Mitochondrial complex II in intestinal epithelial cells regulates T cell-mediated immunopathology.

Intestinal epithelial cell (IEC) damage by T cells contributes to graft-versus-host disease, inflammatory bowel disease and immune checkpoint blockade-mediated colitis. But little is known about the target cell-intrinsic features that affect disease severity. Here we identified disruption of oxidative phosphorylation and an increase in succinate levels in the IECs from several distinct in vivo models of T cell-mediated colitis. Metabolic flux studies, complemented by imaging and protein analyses, identified disruption of IEC-intrinsic succinate dehydrogenase A (SDHA), a component of mitochondrial complex II, in causing these metabolic alterations. The relevance of IEC-intrinsic SDHA in mediating disease severity was confirmed by complementary chemical and genetic experimental approaches and validated in human clinical samples. These data identify a critical role for the alteration of the IEC-specific mitochondrial complex II component SDHA in the regulation of the severity of T cell-mediated intestinal diseases.

Ambient oxygen levels regulate intestinal dysbiosis and GVHD severity after allogeneic stem cell transplantation.

The severity of T cell-mediated gastrointestinal (GI) diseases such as graft-versus-host disease (GVHD) and inflammatory bowel diseases correlates with a decrease in the diversity of the host gut microbiome composition characterized by loss of obligate anaerobic commensals. The mechanisms underpinning these changes in the microbial structure remain unknown. Here, we show in multiple specific pathogen-free (SPF), gnotobiotic, and germ-free murine models of GI GVHD that the initiation of the intestinal damage by the pathogenic T cells altered ambient oxygen levels in the GI tract and caused dysbiosis. The change in oxygen levels contributed to the severity of intestinal pathology in a host intestinal HIF-1α- and a microbiome-dependent manner. Regulation of intestinal ambient oxygen levels with oral iron chelation mitigated dysbiosis and reduced the severity of the GI GVHD. Thus, targeting ambient intestinal oxygen levels may represent a novel, non-immunosuppressive strategy to mitigate T cell-driven intestinal diseases.

Gut microbiome-derived metabolites modulate intestinal epithelial cell damage and mitigate graft-versus-host disease.

The effect of alterations in intestinal microbiota on microbial metabolites and on disease processes such as graft-versus-host disease (GVHD) is not known. Here we carried out an unbiased analysis to identify previously unidentified alterations in gastrointestinal microbiota-derived short-chain fatty acids (SCFAs) after allogeneic bone marrow transplant (allo-BMT). Alterations in the amount of only one SCFA, butyrate, were observed only in the intestinal tissue. The reduced butyrate in CD326(+) intestinal epithelial cells (IECs) after allo-BMT resulted in decreased histone acetylation, which was restored after local administration of exogenous butyrate. Butyrate restoration improved IEC junctional integrity, decreased apoptosis and mitigated GVHD. Furthermore, alteration of the indigenous microbiota with 17 rationally selected strains of high butyrate-producing Clostridia also decreased GVHD. These data demonstrate a heretofore unrecognized role of microbial metabolites and suggest that local and specific alteration of microbial metabolites has direct salutary effects on GVHD target tissues and can mitigate disease severity.

Collection efficiency and safety of large-volume leukapheresis for the manufacturing of tisagenlecleucel.

BACKGROUND: In patients with relapsed or refractory B cell acute lymphoblastic leukemia or B cell non-Hodgkin lymphoma (r/r B-ALL/B-NHL) with low CD3+ cells in the peripheral blood (PB), sufficient CD3+ cell yield in a single day may not be obtained with normal-volume leukapheresis (NVL). Large-volume leukapheresis (LVL) refers to the processing of more than three times the total blood volume (TBV) in a single session for PB apheresis; however, the efficiency and safety of LVL for manufacturing of tisagenlecleucel (tisa-cel) remain unclear. This study aimed to investigate the tolerability of LVL. STUDY DESIGN AND METHODS: We retrospectively collected data on LVL (≥3-fold TBV) and NVL (<3-fold TBV) performed for patients with r/r B-ALL/B-NHL in our institution during November 2019 and September 2023. All procedures were performed using a continuous mononuclear cell collection (cMNC) protocol with the Spectra Optia. RESULTS: Although pre-apheresis CD3+ cells in the PB were significantly lower in LVL procedures (900 vs. 348/µL, p < .01), all patients could obtain sufficient CD3+ cell yield in a single day with a comparably successful rate of final products (including out-of-specification) between the two groups (97.2% vs. 100.0%, p = 1.00). The incidence and severity of citrate toxicity (no patients with grade ≥ 3) during procedures was not significantly different between the two groups (22.2% vs. 26.1%, p = .43) and no patient discontinued leukapheresis due to any complications. CONCLUSION: LVL procedures using Spectra Optia cMNC protocol was well tolerated and did not affect the manufacturing of tisa-cel.

