[Successful immunosuppressive therapy in female hemophilia A developing inhibitor after perioperative administration of factor VIII products].

A 62-year-old woman was diagnosed as a hemophilia A carrier (factor VIII activity 35%) on preoperative examination of an ovarian tumor. A total of 35,600 units of recombinant factor VIII products was administered perioperatively. On postoperative day 95, a subcutaneous hematoma formed and immunosuppressive therapy with prednisolone was started based on an APTT of 66 seconds, factor VIII (FVIII) activity of 3%, and FVIII inhibitor of 1 BU/ml. During this treatment, the patient was hospitalized due to ankle joint bleeds and required hemostatic treatment, but the inhibitor disappeared and FVIII activity recovered to 30% after postoperative day 438 with cyclophosphamide. F8 analysis revealed the patient carried a heterozygosity of p.Arg391Cys, which has previously been categorized as cross-reacting material (CRM)-positive severe hemophilia A. No high-risk mutations for inhibitor development were found. We also report the results of a desmopressin acetate hydrate test administered to the patient to prepare for future treatment in case of hemorrhage, since high-dose FVIII administration may have been a factor in inhibitor development.

Correlation of ex vivo and in vivo ammonia production with L-asparaginase biological activity in adults with lymphoid malignancies.

Silent inactivation of L-asparaginase (L-Asp) represents rapid clearance of L-Asp by anti-L-Asp IgG antibodies without clinical symptoms. Measurement of L-Asp activity is the gold standard for diagnosis of silent inactivation, but this test is not commercially available in Japan as of 2023. We evaluated ex vivo and in vivo ammonia production in relation to L-Asp activity. Blood samples from ten adult patients treated with L-Asp were collected to measure ammonia levels and L-Asp activity before the first dose and 24 h after the last dose of L-Asp, during each cycle of treatment. Plasma ammonia levels were analyzed immediately and 1 h after incubation at room temperature, and ex vivo ammonia production was defined as the increase in ammonia concentration. Ex vivo ammonia production correlated with L-Asp activity (R2 = 0.741), and ammonia levels measured immediately after blood collection were moderately correlated with L-Asp activity (R2 = 0.709). One patient with extranodal NK/T-cell lymphoma showed an increase in ammonia levels during the first cycle, but no increase in ammonia levels or L-Asp activity after L-Asp administration during the second cycle. Both ex vivo and in vivo ammonia production and surrogate markers are used for L-Asp biological activity.

[FLT3-ITD and NPM1 mutation positive acute myeloid leukemia with cuplike blasts mimicking acute promyelocytic leukemia].

FMS-like tyrosine kinase 3 (FLT3) inhibitors improve the prognosis of FLT3-internal tandem duplication (ITD)-positive acute myeloid leukemia (AML). Case 1 is a 47-year-old male patient who presented with a white blood cell count (WBC) of 95,700/ml with 94% blast accompanied by cuplike nuclei, lactate dehydrogenase (LDH) of 2,434 IU/l, fibrin degradation products (FDP) of 476 mg/ml, and a bone marrow examination that revealed blastic marrow with chromosome 46, XY, positive FLT3-ITD, and positive nucleophosmin 1 (NPM1) mutation type A. Flow cytometry revealed that blasts were positive for CD33 and negative for CD34, CD117, and human leukocyte antigen-DR isotype (HLA-DR). The patient had no response to idarubicin combined cytarabine; however, qiuzartinib administration resulted in the first complete remission. Case 2 is a 71-year-old female patient, who presented with 94,900/ml of WBC with a 91% blast accompanied with cup-like nuclei, LDH of 19,03 IU/l, FDP of 112 mg/ml, and a peripheral blood examination that revealed chromosome 46, XX, positive FLT3-ITD, and positive NPM1 mutation type B. Flow cytometry revealed that blasts were positive for CD33 and negative for CD34, CD117, and HLA-DR. She had a partial response to venetoclax combined with azacytidine, and qiuzartinib administration resulted in the first complete remission. Both cases were CD34- and HLA-DR-negative with disseminated intravascular coagulation mimicking acute promyelocytic leukemia (APL). Additionally, recognizing the cuplike blasts is useful to differentiate FLT3 mutant AML from APL for the proper use of FLT3 inhibitors.

[Allogeneic hematopoietic stem cell transplantations for relapsed and refractory acute lymphoblastic leukemia following inotuzumab ozogamicin treatment].

