Other canonical microglial genes expressed by the STR‐M progenitor cell compartment include CD33, GPR56, CABLES1, BHLHE41, TMEM119, TGFBR1, ENTPD1, ITGB2, ITGAM, AIF, IRF8, ADORA3, and PPARD. 30, 31, 33, 34, 35We also detected expression of TREM2 and CD33, which are involved in neurodegenerative diseases like Alzheimer's disease and are only expressed by resident microglia.4 Here, TGFBR1 is linked to early-onset autosomal dominant Alzheimer disease.