Next, we sought to examine iMGLs within the context of a CNS environment in vivo. To this end, iMGLs (day 38) were transplanted into the cortex of MITRG mice that are Rag2-deficient and IL2rγ-deficient mice and also express the human forms of four cytokines knocked-in (M-CSFh;IL-3/GM-CSFh;TPOh), allowing for xenotransplantation and survival of myeloid and other leukocytes (Rongvaux et al., 2014). Two months after transplantation, the homeostatic state and identity of transplanted microglia were assessed with P2ry12 and the human-specific Tmem119 antibodies, respectively (Bennett et al., 2016; Butovsky et al., 2014; Haynes et al., 2006)(Figure 7). Human specific markers, cytoplasmic ku80 (hNuclei) and SC121 (hCyto) distinguished iMGLs from endogenous microglia. Transplanted human iMGLs co-expressing both ku80 and P2ry12 were abundant within MITRG brains suggesting long-term engraftment potential (Figure 7A–D). At higher magnification, P2ry12 is expressed in highly ramified iMGLs resembling quiescent cortical microglia; the membrane distribution accentuates the finer extended processes (Figure 7B–D)(Baron et al., 2014). Tmem119 and Iba1 were also expressed in both hCyto+ soma and in highly arborized iMGL processes (Figure 7E–L). At higher magnification, Tmem119 is predominately membrane-bound
