Induced pluripotent stem cell-derived primitive macrophages as a cellular platform to model tissue-resident macrophage differentiation and function

Specialized tissue macrophages arise during embryogenesis from yolk-sac (YS) progenitors that migrate into developing tissues and terminally differentiate in situ. Until recently, it has been impossible to isolate or derive sufficient numbers of YS-derived macrophages for further study, but data now suggest that induced pluripotent stem cells (iPSCs) can be driven to undergo a process reminiscent of YS-hematopoiesis in vitro. We asked whether iPSC-derived primitive macrophages (iMac) can terminally differentiate into specialized macrophages using growth factors and organ-specific cues. Co-culturing murine iMac with iPSC-derived neurons promoted differentiation into microglia-like cells in vitro. Furthermore, murine iMac differentiated in vivo into microglia following injection into the brain, and functional alveolar macrophages after engraftment in the lung.