Cytokine profiles in various graft-versus-host disease target organs following hematopoietic stem cell transplantation

Interspecies transcriptome profiles of human T cell activation and liver inflammation in a xenogeneic graft-versus-host disease model

Background

Xenogeneic transplantation induces acute graft-versus-host disease (aGvHD) and subsequent vital organ damage. Herein, we aimed to examine hepatic damage associated with aGvHD using histopathology and gene expression profiles.

Methods

A xenografic GvHD model was established by engrafting human peripheral blood mononuclear cells (PBMCs) into immunodeficient NOD-scid IL2Rγnull (NSG) mice after busulfan conditioning. NSG mice were assigned to groups treated with saline (S group) or a combination of busulfan and PBMCs (BP group). Histological lesions and RNA sequencing analysis of gene profiles in the BP group (GvHD model) were compared with those in the P group.

Results

Predominant T cell subsets (95 %) in the blood of the BP group were identified as cytotoxic CD8+ T cells (56 %) and helper CD4+ T cells (31 %). Symptoms of aGvHD, including hepatocyte necrosis, bile duct hyperplasia, and human T cell infiltration, were observed. Gene expression analysis revealed upregulation of Th1 and Th2 cell differentiation (STAT4, IL4R, and NFACT1), T cell receptor signaling pathway (CD226 and GBP1), IL-1 pathway (CCL3, NAIP, and IRAK4), cell cycle (CDCA5, CDCA8, MCM5, KNL1, BUB1B, FBXO5, and CENPE) in human cells. In mouse cells, Il1a, Ifngr, Tnfrsf, and Il6ra genes (cytokines or their receptors) and Icam, Vcam, and Endra genes (adhesion molecules) were upregulated, whereas genes related to chromosome condensation (H2ac and H2bc) and fatty acid/steroid metabolism (Fasn, Rdh, and Scd) were downregulated. Interspecies gene network analysis revealed that activated human T cells are associated with liver damage through inflammatory and metabolic pathways, accompanied by increased mouse cell adhesion molecules and cytokines.

Conclusion

Our findings offer valuable insights into the pathophysiology and biomarkers of aGvHD and may contribute to the development of novel therapeutics.

Feasibility of intravenous vitamin C supplementation in allogeneic hematopoietic cell transplant recipients

Introduction

Intravenous vitamin C was administered following hematopoietic stem cell transplant to mitigate nonrelapse mortality (NRM) in a Phase II clinical trial.

Methods

Patients with advanced hematologic malignancies received IV vitamin C, 50 mg/kg/day, in three divided doses on days 1-14 after HSCT, followed by 500 mg bid oral until 6 months.

Results

All patients enrolled (55) were deficient in vitamin C at day 0 and had restoration to normal levels. Vitamin C recipients had a trend for lower nonrelapse mortality (NRM, 11% vs. 25%, p-value = 0.07) compared with propensity score-matched historical controls. A similar trend toward improved survival was observed (82% vs. 62% p = 0.06), with no attributable grade 3 and 4 toxicities to vitamin C.

Conclusion

In patients undergoing allogeneic HSCT, repletion of vitamin C is feasible and may reduce NRM and improve overall survival. Randomized trials in large uniform cohorts of patients are needed to confirm the utility of this easily available and inexpensive therapy.

OBSERVE: guidelines for the refinement of rodent cancer models

Existing guidelines on the preparation (Planning Research and Experimental Procedures on Animals: Recommendations for Excellence (PREPARE)) and reporting (Animal Research: Reporting of In Vivo Experiments (ARRIVE)) of animal experiments do not provide a clear and standardized approach for refinement during in vivo cancer studies, resulting in the publication of generic methodological sections that poorly reflect the attempts made at accurately monitoring different pathologies. Compliance with the 3Rs guidelines has mainly focused on reduction and replacement; however, refinement has been harder to implement. The Oncology Best-practices: Signs, Endpoints and Refinements for in Vivo Experiments (OBSERVE) guidelines are the result of a European initiative supported by EurOPDX and INFRAFRONTIER, and aim to facilitate the refinement of studies using in vivo cancer models by offering robust and practical recommendations on approaches to research scientists and animal care staff. We listed cancer-specific clinical signs as a reference point and from there developed sets of guidelines for a wide variety of rodent models, including genetically engineered models and patient derived xenografts. In this Consensus Statement, we systematically and comprehensively address refinement and monitoring approaches during the design and execution of murine cancer studies. We elaborate on the appropriate preparation of tumor-initiating biologicals and the refinement of tumor-implantation methods. We describe the clinical signs to monitor associated with tumor growth, the appropriate follow-up of animals tailored to varying clinical signs and humane endpoints, and an overview of severity assessment in relation to clinical signs, implantation method and tumor characteristics. The guidelines provide oncology researchers clear and robust guidance for the refinement of in vivo cancer models.

