Allogeneic hematopoietic stem cell transplantation (allo-HSCT) has become widely applied for hematological (and more recently even for non-hematological) disorders. However, allo-HSCT is a “two-edged” sword; this treatment has preferable strong graft-versus-tumor effects (GVT) to cure diseases, while at the same time causes graft-versus-host disease (GVHD) which could lead to the adverse prognoses of treated patients. As a hematologist, I observed many of the complications including GVHD after allo-HSCT, and as a researcher, elucidated the effects of GVHD on hematopoiesis/hematopoietic niche. I continue to pursue my research in this field of transplantation immunology, trying to reveal the detailed mechanisms of GVHD and GVT. I'm currently focusing attention on a network hub controlling immunity, inflammation, and cancer, which would contribute to GVHD/GVT. Intestinal damages are also important to initiate/sustain GVHD, so my projects also include models using knock-out mice of specific genes relevant to intestinal immune homeostasis. The ultimate goal is to develop promising methods to improve clinical outcomes of allo-HSCT.