Transplantation of iPSC NSCs within the neonatal

Transplantation of iPSC-NSCs within the neonatal cyclooxygenase pathway yielded stable engraftment across the neuroaxis for at least 4 months, but only within and adjacent to white matter tracts. Although the precise mechanisms are unclear, NSCs from various sources display a tropism for white matter in both normal and pathological contexts (Carney and Shah, 2011; Gupta et al., 2012; Maciaczyk et al., 2009; Tabar et al., 2005). The affinity for white-matter tracts may be useful for treating leukodystrophies or as a pathway for NSC dissemination. The limited migration of transplanted NSCs within gray matter may be a barrier to widespread delivery for some diseases with global CNS pathology; however, axonal transport can facilitate wider distribution of lysosomal proteins within this group of diseases (Passini et al., 2002). We transplanted iPSC-NSCs into neonatal mice in order to evaluate their behavior in a more appropriate developmental context. Many cues required for the survival and migration of NSCs are present in neonates, but not in healthy adults (Guzman et al., 2007). We found that iPSC-NSCs engraft widely, but sparsely, which is consistent with neonatal transplants of primary mouse NSCs (Chaubey and Wolfe, 2013). Following transplantation directly into gray matter (adult striatum), the iPSC-NSCs remain localized to the injection tract. As a consequence, microglial pathology was corrected in a zone surrounding the graft, corresponding to the distribution of enzyme in three dimensions in the brain parenchyma (Taylor and Wolfe, 1997). Thus, substantial improvements to increase the distribution of donor cells within the brain will be needed to deliver the therapeutic enzyme to more areas of the brain to advance clinically relevant NSC therapy further for LSDs. The engrafted iPSC-NSCs showed very little evidence of differentiation, even 4-months post-transplant. The absence of mature neurons and glia following neonatal and adult transplantation stands in contrast to the proficiency with which iPSC-NSCs are able to undergo terminal differentiation in vitro. This result underscores the need for a better understanding of the factors governing NSC differentiation. However, for use in correcting most LSDs, the differentiation status is not critical, provided that engrafted cells do not cause deleterious effects in the brain. Undifferentiated cells may in fact be advantageous, as inappropriate neurotransmitter release from mature engrafted neurons can be harmful in some settings. One example of this is the graft-induced dyskinesias resulting from cell replacement therapy for Parkinson’s disease (Lane et al., 2010). Gene- and cell-based therapies that successfully deliver lysosomal enzymes in the brain reduce pathology in many animal models of LSD (Simonato et al., 2013). To test whether genetically corrected patient iPSC-NSCs could deliver corrective levels of GUSB, we evaluated pathology in the striatum surrounding engrafted cells in adult MPS VII brains. We assayed disease-associated neuroinflammation as a biomarker, using CD68-positive activated microglia. A microglial contribution to MPS VII pathology was previously shown via microarray analysis of normal and diseased brains (Parente et al., 2012). Microglia involvement has been well documented in some, but not all, storage diseases, including MPS IIIb and Sandhoff disease (Ohmi et al., 2003; Wada et al., 2000), and activated CD68-positive microglia have been used as a biomarker for correction of pathology (Lee et al., 2007). We show here that microglia are a significant and early component of MPS VII neuropathology. The CD68-positive microglia are particularly useful as a quantifiable biomarker of MPS VII neuropathology because of their distended size, spherical morphology, and uniform distribution.
Experimental Procedures
Author Contributions
Acknowledgments
Introduction