Innovations in treating acute graft-versus-host disease: a review of preclinical targets and strategies.

INTRODUCTION: Acute graft-versus-host disease (aGVHD) is a major complication of post-allogeneic hematopoietic stem cell transplantation (allo-HSCT) that severely impacts patient survival and quality of life. Despite advancements in standard care, therapeutic outcomes remain suboptimal, necessitating the exploration of innovative strategies. AREAS COVERED: This review synthesizes preclinical research focusing on novel therapeutic targets and strategies that may enhance treatment efficacy. We critically analyzed the role of specific T-cell subsets, cytokine modulators, and intracellular signaling pathways in reducing aGVHD severity. Emphasis is placed on experimental findings that illuminate the mechanisms of immune tolerance and survival improvement. We discuss the translation of these findings into potential clinical trials and evaluate the challenges and progress in implementing these strategies, including scalability and impact on the graft-versus-leukemia (GVL) effect. EXPERT OPINION: Our review summarizes the latest therapeutic targets and strategies in preclinical research for aGVHD, aiming to bridge the gap between clinical and experimental medicine. By integrating immunology, genetics, and cytology, we seek to enhance the translation of preclinical findings into clinical strategies. This multidisciplinary approach is expected to improve patient outcomes in aGVHD treatment, ultimately leading to more effective and safer therapies.

Immune isolation-enabled nanoencapsulation of donor T cells: a promising strategy for mitigating GVHD and treating AML in preclinical models.

BACKGROUND: In allogeneic-hematopoietic stem cell transplantation for acute myeloid leukemia (AML), donor T cells combat leukemia through the graft-versus-leukemia (GVL) effect, while they also pose a risk of triggering life-threatening graft-versus-host disease (GVHD) by interacting with recipient cells. The onset of GVHD hinges on the interplay between donor T cells and recipient antigen-presenting cells (APCs), sparking T-cell activation. However, effective methods to balance GVHD and GVL are lacking. METHODS: In our study, we crafted nanocapsules by layering polycationic aminated gelatin and polyanionic alginate onto the surface of T cells, examining potential alterations in their fundamental physiological functions. Subsequently, we established an AML mouse model and treated it with transplantation of bone marrow cells (BMCs) combined with encapsulated T cells to investigate the GVL and anti-GVHD effects of encapsulated T cells. In vitro co-culture was employed to probe the effects of encapsulation on immune synapses, co-stimulatory molecules, and tumor-killing pathways. RESULTS: Transplantation of BMCs combined with donor T cells selectively encapsulated onto AML mice significantly alleviates GVHD symptoms while preserving essential GVL effects. Encapsulated T cells exerted their immunomodulatory effects by impeding the formation of immune synapses with recipient APCs, thereby downregulating co-stimulatory signals such as CD28-CD80, ICOS-ICOSL, and CD40L-CD40. Recipient mice receiving encapsulated T-cell transplantation exhibited a marked increase in donor Ly-5.1-BMC cell numbers, accompanied by unaltered in vivo expression levels of perforin and granzyme B. While transient inhibition of donor T-cell cytotoxicity in the tumor microenvironment was observed in vitro following single-cell nanoencapsulation, subsequent restoration to normal antitumor activity ensued, attributed to selective permeability of encapsulated vesicle shells and material degradation. Moreover, the expression of apoptotic proteins and FAS-FAS ligand pathway at normal levels was still observed in leukemia tumor cells. CONCLUSIONS: Encapsulated donor T cells effectively mitigate GVHD while preserving the GVL effect by minimizing co-stimulatory signaling with APCs through early immune isolation. Subsequent degradation of nanocapsules restores T-cell cytotoxic efficacy against AML cells, mediated by cytotoxic pathways. Using transplant-encapsulated T cells offers a promising strategy to suppress GVHD while preserving the GVL effect.

Minor histocompatibility antigens to predict, monitor or manipulate GvL and GvHD after allogeneic hematopoietic cell transplantation.

