COMPARISON OF NATURAL-KILLER ACTIVITY OF HUMAN BONE-MARROW AND BLOOD-CELLS IN CULTURES CONTAINING IL-2,IL-7 AND IL-12

Previous studies have suggested that autologous bone marrow or mobiliz ed peripheral blood progenitor cell transplants activated by prior cul ture of the cells in IL-2 may capture some of the beneficial graft-ver sus-leukemia effects obtained with unmanipulated allogeneic, but not a utologous, transplants. To investigate ways of improving this approach , we have compared the ability of two other immunomodulating cytokines , IL-7 and IL-12, either alone or in combination with IL-2, to stimula te human bone marrow cells (BMC) or peripheral blood cells (PBC) to ac quire the potential to lyse K562 or Daudi cells. For these studies, we measured the cytotoxic activity of BMC or PBC both before and at the end of their incubation with various cytokine(s) using a standard (51) -chromium release assay. Results suggest that IL-2 at optimal concentr ation induces cytotoxicity significantly higher than IL-7 or IL-12 whe n tested alone. At optimal concentration, the combination of IL-2 and IL-12 showed a synergistic effect for BMC. Such a synergistic effect c ould be observed for PBC only when suboptimal concentrations of IL-2 w ere used. In addition, the ability of the hematopoietic cells to reduc e the number of K562 cells remaining at the end of various culture per iods in the presence of the cytokines was measured. This was made poss ible by the use of a G418-resistant K562 cell line which could, in con trast to normal human BMC or PBC, form colonies that were detectable a fter 1 week in methylcellulose cultures containing the neomycin analog G418. Normal human PBC, stimulated by either IL-7 or IL-12 alone effe ctively suppressed K562 proliferation in both of these assays, whereas no activity could be detected when BMC were incubated under the same conditions. On the other hand, cells from both sources displayed anti- leukemic activity when incubated with IL-2 and IL-12 together, althoug h IL-2/IL-12-activated PBC suppressed the growth of co-cultivated K562 -neo(r) cells about eight-fold more efficiently than IL-2/IL-12-activa ted BMC. Cryopreservation and subsequent stimulation of BMC and PBC wi th cytokines did not cause a significant decrease in cytotoxicity or t heir ability to inhibit the growth of co-cultivated K562 cells compare d to fresh cells. However, the synergistic effect observed with the co mbination of IL-2/IL-12 was no longer detectable for BMC. These result s suggest that (1) PBC are superior to BMC with respect to developing effective natural killer (NK) activity after culture in cytokines and that, (2) the combination of IL-2 and IL-12 may be more effective than IL-2 alone to inhibit proliferation/growth of K562 cells.