Characterization of hematopoietic stem cell-derived microglia-like cells in nonhuman primates

Hematopoietic stem cell transplantation (HSCT) is the current standard of care for a number of neurotrophic lysosomal storage disorders. The therapeutic mechanism of HSCT is believed to be mediated by engraftment of HSC progeny to the brain as microglia-like cells (MLCs). However, the engraftment of MLCs and their transcriptomic identity relative to endogenous microglia is poorly understood. Here, we utilize the autologous nonhuman primate (NHP) HSCT model to investigate the engraftment of MLCs after gene-modified autologous HSCT. We observed engraftment of gene-marked MLCs across a cohort of five NHPs. MLCs engrafted through diverse brain regions; adopted a homeostatic, ramified morphology, and upregulated core microglial transcripts. We then utilized single cell RNA sequencing to more rigorously evaluate the transcriptome of MLCs, revealing a border-associated macrophage-like phenotype. Our findings offer critical insights into the engraftment and behavior of MLCs post-HSCT, laying the groundwork for their future utilization as a directed therapeutic.