Manufacturing CD20/CD19-targeted iCasp9 regulatable CAR-TSCM cells using a Quantum pBac-based CAR-T engineering system

CD19-targeted chimeric antigen receptor (CAR) T cell therapies have driven a paradigm shift in the treatment of relapsed/refractory B-cell malignancies. However, >50% of CD19-CAR-T-treated patients experience progressive disease mainly due to antigen escape and low persistence. Clinical prognosis is heavily influenced by CAR-T cell function and systemic cytokine toxicities. Furthermore, it remains a challenge to efficiently, cost-effectively, and consistently manufacture clinically relevant numbers of virally engineered CAR-T cells. Using a highly efficient piggyBac transposon-based vector, Quantum pBac™ (qPB), we developed a virus-free cell-engineering system for development and production of multiplex CAR-T therapies. Here, we demonstrate in vitro and in vivo that consistent, robust and functional CD20/CD19 dual-targeted CAR-T stem cell memory (CAR-TSCM) cells can be efficiently produced for clinical application using qPB™. In particular, we showed that qPB™-manufactured CAR-T cells from cancer patients expanded efficiently, rapidly eradicated tumors, and can be safely controlled via an iCasp9 suicide gene-inducing drug. Therefore, the simplicity of manufacturing multiplex CAR-T cells using the qPB™ system has the potential to improve efficacy and broaden the accessibility of CAR-T therapies.

Serum cytokine profiles during engraftment syndrome and acute graft-versus-host disease in adult patients after hematopoietic stem cell transplantation

BACKGROUND

The underlying biology of engraftment syndrome (ES) following allogeneic hematopoietic stem cell transplantation (HSCT) is not fully elucidated, and the extent of its overlap with acute graft-versus-host disease (aGvHD) remains unclear. In order to establish potential indicator to distinguish ES more accurately, we conducted a retrospective analysis of cytokine levels during HSCT.

METHODS

A total of 121 consecutive adult patients who underwent HSCT were enrolled in this study. Blood samples for interleukin (IL)-2, IL-2R, IL-4, IL-5, IL-6, IL-8, IL-10, IL-1β, IL-12p70, interferon (IFN)-γ, IFN-α, tumor necrosis factor alpha (TNF-α) and C-reactive protein CRP were regularly assessed after transplantation and during transplantation related adverse events. Additionally, the balance of naïve, central memory and effector memory of CD4+ and CD8+ was analyzed around 30 and 60 days after stem cell infusion, respectively.

RESULTS

Thirty (24.79 %) and 33 (27.27 %) patients were diagnosed with ES and aGvHD, respectively. ES was characterized by a significant increase in level of IL-5, IL-6, IL-8 and sIL-2R, while aGvHD was associated with a significant upregulation of IL-6, IL-5, IL-10 and sIL-2R in the patients from grade I to grade IV. Notably, patients got much higher levels of IL-6, IL-5 and sIL-2R when developed to ES than to aGvHD. Moreover, a pronounced shift from naïve to memory cells, both in CD4+ and CD8+ subsets, was found in ES patients.

CONCLUSIONS

These findings suggest that cytokine profiles could serve as potential indicators for detecting and differentiating ES and aGvHD, enabling timely clinical intervention. Prospective clinical trials involving larger, independent patient cohorts are required to validate these observations.

Follicular helper- and peripheral helper-like T cells drive autoimmune disease in human immune system mice

Human immune system (HIS) mice constructed in various ways are widely used for investigations of human immune responses to pathogens, transplants and immunotherapies. In HIS mice that generate T cells de novo from hematopoietic progenitors, T cell-dependent multisystem autoimmune disease occurs, most rapidly when the human T cells develop in the native NOD.Cg- Prkdc scid Il2rg tm1Wjl (NSG) mouse thymus, where negative selection is abnormal. Disease develops very late when human T cells develop in human fetal thymus grafts, where robust negative selection is observed. We demonstrate here that PD-1 + CD4 + peripheral (Tph) helper-like and follicular (Tfh) helper-like T cells developing in HIS mice can induce autoimmune disease. Tfh-like cells were more prominent in HIS mice with a mouse thymus, in which the highest levels of IgG were detected in plasma, compared to those with a human thymus. While circulating IgG and IgM antibodies were autoreactive to multiple mouse antigens, in vivo depletion of B cells and antibodies did not delay the development of autoimmune disease. Conversely, adoptive transfer of enriched Tfh- or Tph-like cells induced disease and autoimmunity-associated B cell phenotypes in recipient mice containing autologous human APCs without T cells. T cells from mice with a human thymus expanded and induced disease more rapidly than those originating in a murine thymus, implicating HLA-restricted T cell-APC interactions in this process. Since Tfh, Tph, autoantibodies and LIP have all been implicated in various forms of human autoimmune disease, the observations here provide a platform for the further dissection of human autoimmune disease mechanisms and therapies.

Mesenchymal stromal cells with chimaeric antigen receptors for enhanced immunosuppression

Allogeneic mesenchymal stromal cells (MSCs) are a safe treatment option for many disorders of the immune system. However, clinical trials using MSCs have shown inconsistent therapeutic efficacy, mostly owing to MSCs providing insufficient immunosuppression in target tissues. Here we show that antigen-specific immunosuppression can be enhanced by genetically modifying MSCs with chimaeric antigen receptors (CARs), as we show for E-cadherin-targeted CAR-MSCs for the treatment of graft-versus-host disease in mice. CAR-MSCs led to superior T-cell suppression and localization to E-cadherin+ colonic cells, ameliorating the animals' symptoms and survival rates. On antigen-specific stimulation, CAR-MSCs upregulated the expression of immunosuppressive genes and receptors for T-cell inhibition as well as the production of immunosuppressive cytokines while maintaining their stem cell phenotype and safety profile in the animal models. CAR-MSCs may represent a widely applicable therapeutic technology for enhancing immunosuppression.

