A 3D hydrogel system for hematopoietic differentiation of iPSCs has provided a tool for hematological disease modeling of Down syndrome-associated transient myeloproliferative disorder (TMD) which is a pre-leukemic stage present in 10–20% of children with trisomy 21 possessing the mutation in the transcription factor GATA-1 (Grimm et al., 2021). Here, GATA1 is linked to transient myeloproliferative syndrome.