Total Body Irradiation and Acute Graft-Versus-Host Disease: The Role of Gastrointestinal Damage and Inflammatory Cytokines

Selective H2-O tissue expression reduces risk for graft-versus-host disease in an in vivo transplantation model

BACKGROUND

Allogeneic stem cell transplantation (aSCT) is frequently used to treat patients with hematological malignancies. The therapeutic effect relies mainly on the graft-versus-leukemia (GvL) effect, in which donor T-cells eliminate residual malignant cells. Unfortunately, the beneficial GvL is often accompanied by detrimental graft-versus-host disease (GvHD). A successful separation of both effects could not yet be achieved. In previous work, we identified two groups of HLA-class II restricted antigens depending on their behavior towards HLA-DM. DM-resistant antigens are presented in the presence of HLA-DM, whereas presentation of DM-sensitive antigens relies on the inhibitory molecule HLA-DO. Due to the unique expression pattern of HLA-DO, DM sensitive antigens cannot be presented efficiently by non-hematopoietic cells even under inflammatory conditions. This suggests that CD4+ T-cells directed against DM-sensitive antigens may be able to separate GvL from GvHD.

OBJECTIVE

In this study, we wanted to demonstrate convincingly that HLA-DO expression strongly influences the severity of GvHD in allogeneic stem cell transplantation.

METHODS

Therefore, we generated a modified CD4 donor lymphocyte infusion (DLI) depleted of CD4+ T-cells directed against DM resistant antigens to address its potential to induce GvHD in an in vivo MHC mismatch transplantation model in dependency on selective tissue expression of H2-O using H2-O wildtype, knockout and transgenic recipients.

RESULTS

Intriguingly, we could demonstrate that our modified CD4 DLI targeting DM-sensitive antigens only induced mild GvHD in wildtype recipients with endogenous selective H2-O expression and none in H2-O knockouts, while assessing the immunogenic potential of DM-sensitive antigens in H2-O transgenic recipients.

CONCLUSION

The results of the present work provide evidence that DM-resistant antigens are main targets of GvHD and addressing DM-sensitive antigens might be a promising tool to improve outcome after aSCT by separating GvL from GvHD.

Improving bench-to-bedside translation for acute graft-versus-host disease models

The transplantation of allogeneic hematopoietic stem cells is a potentially curative treatment for hematological malignancies, inherited blood disorders and immune deficiencies. Unfortunately, 30-50% of patients receiving allogeneic hematopoietic stem cells will develop a potentially life-threatening inflammatory disease called acute graft-versus-host disease (aGVHD). In patients with aGVHD, graft-associated T cells, which typically target the skin, intestinal tract and liver, can also damage the lungs and lymphoid tissue. Damage to lymphoid tissue creates prolonged immunodeficiency that markedly increases the risk of infections and bleeding, resulting in considerable morbidity and mortality. Although mouse models of aGVHD have been instrumental to our understanding of this condition's pathogenesis, translation of preclinical data into new and more effective treatments for human disease has been limited for reasons that remain to be fully understood. However, evidence suggests that factors associated with mouse models of aGVHD likely contribute to these unsatisfactory results. In this Review, we identify and discuss the specific factors inherent to mouse models of aGVHD that may limit the translation of preclinical data to patient treatment, and suggest how to improve the translatability of these models.

The role of lncRNA NEAT1 in acute graft-versus-host disease: Regulation of macrophage polarization and inflammatory cytokine secretion via JNK/NLRP3 pathway

BACKGROUND

Acute graft-versus-host disease (aGVHD) is a complication of allogeneic hematopoietic stem cell transplantation (allo-HSCT). The role of macrophages as proficient antigen-presenting cells in aGVHD is a prominent area of investigation in contemporary research. The association between long noncoding RNA nuclear enriched abundant transcript 1 (lncRNA NEAT1) and the macrophage function is of significant interest. However, the role of lncRNA NEAT1 in aGVHD needs to be further explored.

METHODS

Peripheral blood mononuclear cells (PBMCs) were collected from patients with or without aGVHD (non-aGVHD) after allo-HSCT. RAW264.7 cells and bone marrow-derived macrophages (BMDMs) were transduced with NEAT1 lentiviral vector or transfected with NEAT1 small interfering RNA to change the expression level of lncRNA NEAT1. Finally, an aGVHD mouse model was established to evaluate the role of JNK inhibitor or NLRP3 inhibitor in aGVHD.

RESULTS

Compared with non-aGVHD patients, lncRNA NEAT1 was significantly up-regulated in the PBMCs of aGVHD patients. ROC and AUC analysis confirmed that the expression of lncRNA NEAT1 was correlated with the occurrence of aGVHD. The overexpression of lncRNA NEAT1 in RAW264.7 could significantly promote the proliferation, migration, and differentiation into M1 macrophages. Knockdown of lncRNA NEAT1 could significantly decrease the proportion of M1 macrophages, regulate pro-inflammatory cytokines secretion, and affect the JNK/NLRP3 pathway in lipopolysaccharides (LPS)-induced BMDMs. Correspondingly, JNK and NLRP3 inhibitors reduced LPS-induced pro-inflammatory responses in macrophages. Furthermore, JNK and NLRP3 inhibitors regulated macrophage polarization and improved symptoms in aGVHD mice.

CONCLUSIONS

The aforementioned data suggest that lncRNA NEAT1 potentially plays a significant role in macrophage polarization and the secretion of inflammatory cytokines through its modulation of the JNK/NLRP3 pathway. Consequently, this study establishes a foundation for the development of novel therapeutic approaches targeting aGVHD.

Pathophysiology and preclinical relevance of experimental graft-versus-host disease in humanized mice

Graft-versus-host disease (GVHD) is a life-threatening complication of allogeneic hematopoietic cell transplantations (allo-HCT) used for the treatment of hematological malignancies and other blood-related disorders. Until recently, the discovery of actionable molecular targets to treat GVHD and their preclinical testing was almost exclusively based on modeling allo-HCT in mice by transplanting bone marrow and splenocytes from donor mice into MHC-mismatched recipient animals. However, due to fundamental differences between human and mouse immunology, the translation of these molecular targets into the clinic can be limited. Therefore, humanized mouse models of GVHD were developed to circumvent this limitation. In these models, following the transplantation of human peripheral blood mononuclear cells (PBMCs) into immunodeficient mice, T cells recognize and attack mouse organs, inducing GVHD. Thereby, humanized mice provide a platform for the evaluation of the effects of candidate therapies on GVHD mediated by human immune cells in vivo. Understanding the pathophysiology of this xenogeneic GVHD is therefore crucial for the design and interpretation of experiments performed with this model. In this article, we comprehensively review the cellular and molecular mechanisms governing GVHD in the most commonly used model of xenogeneic GVHD: PBMC-engrafted NOD/LtSz-PrkdcscidIL2rγtm1Wjl (NSG) mice. By re-analyzing public sequencing data, we also show that the clonal expansion and the transcriptional program of T cells in humanized mice closely reflect those in humans. Finally, we highlight the strengths and limitations of this model, as well as arguments in favor of its biological relevance for studying T-cell reactions against healthy tissues or cancer cells.

Interventions to reduce the risk of side-effects of cancer treatments in childhood

INTRODUCTION

Childhood cancers as a group affect around 1 in 500 children but each individual diagnosis is a rare disease. While research largely focuses on improving cure rates, the management of side effects of treatment are high priority for clinicians, families and children and young people.

AREAS COVERED

The prevention and efficient management of infectious complications, oral mucositis, nausea and vomiting and graft-vs-host disease illustrated with examples of implementation research, translation of engineering to care, advances in statistical methodologies, and traditional bench-to-patient development. The reviews draw from existing systematic reviews and well conducted clinical practice guidelines.

EXPERT OPINION

The four areas are driven from patient and family priorities. Some of the problems outlined are ready for proven interventions, others require us to develop new technologies. Advancement needs us to make the best use of new methods of applied health research and clinical trial methodologies. Some of the greatest challenges may be those we're not fully aware of, as new therapies move from their use in adult oncological practice into children. This will need us to continue our collaborative, multi-professional, multi-disciplinary and eclectic approach.

Comparative analysis of reduced toxicity conditioning regimens between fludarabine plus melphalan and fludarabine plus busulfex in adult patients with acute lymphoblastic leukemia

Reduced-toxicity conditioning (RTC) regimens aim to mitigate regimen-related toxicity while maintaining anti-leukemic efficacy in allogeneic hematopoietic stem cell transplantation (allo-HSCT). We assessed outcomes of RTC regimens utilizing melphalan versus intravenous busulfan combined with fludarabine in adult acute lymphoblastic leukemia (ALL) patients. A retrospective analysis was conducted with 149 consecutive adult ALL patients (median age 51, range 18-60) in remission undergoing allo-HSCT. Patients received either fludarabine 150 mg/BSA plus 2 days of melphalan 70 mg/BSA (FM140, n = 76) from 2009 to 2015 or fludarabine plus 3 days of busulfan 3.2 mg/kg (FB9.6, n = 73) from 2016 to 2021. At 5 years post-HSCT, FM140 demonstrated superior disease-free survival (53.4% vs. 30.5%, p = 0.007) and lower cumulative relapse (27.4% vs. 46.8%, p = 0.026) than FB9.6. Five-year overall survival and non-relapse mortality did not significantly differ. FM140 exhibited a higher incidence of acute graft-versus-host disease (GVHD) grades II-IV (49.3% vs. 30.3%, p = 0.016), though rates of acute GVHD grades III-IV and chronic GVHD were similar. Multivariate analysis identified Philadelphia chromosome and minimal residual disease positive status, and FB9.6 conditioning as predictors of increased relapse and poorer disease-free survival. FM140 RTC regimen displayed significantly reduced relapse and superior disease-free survival compared to FB9.6 in ALL patients undergoing allo-HSCT, highlighting its current clinical utility.

