HIGHER FREQUENCY OF SELECTIVE LOSSES OF HLA-A AND HLA-B ALLOSPECIFICITIES IN METASTASIS THAN IN PRIMARY MELANOMA LESIONS

Expression of HLA class I molecules is essential for the recognition o f tumor cells by CD8(+) T cells. In this study, 48 bioptic samples of 42 patients in all stages of melanoma were investigated after short-ti me cultivation of tumor cells. To confirm melanocytic origin of cultur ed cells, samples were screened for mRNA expression of melanoma marker s gp100, tyrosinase, MAGE-3, MelanA, and MUC18 by reverse transcriptas e-polymerase chain reaction. Surface expression of specific HLA-A and -B allospecificities on melanoma cells were analyzed with a standard m icrocytotoxicity assay after stimulation with interferon (IFN)-alpha a nd compared with the background found in peripheral blood mononuclear cells from the corresponding patients. Immunohistochemistry and flow c ytometry confirmed specific losses in cases where the appropriate mono clonal antibodies were available. The level of expression of HLA-I, HL A-II, and intercellular adhesion molecule 1 antigens on melanoma cells cultured in the presence or absence of IFN-alpha and IFN-gamma was de termined cytofluorometrically. All cell cultures tested were found to be positive for one or more melanocytic markers by reverse transcripta se-polymerase chain reaction. The specific HLA-I alleles on the cultur ed cells were detectable in 45 of 48 samples. In 11 cases a specific l oss of one HLA-I allele was observed (2xA2, B7, B8, B18, 4xB44, B47, B 49). Ten of these samples were derived from locoregional lymphnode met astases or from distant metastatic tumors. Only one sample from a prim ary melanoma showed a specific loss of HLA-I (B47), IFN-alpha upregula ted expression of HLA-I up to 4-fold. IFN-gamma enhanced the appearanc e of HLA-II up to 35-fold and the expression of intercellular adhesion molecule 1 up to 40-fold. Selective loss of HLA-I allospecificities m ight be a major step in tumor progression.