Sigle Agent of Posttransplant Cyclophosphamide Without Calcineurin Inhibitor Controls Severity of Experimental Chronic GVHD.

Chronic graft-versus-host disease (GVHD) is a major cause of late death and morbidity following allogeneic hematopoietic cell transplantation (HCT), but its pathogenesis remains unclear. Recently, haplo-identical HCT with post-transplant cyclophosphamide (Haplo-HCT with PTCY) was found to achieve a low incidence rate of acute GVHD and chronic GVHD. However, while the pathogenesis of acute GVHD following Haplo-HCT with PTCY has been well investigated, that of chronic GVHD remains to be elucidated, especially in HLA-matched HCT with PTCY. Based on its safety profile, PTCY is currently applied for the human leucocyte antigen (HLA)-matched HCT setting. Here, we investigated the mechanisms of chronic GVHD following HLA-matched HCT with PTCY using a well-defined mouse chronic GVHD model. PTCY attenuated clinical and pathological chronic GVHD by suppressing effector T-cells and preserving regulatory T-cells compared with a control group. Additionally, we demonstrated that cyclosporine A (CsA) did not show any additional positive effects on attenuation of GVHD in PTCY-treated recipients. These results suggest that monotherapy with PTCY without CsA could be a promising strategy for the prevention of chronic GVHD following HLA-matched HCT.

[Relapsed primary central nervous system lymphoma treated with CD19 chimeric antigen receptor T-cell therapy and allogeneic hematopoietic stem cell transplantation].

Relapsed and/or refractory (R/R) primary central nervous system lymphoma (PCNSL) has a poor prognosis. A 57-year-old man diagnosed with PCNSL achieved a complete response by high-dose methotrexate-based chemotherapy followed by autologous hematopoietic stem cell transplantation (ASCT). The disease was not cured, so he was treated with the anti-CD19 chimeric antigen receptor (CAR) T-cell therapy tisagenlecleucel after the third relapse. However, the disease relapsed again 28 days after CAR T-cell therapy. Allogeneic hematopoietic stem cell transplantation (allo-HSCT) was attempted as curative therapy after bridging with second ASCT and tirabrutinib monotherapy. Although a temporary response was achieved, the disease relapsed 98 days after allo-HSCT. While receiving tirabrutinib for relapse after allo-HSCT, the patient developed acute respiratory failure due to transplant-related toxicity and post-transplant thrombotic microangiopathy. He died 175 days after allo-HSCT. Although various treatments for PCNSL have been investigated in recent years, the treatment strategy for R/R PCNSL has not been established. Further studies are warranted to improve the outcomes of patients with R/R PCNSL.

Bone marrow microenvironment disruption and sustained inflammation with prolonged haematologic toxicity after CAR T-cell therapy.

Mechanisms of prolonged cytopenia (PC) after chimeric antigen receptor (CAR) T-cell therapy, an emerging therapy for relapsed or refractory diffuse large B-cell lymphoma, remain elusive. Haematopoiesis is tightly regulated by the bone marrow (BM) microenvironment, called the 'niche'. To investigate whether alterations in the BM niche cells are associated with PC, we analysed CD271+ stromal cells in BM biopsy specimens and the cytokine profiles of the BM and serum obtained before and on day 28 after CAR T-cell infusion. Imaging analyses of the BM biopsy specimens revealed that CD271+ niche cells were severely impaired after CAR T-cell infusion in patients with PC. Cytokine analyses after CAR T-cell infusion showed that CXC chemokine ligand 12 and stem cell factor, niche factors essential for haematopoietic recovery, were significantly decreased in the BM of patients with PC, suggesting reduced niche cell function. The levels of inflammation-related cytokines on day 28 after CAR T-cell infusion were consistently high in the BM of patients with PC. Thus, we demonstrate for the first time that BM niche disruption and sustained elevation of inflammation-related cytokines in the BM following CAR T-cell infusion are associated with subsequent PC.

Evaluating the efficiency and safety of large-volume leukapheresis using the Spectra Optia continuous mononuclear cell collection protocol for peripheral blood stem cell collection from healthy donors: A retrospective study.

