The recent molecular cloning of the complementary DNA encoding T cell--replacing factor (TRF) has demonstrated that a single molecule is responsible for B cell growth factor II (BCGF-II) activity and eosinophil differentiation activity. It has been proposed that this molecule be called interleukin 5 (IL-5). We previously reported that purified rIL-5 supports the terminal differentiation and proliferation of eosinophilic precursors. In this study, we examined the effects of IL-5 on functional activities of mature eosinophils. IL-5 maintained the viability of mature eosinophils obtained from peritoneal exudate cells of mice infected with parasites. It also induced superoxide anion production in a dose-dependent manner. The Boyden's chamber Millipore assay revealed that IL-5 had a marked chemokinetic effect on eosinophils in a dose-dependent manner. Moreover, IL-5 was found to be an eosinophil chemotactic factor by the checkerboard assay. In conclusion, IL-5 is suggested to play an important role in increasing the functional activities of eosinophils as well as their production in allergic and parasitic diseases.

Using a clonal culture system, we investigated the hemopoietic effects of purified recombinant IL-5 obtained from conditioned media of transfected Xenopus oocytes. IL-5 alone acted on untreated bone marrow cells and supported the formation of a small number of colonies, all of which were predominantly eosinophilic. However, it did not support colony formation by spleen cells from 5-FU-treated mice, in which only primitive stem cells had survived, while IL-3 and G-CSF did. Eosinophil-containing colonies were formed from these cells in the presence of IL-5 and G-CSF together. In contrast, G-CSF alone did not support any eosinophil colonies. The eosinophilopoietic effect of IL-5 was dose-dependent, and was neutralized specifically by anti-IL-5 antibody. To exclude the possibility of interactions with accessory cells in the same culture dish, we replated a small number (200 cells/dish) of enriched hemopoietic progenitors, obtained from blast cell colonies, which were formed by cultivation of spleen cells from 5-FU-treated mice in the presence of IL-3 or G-CSF. From these replated blast cells, eosinophil colonies were induced in dishes containing IL-5 but not in those containing G-CSF alone. From these findings, it was concluded that IL-5 did not act on primitive hemopoietic cells, but on blast cells induced by IL-3 or G-CSF. IL-5 specifically facilitated the terminal differentiation and proliferation of eosinophils. In this respect, the role of IL-5 in eosinophilopoiesis seems to be analogous to erythropoietin, which promotes the terminal differentiation and amplification of erythroid cells. Moreover, IL-5 maintained the viability of mature eosinophils obtained from peritoneal exudate cells of the mice infected with parasites, indicating mature functional eosinophils carried IL-5 receptors. The synergistic effects of IL-5 and colony-stimulating factors on the expansion of eosinophils is supposed to contribute to the urgent mobilization of eosinophils at the time of helminthic infections and allergic responses.

c-kit is expressed on hematopoietic stem cells and progenitor cells, but not on lymphohematopoietic differentiated cells. Lineage marker- negative, c-kit-positive (Lin-c-kit+) bone marrow cells were fractionated by means of Ly6A/E or Sca-1 expression. Lin-c-kit+Sca-1+ cells, which consisted of 0.08% of bone marrow nucleated cells, did not contain day-8 colony-forming units-spleen (CFU-S), but 80% were day-12 CFU-S. One hundred cells rescued the lethally irradiated mice and reconstituted hematopoiesis. On the other hand, 2 x 10(3) of Lin-c- kit+Sca-1- cells formed 20 day-8 and 11 day-12 spleen colonies, but they could not rescue the lethally irradiated mice. These data indicate that Lin-c-kit+Sca-1+ cells are primitive hematopoietic stem cells and that Sca-1-cells do not contain stem cells that reconstitute hematopoiesis. Lin-c-kit+Sca-1+ cells formed no colonies in the presence of stem cell factor (SCF) or interleukin-6 (IL-6), and only 10% of them formed colonies in the presence of IL-3. However, approximately 50% of them formed large colonies in the presence of IL-3, IL-6, and SCF. Moreover, when single cells were deposited into culture medium by fluorescence-activated cell sorter clone sorting system, 40% of them proliferated on a stromal cell line (PA-6) and proliferated for more than 2 weeks. In contrast, 15% of the Lin-c- kit+Sca-1-cells formed colonies in the presence of IL-3, but no synergistic effects were observed in combination with SCF plus IL-6 and/or IL-3. Approximately 10% proliferated on PA-6, but most of them degenerated within 2 weeks. The population ratio of c-kit+Sca-1+ to c-kit+Sca-1- increased 2 and 4 days after exposure to 5-fluorouracil (5-FU). These results are consistent with the relative enrichment of highly proliferative colony-forming cells by 5-FU. These data show that, although c-kit is found both on the primitive hematopoietic stem cells and progenitors, Sca-1+ cells are more primitive and respond better than Sca-1- cells to a combination of hematopoietic factors, including SCF and stromal cells.

