Chronicgraft-versus-host disease (cGVHD) is an increasingly common cause of morbidity and mortality in allogeneic stem cell transplantation (alloSCT). Relative to acute GVHD (aGVHD), much less is understood about cGVHD. Using the B10.D2 3 BALB/c murine cGVHD model, which shares critical pathologic features with human cGVHD, we find that radiation-resistant host T cells regulate cGVHD. We initially observed that recipients lacking all lymphocytes developed accelerated and more severe cGVHD. Using genetically deficient recipients, we determined that ␣ ؉ CD4 ؉ T cells were required to regulate cGVHD. Increased cGVHD severity was not due to the absence of T cells per se. Rather, the potency of regulation was proportional to host T-cell receptor (TCR) diversity. Only CD4 ؉ CD25 ؉ , and not CD4 ؉ CD25 ؊ , host T cells ameliorated cGVHD when added back, indicating that host T cells acted not via host-versus-graft activity or by reducing homeostatic proliferation but by an undefined regulatory mechanism. Thus, preparative regimens that spare host CD4 ؉ CD25 ؉ T cells may reduce
IntroductionChronic graft-versus-host disease (cGVHD) is an increasingly common complication of allogeneic stem cell transplantation (alloSCT). Its incidence, as high as 80% in some series, is thought to be on the rise at least in part due to the use of peripheral blood as a stem cell source, nonmyeloablative conditioning, withdrawal of immunosuppression to induce antitumor activity, better supportive care allowing longer survival, and the number of patients receiving donor leukocyte infusions. [1][2][3][4][5][6][7] Even with a wide range of therapeutic options including agents that target tumor necrosis factor-␣ (TNF-␣) and the interleukin-2 (IL-2) receptor, cGVHD and the infectious complications of its management are major causes of late mortality for alloSCT recipients. 8 Acute GVHD (aGVHD) and cGVHD are traditionally diagnosed primarily by time of onset, with cGVHD occurring after day 100 after transplantation. 9 However, cGVHD has distinct clinicopathologic features and is often diagnosed based on these features regardless of time of onset. 10 aGVHD typically presents with inflammatory skin, gastrointestinal, and/or hepatic disease, while cGVHD is characterized by cutaneous fibrosis, involvement of exocrine glands, myositis, and hepatic disease. 9,10 Often cGVHD occurs in patients who have had prior aGVHD, although de novo cGVHD without aGVHD is not uncommon and the relationship between the two is unclear. In particular, de novo cGVHD occurs with some frequency after delayed leukocyte infusion given for the treatment of relapsed leukemia. Importantly, both de novo cGVHD and that which emerges from prior aGVHD share clinicopathologic features. Donor T cells cause cGVHD, but much about the pathobiology of cGVHD is unknown. Most animal research on GVHD has been performed in murine models of aGVHD, with donor and recipient strains partially or fully mismatched at the major histocompatibility complex (MHC) locus. Broadly speaking, disease in th...