Allogeneic hematopoietic cell transplantation (alloHCT) provides a potential curative treatment for haematological malignancies. The therapeutic Graft-versus-Leukaemia (GvL) effect is induced by donor T cells attacking patient hematopoietic (malignant) cells. However, if healthy non-hematopoietic tissues are targeted, Graft-versus-Disease (GvHD) may develop. After HLA-matched alloHCT, GvL and GvHD are induced by donor T cells recognizing polymorphic peptides presented by HLA on patient cells, so-called minor histocompatibility antigens (MiHAs). The balance between GvL and GvHD depends on the tissue distribution of MiHAs and T-cell frequencies targeting these MiHAs. T cells against broadly expressed MiHAs induce GvL and GvHD, whereas those targeting MiHAs with hematopoietic-restricted expression induce GvL without GvHD. Recently, the MiHA repertoire identified in natural immune responses after alloHCT was expanded to 159 total HLA-I-restricted MiHAs, including 14 hematopoietic-restricted MiHAs. This review explores their potential relevance to predict, monitor, and manipulate GvL and GvHD for improving clinical outcome after HLA-matched alloHCT.

Icariin protects against acute graft-versus-host disease while preserving graft-versus-leukemia activity after allogeneic hematopoietic stem cell transplantation.

BACKGROUND: Acute graft-versus-host disease (aGVHD), which is mainly mediated by allogeneic T cells, is a decisive factor in the success of allogeneic hematopoietic stem cell transplantation (allo-HCT). Prophylaxis for aGVHD in clinical patients is unsatisfactory, and there is still a huge unmet need for novel approaches. Icariin (ICA) shows potent anti-inflammatory activity and suppresses T cell-mediated immune responses. Thus, ICA is a potential drug for the prevention of aGVHD. However, there is no data assessing the impact of ICA on aGVHD after allo-HCT. PURPOSE: This study aimed to investigate the protective effect of ICA against aGVHD and its mechanisms. Moreover, the impact of ICA on the graft-versus-leukemia (GVL) effect and engraftment of donor hematopoietic and immune cells were assessed. METHODS: Different murine models of allo-HCT were developed to study the influence of the ICA on GVHD and GVL effect. Flow cytometry was used to analyze the growth of leukemia cells, alterations in different immune cells, and apoptosis. Cell proliferation was determined using a CCK-8 assay. RNA sequencing and quantitative proteomic analysis were performed to elucidate the underlying mechanisms, which were further verified by polymerase chain reaction or functional experiments. RESULTS: Different concentrations of ICA exhibited opposite effects: low-concentration ICA promoted, while high concentrations suppressed the proliferation and function of T cells. A high dose of ICA administration during days +3 to +5 post-allo-HCT can alleviate murine aGVHD but does not affect the course of chronic GVHD (cGVHD), the GVL effect against both acute myeloid and lymphoblastic leukemia, or the recovery of donor hematological and immune cells. ICA extensively represses the expansion, function, and infiltration of donor alloreactive T cells, while preserving regulatory T cells (Tregs) and myeloid-derived suppressor cells (MDSC). Quantitative proteomic analysis showed that downregulation of integrin-linked kinase (ILK) and lymphocyte cytosolic protein 2 (LCP2) expression was possibly associated with ICA-mediated aGVHD protective effects. Furthermore, an inhibitor of ILK, which can alleviate murine aGVHD administered early after allo-HCT. CONCLUSION: These findings suggest that the bioactivities of ICA are associated with its concentration and that ICA can effectively mitigate aGVHD without losing GVL activity or engraftment of donor hematopoietic and immune cells. Thus, ICA may be a promising drug for preventing aGVHD in clinical settings.

Endoplasmic Reticulum Stress Response Mediator IRE-1α Promotes Host Dendritic Cells in Graft-versus-Host Disease Development.