Withania Somnifera Extract Mitigates Experimental Acute Graft versus Host Disease Without Abrogating Graft Versus Leukemia Effect

Acute graft versus host disease (aGvHD) is the major contributor of nonrelapse mortality in alloHSCT. It is associated with an inflammatory immune response manifesting as cytokine storm with ensuing damage to target organs such as liver, gut, and skin. Prevention of aGvHD while retaining the beneficial graft versus leukemia (GvL) effect remains a major challenge. Withania somnifera extract (WSE) is known for its anti-inflammatory, immune-modulatory, and anticancer properties, which are appealing in the context of aGvHD. Herein, we demonstrated that prophylactic and therapeutic use of WSE in experimental model of alloHSCT mitigates aGvHD-associated morbidity and mortality. In the prophylaxis study, a dose of 75 mg/kg of WSE offered greatest protection against death due to aGvHD (hazard ratio [HR] = 0.15 [0.03-0.68], P ≤ .01), whereas 250 mg/kg was most effective for the treatment of aGvHD (HR = 0.16 [0.05-0.5], P ≤ .01). WSE treatment protected liver, gut, and skin from damage by inhibiting cytokine storm and lymphocytic infiltration to aGvHD target organs. In addition, WSE did not compromise the GvL effect, as alloHSCT with or without WSE did not allow the leukemic A20 cells to grow. In fact, WSE showed marginal antileukemic effect in vivo. WSE is currently under clinical investigation for the prevention and treatment of aGvHD.

INTRAVENOUS VITAMIN C SUPPLEMENTATION IN ALLOGENEIC HEMATOPOIETIC CELL TRANSPLANT RECIPIENTS: SALUTARY IMPACT ON CLINICAL OUTCOMES

Intravenous (IV) vitamin C improves organ function and reduces inflammation in sepsis, an inflammatory state like the post-hematopoietic stem cell transplant (SCT) milieu. The safety and efficacy of parenteral vitamin C after allogeneic hematopoietic stem cell transplant (HSCT) were evaluated in a phase I/II trial and clinical outcomes compared with a propensity score - matched historical control.

Methods

Patients with advanced hematologic malignancies were enrolled in a phase 2 clinical trial, receiving IV vitamin C, 50mg/kg/d, divided into 3 doses given on days 1-14 after HSCT, followed by 500 mg bid oral from day 15 until 6 months post-SCT.

Results

55 patients received IV vitamin C: these include 10/10 HLA-MRD and MUD (n=48) and 9/10 HLA MUD recipients (n=7). All patients enrolled were deficient in vitamin C at day 0 and had restoration to normal levels for the remainder of the course. Vitamin C recipients had lower non-relapse mortality (11% vs. 25%, p-value = 0.07) and consequently, improved survival compared to historical controls (82% vs 62% p=0.06), with no attributable grade 3 and 4 toxicities to vitamin C. Patients with myeloid malignancies had improved survival (83% vs. 54%, p=0.02) and non-relapse mortality (NRM) (10% vs. 37%, p=0.009), as well as chronic GVHD, with similar relapse rates compared to controls.

Conclusions

In patients undergoing allogeneic HSCT the administration of IV vitamin C is safe and reduces non-relapse mortality improving overall survival. Randomized trials are needed to confirm the utility of this easily available and inexpensive therapy.

Animal Welfare in Radiation Research: The Importance of Animal Monitoring System

Long-term research into radiation exposure significantly expanded following World War II, driven by the increasing number of individuals falling ill after the detonation of two atomic bombs in Japan. Consequently, researchers intensified their efforts to investigate radiation's effects using animal models and to study disease models that emerged post-catastrophe. As a result, several parameters have been established as essential in these models, encompassing radiation doses, regimens involving single or multiple irradiations, the injection site for transplantation, and the quantity of cells to be injected. Nonetheless, researchers have observed numerous side effects in irradiated animals, prompting the development of scoring systems to monitor these animals' well-being. The aim of this review is to delve into the historical context of using animals in radiation research and explore the ethical considerations related to animal welfare, which has become an increasingly relevant topic in recent years. These concerns have prompted research groups to adopt measures aimed at reducing animal suffering. Consequently, for animal welfare, the implementation of a scoring system for clinical and behavioral monitoring is essential. This represents one of the primary challenges and hurdles in radiation studies. It is concluded that implementing standardized criteria across all institutions is aimed at ensuring result reproducibility and fostering collaboration within the scientific community.

M-CSF directs myeloid and NK cell differentiation to protect from CMV after hematopoietic cell transplantation

Therapies reconstituting autologous antiviral immunocompetence may represent an important prophylaxis and treatment for immunosuppressed individuals. Following hematopoietic cell transplantation (HCT), patients are susceptible to Herpesviridae including cytomegalovirus (CMV). We show in a murine model of HCT that macrophage colony-stimulating factor (M-CSF) promoted rapid antiviral activity and protection from viremia caused by murine CMV. M-CSF given at transplantation stimulated sequential myeloid and natural killer (NK) cell differentiation culminating in increased NK cell numbers, production of granzyme B and interferon-γ. This depended upon M-CSF-induced myelopoiesis leading to IL15Rα-mediated presentation of IL-15 on monocytes, augmented by type I interferons from plasmacytoid dendritic cells. Demonstrating relevance to human HCT, M-CSF induced myelomonocytic IL15Rα expression and numbers of functional NK cells in G-CSF-mobilized hematopoietic stem and progenitor cells. Together, M-CSF-induced myelopoiesis triggered an integrated differentiation of myeloid and NK cells to protect HCT recipients from CMV. Thus, our results identify a rationale for the therapeutic use of M-CSF to rapidly reconstitute antiviral activity in immunocompromised individuals, which may provide a general paradigm to boost innate antiviral immunocompetence using host-directed therapies.

