| Abstract |
Abnormality in HLA-class I antigen expression in primary and metastatic
melanoma lesions, evidenced by immunohistochemical staining with mAbs, are
reported in several studies. Defects range from total HLA class I antigen
loss to selective loss of one of the HLA class I specificities (Ferrone S.,
Immunology today, 1995; 16: 487). Since HLA antigens are the restricting
elements presenting several melanoma associated antigens-derived peptides
to cytotoxic T-lymphocytes, the down-regulation of HLA class I antigen
expression can represent a mechanism of tumor escape from immune
surveillance (Seliger B., Immunology today, 2000; 21: 455). To investigate
the involvement of membrane associated antigens in functional recognition
of melanoma cells by immune effectors, we stabilised in vitro 25 human
melanoma cell lines starting from surgical removed primary and/or
metastatic tumors. All the lines showed, by cytofluorimetric analysis,
significant expression of HMW-MAA, a melanoma associated antigen.
Moreover, HLA Class-I and Class-II expression revealed complete HLA class-I
loss only in two cell lines, ANAD-63 and COPA-159, whereas aberrant
Class-II expression was observed in 5/25 melanoma cell lines. Our
attention is now focused on the lines that seem to have aberrant
expression of HLA antigens trying to understand, by molecular techniques,
the mechanism of possible loss of HLA antigens expression (Wang BZ, J Exp
Med, 1999;190: 205). The HLA class 1 negative melanoma cell line ANAD-63
shows, indeed, a deletion, in frame, of 24 bp in the exon 2 of the beta2-
microglobuline gene, by sequence analysis (codon 59-66). The detected
mutation does not affect synthesis of either m-RNA, revealed by RT-PCR, or
protein, detected by intracellular cytofluorimetric analysis. In
conclusion, loss of HLA class I expression in ANAD-63 appears to be
dependent to a new mutation of the B2-microglobulin gene whereas the
defect in COPA-159 needs a better characterisation.
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