Adhesion-Dependent Survival of Normal and Leukemic Human B

We investigated the requirement for intimate contact be-tween bone marrow stroma and B lymphoblasts from nor-mal donors and children with leukemia. By scanning &c-trOn microscopy. both normal and leukemic cells seeded onto stroma were surrounded by folds of stromal cells or were linked to the stroma by fine tendrils and uropods. Sep-aration of normal B progenitors from stroma by use of microporous membranes led to significantly lower cell re-coveries compared with results when contact was unim-peded. For instance, 22.5 % 2 1.8 % (mean f SEM) of CD1 9+, CD34+ cells (most immature subset) were recov-ered after a 7-day culture directly on stroma, compared with 5.2 % & 0.7 % after growth on membranes (P <.001 by Student’s t test). In 6 of 11 cases of B-lineage acute HE HOMEOSTATIC CONTROL of human B-lineag