Allogeneic hematopoietic cell transplantation is an effective treatment for hematologic malignancies, but the complications such as graft-versus-host disease (GVHD) can limit its benefit. The conditioning regimens before transplant, including chemotherapy or irradiation, can trigger endoplasmic reticulum stress. IRE-1α is a major endoplasmic reticulum stress mediator that can further activate both spliced XBP-1 (XBP-1s) and regulated IRE-1-dependent decay (RIDD). IRE-1α-XBP-1s signaling controls dendritic cell (DC) differentiation and Ag presentation, crucial in GVHD progression. In this study, we used DC-specific XBP-1-deficient mice as donors or recipients and observed that XBP-1s was crucial for host DCs in the induction of GVHD but dispensable for the graft-versus-leukemia response. To specifically target IRE-1α in the host, we treated recipient mice with the IRE-1α inhibitor B-I09 for 3 d prior to bone marrow transplantation, which significantly suppressed GVHD development while maintaining the graft-versus-leukemia effect. XBP-1-deficient or BI09-treated recipients showed reduced DC survival after irradiation and bone marrow transplantation. Inhibition of IRE-1α also led to a reduction in DC alloreactivity, subsequently decreasing the proliferation and activation of allogeneic T cells. With further study using RIDD-deficient DCs, we observed that RIDD was also required for optimal DC activation. Taken together, XBP-1s and RIDD both promote host DC survival and alloreactivity that contribute to GVHD development.

Oncogene-induced TIM-3 ligand expression dictates susceptibility to anti-TIM-3 therapy in mice.

Leukemia relapse is a major cause of death after allogeneic hematopoietic cell transplantation (allo-HCT). We tested the potential of targeting T cell (Tc) immunoglobulin and mucin-containing molecule 3 (TIM-3) for improving graft-versus-leukemia (GVL) effects. We observed differential expression of TIM-3 ligands when hematopoietic stem cells overexpressed certain oncogenic-driver mutations. Anti-TIM-3 Ab treatment improved survival of mice bearing leukemia with oncogene-induced TIM-3 ligand expression. Conversely, leukemia cells with low ligand expression were anti-TIM-3 treatment resistant. In vitro, TIM-3 blockade or genetic deletion in CD8+ Tc enhanced Tc activation, proliferation, and IFN-γ production while enhancing GVL effects, preventing Tc exhaustion, and improving Tc cytotoxicity and glycolysis in vivo. Conversely, TIM-3 deletion in myeloid cells did not affect allogeneic Tc proliferation and activation in vitro, suggesting that anti-TIM-3 treatment-mediated GVL effects are Tc induced. In contrast to anti-programmed cell death protein 1 (anti-PD-1) and anti-cytotoxic T lymphocyte-associated protein 4 (anti-CTLA-4) treatment, anti-TIM-3-treatment did not enhance acute graft-versus-host disease (aGVHD). TIM-3 and its ligands were frequently expressed in acute myeloid leukemia (AML) cells of patients with post-allo-HCT relapse. We decipher the connections between oncogenic mutations found in AML and TIM-3 ligand expression and identify anti-TIM-3 treatment as a strategy for enhancing GVL effects via metabolic and transcriptional Tc reprogramming without exacerbation of aGVHD. Our findings support clinical testing of anti-TIM-3 Ab in patients with AML relapse after allo-HCT.

Memory T-cell enriched haploidentical transplantation with NK cell addback results in promising long-term outcomes: a phase II trial.

BACKGROUND: Relapse remains a challenge after transplantation in pediatric patients with hematological malignancies. Myeloablative regimens used for disease control are associated with acute and long-term adverse effects. We used a CD45RA-depleted haploidentical graft for adoptive transfer of memory T cells combined with NK-cell addback and hypothesized that maximizing the graft-versus-leukemia (GVL) effect might allow for reduction in intensity of conditioning regimen. METHODS: In this phase II clinical trial (NCT01807611), 72 patients with hematological malignancies (complete remission (CR)1: 25, ≥ CR2: 28, refractory disease: 19) received haploidentical CD34 + enriched and CD45RA-depleted hematopoietic progenitor cell grafts followed by NK-cell infusion. Conditioning included fludarabine, thiotepa, melphalan, cyclophosphamide, total lymphoid irradiation, and graft-versus-host disease (GVHD) prophylaxis consisted of a short-course sirolimus or mycophenolate mofetil without serotherapy. RESULTS: The 3-year overall survival (OS) and event-free-survival (EFS) for patients in CR1 were 92% (95% CI:72-98) and 88% (95% CI: 67-96); ≥ CR2 were 81% (95% CI: 61-92) and 68% (95% CI: 47-82) and refractory disease were 32% (95% CI: 11-54) and 20% (95% CI: 6-40). The 3-year EFS for all patients in morphological CR was 77% (95% CI: 64-87) with no difference amongst recipients with or without minimal residual disease (P = 0.2992). Immune reconstitution was rapid, with mean CD3 and CD4 T-cell counts of 410/µL and 140/µL at day + 30. Cumulative incidence of acute GVHD and chronic GVHD was 36% and 26% but most patients with acute GVHD recovered rapidly with therapy. Lower rates of grade III-IV acute GVHD were observed with NK-cell alloreactive donors (P = 0.004), and higher rates of moderate/severe chronic GVHD occurred with maternal donors (P = 0.035). CONCLUSION: The combination of a CD45RA-depleted graft and NK-cell addback led to robust immune reconstitution maximizing the GVL effect and allowed for use of a submyeloablative, TBI-free conditioning regimen that was associated with excellent EFS resulting in promising long-term outcomes in this high-risk population. The trial is registered at ClinicalTrials.gov (NCT01807611).