BACKGROUND: Large-volume leukapheresis (LVL) refers to processing of more than three volumes of blood in a single session for peripheral blood stem cell collection. Recently, continuous mononuclear cell collection (cMNC) protocol has been developed using the Spectra Optia system, which is a widely used apheresis device. LVL using the novel protocol has been investigated in patients. However, the efficiency and safety of LVL in healthy donors using this protocol has not been characterized. Therefore, this study aimed to evaluate the efficiency and tolerability of CD34+ collection of LVL with the cMNC protocol in healthy donors. STUDY DESIGN AND METHODS: We retrospectively collected data on LVL (>3 total blood volume) and normal-volume leukapheresis (NVL) performed in healthy donors between October 2019 and December 2021. All procedures were performed using the cMNC protocol. RESULTS: Although pre-apheresis CD34+ cell count was lesser in LVL (23.5 vs. 58.0/µL, p < .001), CD34+ collection efficiency was comparable between LVL and NVL (61.2% vs. 61.4%, p = .966). Platelet loss was significantly higher in LVL compared to NVL (38.0% vs. 29.4%, p < .001), with no correlation between attrition of platelet and processing blood volume. Moreover, the incidence of citrate toxicity during procedures was comparable between the two groups (31.6% vs. 21.4%, p = .322). All LVL procedures could be completed without any adverse events. CONCLUSION: Allogeneic LVL procedure using Spectra Optia cMNC protocol was well tolerated by the donors and resulted in efficient collection of CD34+ cells, which was comparable to that of NVL.

Efficient granulocyte collection method using high concentrations of medium molecular weight hydroxyethyl starch.

BACKGROUND: Granulocyte transfusion therapy is a rational therapeutic option for patients with prolonged, severe neutropenia. Although high molecular weight hydroxyethyl starch (hHES) facilitates the separation of red blood cells during granulocyte collection, renal dysfunction has been noted as a potential side effect. HES130/0.4 (Voluven®) is a medium molecular weight HES (mHES) with superior safety profiles compared to hHES. Although HES130/0.4 is reportedly effective in the collection of granulocytes, we lack studies comparing the efficiency of granulocyte collection using HES130/0.4 and hHES. STUDY DESIGN AND METHODS: We retrospectively collected the data from 60 consecutive apheresis procedures performed on 40 healthy donors at the Okayama University Hospital between July 2013 and December 2021. All procedures were performed using the Spectra Optia system. Based on the HES130/0.4 concentration in the separation chamber, granulocyte collection methods using HES130/0.4 were classified into m0.46, m0.44, m0.37, and m0.8 groups. We used HES130/0.4 and hHES groups to compare the various sample collection methods. RESULTS: The median granulocyte collection efficiency (CE) was approximately 24.0% and 28.1% in the m0.8 and hHES groups, respectively, which were significantly higher than those in the m0.46, m0.44, and m0.37 groups. One month following granulocyte collection with HES130/0.4, no significant changes were observed in serum creatinine levels compared to those before the donation. CONCLUSION: Therefore, we propose a granulocyte collection approach employing HES130/0.4, which is comparable to the use of hHES in terms of the granulocyte CE. A high concentration of HES130/0.4 in the separation chamber was considered crucial for granulocyte collection.

[Myelodysplastic syndrome with der (1;7)(q10;p10) complicated with eosinophilia and organizing pneumonia].

The unbalanced translocation der (1;7)(q10;p10) is a characteristic cytogenetic abnormality observed in myelodysplastic syndrome (MDS). A 63-year-old man presented to our hospital with fever and lung disease. The chromosomal analysis of bone marrow cells showed 46, XY, +1, der (1;7)(q10;p10) in all four metaphases. The patient was diagnosed with MDS. Bronchoscope examination revealed organizing pneumonia. The patient's eosinophil count rose to 39% after 30 days. His fever and dyspnea worsened, and a skin rash (systemic erythema) appeared simultaneously. Therefore, the patient was commenced on azacitidine and corticosteroids. Although treatment with both drugs could control disease progression transiently, the WT-1 value and the percentage of myeloblasts in the patient's bone marrow increased. Therefore, the patient received hematopoietic stem cell transplantation from his haplo-identical donor daughter. Some reports have demonstrated that patients with MDS with der (1;7)(q10;p10) have better prognosis than those with other abnormalities, such as -7/7q-. However, reported cases with severe complications show very poor prognosis. MDS with der (1;7)(q10;p10) complicated by eosinophilia and organizing pneumonia have not been reported, and its prognosis is expected to be very poor. Our case suggests that such cases might quickly require hematopoietic stem cell transplantation before the disease worsens.