Microbiota dictate T cell clonal selection to augment graft-versus-host disease after stem cell transplantation

Allogeneic T cell expansion is the primary determinant of graft-versus-host disease (GVHD), and current dogma dictates that this is driven by histocompatibility antigen disparities between donor and recipient. This paradigm represents a closed genetic system within which donor T cells interact with peptide-major histocompatibility complexes (MHCs), though clonal interrogation remains challenging due to the sparseness of the T cell repertoire. We developed a Bayesian model using donor and recipient T cell receptor (TCR) frequencies in murine stem cell transplant systems to define limited common expansion of T cell clones across genetically identical donor-recipient pairs. A subset of donor CD4+ T cell clonotypes differentially expanded in identical recipients and were microbiota dependent. Microbiota-specific T cells augmented GVHD lethality and could target microbial antigens presented by gastrointestinal epithelium during an alloreactive response. The microbiota serves as a source of cognate antigens that contribute to clonotypic T cell expansion and the induction of GVHD independent of donor-recipient genetics.

Phase 1 Study of Bortezomib, Fludarabine, and Melphalan, With or Without Total Marrow Irradiation, as Allogeneic Hematopoietic Stem Cell Transplant Conditioning for High-risk or Relapsed/Refractory Multiple Myeloma

OBJECTIVE

We conducted a phase 1 study of a conditioning regimen with or without total marrow irradiation (TMI) before allogeneic hematopoietic stem cell transplantation for patients with high-risk or refractory multiple myeloma.

METHODS

Eighteen patients were enrolled on one of 2 strata. Patients with no prior radiation received TMI (900 cGy), fludarabine (FLU), and melphalan (MEL) conditioning, with bortezomib added in the second cohort (stratum I). Patients with prior radiation received FLU, MEL, and bortezomib, without TMI (stratum II).

RESULTS

Eight patients were enrolled in the TMI arm (stratum I). One of 3 patients in cohort 1 experienced dose-limiting toxicity (DLT), which led to the expansion to 3 more patients with no DLT. Cohort 2 enrolled only 2 patients due to low accrual, with bortezomib, added at 0.5 mg/m 2 ; neither experienced DLT. Nine patients were enrolled in the non-TMI arm (stratum II). Three patients were enrolled in cohort 1 (bortezomib 0.5 mg/m 2 ) and none experienced DLT. Three were enrolled in cohort 2 (bortezomib 0.7 mg/m 2 ), and 1 experienced DLT; therefore, the cohort expanded to 3 more patients. One more patient experienced DLT. Median overall survival on strata I and II was 44.5 months (95% CI: 1.73-not reached) and 21.6 months (95% CI: 4.1-72.7), respectively. Median progression-free survival on strata I and II was 18.1 months (95% CI: 1.73-not reached) and 8.9 months (95% CI: 2.7-24.4), respectively.

CONCLUSION

TMI 900 cGy, FLU, and MEL are considered feasible as conditioning for allogeneic stem cell transplantation and may warrant further investigation due to favorable response rates and survival.

Reactions and adverse events induced by T-cell engagers as anti-cancer immunotherapies, a comprehensive review

T-cell engagers (TCE) are cancer immunotherapies that have recently demonstrated meaningful benefit for patients with hematological malignancies and solid tumors. The anticipated widespread use of T cell engagers poses implementation challenges and highlights the need for guidance to anticipate, mitigate, and manage adverse events. By mobilizing T-cells directly at the contact of tumor cells, TCE mount an obligatory and immediate anti-tumor immune response that could result in diverse reactions and adverse events. Cytokine release syndrome (CRS) is the most common reaction and is largely confined to the first drug administrations during step-up dosage. Cytokine release syndrome should be distinguished from infusion related reaction by clinical symptoms, timing to occurrence, pathophysiological aspects, and clinical management. Other common reactions and adverse events with TCE are immune effector Cell-Associated Neurotoxicity Syndrome (ICANS), infections, tumor flare reaction and cytopenias. The toxicity profiles of TCE and CAR-T cells have commonalities and distinctions that we sum-up in this review. As compared with CAR-T cells, TCE are responsible for less frequently severe CRS or ICANS. This review recapitulates terminology, pathophysiology, severity grading system and management of reactions and adverse events related to TCE.

Global research trends in Total Body Irradiation: a bibliometric analysis

Objectives

This manuscript presents a bibliometric and visualization analysis of Total Body Irradiation (TBI) research, aiming to elucidate trends, gaps, and future directions in the field. This study aims to provide a comprehensive overview of the global research landscape of TBI, highlighting its key contributions, evolving trends, and potential areas for future exploration.

Methods

The data for this study were extracted from the Web of Science Core Collection (WoSCC), encompassing articles published up to May 2023. The analysis included original studies, abstracts, and review articles focusing on TBI-related research. Bibliometric indicators such as total publications (TP), total citations (TC), and citations per publication (C/P) were utilized to assess the research output and impact. Visualization tools such as VOS Viewer were employed for thematic mapping and to illustrate international collaboration networks.

Results

The analysis revealed a substantial body of literature, with 7,315 articles published by 2,650 institutions involving, 13,979 authors. Full-length articles were predominant, highlighting their central role in the dissemination of TBI research. The authorship pattern indicated a diverse range of scholarly influences, with both established and emerging researchers contributing significantly. The USA led in global contributions, with significant international collaborations observed. Recent research trends have focused on refining TBI treatment techniques, investigating long-term patient effects, and advancing dosimetry and biomarker studies for radiation exposure assessments.

Conclusions

TBI research exhibits a dynamic and multifaceted landscape, driven by global collaboration and innovation. It highlights the clinical challenges of TBI, such as its adverse effects and the need for tailored treatments in pediatric cases. Crucially, the study also acknowledges the fundamental science underpinning TBI, including its effects on inflammatory and apoptotic pathways, DNA damage, and the varied sensitivity of cells and tissues. This dual focus enhances our understanding of TBI, guiding future research toward innovative solutions and comprehensive care.

Autophagy prevents graft failure during murine graft-versus-host disease

ABSTRACT

Autophagy is an intracellular survival process that has established roles in the long-term survival and function of hematopoietic stem cells (HSC). We investigated the contribution of autophagy to HSC fitness during allogeneic transplantation and graft-versus-host disease (GVHD). We demonstrate in vitro that both tumor necrosis factor and IL-1β, major components of GVHD cytokine storm, synergistically promote autophagy in both HSC and their more mature hematopoietic progenitor cells (HPC). In vivo we demonstrate that autophagy is increased in donor HSC and HPC during GVHD. Competitive transplant experiments demonstrated that autophagy-deficient cells display reduced capacity to reconstitute the hematopoietic system compared to wild-type counterparts. In a major histocompatibility complex-mismatched model of GVHD and associated cytokine dysregulation, we demonstrate that autophagy-deficient HSC and progenitors fail to establish durable hematopoiesis, leading to primary graft failure and universal transplant related mortality. Using several different models, we confirm that autophagy activity is increased in early progenitor and HSC populations in the presence of T-cell-derived inflammatory cytokines and that these HSC populations require autophagy to survive. Thus, autophagy serves as a key survival mechanism in HSC and progenitor populations after allogeneic stem cell transplant and may represent a therapeutic target to prevent graft failure during GVHD.

CSF1R inhibition promotes neuroinflammation and behavioral deficits during graft-versus-host disease in mice

ABSTRACT

Chronic graft-versus-host disease (cGVHD) remains a significant complication of allogeneic hematopoietic stem cell transplantation. Central nervous system (CNS) involvement is becoming increasingly recognized, in which brain-infiltrating donor major histocompatibility complex (MHC) class II+ bone marrow-derived macrophages (BMDM) drive pathology. BMDM are also mediators of cutaneous and pulmonary cGVHD, and clinical trials assessing the efficacy of antibody blockade of colony-stimulating factor 1 receptor (CSF1R) to deplete macrophages are promising. We hypothesized that CSF1R antibody blockade may also be a useful strategy to prevent/treat CNS cGVHD. Increased blood-brain barrier permeability during acute GVHD (aGVHD) facilitated CNS antibody access and microglia depletion by anti-CSF1R treatment. However, CSF1R blockade early after transplant unexpectedly exacerbated aGVHD neuroinflammation. In established cGVHD, vascular changes and anti-CSF1R efficacy were more limited. Anti-CSF1R-treated mice retained donor BMDM, activated microglia, CD8+ and CD4+ T cells, and local cytokine expression in the brain. These findings were recapitulated in GVHD recipients, in which CSF1R was conditionally depleted in donor CX3CR1+ BMDM. Notably, inhibition of CSF1R signaling after transplant failed to reverse GVHD-induced behavioral changes. Moreover, we observed aberrant behavior in non-GVHD control recipients administered anti-CSF1R blocking antibody and naïve mice lacking CSF1R in CX3CR1+ cells, revealing a novel role for homeostatic microglia and indicating that ongoing clinical trials of CSF1R inhibition should assess neurological adverse events in patients. In contrast, transfer of Ifngr-/- grafts could reduce MHC class II+ BMDM infiltration, resulting in improved neurocognitive function. Our findings highlight unexpected neurological immune toxicity during CSF1R blockade and provide alternative targets for the treatment of cGVHD within the CNS.

