Loss of heterozygosity of DQ alpha gene in human malignant melanoma.

DNAs from human melanoma cells, used at early in vitro passage, were evaluated by Southern blot analysis for somatic loss of heterozygosity at the DQ alpha gene. A total of 7 melanomas, 3 primary and 4 metastatic derived from 5 different patients were studied; in one case (pt 665) cell lines were derived from two anatomically different subcutaneous metastasis, whereas in a second case (pt 9923) both the primary tumor and a lymph node metastasis were available. Restriction length polymorphism (RFLP) analysis, performed on autologous peripheral blood lymphocyte (PBL) DNA digested with different enzymes, showed a pattern of bands compatible with the constitutional heterozygous typing at DQ alpha gene in 4 cases whereas 1 case revealed an homozygous typing. When melanoma DNAs were analysed, 1 out of the 4 informative cases (pt 1007) showed a loss of a diagnostic fragment for DQ alpha gene when digested with both Taq I and Bgl I enzymes. These results indicate that class II allelic losses detectable by RFLP can be found on malignant melanoma and add further complexity on the involvement of chromosome 6 whose cytogenetic abnormality are the most consistent in this human neoplasia.