Our study is one of the first to describe a fully-defined, serum-free protocol for generating microglial cells from induced pluripotent stem cells with the exception of a recently published resource from Muffat and colleagues (Muffat et al., 2016). However, their approach uses hematopoietic cells derived from embryoid bodies (EB) as microglia precursors. One challenge with the use of an EB-based method and selection by cell adhesion (Muffat et al protocol) is the potential contamination by other cell types that spontaneously arise from EBs i.e. neuroectoderm including astrocytes. More recently, a protocol described the production of microglia-like cells reliant on astrocyte co-cultures and a serum-based media formulation. This protocol produces cell quantities comparable to Muffat et al., that exhibit amoeboid-like morphology in vitro and in vivo (Pandya et al., 2017). Thus, some questions remain in terms of yield, scalability, and purity of homeostatic microglia using these other methods and whether the resulting cells can be used to interrogate microglial function in quantitative assays that require large numbers of pure microglia-like cells.
