Both granulocyte colony-stimulating factor (G-CSF) and cyclophosphamide (CY) are employed in the clinic as mobilizing agents to stimulate the egress of haematopoietic stem/progenitor cells (HSPC) from bone marrow (BM) into peripheral blood (PB). However, although both compounds are effective, the simultaneous administration of G-CSF + CY allows for optimal mobilization. The aim of this study was to compare morphological changes in major haematopoietic organs in mice mobilized by G-CSF + CY. We employed the standard G-CSF + CY mobilization protocol, in which mice were injected at day 0 with a single dose of CY followed by daily injection of G-CSF for 6 consecutive days. We noticed that the cytoreductive effect of CY on BM and spleen tissue was compensated at day 2 by the pro-proliferative effect of G-CSF. Furthermore, as evidenced by histological examination of BM sections at day 4, egress of haematopoietic cells from BM was accelerated by 2 days as compared to mobilization by G-CSF or CY alone; also, by day 6 there was accumulation of early haematopoietic (Thy-l(low) c-kit+) cells in the spleens and livers of mobilized animals. This implies that HSPC that are mobilized from BM and circulate in PB may 'home' to peripheral organs. We envision that such an accumulation of these cells in the spleen (which is a major haematopoietic organ in mouse) allows them to participate in haematopoietic reconstitution. Their homing to other sites (for example the liver) is evidence that BM-derived stem cells are playing a pivotal role in organ/tissue regeneration. The potential involvement of major chemoattractants for stem cells, like stromal-derived factor-1 which is induced by CY in various regenerating organs such as the liver, requires further study. We conclude that inclusion of CY into mobilization protocols on the one hand efficiently increases the egress of HSPC from the BM, but on the other hand may lead to the relocation of BM stem cell pools to peripheral tissues.
Cyclophosphamide (CY), the agent with cytoreductive activity, is widely exploited in cancer chemotherapy, and can be used alone or in combination with various cytokines and growth factors to stimulate the egress of hematopoietic stem/progenitor cells (HSPC) from the BM compartment. The aim of the present study was to exam the morphology and ultrastructure of the bone marrow, spleen and liver of mice injected intraperitoneally with a single dose of cyclophosphamide (200 mg/kg bw) and the localization of cells expressing markers of early hematopoietic cells in studied organs and the peripheral blood. We observed that the CY-induced morphological changes in the BM and spleen were reconstructed on day 4. of experiment, and the spleen was repopulated by HSPC on the 6 th day. In this time, the highest number of c-Kit-R-positive cells was determined by flow cytometry in the peripheral blood. The results confirmed, that the egress of HSPC from the bone marrow into the peripheral blood was delayed compared to mice treated with G-CSF or GCS-F plus CY.
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