In this study, we used human HPS2 iPSCs instead of the non-informative animal models, as a model system to study neutrophil development in this very rare congenital neutropenia disorder (3, 5, 13, 14, 15) The neutropenia in HPS2 seems to be a consequence of both a reduced rate of myeloid differentiation and macrophage-mediated phagocytosis. Here, AP3B1 is linked to neutropenia.