Differential methylation of class I histocompatibility antigen genes in T-cell lines derived from two different types of T-cell malignancies.

We have previously shown that two human T-cell lines (HSB and 8402) derived from patients with childhood T-cell ALL (T-ALL) do not synthesize detectable mRNA for HLA-DR alpha. The DR alpha genes in both cell lines are hypermethylated relative to the same genes in T-cell lines infected with human T-cell leukemia virus (HTLV) and derived from patients with adult T-cell leukemia/lymphoma (ATL). These latter cell lines do express HLA-DR alpha-mRNA, as well as HLA-DR surface antigens. We report here that the genes for HLA class I antigens are also highly methylated in the T-ALL T-cell lines relative to the same genes in the ATL T-cell lines, normal peripheral blood T cells, and autologous normal B-cell lines. In spite of substantial differences in the extent of methylation of class I-related genes, no obvious differences exist among these cell types in their levels of expression of HLA-A and -B antigens. The data clearly indicate, however, that the class I and class II components of the major histocompatibility complex are unusually hypermethylated in several T-ALL-derived cell lines, while ATL T-cell lines do not substantially differ in this respect from normal peripheral blood T-cells.