Coexpression of the human HLA-A2 or HLA-B7 heavy chain gene and human β2-microglobulin gene in L cells

L cells expressing human HLA-A2 or HLA-B7 class I antigen heavy chains are not recognized by human cytotoxic T lymphocytes directed at HLA-A2 or HLA-B7 antigens. To test whether the absence of human β2-m was the cause of the lack of recognition by the human cytotoxic T lymphocytes, coexpression of the human β2-m gene and the HLA-A2 or HLA-B7 heavy chain in L cells ('double transfectants') was obtained. In addition, L cells expressing HLA-A2 or HLA-B7 antigens in association with human β2-m were obtained by an exchange reaction, in which human β2-m from serum replaced the endogenous murine β2-m. Both types of transfectant cells were used in ⁵¹Cr-release assays and cold target inhibition assays for human cytotoxic T cell clones which were directed at HLA-A2 or HLA-B7. Neither human CTL clones nor a mixture of CTL specific for HLA-A2 and HLA-B7 were able to recognize these cells. Several alternative explanations for these observations are discussed.