Nuclear Matrix-associated Protein SMAR1 Attenuated Acute Graft-versus-host Disease by Targeting JAK-STAT Signaling in CD4 + T Cells

BACKGROUND

Acute graft-versus-host disease (aGVHD) mediated by alloreactive T cells remains a serious and life-threatening complication of allogeneic hematopoietic cell transplantation (allo-HCT). The contribution of the different CD4 + T helper cell subtypes to the pathogenesis and regulation of aGVHD is a central point in current research. The specialized effector subsets of T cells that differentiate from naive T cells into mature cells are closely related to scaffold/matrix-associated region-1-binding protein (SMAR1). However, the role of SMAR1 in aGVHD is unclear.

METHODS

Peripheral blood was collected from the patients with or without aGVHD after allo-HCT. The differences in CD4 + T cells transduced with the SMAR1 lentivirus vector and empty vector were analyzed. A humanized aGVHD mouse model was constructed to evaluate the function of SMAR1 in aGVHD.

RESULTS

The expression of SMAR1 was significantly reduced in the CD4 + T cells from aGVHD patients and related to the occurrence of aGVHD. SMAR1 overexpression in human CD4 + T cells regulated CD4 + T-cell subsets differentiation and inflammatory cytokines secretion and inhibited the Janus kinase/signal transducer and activator of transcription pathway. Moreover, SMAR1 changed chromatin accessibility landscapes and affected the binding motifs of key transcription factors regulating T cells. Additionally, upregulation of SMAR1 expression in CD4 + T cells improved the survival and pathology in a humanized aGVHD mouse model.

CONCLUSIONS

Our results showed that upregulation of SMAR1 regulated the CD4 + T-cell subpopulation and cytokines secretion and improved survival in a humanized aGVHD mouse model by alleviating inflammation. This study provides a promising therapeutic target for aGVHD.

Corticosteroids impair epithelial regeneration in immune-mediated intestinal damage

Corticosteroid treatment (CST) failure is associated with poor outcomes for patients with gastrointestinal (GI) graft-versus-host disease (GVHD). CST is intended to target the immune system, but the glucocorticoid receptor (GR) is widely expressed, including within the intestines, where its effects are poorly understood. Here, we report that corticosteroids (CS) directly targeted intestinal epithelium, potentially worsening immune-mediated GI damage. CS administered to mice in vivo and intestinal organoid cultures ex vivo reduced epithelial proliferation. Following irradiation, immediate CST mitigated GI damage but delayed treatment attenuated regeneration and exacerbated damage. In a murine steroid-refractory (SR) GVHD model, CST impaired epithelial regeneration, worsened crypt loss, and reduced intestinal stem cell (ISC) frequencies. CST also exacerbated immune-mediated damage in organoid cultures with SR, GR-deficient T cells or IFN-γ. These findings correlated with CS-dependent changes in apoptosis-related gene expression and STAT3-related epithelial proliferation. Conversely, IL-22 administration enhanced STAT3 activity and overcame CS-mediated attenuation of regeneration, reducing crypt loss and promoting ISC expansion in steroid-treated mice with GVHD. Therefore, CST has the potential to exacerbate GI damage if it fails to control the damage-inducing immune response, but this risk may be countered by strategies augmenting epithelial regeneration, thus providing a rationale for clinical approaches combining such tissue-targeted therapies with immunosuppression.

Inhibition of RIP1 improves immune reconstitution and reduces GVHD mortality while preserving graft-versus-leukemia effects

Graft-versus-host disease (GVHD) remains the major cause of morbidity and nonrelapse mortality (NRM) after hematopoietic cell transplantation (HCT). Inflammatory cytokines mediate damage to key GVHD targets such as intestinal stem cells (ISCs) and also activate receptor interacting protein kinase 1 (RIP1; RIPK1), a critical regulator of apoptosis and necroptosis. We therefore investigated the role of RIP1 in acute GVHD using samples from HCT patients, modeling GVHD damage in vitro with both human and mouse gastrointestinal (GI) organoids, and blocking RIP1 activation in vivo using several well-characterized mouse HCT models. Increased phospho-RIP1 expression in GI biopsies from patients with acute GVHD correlated with tissue damage and predicted NRM. Both the genetic inactivation of RIP1 and the RIP1 inhibitor GNE684 prevented GVHD-induced apoptosis of ISCs in vivo and in vitro. Daily administration of GNE684 for 14 days reduced inflammatory infiltrates in three GVHD target organs (intestine, liver, and spleen) in mice. Unexpectedly, GNE684 administration also reversed the marked loss of regulatory T cells in the intestines and liver during GVHD and reduced splenic T cell exhaustion, thus improving immune reconstitution. Pharmacological and genetic inhibition of RIP1 improved long-term survival without compromising the graft-versus-leukemia (GVL) effect in lymphocytic and myeloid leukemia mouse models. Thus, RIP1inhibition may represent a nonimmunosuppressive treatment for GVHD.

CSF-1R inhibitor PLX3397 attenuates peripheral and brain chronic GVHD and improves functional outcomes in mice

Graft-versus-host disease (GVHD) is a serious complication of otherwise curative allogeneic haematopoietic stem cell transplants. Chronic GVHD induces pathological changes in peripheral organs as well as the brain and is a frequent cause of late morbidity and death after bone-marrow transplantation. In the periphery, bone-marrow-derived macrophages are key drivers of pathology, but recent evidence suggests that these cells also infiltrate into cGVHD-affected brains. Microglia are also persistently activated in the cGVHD-affected brain. To understand the involvement of these myeloid cell populations in the development and/or progression of cGVHD pathology, we here utilized the blood-brain-barrier permeable colony stimulating factor-1 receptor (CSF-1R) inhibitor PLX3397 (pexidartinib) at varying doses to pharmacologically deplete both cell types. We demonstrate that PLX3397 treatment during the development of cGVHD (i.e., 30 days post-transplant) improves disease symptoms, reducing both the clinical scores and histopathology of multiple cGVHD target organs, including the sequestration of T cells in cGVHD-affected skin tissue. Cognitive impairments associated with cGVHD and neuroinflammation were also attenuated by PLX3397 treatment. PLX3397 treatment prior to the onset of cGVHD (i.e., immediately post-transplant) did not change in clinical scores or histopathology. Overall, our data demonstrate significant benefits of using PLX3397 for the treatment of cGVHD and associated organ pathologies in both the periphery and brain, highlighting the therapeutic potential of pexidartinib for this condition.

Effect of lethal total body irradiation on bone marrow chimerism, acute graft-versus-host disease, and tumor engraftment in mouse models: impact of different radiation techniques using low- and high-energy X-rays

PURPOSE

Effects of X‑ray energy levels used for myeloablative lethal total body irradiation (TBI) delivery prior to bone marrow transplantation (BMT) in preclinical mouse models were examined.

MATERIALS AND METHODS

In mouse models, single-fraction myeloablative TBI at a lethal dose was delivered using two different X‑ray devices, either low (160 kV cabinet irradiator) or high energy (6 MV linear accelerator), before semi-allogeneic hematopoietic stem-cell transplantation (HSCT) to ensure bone marrow (BM) chimerism, graft-versus-host disease (GVHD), and tumor engraftment. Recipient mice were clinically followed for 80 days after bone marrow transplantation (BMT). Flow cytometry was performed to assess donor chimerism and tumor engraftment in recipient mice.

RESULTS

Both X‑ray irradiation techniques delivered a 10 Gy single fraction of TBI, presented a lethal effect, and could allow near-complete early donor chimerism on day 13. However, low-energy irradiation increased T cells' alloreactivity compared to high-energy irradiation, leading to clinical consequences for GVHD and tumor engraftment outcomes. The alloreactive effect differences might be attributed to the distinction in inflammatory status of irradiated recipients at donor cell infusion (D0). Delaying donor cell administration (D1 after lethal TBI) attenuated T cells' alloreactivity and clinical outcomes in GVHD mouse models.

CONCLUSION

Different X‑ray irradiation modalities condition T cell alloreactivity in experimental semi-allogeneic BMT. Low-energy X‑ray irradiator induces a post-TBI inflammatory burst and exacerbates alloreactive reactions. This technical and biological information should be considered in interpreting GVHD/ graft-versus-leukemia effect results in mice experimental models of BMT.

Feasibility of a dietary intervention to modify gut microbial metabolism in patients with hematopoietic stem cell transplantation

Evaluation of the impact of dietary intervention on gastrointestinal microbiota and metabolites after allogeneic hematopoietic stem cell transplantation (HCT) is lacking. We conducted a feasibility study as the first of a two-phase trial. Ten adults received resistant potato starch (RPS) daily from day -7 to day 100. The primary objective was to test the feasibility of RPS and its effect on intestinal microbiome and metabolites, including the short-chain fatty acid butyrate. Feasibility met the preset goal of 60% or more, adhering to 70% or more doses; fecal butyrate levels were significantly higher when participants were on RPS than when they were not (P < 0.0001). An exploratory objective was to evaluate plasma metabolites. We observed longitudinal changes in plasma metabolites compared to baseline, which were independent of RPS (P < 0.0001). However, in recipients of RPS, the dominant plasma metabolites were more stable compared to historical controls with significant difference at engraftment (P < 0.05). These results indicate that RPS in recipients of allogeneic HCT is feasible; in this study, it was associated with significant alterations in intestinal and plasma metabolites. A phase 2 trial examining the effect of RPS on graft-versus-host disease in recipients of allogeneic HCT is underway. ClinicalTrials.gov registration: NCT02763033 .

