Cd19-iCre mice are generated by knocking the P2A-iCre-CYAGEN cassette into the endogenous Cd19 gene, enabling expression of iCre (a codon-optimized Cre with higher recombination activity) driven by Cd19 gene regulatory elements. When crossed with mice containing loxP sites, their offspring undergo Cre recombinase-mediated recombination between loxP sites specifically in B lymphoid lineage cells.