We studied the specific binding of the CD133 antibody clone 293C3 to determine the surface expression of CD133 on the B-ALL cell lines REH, RS4;11, and SEM, primary leukemic cells of 28 patients diagnosed with B-ALL, as well as on PBMCs and bone marrow cells of healthy donors. The gene discussed is PROM1; the disease is acute lymphoblastic leukemia.