CD34+ HSCs from cord blood or human BM can also support the systemic development of human immune system (10, 14); (3) the graft-versus-host disease (GVHD) rarely happens in NRG-hu HSC mice, while the incident of GVHD is high in NRG-hu Thy/HSC or BLT mice (50) probably due to the mature human thymocytes in the transplanted thymic fragments; and (4) neonate immunodeficient mice are used to generate NRG-hu HSC mice, while 6- to 8-week-old mice are used for NRG-hu Thy/HSC or BLT mice construction. The gene discussed is CD34; the disease is graft versus host disease.