ACCELERATED RECONSTITUTION OF PLATELETS AND ERYTHROCYTES AFTER SYNGENEIC TRANSPLANTATION OF BONE-MARROW CELLS DERIVED FROM THROMBOPOIETIN PRETREATED DONOR MICE

The recent cloning of the ligand of the c-Mpl hematopoietin receptor h as indicated a major role for this cytokine in the development of mega karyocytes. In this study we have applied c-Mpl ligand (thrombopoietin [TPO]) in the setting of syngeneic transplantation in an attempt to a ccelerate the reconstitution of platelets. Donor mice were treated wit h 20 kilounits (kU)/d TPO intraperitoneally (ip) for 5 days. This resu lted in a 2.5-fold increment in platelet counts from 1,119 x 10(9)/L t o 2,582 x 10(9)/L (mean, n = 7). Total numbers of hematopoietic progen itor cells in bone marrow (BM) and spleen, as assessed in a colony-for ming unit-granulocyte erythroid monocyte macrophage (CFU-GEMM) colony assay (55.3 v 38.6 x 10(3) CFU/femur; 27.3 v 16.3 x 10(3) CFU/spleen, mean, n = 7) as well as total numbers of burst-forming unit-erythroid (BFU-E) (24.0 v 16.4 x 10(3)/femur; 10.2 v 1.9 x 10(3)/spleen, mean, n = 7), were significantly higher in TPO-treated donors than in saline- treated controls. Female Balb-C mice were lethally (8.5 Gy) irradiated and transplantated with 10(5) BM cells. After transplantation, groups of mice were treated with recombinant murine TPO at a dose of 20 to 3 0 kU/d ip or subcutaneously (SC) for 5 to 14 days. Using this dose and schedule, TPO did not stimulate the recovery of platelets in comparis on with control animals transplanted with equal cell numbers but given vehicle alone. In other experiments, 10(5) BM cells were procured fro m TPO-treated donor mice and transplanted into lethally irradiated rec ipient mice. In comparison with animals transplanted with an equal num ber of BM cells derived from saline-treated controls, recipients of TP O-treated BM cells had significantly faster platelet recovery and high er platelet nadir counts (88 v 30 x 10(9)/L, mean, n = 20). Transplant ation of TPO-treated BM cells also resulted in an accelerated recovery of erythrocytes and increased erythrocyte nadir counts (7.2 v 5.0 x 1 0(12)/L, mean, n = 20), At the day of platelet nadir (day 12 after tra nsplantation) these animals had higher numbers of BFU-Es (770 v 422, m ean, n = 5) in the marrow and also had higher reticulocyte counts (44 parts per thousand v 8 parts per thousand, mean, n = 5) in the blood. Therefore, the accelerated recovery of erythrocytes may be a direct ef fect of TPO on erythropoiesis. Our results indicate that pretreatment of donor animals with TPO before marrow procurement may be an effectiv e alternative method to accelerate the reconstitution of platelets and erythrocytes after lethal irradiation and syngeneic stem cell transpl antation. (C) 1995 by The American Society of Hematology.