Inhibitor of normal granulopoiesis produced by cells of MDS patients.

Low-density blood cells from patients with refractory anemia with excess of blasts (RAEB) and RAEB in transformation (RAEB-T) release a high molecular weight inhibitory substance that reduces the entry of normal progenitor cells of granulocytes and macrophages (CFU-GM) into the S-phase. Out of 20 patients with refractory anemia (RA and RAS) only 3 were positive. One patient with CMML was negative. Serial examination of 3 patients (two RA and one CMML) revealed that the production of the inhibitory activity preceded the development of the disease into RAEB, RAEB-T, or AML. With one exception, the inhibitory activity in positive cases was neutralized by antiserum against human placental ferritin.