Melanoma is a type of skin cancer derived from melanocytes, with a high mortality rate and a poor prognosis. Interestingly, it has been demonstrated that melanoma patients present a spontaneous T-cell response against their tumor, but at a certain time, the immune response becomes ineffective. In this process, T cells are suppressed, favoring tumor escape and growth. In order to investigate whether the immune system itself could favor tumor evasion, we explored the potential of the secretome generated by melanoma to control T cell functions, considering the exposure of tumor cells to an inflammatory or non-inflammatory environment.

Initially, PBMCs were isolated from healthy donors (n = 4) and cultured for 3 days in RPMI media (conditioned media – rCM) or in RPMI media supplemented with PHA (inflammatory-conditioned media – iCM). The melanoma lineage MEWO was expanded in RPMI until reaching 70% confluence, then some of them were treated with rCM, or iCM for 24 hours. On the last day of cultivation, RPMI, rCM, and iCM were removed, the cells were washed and cultured for 15 hours in RPMI medium without animal protein. The media were aliquoted and used as secretome from melanoma previously submitted to a control (RPMI), non-inflammatory (Sec), and inflammatory stimulus (iSec). Initially, we used CFSE dye to investigate by Flow Cytometry whether RPMI, Sec, and iSec exert any effects on T-cell proliferation. Also, we determined the expression of the activation markers HLA-II and CD69 on T-cells.

Interestingly, we found that all the secretomes used were able to significantly control the proliferation of T cells, however, the most pronounced effect occurred in T cells treated with iSec. Corroborating this finding, T cells submitted to the iSec showed reduced expression of activation markers CD69 and HLA-II.

These findings show that although melanoma has a constitutive capacity to control T-cells function and escape from immune surveillance, the exposure of tumor cells to the inflammatory environment plays an important role in enabling these cells to perform a more potent immunosuppressive function.