Expansion of human bone marrow-derived mesenchymal stromal cells with enhanced immunomodulatory properties

BACKGROUND

Mesenchymal stromal cells (MSCs) have broad potential as a cell therapy including for the treatment of drug-resistant inflammatory conditions with abnormal T cell proliferation such as graft-versus-host disease (GVHD). Clinical success, however, has been complicated by the heterogeneity of culture-expanded MSCs as well as donor variability. Here, we devise culture conditions that promote expansion of MSCs with enhanced immunomodulatory functions both in vitro and in animal models of GVHD.

METHODS

Human bone marrow-derived MSCs were expanded at high-confluency (MSCHC) and low-confluency state (MSCLC). Their immunomodulatory properties were evaluated with in vitro co-culture assays based on suppression of activated T cell proliferation and secretion of pro-inflammatory cytokines from activated T cells. Metabolic state of these cells was determined, while RNA sequencing was performed to explore transcriptome of these MSCs. Ex vivo expanded MSCHC or MSCLC was injected into human peripheral blood mononuclear cells (PBMC)-induced GVHD mouse model to determine their in vivo therapeutic efficacy based on clinical grade scoring, human CD45+ blood count and histopathological examination.

RESULTS

As compared to MSCLC, MSCHC significantly reduced both the proliferation of anti-CD3/CD28-activated T cells and secretion of pro-inflammatory cytokines upon MSCHC co-culture across several donors even in the absence of cytokine priming. Mechanistically, metabolic analysis of MSCHC prior to co-culture with activated T cells showed increased glycolytic metabolism and lactate secretion compared to MSCLC, consistent with their ability to inhibit T cell proliferation. Transcriptome analysis further revealed differential expression of immunomodulatory genes including TRIM29, BPIFB4, MMP3 and SPP1 in MSCHC as well as enriched pathways including cytokine-cytokine receptor interactions, cell adhesion and PI3K-AKT signalling. Lastly, we demonstrate in a human PBMC-induced GVHD mouse model that delivery of MSCHC showed greater suppression of inflammation and improved outcomes compared to MSCLC and saline controls.

CONCLUSION

Our study provides evidence that ex vivo expansion of MSCs at high confluency alters the metabolic and transcriptomic states of these cells. Importantly, this approach maximizes the production of MSCs with enhanced immunomodulatory functions without priming, thus providing a non-invasive and generalizable strategy for improving the use of MSCs for the treatment of inflammatory diseases.

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.

Advantage of First-Line Therapeutic Drug Monitoring-Driven Use of Infliximab for Treating Acute Intestinal and Liver GVHD in Children: A Prospective, Single-Center Study

The high serum concentrations of TNF-α characterize acute graft-versus-host disease (aGVHD), for which infliximab treatment may be beneficial. In 28 pediatric patients, four doses of 10 mg/kg infliximab every seven days were administered after steroid failure (Standard Group, n = 14) or as a first-line therapy (Early Group, n = 14). Population pharmacokinetic analyses and evaluation of serum cytokines were performed. After two months of treatment, complete response in gastrointestinal and liver aGVHD was achieved in 43% and 100% of patients in the Standard and Early groups, respectively. During follow-up, four patients in the Standard Group (but none in the Early Group) experienced an aGVHD recurrence. Viral infections occurred more frequently in the Standard Group after the fifth dose. Infliximab clearance did not differ between groups or according to treatment outcome for each organ involved in aGVHD, whereas serum levels of cytokines significantly differed. Therefore, present findings show that use of first-line, TDM-driven infliximab to treat aGVHD in children may result in better clinical outcomes and tolerability, with a different pattern of cytokines generated according to the moment of beginning of treatment.

Universal allogeneic CAR T cells engineered with Sleeping Beauty transposons and CRISPR-CAS9 for cancer immunotherapy

Allogeneic CD19-specific chimeric antigen receptor (CAR) T cells with inactivated donor T cell receptor (TCR) expression can be used as an "off-the-shelf" therapeutic modality for lymphoid malignancies, thus offering an attractive alternative to autologous, patient-derived T cells. Current approaches for T cell engineering mainly rely on the use of viral vectors. Here, we optimized and validated a non-viral genetic modification platform based on Sleeping Beauty (SB) transposons delivered with minicircles to express CD19-28z.CAR and CRISPR-Cas9 ribonucleoparticles to inactivate allogeneic TCRs. Efficient TCR gene disruption was achieved with minimal cytotoxicity and with attainment of robust and stable CD19-28z.CAR expression. The CAR T cells were responsive to CD19+ tumor cells with antitumor activities that induced complete tumor remission in NALM6 tumor-bearing mice while significantly reducing TCR alloreactivity and GvHD development. Single CAR signaling induced the similar T cell signaling signatures in TCR-disrupted CAR T cells and control CAR T cells. In contrast, TCR disruption inhibited T cell signaling/protein phosphorylation compared with the control CAR T cells during dual CAR/TCR signaling. This non-viral SB transposon-CRISPR-Cas9 combination strategy serves as an alternative for generating next-generation CD19-specific CAR T while reducing GvHD risk and easing potential manufacturing constraints intrinsic to viral vectors.

Human induced-T-to-natural killer cells have potent anti-tumour activities

BACKGROUND

Adoptive cell therapy (ACT) is a particularly promising area of cancer immunotherapy, engineered T and NK cells that express chimeric antigen receptors (CAR) are being explored for treating hematopoietic malignancies but exhibit limited clinical benefits for solid tumour patients, successful cellular immunotherapy of solid tumors demands new strategies.

