KO mice, we found that preferential activation of CD8+ T cells to P1E is not solely due to thymic negative selection. The major role of “mutated” antigens in tumor resistance has been recently highlighted in humans and raises an interesting question about the immune mechanisms of tumor rejection. Additionally to its effect on the specific immune response, cyclophosphamide promotes tumor infiltration by effector memory (P1E/H-2Kd)+ CD8+ T cells which are characterized by higher expression of KLRG1 and Eomes. Our data point to a role of IL-15 and type 1 IFNs for their development, as increased levels of IL-15 and IRF7 were measured in tumor after cyclophosphamide. IFNAR1 blockade interferes with the tumor rejection in 50% of mice and decreases the (P1E/H-2Kd)+ CD8+ T cell infiltration induced by cyclophosphamide, suggesting a role of this cytokine in the expansion and/or recruitment of (P1E/H-2Kd)+ CD8+ T cells in vivo.Altogether, our results suggest that type 1 IFNs and IL-15 induced after cyclophosphamide promote the reprogramming of CD8+ T cells specific for the “mutated” P1E/H-2Kd antigen into effector memory lymphocytes. / Option Biologie moléculaire du Doctorat en Sciences / info:eu-repo/semantics/nonPublished