Identification of immune correlates of clinical activity and/or disease outcome in melanoma patients undergoing targeted therapy

BRAF inhibitors (BRAFi) have been shown to modulate the immune responses in metastatic melanoma (MM) patients treated with this agent. In this study, Peripheral Blood Mononuclear Cells (PBMCs) were collected from 34 MM patients, selected on the basis of HLA-A typing, at baseline and at three different time points post-BRAFi treatment (week 4 - 12 - 18). The recognition by circulating T cells of tumor cell lines and tumor associated antigens (TAAs; NY-ESO-1, MAGE-A1, A2 or A3, Gp100, MART-1, TYR, H-TERT, SVV-1, SOX-2) was evaluated by IFN-γ release assay. The correlation between antigen-specific T cell responses and patients’ clinical outcome was determined by statistical analysis. Mixed Lymphocyte Tumor Cell Cultures (MLTC) were generated as well with or without BRAFi, by using autologous tumor cells as source of antigens to elicit anti-tumor T cells responses. The susceptibility of PBMCs, tumor infiltrating lymphocytes (TILs) and MLTCs from MM patients to the in vitro treatment with BRAFi (10, 2 and 0.2 µM) was assessed by cytofluorimetric analysis. The anti-tumor reactivity of MLTCs and TILs was assessed by ELISpot assay. At baseline, antigen-specific T cell responses were detectable in 14 MM patients and, interestingly, novel TAA responses were found at post-treatment time points in 10 patients. Mage-A2, H-TERT and TYR were the most commonly antigens recognized by T cells in MM patients. A positive association was observed between the detection of TAA-specific T cell responses and overall response rate (ORR; p>0.01) of MM patients. The cellular proliferation of both PBMCs, TILs and MLTCs treated in vitro with BRAFi was reduced in dose response manner as compared with untreated cells. The anti-tumor reactivity of MLTCs was completely abrogated by BRAFi treatment as compared with control MLTCs. On the contrary, autologous tumor recognition by TILs was augmented by the pre-treatment with BRAFi. We could assess that TAA-specific T cell responses could be modulated in PBMCs isolated from MM patients treated with BRAFi, with an association with their clinical benefit. Our in vitro results indicate that BRAFi can differently affect anti-tumor T cell responses depending on the origin and the activation status of T lymphocytes. This drug can negatively affect the induction of anti-tumor T cells deriving from PBMCs while it can potentiate the tumor reactivity of TILs, in which the frequency of anti-TAA specific T cells is potentially enriched. Taken together, these results, though need to be investigated in a larger number of patients, may have relevant implications for the design of combined targeted and immune-based therapies for melanoma patients.