METHODS

Inactivation of BCL11B were performed by CRISPR/Cas9 in human T cells. Immunophenotypic and transcriptional profiles of sgBCL11B T cells were characterized by cytometer and transcriptomics, respectively. sgBCL11B T cells are further engineered with chimeric antigen receptor. Anti-tumor activity of ITNK or CAR-ITNK cells were evaluated in preclinical and clinical studies.

RESULTS

We report that inactivation of BCL11B in human CD8⁺ and CD4⁺ T cells induced their reprogramming into induced T-to-natural killer cells (ITNKs). ITNKs contained a diverse TCR repertoire; downregulated T cell-associated genes such as TCF7 and LEF1; and expressed high levels of NK cell lineage-associated genes. ITNKs and chimeric antigen receptor (CAR)-transduced ITNKs selectively lysed a variety of cancer cells in culture and suppressed the growth of solid tumors in xenograft models. In a preliminary clinical study, autologous administration of ITNKs in patients with advanced solid tumors was well tolerated, and tumor stabilization was seen in six out nine patients, with one partial remission.

CONCLUSIONS

The novel ITNKs thus may be a promising novel cell source for cancer immunotherapy.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT03882840 . Registered 20 March 2019-Retrospectively registered.

Mature naive B cells regulate the outcome of murine acute graft-versus-host disease in an IL-10 independent manner

Graft-versus-host disease (GVHD) is the main complication of bone marrow transplantation (BMT). T CD4+ lymphocytes are the main effector cells for disease development but other cell types can determine disease outcome through cytokine production and antigen presentation. B cells are abundant in BMT products and are involved in chronic GVHD immunopathogenesis. However, their role in acute GVHD is still unclear. Here, we studied the role of donor resting B cells in a model of acute GVHD. Animals receiving transplants depleted of B cells presented a more severe disease, indicating a protective role for B cells. Mice transplanted with IL-10 KO B cells developed GVHD as severe as those receiving WT B cells. Besides that, mice transplanted with MHC II deficient B cells and as so, unable to present antigen to CD4+ T cells, developed as severe GVHD as animals transplanted without B cells. This result suggests that protection provided by mature naive B cells depends on antigen presentation and not IL-10 production by B cells. In the absence of donor B cells, transplanted mice exhibited disorganized lymphoid splenic tissue. Additionally, donor B cell depletion diminished the follicular T (Tfh)/T effector (Teff) ratio suggesting that protection was correlated with a shift to Tfh differentiation, reducing the number of effector T cells. Importantly, the Tfh/Teff shift impacts disease outcome since observed proinflammatory cytokine levels and tissue damage in target organs were consistent with disease protection. The role of transplanted B cells in the outcome of BMT and the development of acute GVHD should be carefully studied, since these cells are abundant in BMT products and are potent modulator and effector cells in allogeneic response. Extended Abstract Background: B cells are widely known for their ability to produce antibodies. In addition, B cells can act efficiently as antigen-presenting cells, implying the mutual regulation of both T and B lymphocyte subsets. T cell help for B cells has been known for more than 50 years; however, B cell help for T cells, especially regarding the modulation of follicular and regulatory phenotypes, had only lately been explored. Here, we studied the role of resting B cells in a model of systemic inflammatory disease mediated by T cells, graft-versus-host disease (GVHD), which is the main complication of allogeneic bone marrow transplantation. Objetive: The objective of this paper is to investigate the role of donor B cells in acute Graft-versus-Host Disease.

STUDY DESIGN

To investigate the role of donor B cells in aGVHD, we used a full MHC-mismatched bone marrow transplantation model. We infused C57BL/6 BM cells along with splenocytes depleted or not of B220⁺ cells into lethally irradiated BALB/c mice. We also used B cells from IL-10 KO mice to investigate the role of IL-10 produced by donor B cells and B cells from mice which cannot express MHC-II (CIITA KO) to investigate the role of cognate interaction between donor B and T cells.

RESULTS

Animals receiving transplants depleted of B cells presented a more severe disease, showing the existence of B cell-dependent protection. This protection was dependent on the T cell-B cell cognate interaction but not on IL-10 or Treg induction. In the absence of donor B cells, transplanted mice exhibited fewer GCs and a lower follicular T (Tfh)/T effector (Teff) ratio than mice transplanted in the presence of B cells. Protection was correlated with a shift to Tfh differentiation, reducing the number of effector cells. Importantly, the Tfh/Teff shift impacts disease outcome with less T cell-mediated disease due to more B cell-dependent Tfh generation with fewer effector T cells and lower proinflammatory cytokine levels detected in target organs.

CONCLUSION

We show that B-cell depleted bone marrow transplantation leads to a more severe disease, with earlier mortality related to increased organ damage. Such differences depend on cognate interactions between T cells and B cells, are IL-10 independent and are related to a shift in the differentiation of lymphocytes from the follicular helper phenotype to the effector phenotype. Therefore, Teffs, which are circulating cells, become relatively more numerous and can reach and damage the target tissues. These results point to caution in the early posttransplantation elimination of donor B cells. It is not a matter of eliminating only antibody-forming cells or cells that mediate Tfh generation but of B cells, which interact and modulate T cell activity, impacting a disease that is not antibody mediated.

