Experiments with pre-B cells isolated from the bone marrow of Pecam1−/−, Cd300a−/−, and Lair1fl/fl mice and wild type controls and expanded with IL7 or transformed with BCR-ABL1 to model human Ph+ ALL showed the functional relevance of the above-mentioned inhibitory receptors. The gene discussed is PECAM1; the disease is acute lymphoblastic leukemia.