Interleukin‐2 Prevents Programmed Cell Death in Adult T‐Cell Leukemia Cells

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Abstract
Adult T‐cell leukemia (ATL) is a prototype of the lymphoma/leukemia syndromes involving immunologically mature T‐lymphocytes. The first retrovirus described in humans, HTLV‐I, is causally related to the disease. In this study, we examined whether ATL cells die in vitro through programmed cell death (PCD), which has been shown to occur in cells affected by several other acute and chronic Icukcmias. When ATL cells from peripheral blood were cultured in serum‐free complete medium, a substantial proportion of them spontaneously died by PCD. After 48 h of culture, approximately 30% of the total DNA was fragmented. Electrophoresis indicated that the DNA of the ATL cells had been cleaved into regular oligonucleosome fragments each comprising approximately 180–200 base pairs. This process was significantly promoted by methylprednisolone and the protein kinase A (PKA) activator Sp‐cAMPS in at least some cases. Since all ATL cells possess interleukin‐2 receptors on the cell membrane, the effect of IL‐2 on spontaneous PCD was assessed. PCD after 48 h of culture was inhibited by 30–50% by 100 U/ml interleukin‐2 (IL‐2). This effect of IL‐2 to prevent spontaneous PCD was dose‐ and time‐dependent. These findings suggest that the viability of ATL cells in vivo is regulated positively and negatively by intrinsic IL‐2, glucocorticoid and regulators of PKA activity. Furthermore, the process of cell death may be involved in the development of the disease.