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Summary. Thrombocytopenia is typically observed in patients undergoing cord blood transplantation. We hypothesized that delayed recovery of the platelet count might be caused by defects in the megakaryocytic differentiation pathway of cord blood progenitors. To test this hypothesis, we compared the features of in vitro megakaryocytopoiesis between cord blood progenitors and those in bone marrow cells after isolation of CD34 cells as progenitors. The proliferative responses of the progenitors in cord blood are higher than those in bone marrow cells in the presence of interleukin (IL)-3, stem cell factor (SCF) and thrombopoietin (TPO). However, the ability to generate mature megakaryocytes was higher in bone marrow progenitors than in cord blood in the same in vitro culture system, when examined by the expression of CD41, polyploidy and proplatelet formation. Furthermore, an earlier induction of c-mpl protein, a receptor for TPO, was observed in the progenitors from bone marrow than in those from cord blood in the presence of SCF and IL-3. Therefore, the ability to generate mature megakaryocytes in bone marrow progenitors is superior to that in cord blood, and the delayed engraftment of platelets after cord blood transplantation might be attributed to the features of cord blood megakaryocyte progenitors.

A new indolocarbazole compound, ED‐110, which was obtained by glucosylating a microbial product (BE‐13793C) and is a potent topoisomerase I inhibitor, showed characteristic inhibitory effects on the growth of 12 human tumor cell lines tested. The IC50 values of ED‐110 against 9 of the 12 lines ranged from 11.5 μg/ml to 0.07 μg/ml, while the remaining 3 lines were quite resistant (IC50, >100μg/ml). In in vivo experiments, i.p. treatment with ED‐110 increased the survival period by more than two‐fold in mice implanted i.p. with P388, L1210, L5178Y or EL4 murine leukemic cells. The minimum effective dose increasing the life‐span of mice bearing P388 leukemia by 25% was <2.5 mg/kg/day × 10 and the maximum tolerated dose was > 160 mg/kg/day × 10. ED‐110 was also effective against the spontaneous metastasis of mouse Meth A fibrosarcoma cells and the growth of xenografted MKN‐ 45 human stomach cancer cells as well as s.c. implanted mouse colon 26 and IMC carcinoma cells. These results indicated that ED‐110 may have potential as a new antineoplastic agent with a large chemotherapeutic index and a wide range of effective doses.

In this study, we report that W/W mutant mice, which have severe macrocytic anemia caused by a deficit of extracellular domain in c-kit molecules and therefore die perinatally, have hemopoietic stem cells (HSCs) and mature hematolymphoid cells in the bone marrow (BM), thymus, and spleen, although there are significant decreases in cell counts. Moreover, the mitogen-induced proliferative response, mixed lymphocyte reaction, and anti-SRBC plaque formation of spleen cells in W/W mice are similar to those in age-matched +/? littermates and normal mice, suggesting that the SCF/c-kit system is necessary for cell proliferation but not essential for HSCs to differentiate.We next examine the stimulatory effects of hepatocyte growth factor (HGF) on hemopoiesis in W/W mice. HGF has a stimulatory effect on the colony formation These results suggest that the SCF/c-kit system is not essential to hemopoiesis but that a compensatory system such as the HGF/c-met system functions in the SCF/c-kit system-deficient mice.