Functions of T cells and recruitment of cellular response afterin vitro mitogenic stimulation of lymphocytes in chronic lymphocytic leukaemia

Summary In vitro stimulation of peripheral blood lymphocytes from ten patients with chronic lymphocytic leukaemia (CLL) was investigated under various culture conditions. It was confirmed that the mitogenic reactivity of whole cell populations (PBL) was delayed and depressed. When CLL rosette-forming cells (RFC) were stimulated, their³H-thymidine uptake was increased, but the pattern of the response was similar to that of whole PBL, thus suggesting some impairment of these cells. Furthermore, in order to evaluate the possible recruitment of B cells, generally thought to be unresponsive, some co-culture experiments were performed in which 10⁴ normal lymphocytes and 10⁵ CLL whole PBL or RFC-depleted cell populations were stimulated with mitogens. An amplified response of the CLL lymphocytes was obtained in all co-cultures, and this effect was more evident when specific T cell stimulants were used; autologous CLL T lymphocytes, on the contrary, failed to display such a ‘synergic’ effect. These results indicate that normal lymphocytes are able to recruit a large number of CLL lymphocytes in the mitogenic response; furthermore, the fact that in co-cultures of CLL T-depleted fractions a better response was obtained with T cell mitogens suggests that the definition of CLL as a clonal expansion of unresponsive ‘B’ lymphocytes may be inadequate.