The role and novel use of natural killer cells in graft-versus-leukemia reactions after allogeneic transplantation.

Allogeneic hematopoietic cell transplantation (HCT) has transformed over the past several decades through enhanced supportive care, reduced intensity conditioning (RIC), improved human leukocyte antigen (HLA) typing, and novel graft-versus-host disease (GVHD)-prevention and treatment strategies. Most notably, the implementation of post-transplantation cyclophosphamide (PTCy) has dramatically increased the safety and availability of this life-saving therapy. Given reductions in nonrelapse mortality (NRM) with these advances, the HCT community has placed even greater emphasis on developing ways to reduce relapse - the leading cause of death after HCT. When using RIC HCT, protection from relapse relies predominantly on graft-versus-leukemia (GVL) reactions. Donor lymphocyte infusion (DLI), adoptive cellular therapy, checkpoint inhibition, and post-HCT maintenance strategies represent approaches under study that aim to augment or synergize with the GVL effects of HCT. Optimizing donor selection algorithms to leverage GVL represents another active area of research. Many of these strategies seek to harness the effects of T cells, which for decades were felt to be the primary mediators of GVL and the focus of investigation in relapse reduction. However, there is growing interest in capitalizing on the ability of natural killer (NK) cells to yield potent anti-tumor effects. A potential advantage of NK cell-based approaches over T cell-mediated is the potential to reduce NRM in addition to relapse. By decreasing infection, without increasing the risk of GVHD, NK cells may mitigate NRM, while still yielding relapse reduction through identification and clearance of cancer cells. Most T cell-focused relapse-prevention strategies must weigh the benefits of relapse reduction against the increased risk of NRM from GVHD. In contrast, NK cells have the potential to reduce both, potentially tipping the scales significantly in favor of survival. Here, we will review the role of NK cells in GVL, optimization of NK cell match or mismatch, and burgeoning areas of research in NK cell therapy such as adoptive transfer and chimeric antigen receptor (CAR) NK cells.

The impact of regulatory T cells on the graft-versus-leukemia effect.

Allogeneic Hematopoietic Stem Cell Transplantation (allo-HSCT) is the only curative therapy for many hematologic malignancies, whereby the Graft-versus-Leukemia (GVL) effect plays a pivotal role in controlling relapse. However, the success of GVL is hindered by Graft-versus-Host Disease (GVHD), where donor T cells attack healthy tissues in the recipient. The ability of natural regulatory T cells (Treg) to suppress immune responses has been exploited as a therapeutical option against GVHD. Still, it is crucial to evaluate if the ability of Treg to suppress GVHD does not compromise the benefits of GVL. Initial studies in animal models suggest that Treg can attenuate GVHD while preserving GVL, but results vary according to tumor type. Human trials using Treg as GVHD prophylaxis or treatment show promising results, emphasizing the importance of infusion timing and Treg/Tcon ratios. In this review, we discuss strategies that can be used aiming to enhance GVL post-Treg infusion and the proposed mechanisms for the maintenance of the GVL effect upon the adoptive Treg transfer. In order to optimize the therapeutic outcomes of Treg administration in allo-HSCT, future efforts should focus on refining Treg sources for infusion and evaluating their specificity for antigens mediating GVHD while preserving GVL responses.

[Evidence of GVHD/GVL in allogeneic hematopoietic stem cell transplantation from sex-mismatched donors].

