Colony formation by transplanted JMML cells. Colony formation by cells from patient bone marrow (nonengrafted), from untreated, transplanted mice, and mice receiving a 4-week treatment with E21R alone and/or MoAb cA2 starting 4 weeks posttransplant (late treatment). Values are the means ± SEM from five mice. # P < .05, ## P < .01, ### P < .001 compared with colony numbers obtained from nonengrafted patient bone marrow cells.