Ruxolitinib as the first post-steroid treatment for acute and chronic graft-versus-host disease

INTRODUCTION

Acute and chronic graft-versus-host disease (GvHD) are potentially life-threatening complications occurring after allogeneic stem cell transplantation (allo-HSCT). Although steroids represent the first-line treatment for both conditions, in those patients who do not adequately benefit from steroid therapy, standardized treatment algorithms are lacking. In recent years, ruxolitinib has emerged as the most promising agent for the second-line therapy of steroid-refractory (SR)-GvHD.

AREAS COVERED

This review will summarize the biological properties and the mechanistic aspects that justify the therapeutic role of ruxolitinib in GvHD. In addition, current treatment options for SR-GvHD will be briefly discussed. Finally, results of the most relevant clinical trials on the use of ruxolitinib for SR-GvHD will be analyzed, with a particular focus on two phase-III randomized trials in which ruxolitinib demonstrated its superiority in comparison with the best available therapy.

EXPERT OPINION

Ruxolitinib has considerably improved the outcome of patients with SR-acute/chronic-GvHD and should be regarded as the standard-of-care option when corticosteroids fail or cannot be tapered. Nevertheless, a number of questions still remain unanswered and significant room for improvement exists. Additional observations derived from a longer follow-up will certainly increase our expertise in the management of this powerful therapy.

Total marrow irradiation for second allogeneic hematopoietic stem cell transplantation in patients with advanced acute leukemia

BACKGROUND

Second allogeneic hematopoietic stem cell transplantation (HSCT) is a treatment option for patients with acute leukemia relapsing after a first HSCT. While a myeloablative (MA) conditioning regimen before the first HSCT is considered better than reduced intensity (RIC) in terms of disease control in acute leukemia patients, the optimal conditioning regimen for the second allogeneic HSCT remains controversial. The most important prognostic factors are the remission disease phase at the time of the second HSCT and more than 12 months from the first to the second HSCT. Total Marrow Irradiation (TMI) is an advanced high-precision radiation treatment that delivers therapeutic doses over extensively selected targets while substantially reducing radiation to vital organs compared to conventional Total Body Irradiation (TBI). Herein we report the results of a retrospective analysis on second allogeneic transplantation treated with TMI as a myeloablative conditioning regimen, intending to limit toxicity.

OBJECTIVE

We investigated the efficacy of a high dose per fraction TMI in combination with thiotepa, fludarabine and melphalan in 13 consecutive patients with acute leukemia relapsed after a first allogeneic HSCT treated between March 2018 and November 2021.

STUDY DESIGN

Donor type was haploidentical (HAPLO, n=10), unrelated (UD n=2), and HLA-identical sibling (SIB, n=1). The conditioning regimen consisted of TMI 8 Gy in 5 patients on day -8 -7 or TMI 12 Gy in 8 patients on day -9 -8 -7, plus Thiotepa 5 mg/Kg on day -6, Fludarabine 50 mg/mq on day -5 -4 -3, Melphalan 140 mg/mq on day -2. TMI was delivered in a hypofractionated daily single dose of 4 Gy for three consecutive fractions. The median age was 45 years (range, 19-70 years); 7 patients were in remission, and 6 had active disease at the time of the second allogeneic HSCT.

RESULTS

The median time to neutrophil counts of > 0.5×10e9/L was 16 days (range 13-22), and platelet counts of > 20×10e9/L were 20 days (range 14-34), respectively. All patients showed a complete donor chimerism on day 30 after the transplant. The cumulative incidence of grade I II acute GvHD (aGvHD) was 43%, and chronic GvHD (cGVHD) was 30%. The median follow-up was 1121 days (range 200-1540). Day +30 and +100 transplant-related mortality (TRM) was 0. Overall cumulative incidence of TRM, relapse rate, and disease free-survival (DFS) were respectively 27%,7%, and 67%.

CONCLUSIONS

This retrospective study showed the safety and efficacy of a hypofractionated TMI conditioning regimen in patients with acute leukemia receiving second HSCT with encouraging outcomes regarding engraftment, early toxicity, GvHD, and relapse.

The Benefits of the Post-Transplant Cyclophosphamide in Both Haploidentical and Mismatched Unrelated Donor Setting in Allogeneic Stem Cells Transplantation

Allogeneic hematopoietic cell transplantation (alloHSCT) is a standard therapeutic approach for acute leukemias and many other hematologic malignancies. The proper choice of immunosuppressants applicable to different types of transplantations still requires strict and careful consideration, and data in this regard are divergent. For this reason, in this single-centered, retrospective study, we aimed to compare the outcome of 145 patients who received post-transplant cyclophosphamide (PTCy) for MMUD and haplo-HSCT or GvHD prophylaxis for MMUD-HSCT alone. We attempted to verify if PTCy is an optimal strategy in MMUD setting. Ninety-three recipients (93/145; 64.1%) underwent haplo-HSCT while 52 (52/145; 35.9%) underwent MMUD-HSCT. There were 110 patients who received PTCy (93 in haplo and 17 in MMUD group) and 35 patients received conventional GvHD prophylaxis based on antithymocyte globulin (ATG), cyclosporine (CsA), and methotrexate (Mtx) in the MMUD group only. Our study revealed that patients receiving post-transplant cyclophosphamide (PTCy) show decreased acute GvHD rates and CMV reactivation as well as a statistically lower number of CMV copies before and after antiviral treatment compared to the CsA + Mtx + ATG group. Taking into account chronic GvHD, the main predictors are donor age, ≥40 years, and haplo-HSCT administration. Furthermore, the survival rate of patients following MMUD-HSCT and receiving PTCy with tacrolimus and mycophenolate mofetil was more than eight times greater in comparison to patients receiving CsA + Mtx + ATG (OR = 8.31, p = 0.003). These data taken together suggest that the use of PTCy displays more benefits in terms of survival rate compared to ATG regardless of the type of transplantation performed. Nevertheless, more studies with a larger sample size are required to confirm the conflicting results in the literature studies.

Glucocorticoid and glycolysis inhibitors cooperatively abrogate acute graft-versus-host disease

Although glucorticosteroids (GCs) are the standard first-line therapy for acute graft-versus-host disease (aGvHD), nearly 50% of aGvHD patients have no response to GCs. The role of T cell metabolism in murine aGvHD was recently reported. However, whether GCs and metabolism regulators could cooperatively suppress T cell alloreactivity and ameliorate aGvHD remains to be elucidated. Increased glycolysis, characterized by elevated 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase 3 (PFKFB3), and higher rates of glucose consumption and lactate production were found in T cells from aGvHD patients. Genetic upregulation of PFKFB3 induced T cell proliferation and differentiation into proinflammatory cells. In a humanized mouse model, PFKFB3-overexpressing or PFKFB3-silenced T cells aggravated or prevented aGvHD, respectively. Importantly, our integrated data from patient samples in vitro, in a humanized xenogeneic murine model of aGvHD and graft-versus-leukaemia (GVL) demonstrate that GCs combined with a glycolysis inhibitor could cooperatively reduce the alloreactivity of T cells and ameliorate aGvHD without loss of GVL effects. Together, the current study indicated that glycolysis is critical for T cell activation and induction of human aGvHD. Therefore, the regulation of glycolysis offers a potential pathogenesis-oriented therapeutic strategy for aGvHD patients. GCs combined with glycolysis inhibitors promises to be a novel first-line combination therapy for aGvHD patients.

Cytokine profiling during conditioning in haploidentical stem cell transplantation and its prognostic impact on early transplant outcomes

Cytokine storm development is a major cause of many transplant-related complications, especially during the conditioning regimen. This study aimed to characterize the cytokine profile and determine its prognostic impact during conditioning in patients undergoing subsequent haploidentical stem cell transplantation. A total of 43 patients were enrolled in this study. Sixteen cytokines associated with cytokine release syndrome (CRS) during anti-thymocyte globulin (ATG) treatment were quantified in patients undergoing haploidentical stem cell transplantation. Thirty-six (83.7%) patients developed CRS during ATG treatment; most of those cases (33/36; 91.7%) were classified as grade 1 CRS, whereas only three (7.0%) developed grade 2 CRS. CRS was observed more frequently on the first (15/43; 34.9%) and second day (30/43; 69.8%) of ATG infusion. No factors were identified that could predict the development of CRS on the first day of ATG treatment. Five of the 16 cytokines (interleukins 6, 8, and 10 (IL-6, IL-8, and IL-10), C-reactive protein (CRP), and procalcitonin (PCT)) were significantly elevated during ATG treatment, although only the level of IL-6, IL-10, and PCT were associated with the severity of CRS. However, neither CRS nor the cytokine levels significantly impacted the development of acute graft-versus-host disease (GVHD) or cytomegalovirus (CMV) infection or affected overall survival.

Advantages of Higher Busulfan Dose Intensity in Fludarabine-Combined Conditioning for Patients with Acute Myeloid Leukemia Undergoing Cord Blood Transplantation

The alkylating agent busulfan is commonly used as conditioning in allogeneic hematopoietic stem cell transplantation for acute myeloid leukemia (AML). However, a consensus has not yet been reached regarding the optimal busulfan dose in cord blood transplantation (CBT). Therefore, we conducted this large nationwide cohort study to retrospectively analyze the outcomes of CBT in patients with AML receiving busulfan at intermediate (6.4 mg/kg i.v.; BU2) or higher (12.8 mg/kg i.v.; BU4) doses within a fludarabine/i.v. busulfan (FLU/BU) regimen. Among 475 patients who underwent their first CBT following FLU/BU conditioning between 2007 and 2018, 162 received BU2 and 313 received BU4. Multivariate analysis identified BU4 as a significant factor for longer disease-free survival (hazard ratio [HR], .85; 95% confidence interval [CI], .75 to .97; P = .014) and a lower relapse rate (HR, .84; 95% CI, .72 to .98; P = .030). No significant differences were observed in non-relapse mortality between BU4 and BU2 (HR, 1.05; 95% CI, .88-1.26; P = .57). Subgroup analyses showed that BU4 provided significant benefits for patients who underwent transplantation while not in complete remission (CR) and those age <60 years. Our present results suggest that higher busulfan doses are preferable in patients undergoing CBT, particularly those not in CR and younger patients.

