MCL1 and lymphoma: This may indicate that loss of one Mcl-1 allele at the earlier CLP stage of lymphoid cell development (i.e., when Rag1-Cre but not CD19-Cre is expressed) is more efficient in killing incipient neoplastic cells and therefore more efficient in delaying lymphoma development compared with Mcl-1fl deletion at the later pro-B-cell stage (when CD19-Cre expression commences).