CPT-11, 7-ethyl-10-[4-(1-piperidino)-1-piperidino]carbonyloxy camptothecin, is a newly developed water-soluble camptothecin derivative now undergoing phase-II evaluation. In an attempt to establish whether the combination of CPT-11 with other standard anti-cancer agents would be of any benefit, we studied the effects of CPT-11 in combination with 11 other anti-cancer agents on a human T-cell leukemia cell line, MOLT-3, in culture. We used both CPT-11 and SN-38 (active substance of CPT-11 in vivo), for our study. Cells were incubated for 3 days in the presence of 2 drugs (CPT-11 or SN-38 and another drug) and cytotoxic effects were determined by MTT assay. The effects of drug combinations on ID50 were analyzed by an improved isobologram method. Supra-additive and marginal supra-additive effects (synergism) were observed for CPT-11 in combination with cisplatin, cytosine arabinoside and mitomycin C. Additive effects were observed for its combination with amsacrine, bleomycin, doxorubicin, etoposide, 5-fluorouracil, mitoxantrone and vincristine. Alternate sub-additive and protective effects (antagonism) were observed for CPT-11 in combination with methotrexate. Similar tendencies were observed for SN-38 in combination with other agents. These results suggest that CPT-11 in simultaneous administration with a majority of anti-cancer agents has an advantage for cytokilling. Of these agents, cisplatin, cytosine arabinoside and mitomycin C are most suitable for simultaneous administration with CPT-11.

The proto-oncogene c-kit encodes a transmembrane tyrosine kinase receptor for stem cell factor (SCF). The c-kit/SCF signal is expected to have an important role in hematopoiesis. A monoclonal antibody (ACK- 2) against the murine c-kit molecule was prepared. Flow cytometric analysis showed that the bone marrow cells that expressed the c-kit molecule (approximately 5%) were B220(B)-, TER119(erythroid)-, Thy1negative-low, and WGA+. A small number of Mac-1(macrophage)+ or Gr- 1(granulocyte)+ cells were c-kit-low positive. Colony-forming unit in culture (CFU-C) and day-8 and day-12 CFU-spleen (CFU-S) existed exclusively in the c-kit-positive fraction. About 20% of the Lin(lineage)-c-kit+ cells were rhodamine-123low and this fraction contained more day-12 CFU-S than day-8 CFU-S. On the basis of these findings, murine hematopoietic stem cells were enriched with normal bone marrow cells. One of two and one of four Thy-1lowLin-WGA+c-kit+ cells were CFU-C and CFU-S, respectively. Long-term repopulating ability was investigated using B6/Ly5 congenic mice. Eight and 25 weeks after transplantation of Lin-c-kit+ cells, donor-derived cells were found in the bone marrow, spleen, thymus, and peripheral blood. In peripheral blood, T cells, B cells, and granulocyte-macrophages were derived from donor cells. Injection of ACK-2 into the irradiated mice after bone marrow transplantation decreased the numbers of day-8 and day-12 CFU-S in a dose-dependent manner. Day-8 spleen colony formation was completely suppressed by the injection of 100 micrograms ACK-2, but a small number of day-12 colonies were spared. Our data show that the c- kit molecule is expressed in primitive stem cells and plays an essential role in the early stages of hematopoiesis.