Locus-Specific Analysis of Human Leukocyte Antigen Class I Expression in Melanoma Cell Lines

Surface expression of human leukocyte antigen (HLA) class I antigens on melanoma lines was evaluated by locus-specific monoclonal antibodies (mAbs) with three different techniques: Fluorescence-activated cell sorting (FACS), immunohistochemistry with cytospin preparation (ICP), and complement- mediated cytotoxicity (CMC). Eleven HLA class I-expressing cell lines developed from metastases were used. Specific expression of HLA loci was examined under routine culture conditions and after 48-h incubation in interferon-γ (IFN-γ 500 U/ ml). Loss of allelic expression was seen in one line (586-MEL): Products of genes coding for HLA-A29 and -B44, in strong linkage disequilibrium, were not detectable. HLA-A antigens were consistently detected by all methodologies and minimally affected by pretreatment with IFN- γ. HLA-B antigens were detectable in 8 of 11 lines by ICP and 3 of 11 lines by CMC. By FACS the supratypic specificity HLA-Bw6 was expressed at low levels in most lines (mean fluorescence 47.2 ± 13.4 and rose to 259.8 ± 45.9 after incubation with IFN-γ p<0.001). HLA-Cw antigen detection by CMC correlated with HLA-B (p<0.01), suggesting that down-regulation and sensitivity to IFN-γ are shared by the two loci. This low expression of the HLA-B antigens may play a role in the evasion of the host immune response and its up-regulation may be useful in allowing tumor antigen recognition.