Hayase et al. show that R-Spondin1 stimulates intestinal stem cells to differentiate to Paneth cells and enhances luminal secretion of α-defensins. Administration of R-Spondin1 or recombinant α-defensin prevents dysbiosis mediated by graft-versus-host disease, representing a novel approach to restore intestinal ecosystems and homeostasis.

Graft-versus-host disease (GVHD) and infection are major obstacles to successful allogeneic hematopoietic stem cell transplantation (HSCT). Intestinal goblet cells form the mucus layers, which spatially segregate gut microbiota from host tissues. Although it is well known that goblet cell loss is one of the histologic features of GVHD, effects of their loss in pathophysiology of GVHD remain to be elucidated. In mouse models of allogeneic HSCT, goblet cells in the colon were significantly reduced, resulting in disruption of the inner mucus layer of the colon and increased bacterial translocation into colonic mucosa. Pretransplant administration of interleukin-25 (IL-25), a growth factor for goblet cells, protected goblet cells against GVHD, prevented bacterial translocation, reduced plasma concentrations of interferon-γ (IFN-γ) and IL-6, and ameliorated GVHD. The protective role of IL-25 was dependent on Lypd8, an antimicrobial molecule produced by enterocytes in the colon that suppresses motility of flagellated bacteria. In clinical colon biopsies, low numbers of goblet cells were significantly associated with severe intestinal GVHD, increased transplant-related mortality, and poor survival after HSCT. Goblet cell loss is associated with poor transplant outcome, and administration of IL-25 represents an adjunct therapeutic strategy for GVHD by protecting goblet cells.

The R-Spondin (R-Spo) family regulates WNT signaling and stimulates the proliferation and differentiation of intestinal stem cells (ISCs). R-Spo plays a critical role in maintaining intestinal homeostasis, but endogenous producers of R-Spo in the intestine remain to be investigated. We found that R-Spo3 was the major R-Spo family member produced in the intestine and it was predominantly produced by CD45−CD90+CD31+ lymphatic endothelial cells (LECs) in the lamina propria of the intestinal mucosa. Transcriptome analysis demonstrated that LECs highly expressed R-Spo receptor, Lgr5, suggesting an autocrine stimulatory loop in LECs. LECs were significantly reduced in number, and their R-Spo3 production was impaired in intestinal graft-versus-host disease (GVHD) after allogeneic hematopoietic stem cell transplantation. The impaired production of R-Spo3 in the intestine may be a novel mechanism of delayed tissue repair and defective mucosal defense in intestinal GVHD. We demonstrate a novel role of intestinal LECs in producing R-Spondin3 to maintain intestinal homeostasis.

Graft-versus-host disease (GVHD) is the major complication after allogeneic stem cell transplantation (SCT). Emerging evidence indicates that GVHD leads to injury of intestinal stem cells. However, it remains to be investigated whether skin stem cells could be targeted in skin GVHD. Lgr5 hair follicle stem cells (HFSCs) contribute to folliculogenesis and have a multipotent capacity to regenerate all epithelial cells in repair. We studied the fate of Lgr5 HFSCs after SCT and explored the novel treatment to protect Lgr5 HFSCs against GVHD using murine models of SCT. We found that GVHD reduced Lgr5 HFSCs in association with impaired hair regeneration and wound healing in the skin after SCT. Topical corticosteroids, a standard of care for a wide range of skin disorders including GVHD, damaged HFSCs and failed to improve skin homeostasis, despite of their anti-inflammatory effects. In contrast, JAK1/2 inhibitor ruxolitinib significantly ameliorated skin GVHD, protected Lgr5 HFSCs, and restored hair regeneration and wound healing after SCT. We, for the first time, found that GVHD targets Lgr5 HFSCs and that topical ruxolitinib represents a novel strategy to protect skin stem cells and maintain skin homeostasis in GVHD.

