The vast majority of lymphocytes infiltrating primary cutaneous melanoma express the CD27 costimulatory receptor: implications for melanoma progression.

Melanoma progression is favoured by prevalence, within the micro-environment of primary cutaneous melanoma, of suppressive forces, e.g. exerted by CD4(+) CD25(+) FOXP3(+) regulatory T lymphocytes, over anti-melanoma immunity, e.g. exerted by CD8(+) cytolytic T lymphocytes. The CD27 glycoprotein is crucial because it is able to identify regulatory T cells endowed with strong suppressive ability, whilst CD8(+) T cells endowed with actual cytolytic ability become CD27(-). The present in situ quantitative immunohistochemical study, including a series of double labelling experiments and morphometrical cell analyses, shows that the vast majority of lymphocytes infiltrating primary cutaneous melanoma express CD27. Specifically, virtually the entire CD4(+) CD25(+) FOXP3(+) T subset infiltrating primary cutaneous melanoma also co-expressed CD27; CD27 was, moreover, co-expressed even by the vast majority of the CD8(+) T cells, and, conversely, effector/cytotoxic CD8(+)CD27(-) cells were very scarcely represented. The overwhelming CD27 co-expression may confer on the CD4(+)CD25(+)FOXP3(+) T subset a consistent capacity to suppress anti-melanoma immunity, whereas the too low CD8(+) CD27(-) cell proportion may presumably be insufficient to confer on the CD8(+) T subset a satisfactory anti-melanoma cytotoxic activity. We therefore propose that these CD27-discriminated pathways may trigger a functional imbalance within the microenvironment of primary cutaneous melanoma, thus favouring melanoma progression.