Inotuzumab ozogamicin (InO) was administered in three cases of relapsed/refractory adult acute lymphoblastic leukemia (ALL) before allogeneic hematopoietic stem cell transplantation (allo-SCT). One case developed extremely severe sinusoidal obstruction syndrome (SOS) but recovered after receiving defibrotide therapy. A gap of 63 days in the SOS case was noted from the last administration of InO to allo-SCT, the duration was 133 and 86 days for the other two cases, and the remaining risk factors for SOS were comparable in the three cases. In contrast to gemtuzumab ozogamicin (GO), the interval between InO exposure and allo-SCT has not been reported as a risk for SOS. Nevertheless, this case suggests that the intervals should be as long as possible.

A case of lymphomatoid granulomatosis with central nervous system involvement successfully treated with IFNα.

Lymphomatoid granulomatosis (LYG) is a rare Epstein-Barr virus (EBV)-driven B-cell lymphoproliferative disease affecting mainly extranodal sites such as the lung, central nervous system (CNS), skin, kidney, and liver. We report a case of low-grade LYG involving the CNS that was successfully treated with interferon alpha (IFNα). A 69-year-old woman developed necrotic erythema of the skin and was initially diagnosed with pyoderma gangrenosum based on skin biopsy. She showed a limited response to prednisolone. Approximately 6 months after the initial onset, low-grade LYG was diagnosed after detection of CNS lesions on brain biopsy. The whole blood EBV-DNA load determined by real-time polymerase chain reaction was slightly elevated. Two months into IFNα therapy, skin and CNS lesions had responded favorably and the EBV-DNA load decreased. IFNα plays an important role in treatment of LYG through its antiproliferative, immunomodulatory, and anti-EBV effects. To our knowledge, this is the first case report of successful treatment with IFNα in Japan. Further investigation is necessary to determine optimal use of IFNα for LYG.

[Use of pegylated granulocyte colony-stimulating factor in dose-adjusted EPOCH-R therapy].

Dose-adjusted (DA)-EPOCH-R causes profound neutropenia requiring relatively long hospital stays with multiple doses of granulocyte colony-stimulating factor (G-CSF). A single-dose pegylated G-CSF (PEG-G-CSF) has been used for the treatment of chemotherapy-induced neutropenia. We retrospectively examined 15 patients (median age 61, range 33-75 years) treated with DA-EPOCH-R. In the first cycle of the DA-EPOCH-R therapy, a G-CSF preparation was used, and since the second cycle, the G-CSF and PEG-G-CSF use groups were divided. The median length of hospitalization after starting chemotherapy in the second-cycle DA-EPOCH-R was significantly shorter with PEG-G-CSF group (n=9) of 9 (7-13) days compared with G-CSF group (n=6) of 18 (15-22) days (P<0.001). Risk factors of febrile neutropenia, such as bone marrow invasion, performance status, serum albumin, and history of febrile neutropenia at the first DA-EPOCH-R cycle or previous chemotherapy were not significantly different for both groups, and the incidence of febrile neutropenia in PEG-G-CSF and G-CSF groups was 2.6% and 46.9%, respectively. These analyses suggest that PEG-G-CSF can be combined with DA-EPOCH-R without compromising treatment outcomes as compared with the daily dose of G-CSF.

Repurposing a novel anti-cancer RXR agonist to attenuate murine acute GVHD and maintain graft-versus-leukemia responses.

The nuclear receptor (NR) subclass, retinoid X receptors (RXRs), exert immunomodulatory functions that control inflammation and metabolism via homodimers and heterodimers, with several other NRs, including retinoic acid receptors. IRX4204 is a novel, highly specific RXR agonist in clinical trials that potently and selectively activates RXR homodimers, but not heterodimers. In this study, in vivo IRX4204 compared favorably with FK506 in abrogating acute graft-versus-host disease (GVHD), which was associated with inhibiting allogeneic donor T-cell proliferation, reducing T-helper 1 differentiation, and promoting regulatory T-cell (Treg) generation. Recipient IRX4204 treatment reduced intestinal injury and decreased IFN-γ and TNF-α serum levels. Transcriptional analysis of donor T cells isolated from intestines of GVHD mice treated with IRX4204 revealed significant decreases in transcripts regulating proinflammatory pathways. In vitro, inducible Treg differentiation from naive CD4+ T cells was enhanced by IRX4204. In vivo, IRX4204 increased the conversion of donor Foxp3- T cells into peripheral Foxp3+ Tregs in GVHD mice. Using Foxp3 lineage-tracer mice in which both the origin and current FoxP3 expression of Tregs can be tracked, we demonstrated that IRX4204 supports Treg stability. Despite favoring Tregs and reducing Th1 differentiation, IRX4204-treated recipients maintained graft-versus-leukemia responses against both leukemia and lymphoma cells. Notably, IRX4204 reduced in vitro human T-cell proliferation and enhanced Treg generation in mixed lymphocyte reaction cultures. Collectively, these beneficial effects indicate that targeting RXRs with IRX4204 could be a novel approach to preventing acute GVHD in the clinic.

