Characterization of a tumorigenic murine T-lymphoid-cell line spontaneously derived from an IL-2-dependent T-cell line.

The establishment of IL-2-independent T-cell lines spontaneously derived from long-term IL-2-dependent cytotoxic T-cell lines is described. Two lines (cloned and uncloned) studied in detail have shown the following characteristics: (1) Permanent loss of IL-2 dependence. (2) Partial or complete loss of both cytotoxic activity and the IL-2 receptor. (3) Increased expression of T-cell membrane markers (Thy1.2, Lyt1.2) compared with the parental line. (4) Lower level of DNA methylation than in freshly obtained lymphoid cells. (5) Different karyotypic pattern from the parental IL-2-dependent line, with a mean number of 39-40 chromosomes and a resemblance to T leukemic lines. (6) Leukemia caused in normal syngeneic C57BL/6 mice by the uncloned line, in contrast to the cloned IL-2-independent line or the parental dependent line. Unlike established leukemic lines, however, the independent line gave rise to tumors which regressed in some mice within a few days of their appearance. These findings suggest that T-cell lines maintained with IL-2 for prolonged periods of time (greater than 3 months) can undergo transformation and, therefore, should not be utilized for immunotherapeutic purposes.