We used the molecular signature specific of microglia, which is distinct from other macrophages 11,29,31, to compare the transcriptome of pMGLs with bona fide primary human microglia. Isolated human fetal microglia and pMGLs were grown in the same maintenance medium for a week (MGM). This comparison is relevant since pMGLs are directly isolated from differentiating pluripotent stem cell cultures and grown in serum-free neuroglial-compatible conditions. We found that pMGLs display a signature strikingly resembling that of fetal human microglia kept in the same conditions. Supplementary Table 3 shows that the top GO categories coincide between both cell types. pMGLs differ in the enrichment of gene categories related to the establishment and modulation of the extracellular matrix (ECM, Suppl. Tables 4 and 5). The differentially expressed genes between primary cells and in vitro derived pMGLs did not include any of the canonical myeloid ontology terms, supporting their use as surrogate for human microglia. Several individual genes were highly expressed in primary human fetal microglia and pMGLs, consistent with their identity (Suppl. Fig. 2a). Among those genes were CD11b (ITGAM), ITGB2, CSF1R,
