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

Summary 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/105 NATD, mean ± SD) to day O (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 ± 109/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.