| Research Abstract |
(1) Frequency of HLA Class I downregulation in melanoma lesions
The aim of this study was to investigate the expression of HLA Class I antigens in surgically removed melanoma lesions. To this end 32 primary and 11 metastatic lesions were stained in the immunoperoxidase reaction with monoclonal antibodies(mAb) to monomorphic, locus specific and polymorphic antigenic determinants. The intensity of staining of melanoma cells was compared to that of keratinocytes surrounding the tumor nest. The patients' HLA phenotype was determined utilizing the conventional lymphocytotoxicity assay. About 20% of primary and about 50% of metastatic lesions were not stained or were stained with reduced intensity by mAb to monomorphic and locus specific antigenic determinants. Moreover about 40% of primary and about 60% of metastatic lesions were not stained or were stained with low intensity, by mAb to HLA Class I allospecificities. These results indicate that the frequency of abnormalities in HLA Class I a
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ntigen expression is high in melanoma lesions. These abnormalities are likely to have a negative impact on T cell based immunotherapy, since they provide melanoma cells with a mechanism to escape from destruction by cytotoxic T cells.
(2) Machinery of HLA Class I downregulation in melanoma cells.
The expression of the proteasome subunits LMP2 and LMP7, the MHC-encoded transporter subunits TAP1 and TAP2 and HLA Class antigens was tested by immunoperoxidase staining in melanoma lesions, since these molecules play an important role in the presentation of melanoma associated antigen derived peptides to cytotoxic T cells. LMP2 was less frequentlt expressed than LMP7 in primary and metastatic lesions. TAP1, TAP2 and HLA Class I antigen expression was more frquently downregulated in metastatic than in primary melanoma lesions. A synchronous downregulation of TAP1, TAP2 and HLA Class I antigen expression was observed in about 60% of primary and metastatic melanoma lesions. Moreover, these downregulation in primary lesions was significantly associated with their thickness, with the stage of the disease, with a reduced time to disease progression and with a reduced survival. These results suggest that TAP plays an important role in HLA Class I downregulation in melanoma cells and in the clinical course of the disease, probably by providing melanoma cells with a mechanism to escape from CTL recognition during disease progression. Less
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