INTERLEUKIN-2 ACTIVATION OF HUMAN BONE-MARROW IN LONG-TERM CULTURES -AN EFFECTIVE STRATEGY FOR PURGING AND GENERATION OF ANTITUMOR CYTOTOXIC EFFECTORS

Our previous studies have shown that IL-2 activated bone marrow cells develop potent tumoricidal activity in vitro and in vivo. With the dua l aim of in vitro purging and generation of effecters which could medi ate graft-versus-leukemia effects in vivo, IL-2 activation of human bo ne marrow in long-term cultures (LTC) was tested. Marked cytotoxicity was seen against A375 (melanoma), K562 (CML) and Daudi (lymphoma) cell lines in IL-2 (1000 U/ml) stimulated cultures. Hematopoietic progenit or cell number in these cultures was assessed by day 14 clonogenic ass ays. In 1-week-old IL-2 stimulated cultures a higher number of clonoge nic cells was seen than control LTCs without IL 2. However, thereafter accelerated decrease in the number of clonogenic cells was seen in IL -2 cultures. In vitro purging efficacy was tested by elimination of A3 75 and K562 cells mixed with normal marrow at 1:10 and 1:100 ratios an d co-cultured for 10 days. In IL-2 stimulated cultures, A375 cells cap able of proliferation were not detectable at both mixing ratios. K562 elimination was complete only at 1:100 ratio. After 10 days in culture , no Phl-positive metaphases were seen in IL-2 stimulated BM cultures of 4 patients with CML. These results indicate that IL-2 activation of BM in 1-2 week cultures can lead to generation of marked anti-tumor c ytotoxicity and effective in vitro purging in a variety of tumor types .