To address this question, we performed immunomonitoring of lymphoid subpopulations of patients with metastatic melanoma before and after a first cycle of DTIC treatment. To our knowledge, this study is the first that performs a systematic study of the effect of alkylating chemotherapy on all blood lymphoid cell subsets in melanoma patients. We observed that chemotherapy modestly but significantly affects the total number of lymphocytes, which is reduced after chemotherapy. This observation could be linked to the toxicity of this anticancer drug. However chemotherapy did not affect the number of CD8 + or CD4 + T cells or Treg or NK cells thus underscoring that such treatment is not a major immunosuppressive treatment. High expression of EOMES gene, encoding eomesodermin is also correlated with longer survival. Eomesodermin has been described as a master regulator of cytotoxic CD8 + T cells, and can also be expressed by NK cells in mice. This suggest that the intrinsic presence of a cytotoxic cellular response could be important for DTIC efficacy, thus corroborating our previous mouse findings that DTIC antitumor effects are dependent on CD8 T cells and NK cells. After treatment, high expression of RORC, coding for RORct, a transcription factor responsible for CD4 + Th17 differentiation, correlates with better survival. Th17 cell induction has already been described with various melanoma treatments, such as vaccination, anti-PD-1, anti-CTLA4, as well as other anticancer drugs such as cyclophosphamide. Furthermore, it has been described that Th17 cells can drive antigendependent tumor shrinkage. We hypothesize that Th17 cell induction after treatment could be a surrogate marker of efficacy. This event could be related to the association of high granulocyte counts in responder patients after treatment, because Th17 cells are well known to be important in the activation and recruitment of neutrophils. Indeed, in chronic inflammatory Clofentezine situations such as cancer, the presence of chronic antigen stimulation leads to an exhausted or senescent memory Nodakenin phenotype of CD4 + T cells. These cells are known to dampen anti-tumor immune response efficacy. Such cells are known to accumulate in peripheral blood of cancer patients. It is possible that the high number of exhausted lymphocytes could impair chemotherapy associated antitumor immune response, thus rendering such drug less effective. In addition, our study corroborates the previous finding that higher Treg rate is associated with advanced clinical stage. Moreover, higher Treg number at baseline is associated with absence of response to DTIC. Such data suggest that high tumor burden and/or immunosuppressive state could impair antitumor efficacy of DTIC probably by inhibiting drug related antitumor immune response. The major finding of this study is the relationship between NK cell activity and response to DTIC. We analyzed the two subsets of peripheral blood NK cells, that are described as functionnaly different : CD56hi NK cells can secrete high amounts of cytokines, and CD56luCD16+ are perceived as cytotoxic. Our results show that, while DTIC did not affect the total number of NK cells, CD56hi NK cells from patients with disease control have a higher activation status than the patients with progressive disease. We previously showed that DTIC can enhance NKG2D ligand expression by melanoma cells. In a mouse model, we showed that this causes IFNc secretion by NK cells, followed by major histocompatibility complex expression by tumor cells, hence better recognition by T cells.