Hematopoietic cell transplantation (HCT) is considered a curative treatment for hematological malignancies. However, HCT recipients often face complications such as graft-versus-host disease (GVHD) and disease relapse. Clinical factors like age and HLA disparity are recognized as risks for GVHD. Notably, sex-mismatched HCT, particularly with female donors and male recipients (F→M), is reported to increase the risk of chronic GVHD. This adverse effect of F→M HCT is thought to result from allogeneic immune response against minor histocompatibility antigens encoded on the Y-chromosome of a male recipient (HY-antigens). Indeed, antibodies against HY-antigens (HY-Abs) were detected three months after F→M HCT, and the cumulative number of HY-Abs was significantly associated with increased risks of chronic GVHD and non-relapse mortality. This review focuses on F→M HCT, shedding light on its impact in several clinical settings and presenting clinical evidence of its allogeneic response, encompassing GVHD and graft-versus-leukemia (GVL) effects. Additionally, potential clinical options to mitigate adverse effects in F→M HCT will be discussed. Further investigation is required to improve clinical outcomes and understand allogenic immunological reconstitution after F→M HCT.

Minnelide suppresses GVHD and enhances survival while maintaining GVT responses.

Allogeneic hematopoietic stem cell transplantation (aHSCT) can cure patients with otherwise fatal leukemias and lymphomas. However, the benefits of aHSCT are limited by graft-versus-host disease (GVHD). Minnelide, a water-soluble analog of triptolide, has demonstrated potent antiinflammatory and antitumor activity in several preclinical models and has proven both safe and efficacious in clinical trials for advanced gastrointestinal malignancies. Here, we tested the effectiveness of Minnelide in preventing acute GVHD as compared with posttransplant cyclophosphamide (PTCy). Strikingly, we found Minnelide improved survival, weight loss, and clinical scores in an MHC-mismatched model of aHSCT. These benefits were also apparent in minor MHC-matched aHSCT and xenogeneic HSCT models. Minnelide was comparable to PTCy in terms of survival, GVHD clinical score, and colonic length. Notably, in addition to decreased donor T cell infiltration early after aHSCT, several regulatory cell populations, including Tregs, ILC2s, and myeloid-derived stem cells in the colon were increased, which together may account for Minnelide's GVHD suppression after aHSCT. Importantly, Minnelide's GVHD prevention was accompanied by preservation of graft-versus-tumor activity. As Minnelide possesses anti-acute myeloid leukemia (anti-AML) activity and is being applied in clinical trials, together with the present findings, we conclude that this compound might provide a new approach for patients with AML undergoing aHSCT.

Strategies to reduce relapse risk in patients undergoing allogeneic stem cell transplantation for acute myeloid leukaemia.

Allogeneic stem cell transplantation is a centrally important curative strategy in adults with acute myeloid leukaemia; however, relapse occurs in a significant proportion of patients and remains the leading cause of treatment failure. The prognosis for patients who relapse post-transplant remains poor, and the development of new strategies with the ability to reduce disease recurrence without increasing transplant toxicity remains a priority. In this review, within the context of our understanding of disease biology and the graft-versus-leukaemia (GVL) effect, we will discuss established, evolving and novel approaches for increasing remission rates, decreasing measurable residual disease pretransplant, future methods to augment the GVL effect and the opportunities for post-transplant maintenance. Future progress depends upon the development of innovative trials and networks, which will ensure the rapid assessment of emerging therapies in prospective clinical trials.

Innovations in conditioning and post-transplant maintenance in AML: genomically informed revelations on the graft-versus-leukemia effect.

