Relapsed/refractory acute myeloid leukemia (AML), a so-called blood cancer, has an extremely poor prognosis because of resistance to anti-cancer drugs and frailty of the patient’s organ functions. A type of anti-tumor immunotherapy called allogeneic hematopoietic cell transplantation, which can exert anti-cancer effect accompanied by severe toxicity, is often performed for patients who are hard to treat with chemotherapy, but relapse still remains.