Impact of oral microbiota on pathophysiology of GVHD

Allogeneic transplantation of hematopoietic cells is the only curative therapy for several hematopoietic disease in which patients receive cytotoxic conditioning regimens followed by infusion of hematopoietic stem cells. Although the outcomes have improved over the past decades, graft-versus-host-disease (GVHD), the most common life-threatening complication, remains a major cause of non-relapse morbidity and mortality. Pathophysiology of acute GVHD characterized by host antigen-presenting cells after tissue damage and donor T-cells is well studied, and additionally the importance of recipient microbiota in the intestine is elucidated in the GVHD setting. Oral microbiota is the second most abundant bacterial flora in the body after the intestinal tract, and it is related to chronic inflammation and carcinogenesis. Recently, composition of the oral microbiome in GVHD related to transplantation has been characterized and several common patterns, dysbiosis and enrichment of the specific bacterial groups, have been reported. This review focuses on the role of the oral microbiota in the context of GVHD.

Native Spleen Preservation During Visceral Transplantation Inhibits Graft-Versus-Host-Disease Development: Clinical and Experimental Study

OBJECTIVE

We aimed to assess whether native spleen preservation during visceral transplantation (VT) affects graft-versus-host-disease (GVHD) incidence.

SUMMARY BACKGROUND DATA

GVHD is one of the most severe and frequently lethal hematological complications after VT procedures. Because there is no specific treatment for GVHD, it is imperative to develop a strategy to reduce donor lymphocyte engraftment and proliferation.

METHODS

Our study included both clinical and experimental data. A total of 108 patients were divided into 3 groups: a native spleen preservation group, a native spleen removal with no donor spleen group, and a donor spleen included (allogeneic spleen) group. We also used an allogeneic VT rat model, in which recipients were divided into 2 groups: a native spleen preservation (+SP) group and a native spleen removal (-S) group. Skin rash appearance, histopathological changes, chimerism, and spleen effects on circulating allogeneic T-cells were assessed.

RESULTS

The patients with native spleen preservation showed a lower rate of GVHD ( P <.001) and better survival ( P <.05) than those in the other groups. Skin and histological signs of GVHD were lower in the rats in the +SP group ( P <.05). The donor T-cell frequency in the bloodstream and skin was also significantly reduced when the native spleen was preserved ( P <.01 and P <.0001, respectively).

CONCLUSIONS

The clinical and experimental data indicate that recipient spleen preservation protects against GVHD after VT, and donor cell clearance from the bloodstream by spleen macrophages could be the underlying mechanism. Therefore, spleen preservation should be considered in VT procedures, whenever possible.

EPC infusion ameliorates acute graft-versus-host disease-related endothelial injury after allogeneic bone marrow transplantation

Introduction

Graft-versus-host disease (GVHD) damages vascular endothelium. Endothelial progenitor cell (EPC) can differentiate to endothelial cell and promote angiogenesis, but its role in endothelial damage in GVHD is unclear.

Methods

In this study, we intend to assess whether EPC infusion promotes the repair of endothelial injury in GVHD mouse model. Male BALB/c mice were randomly divided into 5 groups: control group, total body irradiation group (TBI group), allogeneic bone marrow transplantation group (Allo-BMT group), acute graft versus host disease group (GVHD group), EPC infusion group (GVHD+EPC group) followed by analysis of mice survival, acute GVHD (aGVHD) score, T cell infiltration by immunofluorescence, as well as continuity of vascular endothelium in liver.

Results

Compared with Allo-BMT group, the clinical and pathological score of aGVHD mice were higher. On day 21 after transplantation, a large number of mononuclear cell infiltrations were seen in the target tissues of aGVHD mice and mice died within 30 days. In addition, aGVHD group also presented increased subendothelial infiltration of CD3+ T cells in the liver, decreased VE-cadherin expression and elevated major histocompatibility complex (MHC) II molecule expression in the endothelium. Moreover, expression of MHC-II molecule increased in endothelial cell after irradiation injury and LPS stimulation, indicating abnormally activated endothelial cell with antigen-presenting function. Interestingly, infusion of EPC reduced the clinical and pathological score of aGVHD, decreased infiltration of mononuclear cells, improved survival as well as upregulated VE-cadherin and downregulated MHC-II molecule.

Discussion

EPC infusion can mobilize to affected endothelium to decrease the infiltration of T cells and pathological endothelial activation contributing to ameliorating the damage of endothelium. EPC infusion combined with bone marrow transplantation might be a perspective strategy for the prevention and treatment of aGVHD.

Impact of total marrow/lymphoid irradiation dose to the intestine on graft-versus-host disease in allogeneic hematopoietic stem cell transplantation for hematologic malignancies

Background and purpose

Graft-versus-host disease (GvHD) is a leading cause of non-relapse mortality in patients undergoing allogeneic hematopoietic stem cell transplantation. The Perugia Bone Marrow Transplantation Unit designed a new conditioning regimen with total marrow/lymphoid irradiation (TMLI) and adaptive immunotherapy. The present study investigated the impact of radiotherapy (RT) doses on the intestine on the incidence of acute GvHD (aGvHD) in transplant recipients, analyzing the main dosimetric parameters.

Materials and methods

Between August 2015 and April 2021, 50 patients with hematologic malignancies were enrolled. All patients underwent conditioning with TMLI. Dosimetric parameters (for the whole intestine and its segments) were assessed as risk factors for aGvHD. The RT dose that was received by each intestinal area with aGvHD was extrapolated from the treatment plan for each patient. Doses were compared with those of the whole intestine minus the affected area.

Results

Eighteen patients (36%) developed grade ≥2 aGvHD (G2 in 5, G3 in 11, and G4 in 2). Median time to onset was 41 days (range 23-69 days). The skin was involved in 11 patients, the intestine in 16, and the liver in 5. In all 50 TMLI patients, the mean dose to the whole intestine was 7.1 Gy (range 5.07-10.92 Gy). No patient developed chronic GvHD (cGvHD). No dosimetric variable emerged as a significant risk factor for aGvHD. No dosimetric parameter of the intestinal areas with aGvHD was associated with the disease.

Conclusion

In our clinical setting and data sample, we have found no clear evidence that current TMLI dosages to the intestine were linked to the development of aGvHD. However, due to some study limitations, this investigation should be considered as a preliminary assessment. Findings need to be confirmed in a larger cohort and in preclinical models.

Milestones in acute GVHD pathophysiology

In the past 65 years, over 25 000 referenced articles have been published on graft-versus-host disease (GVHD). Although this included clinically orientated papers or publications on chronic GVHD, the conservative estimate of scientific publications still contains several thousands of documents on the pathophysiology of acute GVHD. Thus, summarizing what we believe are prominent publications that can be considered milestones in our knowledge of this disease is a challenging and inherently biased task. Here we review from a historical perspective what can be regarded as publications that have made the field move forward. We also included several references of reviews on aspects we could not cover in detail.

Long-term follow up of patients with hematological malignancies treated with total body irradiation using intensity modulated radiation therapy

BACKGROUND

With the advent of modern radiation treatment technologies such as intensity modulated radiation therapy (IMRT), there has been increasing interest in its use for total body irradiation (TBI) conditioning regimens for hematopoietic cell transplantation (HCT) to achieve lower doses to critical organs such as the lungs and kidneys. Although this has been reported on in early studies, long-term safety and efficacy data is limited.

METHODS

We performed a single institution matched-pair retrospective analysis of patients treated with IMRT TBI and standard TBI between 2010 and 2020 to provide data on long-term outcomes. Patients with hematologic malignancies, who could not tolerate standing for traditional TBI or who received prior radiation received IMRT TBI. Patients were matched based on age, diagnosis, disease status, and year of transplant, and were matched 2:1 to the standard TBI and IMRT TBI cohorts. Patient and treatment characteristics, toxicity, graft-versus-host disease (GVHD), dosimetry, and outcomes were evaluated for each cohort.

RESULTS

A total of 13 patients met inclusion criteria for the IMRT cohort, leading to 26 patients in the standard TBI cohort. There was no significant difference in relevant clinical factors between the cohorts. Reasons for using IMRT over conventional TBI included being unable to stand (n=5), prior radiation (n=5), and pediatric patient requiring anesthesia (n=3). Among living patients, median follow-up for all patients was 5.1 years in the IMRT TBI cohort and 5.5 years in the standard TBI cohort. The 5-yr estimate of OS was 68% in the IMRT TBI cohort and 60% in the standard TBI cohort (p=0.706). The 5-yr estimate of RFS was 54% in the IMRT TBI cohort and 60% in the standard TBI cohort (p=0.529). There was no clinically significant pneumonitis, nephritis, hypothyroidism, or cataracts reported in the IMRT TBI cohort. 41.7% of patients in the IMRT TBI cohort and 79.2% of patients in the standard TBI cohort experienced Grade II-IV acute GVHD (p=0.023).