Acute Myeloid Leukemia (AML) is the prototype of cancer genomics as it was the first published cancer genome. Large-scale next generation/massively parallel sequencing efforts have identified recurrent alterations that inform prognosis and have guided the development of targeted therapies. Despite changes in the frontline and relapsed standard of care stemming from the success of small molecules targeting FLT3, IDH1/2, and apoptotic pathways, allogeneic stem cell transplantation (alloHSCT) and the resulting graft-versus-leukemia (GVL) effect remains the only curative path for most patients. Advances in conditioning regimens, graft-vs-host disease prophylaxis, anti-infective agents, and supportive care have made this modality feasible, reducing transplant related mortality even among patients with advanced age or medical comorbidities. As such, relapse has emerged now as the most common cause of transplant failure. Relapse may occur after alloHSCT because residual disease clones persist after transplant, and develop immune escape from GVL, or such clones may proliferate rapidly early after alloHSCT, and outpace donor immune reconstitution, leading to relapse before any GVL effect could set in. To address this issue, genomically informed therapies are increasingly being incorporated into pre-transplant conditioning, or as post-transplant maintenance or pre-emptive therapy in the setting of mixed/falling donor chimerism or persistent detectable measurable residual disease (MRD). There is an urgent need to better understand how these emerging therapies modulate the two sides of the GVHD vs. GVL coin: 1) how molecularly or immunologically targeted therapies affect engraftment, GVHD potential, and function of the donor graft and 2) how these therapies affect the immunogenicity and sensitivity of leukemic clones to the GVL effect. By maximizing the synergistic action of molecularly targeted agents, immunomodulating agents, conventional chemotherapy, and the GVL effect, there is hope for improving outcomes for patients with this often-devastating disease.

Metabolic instruction of the graft-versus-leukemia immunity.

Allogeneic hematopoietic cell transplantation (allo-HCT) is frequently performed to cure hematological malignancies, such as acute myeloid leukemia (AML), through the graft-versus-leukemia (GVL) effect. In this immunological process, donor immune cells eliminate residual cancer cells in the patient and exert tumor control through immunosurveillance. However, GVL failure and subsequent leukemia relapse are frequent and associated with a dismal prognosis. A better understanding of the mechanisms underlying AML immune evasion is essential for developing novel therapeutic strategies to boost the GVL effect. Cellular metabolism has emerged as an essential regulator of survival and cell fate for both cancer and immune cells. Leukemia and T cells utilize specific metabolic programs, including the orchestrated use of glucose, amino acids, and fatty acids, to support their growth and function. Besides regulating cell-intrinsic processes, metabolism shapes the extracellular environment and plays an important role in cell-cell communication. This review focuses on recent advances in the understanding of how metabolism might affect the anti-leukemia immune response. First, we provide a general overview of the mechanisms of immune escape after allo-HCT and an introduction to leukemia and T cell metabolism. Further, we discuss how leukemia and myeloid cell metabolism contribute to an altered microenvironment that impairs T cell function. Next, we review the literature linking metabolic processes in AML cells with their inhibitory checkpoint ligand expression. Finally, we focus on recent findings concerning the role of systemic metabolism in sustained GVL efficacy. While the majority of evidence in the field still stems from basic and preclinical studies, we discuss translational findings and propose further avenues for bridging the gap between bench and bedside.

Having it both ways: how STAT3 deficiency blocks graft-versus-host disease while preserving graft-versus-leukemia activity.

Allogeneic hematopoietic cell transplantation can cure patients with high-risk leukemia through graft-versus-leukemia (GVL) effects, the process by which malignant leukemic cells are cleared by donor-derived immune cells from the graft. The problem of harnessing GVL effects while controlling inflammation and host-organ damage linked with graft-versus-host disease (GVHD) has been the most formidable hurdle facing allogeneic hematopoietic cell transplantation. This powerful, curative-intent therapy remains among the most toxic treatments in the hematologist's armamentarium due to the combined risks of GVHD-related morbidity, infections, and leukemia relapse. In this issue of the JCI, Li, Wang, et al. report that T cell Stat3 deficiency can extricate GVL effects from GVHD through tissue-specific programmed death-ligand 1/programmed cell death protein 1-dependent (PD-L1/PD-1-dependent) bioenergetic alterations that blunt harmful T cell effects in GVHD target organs, while preserving their beneficial antitumor activity in lymphohematopoietic tissues.

Donor T cell STAT3 deficiency enables tissue PD-L1-dependent prevention of graft-versus-host disease while preserving graft-versus-leukemia activity.

