TUMOR-SPECIFIC MHC-CLASS-II-RESTRICTED RESPONSES AFTER IN-VITRO SENSITIZATION TO SYNTHETIC PEPTIDES CORRESPONDING TO GP100 AND ANNEXIN-II ELUTED FROM MELANOMA-CELLS

In a search for potentially tumour-specific MHC-class-II-restricted an tigens! the immunogenicity of endogenous peptides that had been eluted from HLA-DR molecules of the human melanoma cell line FM3 (HLA-DRB1*0 2x, DRB1*0401) was tested in vitro. Two 16-mers representing gp100 pos itions 44-59, and annexin II positions 208-223 bound well to isolated DRB1*0401 molecules and are discussed here. HLA-DR-matched normal dono rs' T cells were cultured with peptide-pulsed artificial antigen-prese nting cells (CHO cells cotransfected with genes for HLA-DRB1*0401 and CD80 and coexpressing high levels of both human molecules). Specific s ensitization was achieved against both peptides, as measured in assays of autocrine proliferation and interleukin-2 secretion. Moreover, res ponses to native autologous melanoma cells but not to autologous B cel ls were also observed. In view of the expression of fas by the activat ed T cells and of fas ligand by the melanoma cells, blockade of potent ial fas/fas-ligand interactions was undertaken using monoclonal antibo dies (mAb). The antagonistic fas-specific mAb M3, but not the fas agon ist M33, caused a markedly enhanced T cell response to FM3 cells. Thes e results demonstrate that synthetic peptide antigens are able to sens itize T cells in vitro for effective MHC-class-II-restricted recogniti on of melanoma cells.