AP3B1 and neutropenia: Although HPS2 iPSC neutrophils phenocopied circulating HPS2 neutrophils with an altered granule compartment (6), the HPS2 iPSC cultures show limited outgrowth of macrophages and unexpected uptake of CD15+ myeloid cells, and, taken together with the reduced myeloid commitment, could well explain the observed neutropenia in HPS2.