Beneficial tyrosine kinase inhibitor therapy in a patient with relapsed BCR-ABL1-like acute lymphoblastic leukemia with CCDC88C-PDGFRB fusion.

BCR-ABL1-like acute lymphoblastic leukemia (ALL) is a neoplasm of lymphoblasts committed to the B-cell lineage that lack the BCR-ABL1 translocation but show a pattern of gene expression very similar to that seen in ALL with BCR-ABL1 with poor prognosis. A 22-year-old female was diagnosed with common-B-cell-ALL positive for CD10, CD19, CD22, CD79a, CD34, HLA-DR, and TdT in January 2017, and achieved complete remission (CR) with induction therapy, followed by consolidation therapy and maintenance therapy. In March 2020, 6 months after the completion of maintenance therapy, she relapsed. Inotuzumab ozogamicin (IO) was administered, and on day 28, bone marrow evaluation showed a morphologic CR. She had an HLA-identical sibling, and transplantation in her 2nd CR was planned. Because her ALL had been identified as BCR-ABL1-like ALL with CCDC88C-PDGFRB fusion, she was treated with imatinib for 2 months accompanied by 2 intrathecal methotrexate therapies, and 1 course of L-asparaginase, vincristine, and prednisolone in an outpatient setting. MRD analysis revealed potent efficacy of 2 months imatinib therapy; IgH MRD decreased from 1 × 10-2 to 1 × 10-3, and CCDC88C-PDGFRB/104ABL from 37.3 to 0. It is earnestly desired that well-designed clinical trials of TKI in ABL class-mutant BCR-ABL1-like ALL be conducted in Japan.

[Interleukin-6-producing paraganglioma mimicking multicentric Castleman disease].

Multicentric Castleman disease (MCD) comprises a heterogeneous group of lymphoproliferative disorders. Interleukin 6 (IL-6) plays an important role in the MCD pathophysiology. Here, we report the case of a 17-year-old Japanese man who presented with fever, headache, fatigue, and weight loss, with normal blood pressure. A movable mass was palpated in his lower abdomen. Laboratory tests revealed microcytic anemia and hypoalbuminemia, with elevated IL-6, sIL-2R, and vascular endothelial growth factor. Computed tomography of the abdomen demonstrated a 55-mm-diameter pelvic tumor and enlarged mesenteric lymph nodes. MCD was suspected, and the pelvic tumor resected. After the operation, his blood pressure rose slowly, and resulted to seizures of posterior reversible encephalopathy syndrome. Evaluation of hypertension revealed that plasma norepinephrine and normetanephrine concentrations were elevated, and pathological examinations showed that the resected tumor was positive for IL-6 and chromogranin-A. Therefore, we diagnosed the patient with IL-6-producing paraganglioma with MCD-mimicking symptoms. Moreover, IL-6-producing pheochromocytoma and paraganglioma should be included in differential diagnoses of MCD, even in normotensive patients.

Myeloid differentiation factor 88 signaling in donor T cells accelerates graft-versus-host disease.