DNA/RNA heteroduplex oligonucleotide technology for regulating lymphocytes in vivo

Manipulating lymphocyte functions with gene silencing approaches is promising for treating autoimmunity, inflammation, and cancer. Although oligonucleotide therapy has been proven to be successful in treating several conditions, efficient in vivo delivery of oligonucleotide to lymphocyte populations remains a challenge. Here, we demonstrate that intravenous injection of a heteroduplex oligonucleotide (HDO), comprised of an antisense oligonucleotide (ASO) and its complementary RNA conjugated to α-tocopherol, silences lymphocyte endogenous gene expression with higher potency, efficacy, and longer retention time than ASOs. Importantly, reduction of Itga4 by HDO ameliorates symptoms in both adoptive transfer and active experimental autoimmune encephalomyelitis models. Our findings reveal the advantages of HDO with enhanced gene knockdown effect and different delivery mechanisms compared with ASO. Thus, regulation of lymphocyte functions by HDO is a potential therapeutic option for immune-mediated diseases.

A Novel Mice Model for Studying the Efficacy and IRAEs of Anti-CTLA4 Targeted Immunotherapy

Background

Patient-derived orthotopic xenograft (PDOX) is a popular animal model for translational cancer research. Immunotherapy is a promising therapy against glioblastoma (GBM). However, the PDOX model is limited to evaluating immune-related events. Our study aims to establish GBM humanized PDOX (HPDOX) mice models to study the mechanism of anti-CTLA4 immunotherapy and immune-related adverse events (IRAEs).

Methods

HPDOX models were established by culturing GBM tissues and intracranially implanting them in NSG mice. Meanwhile, peripheral blood mononuclear cells (PBMCs) were separated from peripheral blood and of GBM patients and administrated in corresponding mice. The population of CD45+, CD3+, CD4+, CD8+, and regulatory T (Treg) cells was estimated in the peripheral blood or tumor.

Results

T cells derived from GBM patients were detected in HPDOX mice models. The application of anti-CTLA4 antibodies (ipilimumab and tremelimumab) significantly inhibited the growth of GBM xenografts in mice. Moreover, residual patient T cells were detected in the tumor microenvironment and peripheral blood of HPDOX mice and were significantly elevated by ipilimumab and tremelimumab. Additionally, Treg cells were decreased in mice with IRAEs. Lastly, the proportion of CD4+/CD8+ T cells dramatically increased after the administration of ipilimumab. And the degree of IRAEs may be related to CD56+ expression in HPDOX.

Conclusions

Our study established HPDOX mice models for investigating the mechanism and IRAEs of immunotherapies in GBM, which would offer a promising platform for evaluating the efficacy and IRAEs of novel therapies and exploring personalized therapeutic strategies.

Chimeric CTLA4-CD28-CD3z T Cells Potentiate Antitumor Activity Against CD80/CD86-Positive B Cell Malignancies

The adoptive transfer of chimeric antigen receptor T (CAR T) cells have been recognized as a promising therapeutic strategy for the treatment of hematological malignancies; however, clinical success using CAR T cells for the treatment of solid tumors are still limited since the T-cell function is inhibited by negative signals in the microenvironment of solid tumors. CTLA4 is a well-known immune checkpoint molecule, thus we developed a novel CAR by converting this negative signal to positive signal. The CAR developed consists of the extracellular and transmembrane domains of CTLA4 and the cytoplasmic domains of CD28 and CD3z (CTLA4-CAR T). CTLA4-CAR T cells exhibited superior cytokine secreting activities and cytotoxic to tumor cells in vitro and in xenograft models. CTLA4-CAR T cells were found to accumulate in tumors and are toxic to myeloid-derived suppressor cells (MDSCs) without signs of severe GVHD and CRS in preclinical models. Thus, this chimeric CTLA4-CAR can enhance the antitumor activity of CAR T cells and shed light on the strategy of using armed CAR T cells to target the immunomodulatory tumor microenvironment.

Role of T cell immune response cDNA 7 on the pathology of acute graft-versus-host disease

Activation of T lymphocytes is the initiating factor of the occurrence of acute graft-versus-host disease (aGVHD), and cytotoxic T lymphocyte antigen-4 (CTLA-4) is the inhibitory receptor for activating T cells. T cell immune response cDNA 7 (TIRC7) is considered an upstream regulator of CTLA-4; however, little is understood regarding the effects of TIRC7 on the regulation of CTLA-4 in aGVHD. The purpose of the present study was to evaluate the regulatory effects of TIRC7 on aGVHD, mainly in the pathology. Recipient mice were exposed to a preconditioning dose of 7.5 Gy irradiation on the day of the transplantation and were divided into the following groups: Blank control group, bone marrow transplantation control group, total body irradiation group, mild-moderate aGVHD group and severe aGVHD group. According to the different administration of CTLA-4 and TIRC7 monoclonal antibodies, the mild-moderate and severe aGVHD groups were randomly divided into the hematopoietic stem cell transplantation (HSCT) and HSCT + CTLA-4/TIRC7 groups. Recipient mice were sacrificed at different time points post-HSCT for histopathological analysis by hematoxylin and eosin staining. Compared with the control and other experimental groups, the mice in the combined CTLA-4 and TIRC7 group exhibited ameliorated pathological injury, and lower pathology scores of the liver, lung and intestine. These data revealed that intraperitoneal injection of anti-TIRC7 and/or anti-CTLA-4 monoclonal antibody into mice could effectively alleviate the severity of aGVHD.

