Stem Cell Expansion Ex Vivo

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Yagi and colleagues (95) showed that administration of TPO alone can sustain ex vivo expansion of hematopoietic stem cells in long-term bone marrow cultures (LTBMC) from mice. The continuous presence of TPO resulted in the generation of long- and short-term colony-forming cells and maintained the relative amount of high-proliferative-potential

Platelets x1 (f/L

1.000

Platelets x1 (f/L

1.000

0 3 6 9 12 15 18 21 24 27 Days After Transplantation

Fig. 9. Platelet recovery is improved when mice are transplanted with bone marrow from donor mice treated with thrombopoietin. Mice were transplanted with bone marrow cells from saline-treated or thrombopoietin (TPO)-treated donors. After infusion of marrow, mice were then treated with saline or TPO for 5 d. Marrow from TPO-treated mice produced earlier platelet engraftment than did marrow from untreated animals. The administration of thrombopoietin after marrow infusion was without effect. (Reproduced with permission from ref. 93.)

colony-forming cells (HPP-CFCs). Most importantly, competitive repopulation studies found that the TPO-treated LTBMC cells were as effective as fresh marrow. Subsequent data suggest that the expanded population of stem cells, when transplanted into recipient mice, is adequate for the long-term repopulation.

The thrombocytopenia of three HIV-infected nonhuman primates was rapidly reversed by infusion of PEG-rHuMGDF (Fig. 10) (96). In these animals, the expanded megakaryocyte mass was presumably not producing adequate amounts of platelets owing to premature megakaryocyte apoptosis. Addition of TPO was felt to prevent premature megakaryocyte apoptosis and stimulate effective platelet production.

Approximately 40% of all platelet transfusions are used in surgical settings (97). Preoperative and postoperative thrombocytopenia complicates surgical procedures and mandates platelet transfusions. Although no clinical studies have targeted this important area, one animal model is of interest. The administration of PEG-rHuMGDF to dogs 4 d before surgery decreased thrombocytopenia after cardiopulmonary bypass (98). Despite its 5-d lag time before platelet increase, judicial administration of TPO before surgery may ameliorate preoperative and postoperative thrombocytopenia and reduce the need for platelet transfusions.

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