These data support the notion that specific immune reactivity and homing of specific cells to the tumour can occur in melanoma patients. Moreover, clonally related cells were found in two lesions with a non-brisk infiltrate, while in two lesions with a brisk infiltrate (clinically, a good prognostic factor) no evidence for clonally expanded tumour infiltrating lymphocytes was found. T cells of clonal origin did not show preferential localization to regressive tumour areas. However, no major differences in T-cell diversity, as assessed by PCR analysis, between peri-and intra-tumoural areas became apparent, this despite the known clinical significance of the specific localization of a T-cell infiltrate. In four lesions studied in detail by PCR analysis of microdissected T cells, a limited T-cell diversity and evidence for clonally expanded tumour infiltrating lymphocytes were found. While MDA expression as well as T-cell subset distribution, as assessed by immunohistochemical analysis, was heterogeneous within and between lesions, they were histologically independent phenomena.

To investigate the clinical relevance of melanoma differentiation antigens (MDAs) as T-cell targets, the relationship between the presence and localization of T-cell subsets and the expression of MDAs was studied by immunohistochemistry and the diversity of CD8+ T cells in regressive melanomas was assessed using laser-assisted microdissection. Melanoma-associated antigens may be the driving force behind the lymphocytic infiltrates in melanomas and the occurrence of melanoma regression.

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