Signal requirements for activation of leukaemic T cells from a chronic lymphocytic leukaemia (T‐CLL)

SUMMARY In order to define the signal requirements Tor leukaemic T cell activation, the proliferation and interleukin‐2 (IL‐2) production of peripheral lymphocytes from a patient with a HTLV‐I., CD4 + , CD45RA + CD45RO + CD25 ‐ T‐CLL were evaluated after the delivery of different stimuli. Unlike resting CD4 + normal T lymphocytes that can be activated only by a two‐signal stimulation. T‐CLL cells proliferated and released IL‐2 in response to a pair of anti‐CD2 monoclonal antibodies (MoAbs) or concanavalin A (Con A) in the absence of both accessory cells (AC) and phorbol myristate acetate (PMA). The two stimuli were also able to induce CD25 expression within 12–20 h on the majority of T‐CLL cells. A response to anti‐CD3 and anti‐CD28 MoAbs was detected only in the presence of PMA, similar to that observed in normal resting T lymphocytes matched for phenotype. Both Con A‐and CD2‐induccd proliferation were strongly inhibited by the addition of anti‐CD2S MoAb. Furthermore, T‐CLL lymphocytes acquired anti‐tumour lytic activity after culture in the presence of PMA and ionomycin. We conclude that HTLV1 CD25 T‐CLL can be characterized not only by morphological and phenotypical studies but also on the basis of signal requirements for cell activation.