Leukemia inhibitory factor induces in vivo expansion of bone marrow progenitor cells that accelerate hematopoietic reconstitution but do not enhance radioprotection in lethally irradiated mice.

Leukemia inhibitory factor (LIF) is a pleiotropic cytokine with distinct hematopoietic activities. In vivo treatment of mice with recombinant murine LIF induces thrombocytosis and increases the number of hematopoietic progenitor cells (HPCs) in spleen and bone marrow (BM). In this study, we applied LIF to expand HPCs in vivo prior to syngeneic BM transplantation. BALB/c donor mice were treated with recombinant human LIF at a dose of 2.5 microg/day s.c. for seven days. This resulted in a 1.6-fold increment in platelet counts from 941 to 1,470 x 10(9)/l (mean, n = 20). Mean spleen weight increased from 120 mg to 160 mg (n = 5). The total numbers of HPCs in the spleen as well as in the BM, as assessed in a CFU-GM (colony forming unit-granulocyte-macrophage) assay, were significantly higher in LIF-treated donors than in saline-treated controls (30.1 +/- 14.5 versus 7.4 +/- 5.3 x 10(3) per spleen; mean +/- SD, n = 22,p < 0.001 and 74.4 +/- 17.1 versus 55.3 +/- 16.1 x 10(3) per femur, p < 0.001). Recipient mice were lethally (8.5 Gy) irradiated and transplanted with 3 x 10(5) BM cells derived from LIF- or saline-treated donors. Hematopoietic reconstitution was monitored by tail bleeding at three-day intervals. Platelet and WBC nadir counts in control animals were reached at day 9 (31 +/- 25 x 10(9)/l for platelets and 0.40 +/- 0.10 x 10(9)/l for WBC; mean +/- SD, n = 29 per treatment group); in animals transplanted with LIF-treated BM cells, these counts were 44 +/- 25 x 10(9)/l for platelets, p < 0.05 and 0.60 +/- 0.38 x 10(9)/l for WBC, p < 0.01. In addition, platelet reconstitution was faster in recipients of LIF-treated BM cells (226 +/- 118 versus 126 +/- 62 x 10(9)/l at day 12 and 633 +/- 174 versus 434 +/- 180 x 10(9)/l at day 15, p < 0.001). Similarly, the reconstitution of WBC was also significantly enhanced. The radioprotection rate of lethally irradiated recipients with increasing cell doses of BM cells derived from LIF-treated donors was higher at all cell doses tested then of control animals, but did not reach statistical significance. These results show that in vivo treatment with LIF expands the number of committed progenitor cells and BM repopulating cells that accelerate short-term hematopoietic reconstitution without increasing radioprotection. Our data do not support a major role for LIF as a single factor inducing expansion of hematopoietic stem cells in vivo.