Graft versus host disease (GVHD)

Abstract

Graft-versus-host disease (GVHD), the major complication of allogeneic hematopoietic cell transplantation (HCT), remains lethal and limits the use of this therapy. Acute GVHD and chronic GVHD involve distinct pathological processes. Acute GVHD has strong inflammatory components, whereas chronic GVHD displays more autoimmune and fibrotic features. Acute GVHD begins with tissue damage to the recipient by conditioning regimens that release pro-inflammatory cytokines and gut bacteria and activate antigen-presenting cells (APCs). Following antigen presentation, a strong cytokine response is initiated, promoting greater antigen presentation and recruitment of effector T cells, and innate immune cells further contributing to the inflammatory cytokine milieu. Finally, effector T cells, NK cells, and pro-inflammatory cytokines will result in end-organ damage, clinically recognized as acute GVHD in the skin, gut, and liver. In contrast, one of the hallmarks to chronic GVHD includes damage to the thymus that is associated with the conditioning regimen and the acute GVHD resulting in decreased negative selection of alloreactive CD4 T cells. Dysregulation of B cells has also been implicated as another hallmark that leads to emergence of autoreactive B cells and production of autoreactive antibodies. It has also been proposed that Th2 cytokine pattern deviation may be involved that induces release of fibrogenic cytokines and macrophage activation followed by tissue fibroblast proliferation and activation. These will result in an autoimmune-like systemic syndrome that is mainly associated with fibroproliferative changes and that can occur in almost any organ in the body. In this chapter, we review the recent advances in understanding the pathophysiology of GVHD as well as its diagnosis.