Chronic graft-versus-host disease (GVHD) profoundly affects the quality of life of long-term survivors of allogeneic hematopoietic stem cell transplantation (SCT). The eyes are frequently involved, and dry eye syndrome is the most common manifestation of ocular chronic GVHD. We explored the role of heat shock protein 47 (HSP47) in ocular GVHD and developed a novel antifibrotic topical therapy using vitamin A–coupled liposomes containing HSP47 small interfering RNA (siRNA) against HSP47 (VA-lip HSP47). In a mouse model of chronic GVHD, infiltration of HSP47+ fibroblasts and massive fibrosis surrounding the lacrimal ducts were observed after allogeneic SCT, leading to impaired tear secretion. After ocular instillation, VA-lip HSP47 was distributed to the lacrimal glands, knocked down HSP47 expression in fibroblasts, reduced collagen deposition, and restored tear secretion after allogeneic SCT. Ocular instillation of VA-lip HSP47 also ameliorated established lacrimal gland fibrosis and dry eye syndrome. VA-lip HSP47 eye drops are a promising prophylactic and therapeutic option against dry eye syndrome in chronic GVHD.

Allogeneic hematopoietic stem cell transplantation (allo-SCT) is a potentially curative therapy for FLT3 internal tandem duplication mutant (FLT3-ITD + ) acute myeloid leukemia, but relapse rate is high. A recent study showed that sorafenib, a first generation FLT3 and multikinase inhibitor, enhanced graft-versus-leukemia (GVL) effects against FLT3-ITD + leukemia via interleukin-15 (IL-15) production. However, it remains to be clarified whether this effect could be mediated by selective FLT3 inhibition. We investigated whether gilteritinib, a selective FLT3 inhibitor, could enhance GVL effects against FLT3-ITD transfected Ba/F3 leukemia (Ba/F3-FLT3-ITD) in mice. Oral administration of gilteritinib from day +5 to +14 after allo-SCT reduced expression of the co-inhibitory receptors PD-1 and TIGIT on donor CD8 + T cells and enhanced IL-15 expression in Ba/F3-FLT3-ITD. Bioluminescent imaging using luciferase-transfected Ba/F3-FLT3-ITD demonstrated that gilteritinib significantly suppressed leukemia expansion after allo-SCT, whereas it did not impact the morbidity or mortality of graft-versus-host disease (GVHD), resulting in significant improvement of overall survival. In conclusion, short-term administration of gilteritinib after allo-SCT enhanced GVL effects against FLT3-ITD + leukemia without exacerbating GVHD.

The effects of allogeneic hematopoietic stem cell transplantation (allo-HSCT) on systemic chronic active Epstein-Barr virus infection (sCAEBV) are yet to be analyzed in a large number of patients. Using the Japanese registry database, Transplant Registry

Prophylaxis for and treatment of graft-versus-host disease (GVHD) are essential for successful allogeneic hematopoietic stem cell transplantation (allo-SCT) and mainly consist of immunosuppressants such as calcineurin inhibitors. However, profound immunosuppression can lead to tumor relapse and infectious complications, which emphasizes the necessity of developing novel management strategies for GVHD. Emerging evidence has revealed that tissue-specific mechanisms maintaining tissue homeostasis and promoting tissue tolerance to combat GVHD are damaged after allo-SCT, resulting in exacerbation and treatment refractoriness of GVHD. In the gastrointestinal tract, epithelial regeneration derived from intestinal stem cells (ISCs), a microenvironment that maintains healthy gut microbiota, and physical and chemical mucosal barrier functions against pathogens are damaged by conditioning regimens and/or GVHD. The administration of growth factors for cells that maintain intestinal homeostasis, such as interleukin-22 (IL-22) for ISCs, R-spondin 1 (R-Spo1) for ISCs and Paneth cells, and interleukin-25 (IL-25) for goblet cells, mitigates murine GVHD. In this review, we summarize recent advances in the understanding of GVHD-induced tissue damage and emerging strategies for the management of GVHD.