Bone marrow cells from 62 children with acute leukemia were cultured by the double-layer agar technique. In this system, granulocytic progenitor cells will form colonies (colony forming units or CFU) of mature granulocytes in t h e overlayer when stimulated by factors (colony stimulating activity or CSA) produced by peripheral blood cells of normal individuals in the underlayer. I t was observed that marrow cell cultures from children with acute lymphoblastic leukemia (ALL) i n relapse had substantially decreased numbers of CFU when compared to normal marrow cells. Marrow cell cultures from three children with acute myelogenous leukemia (AML) had normal numbers of CFU a t the time of diagnosis. After inducing a remission with chemotherapy in children with ALL, a n increase in the number of CFU in their marrow cultures was observed. When peripheral blood cells from children with acute leukemia in relapse were used i n the underlayer they did not adequately support the growth of normal CFU. It may be concluded that the defect in granulopoiesis observed i n ALL may be due to a decrease i n CFU as well as decreased production of CSA by their marrow cells.
T H A S BEEN DEMONSTRATED THAT CELLS DE-
I rived from mouse bone marrow will form colonies when cultured in a semisolid medium.2J8 Each colony is believed to arise from the proliferation of a committed granulocytic progenitor cell (colony forming unit or CFU) which is the progeny of a pluripotential hemopoietic stem ce11.28 Certain factors (colony stimulating activity or CSA) are required for sustaining the proliferation of these cells. These factors may be derived from cell feeder layers,2J8 "conditioned medium" from cell cultures,3~5J9 human and animal serum, and urine.s, [20][21][22]26 This culture system has recently been modi-