A two-step fully-defined protocol was developed to efficiently generate microglia-like cells (iMGLs) from iPSCs in just over five weeks (Figure 1A). This approach was used to successfully produce iMGLs from 10 independent iPSC lines (Figure S1A–C). A critical prerequisite is the robust differentiation of iPSCs to hematopoietic progenitors (iHPCs). This recapitulates microglia ontogeny as iHPCs represent early primitive hematopoietic cells derived from the yolk sac that give rise to microglia during development (Ginhoux et al., 2010; Kierdorf et al., 2013). Our protocol (depicted in Figure 1Bi) yields primitive iHPCs that are CD43+/CD235a+/CD41+ after 10 days (Kennedy et al., 2007; Sturgeon et al., 2014). FACS sorting for CD43+ cells reveal that our approach produces iHPCs with a >90% purity (Figure 1Bii). The resulting iHPCs resembled a commercial source (Cellular Dynamics International) and represent the hematopoietic progenitor used to generate iMGLs.
