Interleukin 2 responsiveness of immature T-cell colony-forming cells (T-CFC) from patients with acute T-cell lymphoblastic leukemias.

T-cell colony-forming cells (T-CFC) from 13 of 17 patients with T-ALL generated colonies in methylcellulose in the absence of added growth factors or mitogenic stimulation. As previously described, these colonies were composed of immature T cells displaying the same karyotypic abnormalities as fresh leukemic cells. Biochemically purified (bIL-2) and recombinant IL-2 (rIL-2) without any mitogen enhanced colony growth from both unfractionated and blast-enriched cell fractions in patients with a relatively low (less than 50 colonies/5 X 10(4) cells) plating efficiency. However, dose-response experiments revealed that the optimal dose of rIL-2 needed to enhance colony growth varied from patient to patient. Anti-IL-2 (DMS1) and anti-IL-2 receptor (anti-Tac) moAbs inhibited both spontaneous and rIL-2-induced colony formation in a dose-dependent manner. Direct staining of fresh leukemic cells with anti-Tac revealed less than 10% positive cells in all but two patients. However, cell incubation in the absence of growth factors or mitogens for 2-48 hr resulted in an increase of Tac+ cells. These observations indicate that a subset of immature T-CFC from T-ALL patients display functional IL-2-receptors. In addition, our findings strongly suggest that the IL-2/IL-2-R system could be involved in the spontaneous proliferation of some immature T-CFC of T-ALL patients.