Polyfunctional Melan-A-specific tumor-reactive CD8+ T cells elicited by dacarbazine treatment before peptide-vaccination depends on AKT activation sustained by ICOS

The identification of activation pathways linked to anti-tumor T-cell polyfunctionality in long surviving patients is of great relevance in the new era of immunotherapy. We have recently reported that dacarbazine (DTIC) injected one day before peptide-vaccination plus IFN-α improves the anti-tumor lytic activity and enlarges the repertoire of Melan-A-specific T-cell clones, as compared with vaccination alone, impacting the overall survival of melanoma patients. To identify the mechanisms responsible for this improvement of the immune response, we have analyzed the endogenous and treatment-induced antigen-specific response in a panel of Melan-A-specific CD8+ T-cell clones in terms of differentiation phenotype, inhibitory receptor profile, polyfunctionality and AKT activation. Here we show that Melan-A specific CD8+ T cells isolated from patients treated with chemoimmunotherapy possess a late differentiated phenotype as defined by the absence of CD28 and CD27 co-stimulatory molecules and high levels of LAG-3, TIM-3 and PD-1 inhibitory receptors. Nevertheless they show higher proliferative potential and an improved anti-tumor polyfunctional effector profile in terms of co-production of TNF-α, IFN-γ and Granzyme-B compared with cells derived from patients treated with vaccination alone. Polyfunctionality is dependent on an active AKT signalling related to the engagement of the co-stimulatory molecule ICOS. We suggest that this phenotypic and functional signature is dictated by a fine-tuned balance between TCR triggering, AKT activation, co-stimulatory and inhibitory signals induced by chemoimmunotherapy and may be associated with anti-tumor T cells able to protect patients from tumor recurrence.