Conditional Pdcd1fl/fl;Mb1-Cre;Pax5+/− mice were generated, where Pdcd1 is deleted upon B-lineage commitment at the pro-B-cell stage, and we examined whether Pdcd1fl/fl;Mb1-Cre;Pax5+/− animals were prone to infection-induced B-ALL. This evidence concerns the gene PAX5 and precursor B-cell acute lymphoblastic leukemia.