HLA expression in basal cell carcinomas.

Decreased expression of MHC class I molecules in tumor cells has been reported to be associated with enhanced malignancy both in human and murine tumors. This paper studies HLA-ABC and HLA-DR expression in 56 basal cell carcinomas. Our results show that these tumors have a heterogeneous expression of MHC class I molecules: 11% exhibit uniform staining of most tumor cells; 25% are only partially positive, and the remaining 64% are MHC class I negative. A positive correlation between the level of HLA-ABC molecule expression and the degree of histological differentiation has been found. The expression pattern of tumor cells with anti-class II monoclonal antibodies shows weak homogeneous staining in 5%, staining in only a few areas of the tumor in 32%, whereas 63% has no significant staining for MHC class II antigens. Most mononuclear cells infiltrating the tumor were T lymphocytes (CD-3 positive). Results also show that 68% of the tumors express class II molecules homogeneously in the infiltrate. The expression of class II antigens in infiltrating lymphocytes correlated with the level of class II expression in the tumor cells probably as a consequence of lymphokine production by activated T cells.