CONCLUSIONS

IMRT TBI appears to lead to favorable long-term outcome and dosimetry, and therefore potentially improved long-term toxicity profile compared to conventional TBI. IMRT TBI warrants further investigation as part of larger prospective trials.

Controversies and expectations for the prevention of GVHD: A biological and clinical perspective

Severe acute and chronic graft versus host disease (GVHD) remains a major cause of morbidity and mortality after allogeneic hematopoietic cell transplantation. Historically, cord blood and matched sibling transplantation has been associated with the lowest rates of GVHD. Newer methods have modified the lymphocyte components to minimize alloimmunity, including: anti-thymocyte globulin, post-transplant cyclophosphamide, alpha/beta T cell depletion, and abatacept. These agents have shown promise in reducing severe GVHD, however, can be associated with increased risks of relapse, graft failure, infections, and delayed immune reconstitution. Nonetheless, these GVHD prophylaxis strategies have permitted expansion of donor sources, especially critical for those of non-Caucasian decent who previously lacked transplant options. This review will focus on the biologic mechanisms driving GVHD, the method by which each agent impacts these activated pathways, and the clinical consequences of these modern prophylaxis approaches. In addition, emerging novel targeted strategies will be described. These GVHD prophylaxis approaches have revolutionized our ability to increase access to transplant and have provided important insights into the biology of GVHD and immune reconstitution.

Reversing radiation-induced immunosuppression using a new therapeutic modality

Radiation-induced immune suppression poses significant health challenges for millions of patients undergoing cancer chemotherapy and radiotherapy treatment, and astronauts and space tourists travelling to outer space. While a limited number of recombinant protein therapies, such a Sargramostim, are approved for accelerating hematologic recovery, the pronounced role of granulocyte-macrophage colony-stimulating factor (GM-CSF or CSF2) as a proinflammatory cytokine poses additional challenges in creating immune dysfunction towards pathogenic autoimmune diseases. Here we present an approach to high-throughput drug-discovery, target validation, and lead molecule identification using nucleic acid-based molecules. These Nanoligomer™ molecules are rationally designed using a bioinformatics and an artificial intelligence (AI)-based ranking method and synthesized as a single-modality combining 6-different design elements to up- or downregulate gene expression of target gene, resulting in elevated or diminished protein expression of intended target. This method additionally alters related gene network targets ultimately resulting in pathway modulation. This approach was used to perturb and identify the most effective upstream regulators and canonical pathways for therapeutic intervention to reverse radiation-induced immunosuppression. The lead Nanoligomer™ identified in a screen of human donor derived peripheral blood mononuclear cells (PBMCs) upregulated Erythropoietin (EPO) and showed the greatest reversal of radiation induced cytokine changes. It was further tested in vivo in a mouse radiation-model with low-dose (3 mg/kg) intraperitoneal administration and was shown to regulate gene expression of epo in lung tissue as well as counter immune suppression. These results point to the broader applicability of our approach towards drug-discovery, and potential for further investigation of our lead molecule as reversible gene therapy to treat adverse health outcomes induced by radiation exposure.

Characteristics of Graft-Versus-Host Disease (GvHD) After Post-Transplantation Cyclophosphamide Versus Conventional GvHD Prophylaxis

Post-transplantation cyclophosphamide (PTCy) has been shown to effectively control graft-versus-host disease (GvHD) in haploidentical (Haplo) transplantations. In this retrospective registry study, we compared GvHD organ distribution, severity, and outcomes in patients with GvHD occurring after Haplo transplantation with PTCy GvHD prophylaxis (Haplo/PTCy) versus HLA-matched unrelated donor transplantation with conventional prophylaxis (MUD/conventional). We evaluated 2 cohorts: patients with grade 2 to 4 acute GvHD (aGvHD) including 264 and 1163 recipients of Haplo and MUD transplants; and patients with any chronic GvHD (cGvHD) including 206 and 1018 recipients of Haplo and MUD transplants, respectively. In comparison with MUD/conventional transplantation ± antithymocyte globulin (ATG), grade 3-4 aGvHD (28% versus 39%, P = .001), stage 3-4 lower gastrointestinal (GI) tract aGvHD (14% versus 21%, P = .01), and chronic GI GvHD (21% versus 31%, P = .006) were less common after Haplo/PTCy transplantation. In patients with grade 2-4 aGvHD, cGvHD rate after Haplo/PTCY was also lower (hazard ratio [HR] = .4, P < .001) in comparison with MUD/conventional transplantation without ATG in the nonmyeloablative conditioning setting. Irrespective of the use of ATG, non-relapse mortality rate was lower (HR = .6, P = .01) after Haplo/PTCy transplantation, except for transplants that were from a female donor into a male recipient. In patients with cGvHD, irrespective of ATG use, Haplo/PTCy transplantation had lower non-relapse mortality rates (HR = .6, P = .04). Mortality rate was higher (HR = 1.6, P = .03) during, but not after (HR = .9, P = .6) the first 6 months after cGvHD diagnosis. Our results suggest that PTCy-based GvHD prophylaxis mitigates the development of GI GvHD and may translate into lower GvHD-related non-relapse mortality rate.

Insights into mechanisms of graft-versus-host disease through humanised mouse models

Graft-versus-host disease (GVHD) is a major complication that occurs following allogeneic haematopoietic stem cell transplantation (HSCT) for the treatment of haematological cancers and other blood-related disorders. GVHD is an inflammatory disorder, where the transplanted donor immune cells can mediate an immune response against the recipient and attack host tissues. Despite over 60 years of research, broad-range immune suppression is still used to prevent or treat GVHD, leading to an increased risk of cancer relapse and infection. Therefore, further insights into the disease mechanisms and development of predictive and prognostic biomarkers are key to improving outcomes and reducing GVHD development following allogeneic HSCT. An important preclinical tool to examine the pathophysiology of GVHD and to understand the key mechanisms that lead to GVHD development are preclinical humanised mouse models. Such models of GVHD are now well-established and can provide valuable insights into disease development. This review will focus on models where human peripheral blood mononuclear cells are injected into immune-deficient non-obese diabetic (NOD)-scid-interleukin-2(IL-2)Rγ mutant (NOD-scid-IL2Rγ^null) mice. Humanised mouse models of GVHD can mimic the clinical setting for GVHD development, with disease progression and tissues impacted like that observed in humans. This review will highlight key findings from preclinical humanised mouse models regarding the role of donor human immune cells, the function of cytokines and cell signalling molecules and their impact on specific target tissues and GVHD development. Further, specific therapeutic strategies tested in these preclinical models reveal key molecular pathways important in reducing the burden of GVHD following allogeneic HSCT.

Emerging translational strategies and challenges for enhancing regulatory T cell therapy for graft-versus-host disease

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is a curative therapy for many types of cancer. Genetic disparities between donor and host can result in immune-mediated attack of host tissues, known as graft versus host disease (GVHD), a major cause of morbidity and mortality following HSCT. Regulatory CD4+ T cells (Tregs) are a rare cell type crucial for immune system homeostasis, limiting the activation and differentiation of effector T cells (Teff) that are self-reactive or stimulated by foreign antigen exposure. Adoptive cell therapy (ACT) with Treg has demonstrated, first in murine models and now in patients, that prophylactic Treg infusion can also suppress GVHD. While clinical trials have demonstrated Treg reduce severe GVHD occurrence, several impediments remain, including Treg variability and practical need for individualized Treg production for each patient. Additionally, there are challenges in the use of in vitro expansion techniques and in achieving in vivo Treg persistence in context of both immune suppressive drugs and in lymphoreplete patients being treated for GVHD. This review will focus on 3 main translational approaches taken to improve the efficacy of tTreg ACT in GVHD prophylaxis and development of treatment options, following HSCT: genetic modification, manipulating TCR and cytokine signaling, and Treg production protocols. In vitro expansion for Treg ACT presents a multitude of approaches for gene modification to improve efficacy, including: antigen specificity, tissue targeting, deletion of negative regulators/exhaustion markers, resistance to immunosuppressive drugs common in GVHD treatment. Such expansion is particularly important in patients without significant lymphopenia that can drive Treg expansion, enabling a favorable Treg:Teff ratio in vivo. Several potential therapeutics have also been identified that enhance tTreg stability or persistence/expansion following ACT that target specific pathways, including: DNA/histone methylation status, TCR/co-stimulation signaling, and IL-2/STAT5 signaling. Finally, this review will discuss improvements in Treg production related to tissue source, Treg subsets, therapeutic approaches to increase Treg suppression and stability during tTreg expansion, and potential for storing large numbers of Treg from a single production run to be used as an off-the-shelf infusion product capable of treating multiple recipients.

Total marrow and lymphoid irradiation as conditioning in haploidentical transplant with posttransplant cyclophosphamide

TMLI at 2000 cGy for HaploHCT with PTCy was determined to be safe in patients with high-risk leukemia and MDS.

At 2000 cGy, a 1-year relapse rate of 17% was achieved without increasing GVHD or transplant-related mortality.