Deletion of bone marrow myeloperoxidase attenuates chronic kidney disease accelerated atherosclerosis.

Increased myeloperoxidase (MPO) expression and activity are associated with atherosclerotic disease in patients with chronic kidney disease (CKD). However, the causal relationship between MPO and the development and progression of atherosclerosis in patients with CKD is unknown. Eight-week-old male low-density-lipoprotein-receptor-deficient mice were subjected to 5/6 nephrectomy, irradiated, and transplanted with bone marrow from MPO-deficient mice to induce bone marrow MPO deletion (CKD-bMPOKO) or bone marrow from WT mice as a control to maintain preserved bone marrow MPO(CKD-bMPOWT). The mice were maintained on a high-fat/high-cholesterol diet for 16 weeks. As anticipated, both groups of mice exhibited all features of moderate CKD, including elevated plasma creatinine, lower hematocrit, and increased intact parathyroid hormone but did not demonstrate any differences between the groups. Irradiation and bone marrow transplantation did not further affect body weight, blood pressure, creatinine, or hematocrit in either group. The absence of MPO expression in the bone marrow and atherosclerotic lesions of the aorta in the CKD-bMPOKO mice was confirmed by immunoblot and immunohistochemistry, respectively. Decreased MPO activity was substantiated by the absence of 3-chlorotyrosine, a specific by-product of MPO, in aortic atherosclerotic lesions as determined by both immunohistochemistry and highly sensitive LC-MS. Quantification of the aortic lesional area stained with oil red O revealed that CKD-bMPOKO mice had significantly decreased aortic plaque area as compared with CKD-bMPOWT mice. This study demonstrates the reduction of atherosclerosis in CKD mice with the deletion of MPO in bone marrow cells, strongly implicating bone-marrow-derived MPO in the pathogenesis of CKD atherosclerosis.

Red blood cell depletion in small-volume bone marrow processing using manipulation with third-party red blood cells: A comparison of the performance of the COBE spectra and the spectra Optia systems.

BACKGROUND: For pediatric recipients, red blood cells (RBCs) are added to bone marrow (BM) collections before low RBC volume BM processing using COBE Spectra (COBE) or Spectra Optia (Optia). However, the processing efficiency of this approach has not been evaluated. This study aimed to evaluate RBC depletion and nucleated cell subpopulation recovery rates in third-party RBC-manipulated BM products processed with the COBE or Optia. STUDY DESIGN AND METHODS: We retrospectively collected data on RBC depletion from low RBC volume BM with third-party RBCs (manipulated group) and on conventional large-volume, BM (unmanipulated group) processing performed between September 2010 and December 2021. All procedures were performed using COBE or Optia. RESULTS: The median residual RBC volume in the manipulated group was 9.5 ml in COBE and 2.5 ml in Optia (p = .01). The median total nucleated cell (TNC) and mononuclear cell (MNC) were comparable between the manipulated groups using each cell separator (TNC, 40.8 vs. 47.1%; MNC, 78.3 vs. 79.4%). The manipulation did not adversely affect TNC and MNC recoveries in either device. In addition, Optia achieved similar CD34+ cell recovery to that in large-BM-volume processing using the same device (147.5 vs. 184.5%, p = .112). During a follow-up period, neutrophil engraftment was achieved in all patients who received third-party RBC-manipulated grafts, and platelet engraftment was achieved in all cases, except one. CONCLUSION: The addition of third-party RBC to low RBC volume BM collections from or for pediatric patients does not have any negative impact on either RBC depletion or hematopoietic cell recovery during processing with the widely used cell separator.

Low hematocrit reduces the efficiency of CD34+ cell collection when using the Spectra Optia continuous mononuclear cell collection procedure.

