A phase II randomized clinical study is ongoing in our Institution to prove the clinical efficacy of dacarbazine (DTIC) one day before peptide-vaccination (Melan-A and NY-ESO-1) in the prevention of melanoma relapse in clinically disease-free HLA-A2 patients. In a previous pilot study, this combination therapy (using Melan-A and gp100 peptides) increased the number of tumor-reactive long-lasting effector-memory CD8+ lymphocytes. To identify the mechanisms enhancing the immune response, induced by DTIC combined with peptide-vaccination, we analyzed the endogenous and treatment-induced antigen specific CD8 T-cell response at the clonal level. We analyzed the sequence of the TCR α-chain of these clones and the molecular results were correlated with the expression of CD27/CD28 co-stimulatory molecule, AKT activation and anti-tumor lytic activity. The combination of chemo/immunotherapy elicited in Melan-A-specific, but not in gp100 clones, a renewal of high-avidity/tumor-reactive T-cell clones, with a broadening TCR diversity in long-surviving patients, suggesting that the selection of immune-resistant tumor variants may be circumvented by this combination, and thus prevent tumor recurrence in melanoma. In gp100 clones, AKT activation (pSer473-AKT) canonically correlates with CD28 and/or CD27 expression, independent of the treatment while in Melan-A clones, lacking CD27 and CD28 expression, non-canonical AKT activation was only observed after the combination therapy. The identification of the extracellular stimuli and signaling pathway responsible for DTIC-mediated activation of the AKT signaling are currently under investigation.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4406. doi:1538-7445.AM2012-4406