Local immune cell infiltration in cutaneous acute graft versus host disease

Background

Hematopoietic stem cell transplant is a crucial intervention to definitively treat many hematopoietic malignancies, but it carries great risks of morbidity and mortality often associated with graft-versus-host disease (GVHD). Acute and chronic GVHD are distinct entities, defined by a combination of historical, clinical, and pathologic data, but both are generally thought to stem from self-propagating aberrantly activated immune cells inflicting end organ damage, with the potential to cause significant illness or even death. Event-free survival rates after hematopoietic stem cell transplant continue to improve each year, but GVHD remains a major hurdle in improving the efficacy and safety of transplant.

Objective

Recent studies demonstrating tissue-specific immune effector phenotypes underscore the need for a deeper understanding of the cellular and molecular pathways driving the destruction of target tissues in patients with acute GVHD.

Methods

Samples were collected from lesional and unaffected skin in five patients with acute cutaneous GHVD. Fresh tissue was processed for fluorescence-activated cell sorting and analysis of macrophages and lymphocytes.

Results

The percentage of lymphocytes and macrophages as a representation of total cells varied among patients and was not always consistent between lesional and unaffected sites. The heterogeneity in immune cell profiling observed in patients in this study could reflect the diverse demographics, conditioning, and transplant conditions of each individual.

Conclusion

This study provides initial insight into the underlying molecular mechanisms of cutaneous GVHD progression and paves the way for additional studies to examine the cellular and molecular landscape in greater detail.

TIRC7 inhibits Th1 cells by upregulating the expression of CTLA‑4 and STAT3 in mice with acute graft‑versus‑host disease

In a previous study, it was demonstrated that T‑cell immune response cDNA 7 (TIRC7) levels reflect the efficacy of treatment of patients with acute graft‑versus‑host disease (GVHD). However, the pathogenesis of TIRC7 in acute GVHD remains poorly understood. Lymphocytes from patients with acute GVHD were selected as targeT cells, and the effects of TIRC7 on cytotoxic T lymphocyte antigen‑4 (CTLA‑4), T cell activation and cytokine secretion were observed by electroporation. A mouse model of acute GVHD was established; anti‑TIRC7 and anti‑CTLA‑4 monoclonal antibodies were intraperitoneally injected into recipient mice. Then, the effects of TIRC7 and CTLA‑4 on T cell activation and acute GVHD were monitored. After TIRC7 expression was downregulated, CTLA‑4 levels were decreased and STAT3 phosphorylation was reduced; conversely, the activation capacity of T lymphocytes was elevated, and the secretion of interferon‑γ and other cytokines was increased. The mice in the TIRC7 + CTLA‑4 co‑administration group exhibited the lowest acute GVHD scores, with the longest average survival time and shortest recovery time of hematopoietic reconstitution. In conclusion, the results indicated that TIRC7 may positively regulate the function of CTLA‑4 and inhibit T cell activation, thus suppressing the development and progression of acute GVHD.

Salvianolic acid B ameliorates liver injury in a murine aGvHD model by decreasing inflammatory responses via upregulation of HO-1

Acute graft-versus-host disease (aGvHD) remains lethal, even after allogeneic hematopoietic stem cell transplantation. Inflammatory responses play an important role in aGvHD. Salvianolic acid B (Sal B) has been widely reported to have a major effect on the anti-inflammatory response, but these effects in an aGvHD model have never been reported. B6 donor splenocytes were transplanted into unirradiated BDF1 recipients and liver and serum were collected on day 14 after transplantation with or without Sal B administration. We measured the expression of pro-inflammatory cytokines and chemokines and other manifestations in aGvHD mice after Sal B treatment. Sal B ameliorated liver injury in aGvHD and promoted survival in mice. Sal B treatment resulted in decreased expression of pro-inflammatory cytokines and chemokines whose expressions in liver are normally elevated by aGvHD. Furthermore, Sal B treatment also enhanced PGC-1α expression in liver tissue and HO-1 expression in nonparenchymal cells. In addition, HO-1 inhibitor abrogated the improvement of survival rate of mice with aGvHD. These results indicated that the protective effect of Sal B relies on suppressing the inflammatory response phase in the aGvHD model, presumably by inducing HO-1. Taken together our data showed that Sal B ameliorates liver injury in aGvHD by decreasing inflammatory responses via upregulation of HO-1. It may provide a novel way to deal with this disease.

Determining the Quantitative Principles of T Cell Response to Antigenic Disparity in Stem Cell Transplantation

Alloreactivity compromising clinical outcomes in stem cell transplantation is observed despite HLA matching of donors and recipients. This has its origin in the variation between the exomes of the two, which provides the basis for minor histocompatibility antigens (mHA). The mHA presented on the HLA class I and II molecules and the ensuing T cell response to these antigens results in graft vs. host disease. In this paper, results of a whole exome sequencing study are presented, with resulting alloreactive polymorphic peptides and their HLA class I and HLA class II (DRB1) binding affinity quantified. Large libraries of potentially alloreactive recipient peptides binding both sets of molecules were identified, with HLA-DRB1 generally presenting a greater number of peptides. These results are used to develop a quantitative framework to understand the immunobiology of transplantation. A tensor-based approach is used to derive the equations needed to determine the alloreactive donor T cell response from the mHA-HLA binding affinity and protein expression data. This approach may be used in future studies to simulate the magnitude of expected donor T cell response and determine the risk for alloreactive complications in HLA matched or mismatched hematopoietic cell and solid organ transplantation.

