Combination of DTIC and peptide-vaccination elicit a renewal of high-avidity late-differentiated T-cell clones in melanoma patients (156.6)

Abstract

Abstract Combination of chemo/immunotherapy to increase the effectiveness of the antitumor immune responses associated with a clinical efficacy is an attractive antitumor strategy. We have recently reported that the administration of dacarbazine (DTIC) one day before peptide (Melan-A and gp100)-vaccination in disease-free melanoma patients increases the number of peptide-specific effector-memory CD8+ lymphocytes. Notably, patients treated with DTIC before vaccination, showing a longer survival, display a progressive enhancement of TCR repertoire diversity of Melan-A+ CD8+ clones, accompanied by the maintenance of high-avidity, whereas patients treated with vaccine alone showed a reduction of TCR repertoire diversity and a decline of their tumor lytic activity. To study the phenotype and the functional lytic activity of CD8+ T-cell clones in association with their renewal rate we have analyzed the expression of CD28 and CD27 co-stimulatory molecules, in both Melan-A- and gp100-specific T-cell clones, isolated before and at different times after the treatments. We found newly recruited clones with high-lytic activity and highly-differentiated phenotype only after the combined therapy. Studies are in progress to define the role of replicative senescence in the continuous renewal induced by the combined therapy, by studying activity and regulation of telomerase in endogenous-induced or vaccine-driven clones, in correlation with their different phenotype and anti-tumor lytic capability.