MURINE MARROW-CELLS EXPANDED IN CULTURE WITH IL-3, IL-6, IL-11, AND SCF ACQUIRE AN ENGRAFTMENT DEFECT IN NORMAL HOSTS

Stimulatory cytokines may induce murine hematopoietic progenitor cells (HPCs) to survive, self-renew, proliferate, or differentiate. We stud ied the role of active cell cycling induced by the cytokines interleuk in-3 (IL-3), IL-6, IL-11, and Steel factor (SF) on murine progenitor c ell frequency and cell cycle status in an in vitro system and on engra ftment potential in nonmyeloablated mice. Marrow exposure to IL-3, IL- 6, IL-11, and SF in in vitro liquid culture maintained or expanded sev en factor-responsive high and low proliferative potential colony-formi ng cells (HPP-CFC and LPP-CFC). The HPP-CFC and LPP-CFC were dormant a t the initiation of culture, as determined by H-3-thymidine suicide. T here was an increase in the number and proliferation of HPP-CFC and LP P-CFC at 48 hours; by 48 hours, 62% of HPP-CFC and 56% of LPP-CFC were killed by H-3-TdR exposure. In engraftment studies of cytokine-stimul ated marrow cells into normal hosts, female BALB/c mice received the e quivalent of 40x10(6) starting male marrow cells exposed to cytokines in vitro for 48 hours for 3 consecutive days and were sacrificed 8 wee ks after transplantation. Control groups received either 40x10(6) male uncultured marrow cells, 40x10(6) starting marrow cells cultured in m edium without growth factors for 48 hours, or phosphate-buffered salin e (PBS) for 3 days. Engraftment of male cytokine-treated cells was ana lyzed by Southern blot analysis using the Y-chromosome-specific pY2-cD NA probe. There was minimal engraftment (approaching background levels ) in marrow, spleen, and thymus of nonmyeloablated female recipients. Transplant recipients that had received uncultured marrow directly aft er sacrifice showed engraftment levels of 21% (11 mice; range=8 to 44% ) into marrow, of 9% (range=0 to 22%) into spleen, and 13% (range=2 to 43%) into thymus. We conclude that active cell cycling of marrow cell s induced by cytokine stimulation is associated with an engraftment de fect in the normal host.