Human pluripotent stem cell-derived macrophages modify development of human kidney organoids: a preliminary study.

Introduction. Human fetal kidneys contain macrophages, innate immune cells postulated to enhance their development. Macrophages have also been implicated in the pathobiology of human kidney malformations and Wilms tumour. Human pluripotent stem cell (hPSC)-derived kidney organoids contain nephrons but lack macrophages.
Methods. We hypothesised that combining hPSC-derived macrophages with hPSC-derived kidney precursors would modify nephrogenesis. Macrophages were added in numbers of 1%, 5% or 20% relative to a constant number of nephrogenic cells.
Results. As assessed by CD68 immunostaining, no macrophages were detected in organoids derived from MAN13 hPSCs without added hPSC-derived macrophages. Composite organoids contained macrophages between tubules, mimicking native human fetal kidneys. Quantification of macrophages in histology sections positively correlated with numbers of macrophages added. Assessed by CD31/PECAM-1 and CD68 co-immunostaining, macrophages were scattered through organoids, with some near endothelia. Added macrophages, however, did not alter the extent of CD31/PECAM-1 immunostaining. Macrophages added at 5% were associated with increases in the percentage cross-sectional areas occupied by immunostaining for the glomerular markers synaptopodin and nephrin. Higher numbers (20%) of macrophages disrupted organoid growth.
Conclusion. This preliminary study demonstrates that it is technically feasible to populate hPSC derived-nephron organoids with hPSC- derived maturing macrophages. The study also suggests that, depending on their quantity, added macrophages may have beneficial or harmful effects on nephron organoids. These insights support the proposition that macrophages play roles in normal and abnormal development of human kidneys. Further studies are needed to discover the molecular mechanisms of these effects and to replicate findings using other hPSC lines.