Brains were cryopreserved, embedded in OCT (Tissue-Tek OCT, Sakura Finetek, Torrance, CA) and sectioned at 20 μm, either sagittally or coronally, on a cryostat. Human cells were identified with mouse antihuman nuclei, clone 235-1 at 1:800 (MAB1281, EMD Millipore, Billerica, MA). Myelin basic protein was labeled with rat anti-MBP at 1:25 (Ab7349, Abcam, Cambridge, MA), oligodendrocyte progenitors with anti-human-specific PDGFRa (D13C6, XP® rabbit mAb 5241, 1:300, Cell Signaling Tech), oligodendrocytes with mouse anti-human-specific transferrin (clone HT1/13.6.3, 08691231, MP Biomedicals), astrocytes with anti-human-specific GFAP (SMI 21 at 1:1000, Covance, Princeton, NJ). Alexa Fluor secondary antibodies, goat anti- mouse, rat, and rabbit 488, 568, 594, and 647 were used at 1:400 (Life Technologies, Carlsbad, CA).
