Tissue distribution of a melanoma-associated antigen D-1 immunogenic in patients with melanoma

A human melanoma-associated antigen D-1 was recently identified by screening an expression cDNA library derived from mRNA of cultured melanoma cells with sera of melanoma patients. The aim of this study is to present in vivo expression and precise distribution of D-1 in normal tissues and benign or malignant neoplasms. By in situ hybridization, we found that the D-1 mRNA was exclusively expressed in the cytoplasms of melanoma cells, but not in keratinocytes, fibroblasts and lymphocytes adjacent to melanoma nests. Further immunohistochemical studies revealed that the expression of D-1 antigen was distributed to both the surface and cytoplasm of melanoma cells, indicating that D-1 antigen can be recognized by killer T lymphocytes or antibodies in vivo. No significant mRNA nor peptide of D-1 was detected in basal cell carcinoma, squamous cell carcinoma and other benign tumors such as melanocytic nevi and seborrheic keratosis. We also confirmed that D-1 mRNA and peptide were not expressed in normal organs by dot blot hybridization and western blot analysis, respectively. These results will assess the suitability of recombinant D-1 protein to implement active specific immunotherapy against melanoma.