Jean - Paul Fermand and Jean - Claude Brouet

In the majority o f chronic lymphocytic leukemias (CLL), proliferative B lymphocytes are thought to be frozen in vivo at a given maturat ion stage (1). Recently, several studies have emphasized that CLL cells could be driven to different iate into plasma cells in vitro (with or without proliferation) upon t r iggering by mitogens (2, 3, 4) or T cel l -der ived factors (5, 6). Th u s far, however , no study has been designed to elucidate whether leukemic B cells can be t r iggered by T ce l l -der ived iymphokines that are known to induce normal B cells to proliferate. In prel iminary experiments , we found that leukemic B cells f rom six o f nine CLL patients, when stimulated with anti-~ ant ibody a n d / o r with Staphylococcus aureus Cowan strain I (SAC), prol iferate in the presence of various T ce l l -der ived condi t ioned media, which potentially contained a n u m b e r of lymphokines (unpublished data). Absorption exper iments suggested that interleukin 2 (IL-2) was a potent growth factor for these leukemic B cells. We repor t here that purif ied recombinant IL-2 is indeed able to induce leukemic cells f rom some patients to proliferate. These data, obta ined with monoclonal populations o f B cells, which are likely free o f contaminat ing T cells, provide fu r the r evidence that IL-2 can tr igger activated B cells to proliferate.