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 studied the role of active cell cycling induced by the cytokines interleukin-3 (IL-3), IL-6, IL-11, and Steel factor (SF) on murine progenitor cell frequency and cell cycle status in an in vitro system and on engraftment potential in nonmyeloablated mice. Marrow exposure to IL-3, IL-6, IL-11, and SF in in vitro liquid culture maintained or expanded seven factor-responsive high and low proliferative potential colony-forming cells (HPP-CFC and LPP-CFC). The HPP-CFC and LPP-CFC were dormant at the initiation of culture, as determined by 3H-thymidine suicide. There was an increase in the number and proliferation of HPP-CFC and LPP-CFC at 48 hours; by 48 hours, 62% of HPP-CFC and 56% of LPP-CFC were killed by 3H-TdR exposure. In engraftment studies of cytokine-stimulated marrow cells into normal hosts, female BALB/c mice received the equivalent of 40 x 10(6) starting male marrow cells exposed to cytokines in vitro for 48 hours for 3 consecutive days and were sacrificed 8 weeks after transplantation. Control groups received either 40 x 10(6) male uncultured marrow cells, 40 x 10(6) starting marrow cells cultured in medium without growth factors for 48 hours, or phosphate-buffered saline (PBS) for 3 days. Engraftment of male cytokine-treated cells was analyzed by Southern blot analysis using the Y-chromosome-specific pY2-cDNA 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 after 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 cells induced by cytokine stimulation is associated with an engraftment defect in the normal host.