Neutrophils as regulators of macrophage-induced inflammation in a setting of allogeneic bone marrow transplantation

Clinical data reveal that patients with allogeneic hematopoietic stem cell transplantation (HSCT) are vulnerable to infection and prone to developing severe sepsis, which greatly compromises the success of transplantation, indicating a dysregulation of inflammatory immune response in this clinical setting. Here, by using a mouse model of haploidentical bone marrow transplantation (haplo-BMT), we found that uncontrolled macrophage inflammation underlies the pathogenesis of both LPS- and E.coli-induced sepsis in recipient animals with graft-versus-host disease (GVHD). Deficient neutrophil maturation in GVHD mice post-haplo-BMT diminished modulation of macrophage-induced inflammation, which was mechanistically dependent on MMP9-mediated activation of TGF-β1. Accordingly, adoptive transfer of mature neutrophils purified from wild-type donor mice inhibited both sterile and infectious sepsis in GVHD mice post-haplo-BMT. Together, our findings identify a novel mature neutrophil-dependent regulation of macrophage inflammatory response in a haplo-BMT setting and provide useful clues for developing clinical strategies for patients suffering from post-HSCT sepsis.