Production of cIap1ΔB, cIap2^−/− and cIap1ΔB.cIap2^−/− mice. (A) The wild-type cIap locus was sequentially targeted in ES cells by first introducing FRT sites into cIap2, followed by loxP sites into cIap1. Mice carrying the doubly targeted cIap locus were generated from a single ES cell clone. This approach facilitated independent inactivation of cIap2 and/or cIap1 by Flp- and Cre-mediated recombination, respectively. (B) Breeding strategy used to generate mice containing B cells lacking expression of cIAP1 and/or cIAP2.