Quantitative analysis of T6-positive Langerhans cells in human skin cancers.

Epidermal Langerhans cells (LC) are required for antigen-presentation and for stimulating antigen-specific T cell activation. Similar functions may be important in the immune response to malignant skin tumours. Monoclonal anti-T6 antibody was used to examine LC population in basal and squamous cell carcinomas. Positive control labeling was performed with monoclonal anti-HLA-DR antibody. The number of T6-positive LC per mm2 of section was significantly decreased (p less than 0.01) in the tumour group in comparison with a sex and age-matched control group. The number of sun-exposed and covered regions was taken into consideration in each respective group. Within the tumours, LC were found more frequently in the tumour periphery and in most differentiated tumour areas (horn pearls) than in the rest of the tumour mass. T6-positive LC were rarely found in the dermis. Moreover, LC exhibited morphological changes in specimens from tumours. Staining with anti-HLA-DR antibody revealed less numerous positive cells within tumour nests than labeling with OKT6. A relationship between T6-positive LC quantities and extent of HLA-DR-positive infiltrates around tumours could not be established. These results suggest that immunological surveillance of neoantigen-bearing tumour cells may be impaired in skin cancer. A reason for the reduced LC number may be an altered microenvironment in tumour tissue.