We observed that B-ALL development was significantly increased in Pax5+/−;Myd88+/− mice, where 64% (16 out of 25) developed B-ALL (Fig. 3b), closely resembling the penetrance of B-ALL development in Pax5+/−animals treated with antibiotics13. This evidence concerns the gene MYD88 and precursor B-cell acute lymphoblastic leukemia.