B-chronic lymphocytic leukemia cells exert an in vitro cytotoxicity mediated by tumor necrosis factor α

Tumor necrosis factor alpha (TNFalpha) is constitutively produced by B-chronic lymphocytic leukemia (B-CLL) cells and may act as an autocrine factor for their growth and survival. However, very few data are available on the possible cytotoxic effect of TNFalpha produced by B-CLL cells. This study investigated whether B-CLL cells exert in vitro cytotoxicity by TNFalpha and if so, whether this cytotoxicity can be modulated by cytokines. In 8 of 12 patients (66.6%), B-CLL cells in vitro constitutively produced TNFalpha and exerted a TNFalpha-mediated cytotoxicity, evaluated in an 18-h 51Cr release assay, against the TNFalpha-sensitive Jurkat, U937 and K562 cell lines but not against the TNFalpha-resistant Raji cell line. Involvement of TNFalpha in B-CLL cell cytotoxicity is demonstrated by the fact that anti-TNFalpha antibodies strongly inhibited it and supernatants of cytotoxic cultures contained TNFalpha and mediated a completely TNFalpha-dependent cytotoxicity. When the cytotoxic B-CLL cells were stimulated with interleukin (IL)-2 plus IL-12, there was increased TNFalpha mRNA expression, TNFalpha production and TNFalpha-mediated cytotoxicity. All eight patients with cytotoxic leukemic cells had progressive disease and six of these also expressed high levels of ZAP-70 protein. In the other four patients (33.3%), B-CLL cells did not produce TNFalpha in vitro and were not cytotoxic, either spontaneously or after IL-2 plus IL-12 stimulation. Of these four patients, three had stable disease and one had progressive disease. The patient with progressive disease and one of the three with stable disease expressed low levels of ZAP-70 protein. We conclude that a group of B-CLL patients with progressive disease have leukemic B cells able to exert in vitro a TNFalpha-mediated cytotoxicity, which is modulated by cytokines.