Prognostic value of tumor-infiltrating immune cells in melanoma

Abstract

Host cells representing an integral component of solid tumors, among them cells contributing to the development of native and adaptive immune responses, can exert both positive and negative effects on the outcome of the disease. Infiltration of T lymphocyte subsets and antigen presenting dendritic cells, crucial in mounting an efficient antitumor immune response, is generally associated with favorable prognosis. On the contrary, accumulation of tumor-associated macrophages, mast cells and neutrophils, playing important roles in chronic inflammatory processes promoting tumor progression, predicts unfavorable disease outcome in most cases. In melanoma, studies on the prognostic impact of the lymphoid infiltrate in general, and that of T cells, yielded controversial results. In our studies, density of activated T lymphocytes correlated with patients' survival, and we obtained similar results in the case of B cells and mature dendritic cells. The amount of both B cells and dendritic cells showed correlation with that of activated T lymphocytes, and their combined analysis identified patient subgroups with different prognosis. According to data from the literature, intense infiltration by neutrophil granulocytes could be associated with shorter survival, while no unambiguous conclusions can be drawn from studies on the prognostic value of tumor-associated macrophages and other immune cell types. Our results indicate that a prominent infiltration of dendritic cells, B cells and activated T lymphocytes can be considered as a favorable prognostic factor in malignant melanoma.