mouse strain NOD.Cg-Rag1{tm1Mom}Prf1{tm1Sdz}/SzJ mouse strain A mouse strain in which the targeted gene, Perforin 1 (Pore forming protein) (NCBI Gene ID: 18646), has been modified (allele type: Global Null) to (MGI ID: ). Mice that are homozygous for both targeted mutations are viable, fertile, normal in size and do not display any gross physical or behavioral abnormalities when housed under specific pathogen free conditions. These double homozygote mutant mice have no mature T or B lymphocytes, no detectable NK cell cytotoxic activity, and lack serum immunoglobulin. The number of nucleated spleen cells is significantly reduced in double mutant mice, when compared to the single homozygote, NOD.129S7(B6)-Rag1tm1Mom/J (Stock No. 003729). Although an increased number of DX5+CD122+ NK cells are found in the spleens of double mutants, these NK cells have impaired cytotoxic activity. The disruption of Prf1 ablates NK cell cytotoxic activity resulting in increased engraftment levels over that observed with Stock No. 003729. All mutant mice develop thymic lymphomas. This double mutant mouse strain may be useful in studies involving engraftment of human hematolymphoid cells. NOD.Cg-Rag1{tm1Mom}Prf1{tm1Sdz}/SzJ Person: Mark A. Magnuson, Jill Lindner, Jean-Philippe Cartailler Vanderbilt University Medical Center