Posttransplant cyclophosphamide (PTCy) platform has shown low rates of graft-versus-host disease (GVHD) and nonrelapse mortality (NRM) after haploidentical hematopoietic cell transplantation (HaploHCT). However, because of the limited disease control, relapse rate remains a major cause of treatment failure in high-risk patients. Total marrow and lymphoid irradiation (TMLI) allows for delivery of high radiation to bone marrow and other targeted structures, without increasing off-target radiation exposure and toxicity to end organs. In this phase 1 trial, 31 patients with high-risk and/or active primary refractory leukemias or myelodysplastic syndrome underwent peripheral blood stem cell HaploHCT with TMLI, fludarabine, and cyclophosphamide as the conditioning regimen. Radiation dose was escalated in increments of 200 cGy (1200-2000 cGy). GVHD prophylaxis was PTCy with tacrolimus/mycophenolate mofetil. Grade 2 toxicities by the Bearman scale were mucositis (n = 1), hepatic (n = 3), gastrointestinal (n = 5), and cardiac (n = 2). One patient (1800 cGy) experienced grade 3 pulmonary toxicity (dose-limiting toxicity). At a follow-up duration of 23.9 months for the whole cohort; 2-year NRM was 13%. Cumulative incidence of day 100 grade 2 to 4 and 3 to 4 acute GVHD was 52% and 6%, respectively. Chronic GVHD at 2 years was 35%. For patients treated with 2000 cGy, with a median follow-up duration of 12.3 months, 1-year relapse/progression, progression-free survival, and overall survival rates were 17%, 74%, and 83%, respectively. In conclusion, HaploHCT-TMLI with PTCy was safe and feasible in our high-risk patient population with promising outcomes.

Assessment of systemic and gastrointestinal tissue damage biomarkers for GVHD risk stratification

Two biomarker algorithms that include only systemic inflammation biomarkers predicted response to steroid treatment but not 6-month NRM.

Two biomarker algorithms that include ≥1 biomarker of GI tissue damage predicted both response to treatment and 6-month NRM.

We used a rigorous PRoBE (prospective-specimen collection, retrospective-blinded-evaluation) study design to compare the ability of biomarkers of systemic inflammation and biomarkers of gastrointestinal (GI) tissue damage to predict response to corticosteroid treatment, the incidence of clinically severe disease, 6-month nonrelapse mortality (NRM), and overall survival in patients with acute graft-versus-host disease (GVHD). We prospectively collected serum samples of newly diagnosed GVHD patients (n = 730) from 19 centers, divided them into training (n = 352) and validation (n = 378) cohorts, and measured TNFR1, TIM3, IL6, ST2, and REG3α via enzyme-linked immunosorbent assay. Performances of the 4 strongest algorithms from the training cohort (TNFR1 + TIM3, TNFR1 + ST2, TNFR1 + REG3α, and ST2 + REG3α) were evaluated in the validation cohort. The algorithm that included only biomarkers of systemic inflammation (TNFR1 + TIM3) had a significantly smaller area under the curve (AUC; 0.57) than the AUCs of algorithms that contained ≥1 GI damage biomarker (TNFR1 + ST2, 0.70; TNFR1 + REG3α, 0.73; ST2 + REG3α, 0.79; all P < .001). All 4 algorithms were able to predict short-term outcomes such as response to systemic corticosteroids and severe GVHD, but the inclusion of a GI damage biomarker was needed to predict long-term outcomes such as 6-month NRM and survival. The algorithm that included 2 GI damage biomarkers was the most accurate of the 4 algorithms for all endpoints.

Aryl hydrocarbon receptor-targeted therapy for CD4+ T cell-mediated idiopathic pneumonia syndrome in mice

We previously demonstrated that interferon γ (IFN-γ) derived from donor T cells co-opts the indoleamine 2,3-dioxygenase 1 (IDO1) → aryl hydrocarbon receptor (AHR) axis to suppress idiopathic pneumonia syndrome (IPS). Here we report that the dysregulated expression of AP-1 family genes in Ahr-/- lung epithelial cells exacerbated IPS in allogeneic bone marrow transplantation settings. AHR repressed transcription of Jund by preventing STAT1 from binding to its promoter. As a consequence, decreased interleukin-6 impaired the differentiation of CD4+ T cells toward Th17 cells. IFN-γ- and IDO1-independent induction of Ahr expression indicated that the AHR agonist might be a better therapeutic target for IPS than the IDO1 activator. We developed a novel synthetic AHR agonist (referred to here as PB502) that potently inhibits Jund expression. PB502 was highly effective at inducing AHR activation and ameliorating IPS. Notably, PB502 was by far superior to the endogenous AHR ligand, L-kynurenine, in promoting the differentiation of both mouse and human FoxP3+ regulatory CD4+ T cells. Our results suggest that the IDO1-AHR axis in lung epithelial cells is associated with IPS repression. A specific AHR agonist may exhibit therapeutic activity against inflammatory and autoimmune diseases by promoting regulatory T-cell differentiation.

Human Monocyte-Derived Suppressor Cell Supernatant Induces Immunoregulatory Effects and Mitigates xenoGvHD

Recently developed cell-based therapies have shown potential for graft-versus-host disease (GvHD) mitigation. Our team previously developed a protocol to generate human monocyte-derived suppressor Cells (HuMoSC), a subpopulation of CD33+ suppressor cells of monocytic origin. CD33+HuMoSC successfully reduced xenoGvHD severity in NOD/SCID/IL-2Rγc^-/- (NSG) mice. While CD33+ HuMoSC culture supernatant inhibits T cell activation and proliferation, the recovery of CD33+ HuMoSC immunosuppressive cells and the subsequent production of their supernatant is limited. An attractive solution would be to use both the CD33+ and the large number of CD14+ cells derived from our protocol. Here, we assessed the immunoregulatory properties of the CD14+HuMoSC supernatant and demonstrated that it inhibited both CD4 and CD8 T cell proliferation and decreased CD8 cytotoxicity. In vivo, injection of CD14+HuMoSC supernatant reduced xenoGvHD in NSG mice. Furthermore, CD14+HuMoSC supernatant maintained its immunoregulatory properties in an inflammatory environment. Proteomic and multiplex analyses revealed the presence of immunosuppressive proteins such as GPNMB, galectin-3 and IL-1R(A) Finally, CD14+HuMoSC supernatant can be produced using good manufacturing practices and be used as complement to current immunosuppressive drugs. CD14+HuMoSC supernatant is thus a promising therapy for preventing GvHD. 

High-density lipoprotein infusion protects from acute graft-versus-host disease in experimental allogeneic hematopoietic cell transplantation

Acute graft-versus-host disease (aGVHD) is a major limitation of the therapeutic potential of allogeneic hematopoietic cell transplantation. Lipopolysaccharides (LPS) derived from intestinal gram-negative bacteria are well-known aGVHD triggers and amplifiers. Here, we explored the LPS metabolism in aGVHD mouse models using an innovative quantification method. We demonstrated that systemic LPS accumulation after transplantation was due, at least partly, to a defect in its clearance through lipoprotein-mediated transport to the liver (i.e., the so-called reverse LPS transport). After transplantation, reduced circulating HDL concentration impaired LPS neutralization and elimination through biliary flux. Accordingly, HDL-deficient (Apoa1^tm1Unc ) recipient mice developed exacerbated aGVHD. Repeated administration of HDL isolated from human plasma significantly decreased the mortality and the severity of aGVHD. While the potential role of HDL in scavenging circulating LPS was examined in this study, it appears that HDL plays a more direct immunomodulatory role by limiting or controlling aGVHD. Notably, HDL infusion mitigated liver aGVHD by diminishing immune infiltration (e.g., interferon-γ-secreting CD8⁺ T cells and non-resident macrophages), systemic and local inflammation (notably cholangitis). Hence, our results revealed the interest of HDL-based therapies in the prevention of aGVHD.

Bone marrow transplantation induces changes in the gut microbiota that chronically increase the cytokine response pattern of splenocytes

Bone marrow transplantation (BMT) involves conditioning regimens which acutely induce side effects, including systemic inflammation, intestinal damage and shifts in the gut microbial composition, some of which may persist chronically. As the gut microbiota affect systemic immune responses, we aimed to investigate whether, post-BMT, the peripheral immune system is modulated as a direct consequence of alterations in the gut microbiota. We show that 24 weeks post-BMT, splenocytes but not peritoneal macrophages display increased cytokine response patterns upon ex-vivo stimulation with various pathogens as compared to untreated controls. The pattern of BMT-induced cytokine responses was transferred to splenocytes, and not to peritoneal macrophages, of healthy controls via co-housing and transferred to germfree mice via transplantation of cecum content. Thus, BMT induces changes in gut microbiota that in their turn increase cytokine responsiveness of splenocytes. Thus, BMT establishes a dominant microbiota that attenuates normalization of the immune-response.

Modeling acute graft-versus-host disease (aGVHD) in murine bone marrow transplantation (BMT) models with MHC disparity

For more than 50years, hematopoietic stem cell transplantation (HSCT) has been the major curative therapy for hematological malignancies and genetic disorders, but its success is limited by the development of graft-versus-host disease (GVHD). GVHD represents a post-transplantation disorder representing the immune-mediated attack of transplant-derived T cells against recipient tissue finally leading to increased morbidity and mortality of the recipient. GVHD develops if donor and recipient are disparate in major or minor histocompatibility antigens (MHC, miHA). Most of the initial knowledge about the biology of GVHD is derived from murine bone marrow transplantation (BMT) models. Of course, GVHD mouse models do not reflect one to one the human situation, but they contribute significantly to our understanding how conditioning and danger signals activate the immune system, enlighten the role of individual molecules, e.g., cytokines, chemokines, death-inducing ligands, define the function of lymphocytes subpopulations for GVHD development and have significant impact on establishing new treatment and prevention strategies used in clinical HSCT. This chapter describes in detail the procedure of allogeneic BMT and the development of GVHD in two commonly used allogeneic murine BMT models (B6→B6.bm1, B6→B6D2F1) with different MHC disparities, which can be used as a basis for advanced studies of GVHD pathology or the development of new treatment strategies.

