The Humanized Mouse Core provides breeding and maintenance of NSG (NOD.Cg-Prkdcscid Il2rgtm1Wjl/SzJ) mouse colonies, construction of humanized mice, as well as confirmation of reconstitution of human hematopoietic and lymphoid systems by detection of >25% human cells (including T, B, and myeloid cells) in peripheral blood 8-10 weeks post-engraftment.