Induction and functional characterization of β2-microglobulin (β2-μ)-free HLA class I heavy chains expressed by β2-μ-deficient human FO-1 melanoma cells

Abstract

The frequent loss of β2-microglobulin (β2-μ) in malignant cells has stimulated interest in the functional characteristics of β2-μ-free HLA class I heavy chains, since this information contributes to assess the impact of β2-μ abnormalities on the interaction of malignant cells with immune cells. Therefore, the present study has investigated the ability of β2-μ-free HLA class I heavy chains to modulate NK cell-mediated lysis of melanoma cells and to present melanoma-associated antigen (MAA)-derived peptides to HLA class I-restricted, MAA-specific cytotoxic T lymphocytes (CTL). β2-μ-free HLA class I heavy chains were induced on B2m null FO-1 cells by sequential incubation with IFN-α for 48 h at 37°C and for 24 h at 26°C. Transfection of cells with a wild-type H-2L(d) gene (FO-1L(d)) enhanced the induction of β2-μ-free HLA class I heavy chains under such experimental conditions. β2-μ-free HLA class I heavy chains expressed on the cell membrane did not protect the B2m null FO-1 cells from NK cell-mediated lysis. Furthermore, FO-1 cells which express β2-μ-free HLA-A2 heavy chains following transfection with a wild-type HLA-A2 gene were not lysed by HLA-A2-restricted, MAA-specific CTL lines and clones. These results indicate that association with β2-μ is required for interaction of HLA class I molecules with NK inhibitory receptors and for peptide presentation to CTL.