Donor bone marrow-derived macrophage MHC II drives neuroinflammation and altered behavior during chronic GVHD in mice

Graft-versus-host disease (GVHD) remains the leading cause of nonrelapse mortality after allogeneic stem cell transplantation for hematological malignancies. Manifestations of GVHD in the central nervous system (CNS) present as neurocognitive dysfunction in up to 60% of patients; however, the mechanisms driving chronic GVHD (cGVHD) in the CNS are yet to be elucidated. Our studies of murine cGVHD revealed behavioral deficits associated with broad neuroinflammation and persistent Ifng upregulation. By flow cytometry, we observed a proportional shift in the donor-derived T-cell population in the cGVHD brain from early CD8 dominance to later CD4 sequestration. RNA sequencing of the hippocampus identified perturbations to structural and functional synapse-related gene expression, together with the upregulation of genes associated with interferon-γ responses and antigen presentation. Neuroinflammation in the cortex of mice and humans during acute GVHD was recently shown to be mediated by resident microglia-derived tumor necrosis factor. In contrast, infiltration of proinflammatory major histocompatibility complex (MHC) class II+ donor bone marrow (BM)-derived macrophages (BMDMs) was identified as a distinguishing feature of CNS cGVHD. Donor BMDMs, which composed up to 50% of the CNS myeloid population, exhibited a transcriptional signature distinct from resident microglia. Recipients of MHC class II knockout BM grafts exhibited attenuated neuroinflammation and behavior comparable to controls, suggestive of a critical role of donor BMDM MHC class II expression in CNS cGVHD. Our identification of disease mediators distinct from those in the acute phase indicates the necessity to pursue alternative therapeutic targets for late-stage neurological manifestations.

CCL8 deficiency in the host abrogates early mortality of acute graft-versus-host disease in mice with dysregulated IL-6 expression

Although allogeneic hematopoietic stem cell transplantation (HSCT) is a curative treatment for diverse malignant and nonmalignant diseases, acute graft-versus-host disease (aGVHD) is strongly linked to mortality caused by HSCT. We previously reported that CC chemokine ligand 8 (CCL8) is closely correlated to aGVHD mortality in both humans and mice. To study the role of CCL8 in aGVHD, CCL8 knockout (CCL8-/-) mice were transplanted with fully allogeneic marrow grafts. These mice exhibited a significant reduction in mortality (90.0% vs. 23.4% survival for CCL8-/- vs. wild-type recipients at day 28, p < 0.0001). As a result, apparent prolonged median survival from 9 days in wild-type mice to 45 days in CCL8-/- mice was observed. Acute GVHD pathology and liver dysfunction in CCL8-/- mice were significantly attenuated compared with those in wild-type mice. In association with the reduced mortality, a surge of plasma interleukin (IL)-6 was observed in CCL8-/- recipients with allogeneic marrow, which was significantly increased compared with wild-type mice that received allografts. Donor T-cell expansion and plasma levels of interferon-γ and TNF-α during aGVHD were similar in both types of mice. Collectively, these findings indicate that CCL8 plays a major role in aGVHD pathogenesis with possible involvement of an IL-6 signaling cascade.

A Polymorphism of Bactericidal/Permeability-Increasing Protein Affects Its Neutralization Efficiency towards Lipopolysaccharide

Gram-negative sepsis driven by lipopolysaccharide (LPS) has detrimental outcomes, especially in neonates. The neutrophil-derived bactericidal/permeability-increasing protein (BPI) potently neutralizes LPS. Interestingly, polymorphism of the BPI gene at position 645 (rs4358188) corresponds to a favorable survival rate of these patients in the presence of at least one allele 645 A as opposed to 645 G. When we exploited the existing X-ray crystal structure, the corresponding amino acid at position 216 was revealed as surface exposed and proximal to the lipid-binding pocket in the N-terminal domain of BPI. Our further analysis predicted a shift in surface electrostatics by a positively charged lysine (BPI_216K) exchanging a negatively charged glutamic acid (BPI_216E). To investigate differences in interaction with LPS, we expressed both BPI variants recombinantly. The amino acid exchange neither affected affinity towards LPS nor altered bactericidal activity. However, when stimulating human peripheral blood mononuclear cells, BPI_216K exhibited a superior LPS-neutralizing capacity (IC₅₀ 12.0 ± 2.5 pM) as compared to BPI_216E (IC₅₀ 152.9 ± 113.4 pM, p = 0.0081) in respect to IL-6 secretion. In conclusion, we provide a functional correlate to a favorable outcome of sepsis in the presence of BPI_216K.

Challenges and opportunities targeting mechanisms of epithelial injury and recovery in acute intestinal graft-versus-host disease

Despite advances in immunosuppressive prophylaxis and overall supportive care, gastrointestinal (GI) graft-versus-host disease (GVHD) remains a major, lethal side effect after allogeneic hematopoietic stem cell transplantation (allo-HSCT). It has become increasingly clear that the intestinal epithelium, in addition to being a target of transplant-related toxicity and GVHD, plays an important role in the onset of GVHD. Over the last two decades, increased understanding of the epithelial constituents and their microenvironment has led to the development of novel prophylactic and therapeutic interventions, with the potential to protect the intestinal epithelium from GVHD-associated damage and promote its recovery following insult. In this review, we will discuss intestinal epithelial injury and the role of the intestinal epithelium in GVHD pathogenesis. In addition, we will highlight possible approaches to protect the GI tract from damage posttransplant and to stimulate epithelial regeneration, in order to promote intestinal recovery. Combined treatment modalities integrating immunomodulation, epithelial protection, and induction of regeneration may hold the key to unlocking mucosal recovery and optimizing therapy for acute intestinal GVHD.

mTOR Signaling Regulates the Development and Therapeutic Efficacy of PMN-MDSCs in Acute GVHD

Myeloid-derived suppressor cells (MDSCs) represent a population of heterogeneous myeloid cells, which are characterized by their remarkable ability to suppress T cells and natural killer cells. MDSCs have been proven to play a positive role in protecting acute graft-versus-host disease (aGVHD). Here, we aimed to describe the mechanism behind how mTOR signaling regulates MDSCs' generation and explore its prophylactic and therapeutic potential in aGVHD. Reducing mTOR expression retains myeloid cells with immature characteristics and promotes polymorphonuclear MDSC (PMN-MDSC) immunosuppressive function through STAT3-C/EBPβ pathway. Prophylactic transfusion of mTORKO PMN-MDSCs could alleviate aGVHD while maintaining the graft-versus-leukemia (GVL) effect, which could downregulate the Th1/Th2 ratio, decrease serum proinflammatory cytokines, and increase the proportion of regulatory T cells (Tregs) in aGVHD models at the early stage after transplantation. Moreover, transfusion therapy could promote the reconstruction and function of donor-derived PMN-MDSCs. Not only the percentage and the absolute number of donor-derived PMN-MDSCs significantly increased but also the immunosuppressive ability was much more robust compared to other groups. Altogether, these findings indicated that mTOR is an intrinsic regulator for PMN-MDSCs' differentiation and immunosuppressive function. Together, mTORKO PMN-MDSC transfusion can play a protective role in alleviating cytokine storm at the initial stage and promoting the quantitative and functional recoveries of donor-derived PMN-MDSCs in aGVHD.

Does Total Body Irradiation Have a Favorable Impact on Thrombocyte Engraftment as per Neutrophil Engraftment in Allogeneic Stem Cell Transplantation?

Introduction: In this study, we aim to analyze the effect of total body irradiation (TBI) on neutrophil and thrombocyte engraftment durations in acute leukemia (AL) patients who achieved allogeneic hematopoietic stem cell transplantation (Allo-SCT) at our center.

Methods: The data of 193 acute leukemia patients who were performed Allo-SCT from matched-related donors were analyzed retrospectively.

Results: Thrombocyte engraftment duration was statistically shorter (12 days) in acute lymphoblastic leukemia (ALL) patients who received TBI-based conditioning when compared to ALL patients who received non-TBI-based conditioning (14 days; p=0.037). On the other hand, no statistically significant difference was observed between acute leukemia patients who received TBI or non-TBI-based conditioning regarding neutrophil engraftment duration.

Conclusion: We found that TBI had a favorable impact on thrombocyte engraftment (TE) rather than neutrophil engraftment (NE) in Allo-SCT in patients with acute leukemia. TBI might have an impact on the engraftment of thrombocytes as per than neutrophils may be attributed to immune mechanisms and microenvironment in the patient’s bone marrow (BM).

Translational Clinical Strategies for the Prevention of Gastrointestinal Tract Graft Versus Host Disease

Graft versus host disease (GVHD) is the major non-relapse complication associated with allogeneic hematopoietic stem cell transplantation (HSCT). Unfortunately, GVHD occurs in roughly half of patients following this therapy and can induce severe life-threatening side effects and premature mortality. The pathophysiology of GVHD is driven by alloreactive donor T cells that induce a proinflammatory environment to cause pathological damage in the skin, gastrointestinal (GI) tract, lung, and liver during the acute phase of this disease. Recent work has demonstrated that the GI tract is a pivotal target organ and a primary driver of morbidity and mortality in patients. Prevention of this complication has therefore emerged as an important goal of prophylaxis strategies given the primacy of this tissue site in GVHD pathophysiology. In this review, we summarize foundational pre-clinical studies that have been conducted in animal models to prevent GI tract GVHD and examine the efficacy of these approaches upon subsequent translation into the clinic. Specifically, we focus on therapies designed to block inflammatory cytokine pathways, inhibit cellular trafficking of alloreactive donor T cells to the GI tract, and reconstitute impaired regulatory networks for the prevention of GVHD in the GI tract.