Beginning with pioneering studies by Gumpel and Lachapelle, and independently by Blakemore and colleagues, over 25 years ago (Blakemore et al. 1990; Gumpel et al. 1987; Lachapelle et al. 1983), the ability of transplanted oligodendroglia to effect myelin repair has been studied in a number of model systems, using a number of cellular sources (reviewed in (Ben-Hur and Goldman 2008; Franklin and ffrench-Constant 2008)). Efforts focusing on the specific use of glial progenitor cells rather than their derived oligodendrocytes, and emphasizing the use of human GPCs in particular, are more recent(Windrem et al. 2004; Windrem et al. 2002; Windrem et al. 2008). These studies have been performed in several models of both congenital and acquired dysmyelination, but we will discuss data obtained in only one of these models - arguably the most informative among them for assessing the myelinogenic competence of candidate GPCs - the shiverer mouse. Shiverer (MBP shi/shi) is a congenitally hypomyelinated mouse deficient in myelin basic protein (Popko et al. 1987; Readhead et al. 1987). Using immunodeficient shiverer mice as hosts (rag2−/− x MBP shi/shi) (Windrem et