BACKGROUND: CD34+ cell collection efficiency (CE) is the determining factor when calculating processed blood volume (PBV) for leukapheresis (LP). However, the factors affecting CE in the continuous mononuclear cell collection (cMNC) protocol performed by the Spectra Optia apheresis system are not well established. STUDY DESIGN AND METHODS: We retrospectively collected the data from 147 consecutive apheresis procedures across 106 healthy donors and 27 patients completed between July 2016 and December 2020 at the Okayama University Hospital. All procedures were performed using the Optia cMNC protocol. RESULTS: The median CD34+ CE2 was significantly higher in the donor samples (64.3%) than in the patient samples (46.8%) (p < .0001). WBC counts, hematocrit, and platelet counts were all significantly higher in the donors than in the patients, and there was a moderate positive correlation between CD34+ CE2 and hematocrit (r = .47, p < .0001), with the equation of the line being y = 1.23x + 12.23. In contrast, there was only a very weak correlation between CD34+ CE2 and WBC or platelet count. In addition, low hematocrit correlated with an increased time to interface formation. CONCLUSION: These data revealed the negative impact of low hematocrit on the efficiency of CD34+ cell collection when using the Optia cMNC protocol and suggest that hematocrit values should also be considered when determining PBV.

Successful neutrophil engraftment supported by granulocyte transfusion in adult allogeneic transplant patients with peri-transplant active infection.

Active infection at the time of allogeneic hematopoietic stem cell transplantation (HSCT) is a risk for non-relapse mortality (NRM) after HSCT. Granulocyte transfusion (GTX) has been used to prevent or treat life-threatening infections in patients with severe neutropenia. However, data are limited on the clinical benefits of GTX during HSCT. We retrospectively analyzed the transplant outcomes of HSCT patients who had undergone GTX between 2012 and 2020. Altogether, 20 patients with documented infection had received 55 GTXs during HSCT. No adverse events were observed during the GTX infusion. The average number of granulocytes was 0.40 (range, 0.10-1.59) × 109/kg. The median neutrophil increment one day after GTX was 515 (range, -6 to 6630)/µl, which was significantly correlated with the infused granulocyte dose (p = 0.0007). A total of 17 of 20 patients achieved neutrophil engraftment. The number of infused granulocytes tended to higher in clinical responders (p = 0.12), and patients receiving ≥ 0.5 × 109/kg showed trend toward to better transplant outcomes (GTX-high vs. GTX-low, 1-year OS; 33% vs. 11%, p = 0.19. 1-year NRM; 44% vs.77%, p = 0.11). The type of red blood sedimenting agents was significantly correlated with the amounts of granulocyte collection. In conclusion, GTX, especially with a high amount of containing granulocytes, could be a safe bridging therapy for neutrophil engraftment after HSCT in patients with active infection.

Analysis of Immunity against Measles, Mumps, Rubella, and Varicella Zoster in Adult Recipients of Allogeneic Hematopoietic Stem Cell Transplantation: A Single-Center Experience.

Vaccine-preventable disease (VPD) infections are more severe in immunocompromised hosts. Vaccination against measles, mumps, rubella, and varicella zoster (VZV) (MMRV) is therefore recommended for hematopoietic stem cell transplantation (HCT) recipients. However, studies on adult HCT recipients with VPD infections are limited. At our institution, we have systematically conducted serological MMRV tests as a part of check-up examinations during long-term follow-up (LTFU) after HCT since 2015. This retrospective study aimed to evaluate changes in the serostatus between before and 2 years after allogeneic HCT. Among 161 patients, the pre-transplant seropositivity was 82.7% for measles, 86.8% for mumps, 84.2% for rubella, and 94.3% for VZV. Among 56 patients who underwent LTFU including serological MMRV tests at 2 years after HCT, the percentages maintaining seroprotective antibody levels for measles, mumps, rubella and VZV were 71.5% (40/56), 51.8% (29/56), 48.2% (27/56), and 60.7% (34/56), respectively. Vaccination was recommended for 22 patients, and 12 were vaccinated. Among the 12 vaccinated patients, rates of seroconversion were examined in 2-6 patients for each of the four viruses. They were 100% (3/3) for measles, 33.3% (1/3) for mumps, 50% (3/6) for rubella, and 0% (0/2) for VZV. Further studies are warranted to clarify the effect of vaccination in adult HCT recipients.

[Recent advances in the understanding of the pathophysiology of graft-versus-host disease].

Graft-versus-host disease (GVHD), which is characterized by T-cell activation following allogeneic hematopoietic cell transplantation (allo-HCT), remains one of the most significant hurdles directly or indirectly affecting transplant outcomes. With improved knowledge, experimental and clinical models have been established over the last two decades to predict the clinical utility of novel therapeutic agents, and clinical care has progressed. In addition, recent advances have revealed mechanisms underlying GVHD that focus on the breakdown of tissue tolerance following allo-HCT, complementing established concepts of immunological intolerance that allo-reactive T cells and antigen-presenting cells contribute to the development and aggravation of GVHD. The pathophysiology of GVHD as influenced by various cells and tissues and therapeutic strategies based on mechanistic findings to advance the understanding of GVHD and individualize allo-HCT have been discussed in this review.

