The proposed mechanism of action of iPTH treatment on hematopoietic stem/progenitor cells (HSPCs). Previous studies have suggested that parathyroid hormone (PTH) acts directly on the osteoblasts to mediate the expansion of the HSPC pool (previous model). The study demonstrates that PTH acts to stimulate T cells, which release Wnt10b, which then acts on the osteoblasts and HSPCs (current model).