Megakaryocyte colony stimulating activity in allogenic bone marrow recipients prepared with busulfan and cyclophosphamide.

Increased megakaryocyte colony stimulating activity (MK-CSA) has been reported after total body irradiation (TBI) for bone marrow transplant (BMT). We studied the effect of a busulfan (Bu) and cyclophosphamide (Cy) marrow transplant conditioning regimen, without radiation, on MK-CSA production. Initial screening of MK-CSA was done on previously collected and banked sera from 14 BMT patients. MK-CSA was expressed as the ability to stimulate growth of megakaryocyte progenitors (CFU-MK) in standard plasma clot cultures. In the initial samples, MK-CSA peaked at day 7. This preliminary data led to a prospective study of MK-CSA and clinical parameters in seven allogeneic recipients. MK-CSA activity increased from day -7 pre-transplant (2.9 +/- 1.7 CFU-MK/10(5) NATD, mean +/- SD) to day 0 (10.3 +/- 4.7 CFU-MK) and peaked by day 9 post-transplant (20.6 +/- 6.4 CFU-MK). MK-CSA activity decreased in all seven patients by day 21 at which time five of seven patients studied had recovery of platelet counts to greater than 100 x 10(9)/l. MK-CSA activity rose rapidly in both groups of sera after the initiation of this non-irradiation, BMT preparative regimen. High MK-CSA levels, early after transplant, may contribute to the rapid platelet recovery in some patients.