Myeloid differentiation factor 88 (MyD88) signaling has a crucial role in activation of both innate and adoptive immunity. MyD88 transduces signals via Toll-like receptor and interleukin-1 receptor superfamily to the NFκB pathway and inflammasome by forming a molecular complex with interleukin-1 receptor-associated kinase 4. The MyD88/interleukin-1 receptor-associated kinase 4 pathway plays an important role, not only in innate immunity, but also T-cell immunity; however, its role in donor T cells on the pathophysiology of graft-versus-host disease (GvHD) remains to be elucidated. We addressed this issue by using MyD88-deficient T cells in a mouse model of allogeneic hematopoietic stem cell transplantation (allo-SCT). While MyD88-deficient and wild-type T cells proliferated equivalently after transplantation, MyD88-deficient T cells demonstrated impaired survival and differentiation toward Th1, Tc1, and Th17, and induced less severe GvHD compared to wild-type T cells. Administration of interleukin-1 receptor-associated kinase 4 inhibitor PF-06650833 significantly ameliorated GvHD after allo-SCT. These results thus demonstrate that donor T-cell MyD88/interleukin-1 receptor-associated kinase 4 pathway is a novel therapeutic target against GvHD after allo-SCT.

Complete response following toxic epidermal necrolysis in relapsed adult T cell leukemia/lymphoma after haploidentical stem cell transplantation.

Allogeneic hematopoietic cell transplantation (allo-HSCT) is considered the curative treatment option in patients with aggressive adult T cell leukemia/lymphoma (ATLL), but the treatment of relapse after allo-HSCT remains a major challenge. We report a case of ATLL that was treated with sequential mogamulizumab (MOG) and lenalidomide (LEN) for early relapse after allo-HSCT. A 73-year-old Japanese male with acute-type ATLL underwent haploidentical-HSCT with post-transplant cyclophosphamide. He attained a complete response. However, ATLL relapse was diagnosed by biopsy of skin lesions that appeared on day 67. Discontinuation of immunosuppressant therapy alone did not result in improvement of ATLL, however, the skin lesions disappeared after an immune response was induced by sequential MOG and LEN. Following MOG and LEN, very serious toxic epidermal necrolysis (TEN) developed requiring high-dose intravenous immunoglobulin and methylprednisolone pulse therapy. Although graft-versus-host disease exacerbated and progressed to TEN, a complete response was achieved after successful treatment of TEN. These agents may thus enhance anti-ATLL activity by immune modulation. Further investigation is necessary to determine the optimal use of MOG and LEN in relapsed ATLL after allo-HSCT.

Autologous Bone Marrow Transplantation for Polymyositis Combined with Myasthenia Gravis and Aplastic Anemia: A Case Report.

This is the first report about a patient with concomitant polymyositis (PM), myasthenia gravis (MG), and aplastic anemia (AA). A 54-year-old male developed myalgia and muscle weakness, which gradually progressed over 2 months. He was persistently affected by MG and AA. Brachium magnetic resonance imaging showed increased signal intensity in the left triceps and deltoid muscles on short tau inversion recovery images. A muscle biopsy examination revealed perifascicular atrophication and inflammatory myopathy. We diagnosed the patient with PM combined with MG and AA. He was successfully treated with an autologous bone marrow transplantation (BMT). The present case suggests that BMT is a therapeutic option for PM, MG, and AA.

A Host-Dependent Prognostic Model for Elderly Patients with Diffuse Large B-Cell Lymphoma.

BACKGROUND: Decision-making models for elderly patients with diffuse large B-cell lymphoma (DLBCL) treated with rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone (R-CHOP) are in great demand. PATIENTS AND METHODS: The Society of Lymphoma Treatment in Japan (SoLT-J), in collaboration with the West-Japan Hematology and Oncology Group (West-JHOG), collected and retrospectively analyzed the clinical records of ≥65-year-old patients with DLBCL treated with R-CHOP from 19 sites across Japan to build an algorithm that can stratify adherence to R-CHOP. RESULTS: A total of 836 patients with a median age of 74 years (range, 65-96 years) were analyzed. In the SoLT-J cohort (n = 555), age >75 years, serum albumin level <3.7 g/dL, and Charlson Comorbidity Index score ≥3 were independent adverse risk factors and were defined as the Age, Comorbidities, and Albumin (ACA) index. Based on their ACA index score, patients were categorized into "excellent" (0 points), "good" (1 point), "moderate" (2 points), and "poor" (3 points) groups. This grouping effectively discriminated the 3-year overall survival rates, mean relative total doses (or relative dose intensity) of anthracycline and cyclophosphamide, unanticipated R-CHOP discontinuance rates, febrile neutropenia rates, and treatment-related death rates. Additionally, the ACA index showed comparable results for these clinical parameters when it was applied to the West-JHOG cohort (n = 281). CONCLUSION: The ACA index has the ability to stratify the prognosis, tolerability to cytotoxic drugs, and adherence to treatment of elderly patients with DLBCL treated with R-CHOP. The Oncologist 2017;22:554-560 IMPLICATIONS FOR PRACTICE: Currently, little is known regarding how to identify elderly patients with diffuse large B-cell lymphoma who may tolerate a full dose of chemotherapy or to what extent cytotoxic drugs should be reduced in some specific conditions. The Society of Lymphoma Treatment in Japan developed a host-dependent prognostic model consisting of higher age (>75 years), hypoalbuminemia (<3.7 g/dL), and higher Charlson Comorbidity Index score (≥3) for such elderly patients. This model can stratify the prognosis, tolerability to cytotoxic drugs, and adherence to treatment of these patients and thus help clinicians in formulating personalized treatment strategies for this growing patient population.

