The Mouse Genetics Engineering Center (Centre d’Ingénierie Génétique Murine, CIGM) is the Institut Pasteur’s transgenic mouse core facility. Since its creation in 2003, the CIGM aims to generate new models of transgenic mice by classical or targeted transgenesis. Classical (additive) transgenesis, which includes lentiviral transgenesis, is based on a random insertion of an exogenous gene. Targeted transgenesis consists in a deletion or a specific modification in an endogenous locus using homologous recombination in Embryonic Stem (ES) cells or, more recently, by directly using specific nucleases.