STAT3 deficiency (STAT3-/-) in donor T cells prevents graft-versus-host disease (GVHD), but the impact on graft-versus-leukemia (GVL) activity and mechanisms of GVHD prevention remains unclear. Here, using murine models of GVHD, we show that STAT3-/- donor T cells induced only mild reversible acute GVHD while preserving GVL effects against nonsusceptible acute lymphoblastic leukemia (ALL) cells in a donor T cell dose-dependent manner. GVHD prevention depended on programmed death ligand 1/programmed cell death protein 1 (PD-L1/PD-1) signaling. In GVHD target tissues, STAT3 deficiency amplified PD-L1/PD-1 inhibition of glutathione (GSH)/Myc pathways that regulate metabolic reprogramming in activated T cells, with decreased glycolytic and mitochondrial ATP production and increased mitochondrial ROS production and dysfunction, leading to tissue-specific deletion of host-reactive T cells and prevention of GVHD. Mitochondrial STAT3 deficiency alone did not reduce GSH expression or prevent GVHD. In lymphoid tissues, the lack of host-tissue PD-L1 interaction with PD-1 reduced the inhibition of the GSH/Myc pathway despite reduced GSH production caused by STAT3 deficiency and allowed donor T cell functions that mediate GVL activity. Therefore, STAT3 deficiency in donor T cells augments PD-1 signaling-mediated inhibition of GSH/Myc pathways and augments dysfunction of T cells in GVHD target tissues while sparing T cells in lymphoid tissues, leading to prevention of GVHD while preserving GVL effects.

Withaferin-A alleviates acute graft versus host disease without compromising graft versus leukemia effect.

Acute graft versus host disease (aGvHD) contributes to a significant proportion of non-relapse mortality and morbidity in patients undergoing allogeneic hematopoietic stem cell transplantation (alloHSCT). Withaferin-A (WA), a phytomolecule obtained from Withania somnifera (Ashwagandha), is known to have anti-inflammatory, anti-proliferative and immunomodulatory properties. The efficacy of WA for the prevention and treatment of aGvHD was evaluated using a murine model of alloHSCT. Prophylactic administration of WA to mice mitigated the clinical symptoms of aGvHD and improved survival significantly compared to the GvHD control [HR = 0.07 (0.01-0.35); P < 0.001]. Furthermore, WA group had better overall survival compared to standard prophylactic regimen of CSA + MTX [HR = 0.19 (0.03-1.1), P < 0.05]. At the same time, WA did not compromise the beneficial GvL effect. In addition, WA administered to animals after the onset of aGvHD could reverse the clinical severity and improved survival, thus establishing its therapeutic potential. Our findings suggest that WA reduced the systemic levels of Th1, Th2 and Th17 inflammatory cytokine and increased the anti-inflammatory cytokine IL-10 levels significantly (P < 0.05). WA also inhibited lymphocytes migration to gut, liver, skin and lung and protected these organs from damage. Ex-vivo, WA inhibited proliferation of human peripheral blood mononuclear cells (hPBMCs), modulated immune cell phenotype and decreased cytokine release. In addition, WA inhibited pJAK2 and pSTAT3 protein levels in mouse splenocytes and hPBMCs. In conclusion, our study demonstrates the utility of WA for the prevention and treatment of aGvHD, which should be further evaluated in a clinical setting.

Immunopathogenic mechanisms and modulatory approaches to graft-versus-host disease prevention in acute myeloid leukaemia.

Allogeneic haematopoietic stem cell transplantation (HSCT) remains the only potential cure for intermediate to high-risk acute myeloid leukaemia (AML). The therapeutic effect of HSCT is largely dependent on the powerful donor-derived immune response against recipient leukaemia cells, known as graft-versus-leukaemia effect (GvL). However, the donor-derived immune system can also cause acute or chronic damage to normal recipient organs and tissues, in a process known as graft-versus-host disease (GvHD). GvHD is a leading cause of non-relapse mortality in HSCT recipients. There are many similarities and cross talk between the immune pathways of GvL and GvHD. Studies have demonstrated that both processes require the presence of mismatched alloantigens between the donor and recipient, and activation of immune responses centered around donor T-cells, which can be further modulated by various recipient or donor factors. Dissecting GvL from GvHD to achieve more effective GvHD prevention and enhanced GvL has been the holy grail of HSCT research. In this review, we focused on the key factors that contribute to the immune responses of GvL and GvHD, the effect on GvL with different GvHD prophylactic strategies, and the potential impact of various AML relapse prevention therapy or treatments on GvHD.