Differential expression of HLA-A and B-alleles on uveal melanoma as determined by immuno-histology

HLA molecules play an important role in the presentation of antigens to the immune system, including tumor-specific antigens. Uveal melanomas vary in the level of expression of monomorphic HLA molecules. However, since the HLA system is polymorphic and since antigen-presentation may be linked to the expression of specific HLA alleles, the authors wondered whether allelic differences in expression existed on uveal melanomas. In order to test this, tissue sections from 23 uveal melanomas were stained in an indirect immunoperoxidase technique with monoclonal antibodies against monomorphic and polymorphic determinants of HLA molecules. All uveal melanomas showed a high level of expression of the monomorphic determinants of HLA-Class I. The polymorphic HLA-Class I molecules A2, A3, Bw4 and Bw6 varied in expression, with a higher expression of HLA-A than of HLA-B. A low level of expression of both beta 2-microglobulin and HLA-B locus products was associated with a large tumor diameter. Expression of HLA-Class II molecules was low (0 to 35%). The observation that expression of the HLA-A allelic products was higher than of the HLA-B subtypes may have implications for the search of tumor specific peptides for immunotherapeutic use: it may be worthwhile to select peptides that specifically bind to HLA-A and not to HLA-B.