Abstract
Peripheral blood T cells from a patient with T‐cell chronic lymphocytic leukemia (T‐CLL) failed to respond to mitogenic lectins or alloantigens but could be induced to proliferate by the addition of exogenous interleukin‐2 (IL‐2). The T‐CLL cells also proliferated in response to 12‐O‐tetradecanoyl phorbol‐13‐acetate (TPA), or to TPA in combination with phytohemagglutinin (PHA). These TPA‐mediated proliferative responses were transient, and only small but significant amounts of IL‐2 activity were generated. In contrast, no IL‐2 activity was produced after the T‐CLL cells had been stimulated with PHA only. The T‐CLL cells that were induced to proliferate with PHA and exogenous IL‐2 could be maintained in continous culture by the addition of exogenous IL‐2 at regular intervals. These continuously proliferating T‐CLL cells failed to produce IL‐2 constitutively. However, they could be induced to produce IL‐2 activity by stimulation with TPA or TPA plus PHA. Irradiation of the proliferating T‐CLL cells prior to incubation with TPA or TPA plus PHA resulted in a 9‐fold increase in IL‐2 activity, suggesting that the proliferating T‐CLL cells were able to consume the IL‐2 they produced. Studies on the presence of human T‐cell leukemia/lymphoma virus (HTLV) in the fresh and proliferating T‐CLL cells revealed that 12% of the fresh cells expressed the HTLV p19 structural core protein. HTLV p19 expression was strongly enhanced in the T‐CLL cells induced to proliferate by TPA (66%) and in the continuously growing IL‐2‐dependent T‐CLL cells (82%). In the latter culture, but not in the fresh T‐CLL cells, type‐C virus particles were observed. These results indicate that HTLV expression correlates with T‐CLL cell proliferation but not with IL‐2 production by these cells.