Immunohistological relation between DR antigen expression on melanoma cells and infiltration by CD8+ T cells

Previous studies have suggested that class II major histocompatibility (MHC) antigen expression on melanoma cells may influence immune responses against melanoma and the nature of lymphocytic infiltrates against the tumor. This question was examined further by immunoperoxidase studies on sections from 29 primary and 30 metastatic melanoma with monoclonal antibodies (MAbs) against different lymphocyte subsets. The results indicated that expression of MHC class II DR* antigens on melanoma cells was associated with increased overall lymphocytic infiltration and that this applied particularly to the CD8+ subset of T cells. The CR3 receptor (CD 11b) was expressed predominantly on T cells and not macrophages but infiltration by CD11b+ cells did not correlate strongly with DR expression on melanoma cells. Dual staining with MAbs to CD8 and CD11b revealed that, whereas most of the CD8+ cells in DR- primary melanoma and DR+ metastatic melanoma were CD11b+, only approximately 50% of the CD8+ cells in DR+ primary melanoma were also CD11b+. Expression of CD11b on T cells was reported to define a suppressor subset of T cells. If the latter is correct the present results suggest that DR expression on primary melanoma is associated with infiltration by the cytotoxic T cell subset, whereas in the absence of DR antigens and in metastases this subset is absent and the predominant subset appears to be CD8+ CD11b+ T cells with suppressor activity. The biologic and prognostic significance of these findings remains to be determined.