Activity of the ligand for c‐mpl, thrombopoietin, in early haemopoiesis

Abstract

We examined the role of the ligand for c-mpl. thrombopoietin (TPO). in murine early haemopoiesis. using a serum-free culture system. TPO in combination with the ligand for c-kit (SF) or interleukin-3 (IL-3) supported colony formation by marrow cells of 5-fluorouracil (5-FU)-treated mice whereas TPO alone yielded no colony. When blast cell colonies grown in the presence of TPO plus SF or TPO plus IL-3 were individually replated in suspension cultures containing serum and several growth factors, various combinations of myeloid lineages were seen, indicating that the progenitors supported by TPO plus SF or TPO plus IL-3 are multipotential. Delayed addition experiments demonstrated that TPO has the potential to effectively support the survival of haemopoietic progenitors. We then studied the effects of TPO on proliferative kinetics of cycling progenitors. TPO hastened IL-3-dependent growth of progenitors by shortening the time required for cell cycling. These results suggest that TPO as a single factor, can support the survival of haemopoietic progenitors and TPO synergizes with SF or IL-3 to act on early multipotential haemopoietic progenitors.

Thrombopoietin alone stimulates the early proliferation and survival of human erythroid, myeloid and multipotential progenitors in serum‐free culture

“…Furthermore, the dose-dependent generation of multipotential progenitors by TPO in serum-free suspension culture and the complete inhibition of the generation of these progenitors by an anti-TPO Ab, confirms the notion that TPO alone supports the proliferation of human primitive haemopoietic progenitors. Recently, several investigators (Itoh et al, 1996;Ku et al, 1996;Sitnicka et al, 1996) reported that TPO synergized with early-acting cytokines, including SCF, IL-3, IL-6, IL-11 or G-CSF, to support proliferation of murine primitive haemopoietic progenitors. More recently, Kobayashi et al (1996) showed that TPO acted synergistically with SCF and/or IL-3 on the proliferation of human primitive haemopoietic progenitors using clonal and suspension cultures, whereas they failed to demonstrate the effect of TPO alone on the colony formation by immature progenitors.…”

“…UT-7, Mo-7E, TF-1, HEL and DAMI) and CD34 þ or CD34 þ CD38 ¹ cells (Methia et al, 1993), suggesting that TPO is involved in the development of primitive haemopoietic progenitors. More recently, several investigators have shown that TPO and c-Mpl are involved in proliferation of progenitors for lineages in addition to megakaryocytes in vitro (Carver-Moore et al, 1996), and that TPO has synergistic effects with other cytokines such as EPO, IL-3 or SCF on the proliferation of erythroid and primitive progenitors in murine and human systems in vitro (Kobayashi et al, 1995(Kobayashi et al, , 1996Ku et al, 1996;Itoh et al, 1996). However, information about the roles of TPO alone in human haemopoiesis is still limited.…”

Thrombopoietin has a differentiative effect on late-stage human erythropoiesis

“…TPO alone stimulates the early proliferation and survival of human erythroid, myeloid and multipotential progenitors in serum-free culture. TPO also synergizes with early-acting cytokines including SCF, IL-3, IL-6, IL-11 and G-CSF to support proliferation of murine primitive haemopoietic progenitors (Itoh et al, 1996;Ku et al, 1996;Sitnicka et al, 1996). Transcripts of c-Mpl have been detected by RT-PCR in human pluripotent cell lines, e.g.…”

Apoptosis and megakaryocytic differentiation during ex vivo expansion of human cord blood CD34+ cells using thrombopoietin

“…In vivo administration of TPO to normal mice causes an expansion of granulocyte‐macrophage colony‐forming units (GM‐CFU) and erythroid burst‐forming units (BFU‐E). In addition, several lines of evidence have demonstrated that TPO has an important role in early haematopoiesis (Itoh et al , 1996; Ku et al , 1996; Sitnicka et al , 1996). TPO alone, or in combination with other early acting cytokines such as stem cell factor (SCF), FL or interleukin 3 (IL‐3), supports the proliferation of primitive HPCs in vitro .…”