The Car Knockout mouse was developed by Taconic in collaboration with CXR Biosciences. It was generated by crossing a CAR humanized mouse line (Model 9101) with a PhiC31 deleter mouse. The Humanized CAR Mouse model was created through a knock in of a human CAR construct containing the genomic sequence from the translational start site on exon 2 to exon 9 onto the ATG of murine Car in C57BL/6NTac-derived ES cells. Targeted ES cells were injected into BALB/cJBomTac blastocysts and the resultant chimeras were backcrossed to a Flpe deleter strain on C57BL/6J to eliminate selection markers. The Car Knockout Mouse model was derived from the Humanized CAR Mouse line through a PhiC31-mediated deletion of the human CAR sequence. This deletes all exons coding for functional domains of CAR (exons 3-9). The absence of CAR protein was proven experimentally. Taconic received stock in 2009, and the line was embryo transfer derived. The colony was maintained by mating homozygotes.