[Gut microbiome, metabolites, and tissue metabolism in graft-versus-host disease].

Immune reactions promote not only graft-versus-tumor events but also graft-versus-host disease (GVHD) characterized by the activation of T-cells and antigen-presenting cells. Recent studies have unveiled the effects of microbial flora on GVHD and brought the mechanism other than immune cells. The role of tissue-intrinsic factors contributes to target-tissue resilience, repair, and regeneration and mitigates the severity of GVHD without altering alloreactive immune cells. Antibiotics, specific bacteria, and low microbiota diversity are identified as risk factors for GVHD and mortality. The current focus has shifted to target-tissue homeostasis in GVHD. Most of the gut microbiota symbiotically colonize the gut, and this homeostasis is finely tuned in the gastrointestinal tract, which has a relatively hypoxic environment dominated by anaerobic organisms. Therefore, intestinal epithelial cells (IECs) are uniquely adapted to this hypoxic environment, and cells programmed by "physiological hypoxia" tonally regulate barrier function with commensal bacteria. Metabolic changes in IECs post allo-HCT can affect the gut environment, leading to dysbiosis. This review focuses on the role of metabolism in IECs with microbiota and microbial metabolites in the GVHD setting to promote tissue tolerance.

Effects of Gram-negative Rod Blood Stream Infection on Acute GVHD in Allogeneic Hematopoietic Stem Cell Transplantation: A Single-institute Analysis.

A bloodstream infection (BSI) is the most common serious infectious complication of hematopoietic stem cell transplantation (HSCT). BSI promotes an inflammatory state, which exacerbates acute graft-versus-host disease (GVHD). We investigated whether a Gram-negative rod bloodstream infection (GNR-BSI), which develops early after allo-HSCT, affected the onset or exacerbated acute GVHD in 465 patients who underwent allo-HSCT from 1995 through 2015 at a single institution. Eighty-eight patients (19%) developed BSI during the study period. Among the cultures, 50 (57%) were Gram-positive cocci (GPC) and 31 (35%) were GNR. Of the 465 patients, 187 (40%) developed acute GVHD of grade II or higher within the first 100 days post-allogeneic HSCT: 124 (27%) had acute GVHD grade II, 47 (10%) had grade III, and 16 (3%) had grade IV. Multivariate analysis revealed that GNR-BSI was a significant risk factor for grade II-IV acute GVHD (grade II-IV: hazard ratio [HR] 1.75, 95% confidence interval [CI] 1.03-2.97; grade III-IV: HR 2.37, 95% CI 1.03-5.43). These results suggest that GNR-BSI may predict the onset and exacerbation of acute GVHD.

Mitochondrial Deacetylase SIRT3 Plays an Important Role in Donor T Cell Responses after Experimental Allogeneic Hematopoietic Transplantation.

Allogeneic hematopoietic cell transplantation (allo-HCT) through its graft-versus-tumor (GVT) effects is a curative therapy against many hematological malignancies. However, GVT is linked to harmful graft-versus-host disease (GVHD) after allo-HCT. Both GVT and GVHD require allogeneic T cell responses, which is an energetically costly process that causes oxidative stress. Sirtuin 3 (SIRT3), a mitochondrial histone deacetylase (HDAC), plays an important role in cellular processes through inhibition of reactive oxygen species (ROS). Nonmitochondrial class of HDACs regulate T cell responses, but the role of mitochondrial HDACs, specifically SIRT3, on donor T cell responses after allo-HCT remains unknown. In this study, we report that SIRT3-deficient (SIRT3-/-) donor T cells cause reduced GVHD severity in multiple clinically relevant murine models. The GVHD protective effect of allogeneic SIRT3-/- T cells was associated with a reduction in their activation, reduced CXCR3 expression, and no significant impact on cytokine secretion or cytotoxic functions. Intriguingly, the GVHD protective effect of SIRT3-/- T cells was associated with a reduction in ROS production, which is contrary to the effect of SIRT3 deficiency on ROS production in other cells/tissues and likely a consequence of their deficient activation. Notably, the reduction in GVHD in the gastrointestinal tract was not associated with a substantial reduction in the GVT effect. Collectively, these data reveal that SIRT3 activity promotes allogeneic donor T cell responses and ROS production without altering T cell cytokine or cytolytic functions and identify SIRT3 as a novel target on donor T cells to improve outcomes after allo-HCT.