High-dose cyclophosphamide followed by GM-CSF is a safe and effective procedure for the recruitment of trilineage circulating progenitor cells.

Background: Several methods for the recruitment of circulating progenitor cells (CPC) to be used for hemopoietic rescue after myeloablative therapy have been described. The present study was designed to verify the effectiveness and safeness of one of such procedures, involving the administration of high-dose cyclophosphamide (HD-CTX) and granulocyte-macrophage colony-stimulating factor (GM-CSF).

Methods: Eight tumor patients were treated with HD-CTX (7 g/m2), followed by GM-CSF (7 mcg/Kg/day, continuous infusion) from day +2 to the completion of leukocyte recovery, when aphereses for CPC harvesting were performed. CPC were evaluated by clonogenic assay for granulocyte-macrophage colony-forming units (CFU-GM), megakaryocyte colony-forming units (CFU-Meg) and erythrocyte burst-forming units (BFU-E) before therapy as well as during the hemopoietic recovery.

Results: In each patient, a significant increase of trilineage CPC was observed, at a mean of 14 days from HD-CTX, with peak increment of 224, 268 and 230-fold for CFU-GM, CFU-Meg and BFU-E respectively. The mean duration of leukocyte count < or = 0.5 x 10(9)/l was 6.6 days, with severe thrombocytopenia (grade 4 WHO) lasting 2.8 days in 5 patients. GM-CSF infusion was well tolerated without any need for dose reduction or discontinuation.

Conclusion: The administration of HD-CTX and GM-CSF induces a significant enhancement of CPC including CFU-Meg other than CFU-GM and BFU-E. The procedure is suitable for the recruitment of CPC in patients with CTX sensitive tumors.