Programmed death ligand-1 expression on donor T cells drives graft-versus-host disease lethality.

Programmed death ligand-1 (PD-L1) interaction with PD-1 induces T cell exhaustion and is a therapeutic target to enhance immune responses against cancer and chronic infections. In murine bone marrow transplant models, PD-L1 expression on host target tissues reduces the incidence of graft-versus-host disease (GVHD). PD-L1 is also expressed on T cells; however, it is unclear whether PD-L1 on this population influences immune function. Here, we examined the effects of PD-L1 modulation of T cell function in GVHD. In patients with severe GVHD, PD-L1 expression was increased on donor T cells. Compared with mice that received WT T cells, GVHD was reduced in animals that received T cells from Pdl1-/- donors. PD-L1-deficient T cells had reduced expression of gut homing receptors, diminished production of inflammatory cytokines, and enhanced rates of apoptosis. Moreover, multiple bioenergetic pathways, including aerobic glycolysis, oxidative phosphorylation, and fatty acid metabolism, were also reduced in T cells lacking PD-L1. Finally, the reduction of acute GVHD lethality in mice that received Pdl1-/- donor cells did not affect graft-versus-leukemia responses. These data demonstrate that PD-L1 selectively enhances T cell-mediated immune responses, suggesting a context-dependent function of the PD-1/PD-L1 axis, and suggest selective inhibition of PD-L1 on donor T cells as a potential strategy to prevent or ameliorate GVHD.

Host programmed death ligand 1 is dominant over programmed death ligand 2 expression in regulating graft-versus-host disease lethality.

Programmed death 1 (PD-1) and its ligands, PD-L1 and PD-L2, play an important role in the maintenance of peripheral tolerance. We explored the role of PD-1 ligands in regulating graft-versus-host disease (GVHD). Both PD-L1 and PD-L2 expression were upregulated in the spleen, liver, colon, and ileum of GVHD mice. Whereas PD-L2 expression was limited to hematopoietic cells, hematopoietic and endothelial cells expressed PD-L1. PD-1/PD-L1, but not PD-1/PD-L2, blockade markedly accelerated GVHD-induced lethality. Chimera studies suggest that PD-L1 expression on host parenchymal cells is more critical than hematopoietic cells in regulating acute GVHD. Rapid mortality onset in PD-L1-deficient hosts was associated with increased gut T-cell homing and loss of intestinal epithelial integrity, along with increased donor T-cell proliferation, activation, Th1 cytokine production, and reduced apoptosis. Bioenergetics profile analysis of proliferating alloreactive donor T-cells demonstrated increased aerobic glycolysis and oxidative phosphorylation in PD-L1-deficient hosts. Donor T-cells exhibited a hyperpolarized mitochondrial membrane potential, increased superoxide production, and increased expression of a glucose transporter in PD-L1-deficient hosts. Taken together, these data provide new insight into the differential roles of host PD-L1 and PD-L2 and their associated cellular and metabolic mechanisms controlling acute GVHD.

Inhibiting retinoic acid signaling ameliorates graft-versus-host disease by modifying T-cell differentiation and intestinal migration.

