FLT3 signaling augments macrophage production from human pluripotent stem cells.

Recent advances in cell engineering technologies enable immune cells to be utilized for adoptive cell transfer (ACT) immunotherapy against cancers. Macrophages have the potential to directly and indirectly exterminate cancers and are therefore an attractive option for therapies. To develop new ACT therapies using macrophages, a great number of macrophages are required. Human induced pluripotent stem cells (iPSCs) are expected to be a source of macrophages; therefore, a system to efficiently produce macrophages from human iPSCs is needed. Here, we demonstrated that human iPSCs were robustly differentiated into macrophages by enforced FMS-like tyrosine kinase-3 (FLT3) signaling via the introduction of exogenous FLT3 into iPSCs and the addition of its ligand FLT3L to the macrophage induction culture. These iPSC-derived macrophages were identical to those obtained by standard differentiation induction methods. Thus, our novel system enables the preparation of scalable macrophages from human iPSCs. We believe that this system will be useful to develop a novel ACT therapy using macrophages.