Interleukin-12 synergizes with interleukin-3 and steel factor to enhance recovery of murine hemopoietic stem cells in liquid culture.

Interleukin 12 (IL-12; natural killer cell stimulatory factor, NKSF; cytotoxic lymphocyte maturation factor, CLMF) was studied for its effects on the survival and generation of hemopoietic progenitors (CFU-C, CAFC day 7-14) and long-term culture initiating stem cells (CAFC day 28-35) by post-5-fluorouracil (FU) bone marrow cells (BM) in low-serum liquid culture. Previous data have shown that IL-12 may act as a potent synergistic factor stimulating multilineage expression of hemopoietic stem cells in the presence of IL-3 in combination with Steel factor (SF) or IL-11. IL-12 or IL-11 alone did not support CFU-C production in liquid culture of a low-density fraction of day-6 post-FU BM. IL-11 and SF showed potent synergy with IL-3 to augment output CFU-C numbers and support CAFC-28/35 maintenance; SF as a single factor, or in combination with IL-11 or IL-12, allowed low recovery of CFU-C and all CAFC subsets. IL-12 synergized with IL-3, and with IL-3 + SF, to moderately increase progenitor production in liquid cultures. Similarly, survival and generation of the primitive CAFC-28/35 was consistently increased when IL-12 was used in combination with IL-3, or IL-3 + SF. The combination of 3, SF and 12 supported a significantly higher recovery of CAFC-35 than did the combination of 3, SF and 11, and CAFC-35 were numerically expanded during culture. Furthermore, IL-12 acted synergistically with IL-3 to enhance CFU-C output over a prolonged period using progenitor-depleted 3-day post-FU BM. These data show that IL-12 interacts with IL-3 and SF to regulate survival and growth of myeloid stem cells and progenitor cells.