Graft-versus-host disease (GVHD) is a critical complication after allogeneic bone marrow transplantation. During GVHD, donor T cells are activated by host antigen-presenting cells and differentiate into T-effector cells (Teffs) that migrate to GVHD target organs. However, local environmental factors influencing Teff differentiation and migration are largely unknown. Vitamin A metabolism within the intestine produces retinoic acid, which contributes to intestinal homeostasis and tolerance induction. Here, we show that the expression and function of vitamin A-metabolizing enzymes were increased in the intestine and mesenteric lymph nodes in mice with active GVHD. Moreover, transgenic donor T cells expressing a retinoic acid receptor (RAR) response element luciferase reporter responded to increased vitamin A metabolites in GVHD-affected organs. Increasing RAR signaling accelerated GVHD lethality, whereas donor T cells expressing a dominant-negative RARα (dnRARα) showed markedly diminished lethality. The dnRARα transgenic T cells showed reduced Th1 differentiation and α4ß7 and CCR9 expression associated with poor intestinal migration, low GVHD pathology, and reduced intestinal permeability, primarily via CD4(+) T cells. The inhibition of RAR signaling augmented donor-induced Treg generation and expansion in vivo, while preserving graft-versus-leukemia effects. Together, these results suggested that reagents blunting donor T-cell RAR signaling may possess therapeutic anti-GVHD properties.

Regulation of intestinal inflammation by microbiota following allogeneic bone marrow transplantation.

Despite a growing understanding of the link between intestinal inflammation and resident gut microbes, longitudinal studies of human flora before initial onset of intestinal inflammation have not been reported. Here, we demonstrate in murine and human recipients of allogeneic bone marrow transplantation (BMT) that intestinal inflammation secondary to graft-versus-host disease (GVHD) is associated with major shifts in the composition of the intestinal microbiota. The microbiota, in turn, can modulate the severity of intestinal inflammation. In mouse models of GVHD, we observed loss of overall diversity and expansion of Lactobacillales and loss of Clostridiales. Eliminating Lactobacillales from the flora of mice before BMT aggravated GVHD, whereas reintroducing the predominant species of Lactobacillus mediated significant protection against GVHD. We then characterized gut flora of patients during onset of intestinal inflammation caused by GVHD and found patterns mirroring those in mice. We also identified increased microbial chaos early after allogeneic BMT as a potential risk factor for subsequent GVHD. Together, these data demonstrate regulation of flora by intestinal inflammation and suggest that flora manipulation may reduce intestinal inflammation and improve outcomes for allogeneic BMT recipients.

Histological and immunohistochemical features of gingival enlargement in a patient with AML.

Here, we discuss the pathophysiology of leukemia-associated gingival enlargement based on a case of acute myelomonocytic leukemia (AML-M4) with typical gingival enlargement. Uniquely, this patient was well enough to allow full periodontal examination and incisional gingival biopsy to be performed both before and after chemotherapy. The patient was a 39-year-old Japanese woman with AML-M4 showing gingival enlargement. Histological and immunohistochemical features of gingiva and bacterial counts in the periodontal pockets were examined before and after chemotherapy. The results were as follows: (1) infiltration of myelomonocytic blasts in enlarged gingiva; (2) resolution of gingival enlargement with complete remission of AML by anticancer chemotherapy; and (3) the numbers of bacteria in the periodontal pockets were not high and were not altered before or after chemotherapy. In patients with AML-M4, remarkable mucosal enlargement is not generally observed in the body except in the gingiva. We hypothesized that antigens derived from periodontal bacteria, even if they are not present in large numbers, could act as chemoattractants for myelomonocytic leukemic cells.

The Wnt agonist R-spondin1 regulates systemic graft-versus-host disease by protecting intestinal stem cells.

Graft-versus-host disease (GVHD) is a major complication of allogeneic bone marrow transplantation (BMT), and damage to the gastrointestinal (GI) tract plays a critical role in amplifying systemic disease. Intestinal stem cells (ISCs) play a pivotal role not only in physiological tissue renewal but also in regeneration of the intestinal epithelium after injury. In this study, we have discovered that pretransplant conditioning regimen damaged ISCs; however, the ISCs rapidly recovered and restored the normal architecture of the intestine. ISCs are targets of GVHD, and this process of ISC recovery was markedly inhibited with the development of GVHD. Injection of Wnt agonist R-spondin1 (R-Spo1) protected against ISC damage, enhanced restoration of injured intestinal epithelium, and inhibited subsequent inflammatory cytokine cascades. R-Spo1 ameliorated systemic GVHD after allogeneic BMT by a mechanism dependent on repair of conditioning-induced GI tract injury. Our results demonstrate for the first time that ISC damage plays a central role in amplifying systemic GVHD; therefore, we propose ISC protection by R-Spo1 as a novel strategy to improve the outcome of allogeneic BMT.