In vivo effects of thymustimulin on hematopoiesis of mice treated with cyclophosphamide.

This study reports on the in vivo effects of thymustimulin (TST), a thymic extract, on the hematopoiesis of mice treated with cyclophosphamide (CTX). Peripheral blood counts and both bone marrow pluripotent (spleen colony-forming units, CFU-S) and committed (granulocyte-macrophage colony-forming units, CFU-GM; erythroid burst-forming units, BFU-E) hematopoietic progenitor cells were assayed by in vitro methods. Administration of CTX alone was associated with severe hemotoxicity, which was followed by a gradual recovery of hematopoiesis. Hematotoxic effect of CTX was less pronounced when TST was administered in association with CTX. All the studied parameters were higher in TST + CTX-treated animals than those in CTX-treated animals, especially after Day 5 from the beginning of treatment for blood leukocytes, bone marrow cell counts, and packed red cell volume, and at Day 10 or 15 for CFU-S, CFU-GM, and BFU-E. These findings suggest that, in this experimental model, the simultaneous administration of TST reduces the myelosuppressive activity of CTX in vivo.