Simple, Reproducible, and Efficient Clinical Grading System for Murine Models of Acute Graft-versus-Host Disease

Acute graft-versus-host disease (aGVHD) represents a challenging complication after allogeneic hematopoietic stem cell transplantation. Despite the intensive preclinical research in the field of prevention and treatment of aGVHD, and the presence of a well-established clinical grading system to evaluate human aGVHD, such a valid tool is still lacking for the evaluation of murine aGVHD. Indeed, several scoring systems have been reported, but none of them has been properly evaluated and they all share some limitations: they incompletely reflect the disease, rely on severity stages that are distinguished by subjective assessment of clinical criteria and are not easy to discriminate, which could render evaluation more time consuming, and their reproducibility among different experimenters is uncertain. Consequently, clinical murine aGVHD description is often based merely on animal weight loss and mortality. Here, we propose a simple scoring system of aGVHD relying on the binary (yes or no) evaluation of five important visual parameters that reflect the complexity of the disease without the need to sacrifice the mice. We show that this scoring system is consistent with the gold standard histological staging of aGVHD across several donor/recipient mice combinations. This system is also a strong predictor of survival of recipient mice when used early after transplant and is highly reproducible between experimenters.

Role of CD8 Regulatory T Cells versus Tc1 and Tc17 Cells in the Development of Human Graft-versus-Host Disease

CD8⁺ T cells that secrete proinflammatory cytokines play a central role in exacerbation of inflammation; however, a new subpopulation of CD8 regulatory T cells has recently been characterized. This study analyzes the prominent role of these different subpopulations in the development of graft-versus-host disease (GVHD). Samples from 8 healthy donors mobilized with Filgrastim® (G-CSF) and 18 patients who underwent allogeneic hematopoietic stem cell transplantation (HSCT) were evaluated by flow cytometry. Mobilization induced an increase in Tc1 (p < 0.01), Th1 (p < 0.001), Tc17 (p < 0.05), and CD8⁺IL-10⁺ cells (p < 0.05), showing that G-CSF induces both pro- and anti-inflammatory profiles. Donor-patient correlation revealed a trend (p = 0.06) toward the development of GVHD in patients who receive a high percentage of Tc1 cells. Patients with acute GVHD (aGVHD), either active or controlled, and patients without GVHD were evaluated; patients with active aGVHD had a higher percentage of Tc1 (p < 0.01) and Tc17 (p < 0.05) cells, as opposed to patients without GVHD in whom a higher percentage of CD8 Treg cells (p < 0.01) was found. These findings indicate that the increase in Tc1 and Tc17 cells is associated with GVHD development, while regulatory CD8 T cells might have a protective role in this disease. These tests can be used to monitor and control GVHD.

Dynamic regulation of effector IFN-γ-producing and IL-17-producing T cell subsets in the development of acute graft-versus-host disease

Graft-versus-host disease (GVHD) as the predominant complication of allogeneic hematopoietic stem cell transplantation remains to be fully understood. It is known that the cytokines produced by allogeneic reactive effector CD4+ and CD8+ T cells are involved in GVHD. However, the regulation and coordination of IFN-γ-producing and IL-17-producing effector T cells remain unclear. The present study aimed to investigate the dynamic changes of alloantigen-specific effector CD4+ T and CD8+ T cell subsets by flow cytometry, which produce inflammatory cytokines involved in the multistep GVHD pathogenesis progress. The results demonstrated that IL-17-producing CD8+ T (Tc17) cells and IFN-γ+CD8+ T (Tc1) cells were detected in the early stage of GVHD. The differentiation of CD4+ T cells into Th1 cell (IFN-γ+CD4+ T) and Th17 (IL-17+CD4+ T) cells was later than that of the Tc1 and Tc17 cells. The effector CD4+ T and CD8+ T cell subsets either became exhausted or became memory cells, exhibiting a CD62L-CD44+ phenotype following marked expansion during GVHD. Furthermore, T cell-associated type I (IL-2 and IFN-γ) and type II (IL-4 and IL-10) classical cytokines exhibited coordinated dynamic regulation. It was concluded that the differentiation of cytokine-producing Tc1 and Tc17 cells may be the key step in the initiation of GVHD, whereas CD4+ effector Th1 and Th17 cells are considered to be pathophysiological factors leading to the continuous aggravation of GVHD.

Cytotoxic T Lymphocyte Antigen-4 Down-Regulates T Helper 1 Cells by Increasing Expression of Signal Transducer and Activator of Transcription 3 in Acute Graft-versus-Host Disease

Numerous previous studies have suggested that cytotoxic T lymphocyte antigen-4 (CTLA-4) plays an important role in acute graft-versus-host disease (GVHD). How CTLA-4 acts in regulating acute GVHD remains unknown, however. In the present study, we found that, compared with healthy controls, CTLA-4 plasma and relative mRNA levels in patients with acute GVHD were initially decreased and then markedly elevated after 28 days of treatment. CTLA-4 levels were higher in patients with grade I-II acute GVHD compared with those with grade III-IV acute GVHD both before and after treatment. Up-regulation of CTLA-4 significantly increased the luciferase activity and degree of phosphorylation of signal transducer and activator of transcription 3 (STAT3). Meanwhile, T cell activation was significantly inhibited, and levels of IFN-γ, IL-17, and IL-22 decreased. These findings suggest that CTLA-4 might be involved in the pathogenesis of acute GVHD, and may down-regulate T helper 1 cells by increasing STAT3 expression in acute GVHD.

Increased expression of T cell immune response cDNA 7 in patients with acute graft-versus-host disease

Acute graft-versus-host disease (aGVHD) has become the important complication post-allogeneic hematopoietic stem cell transplantation. Abnormally activated T cells might play an important role in the pathogenesis of aGVHD. But its exact mechanism remains poorly understood. T cell immune response cDNA 7 (TIRC7) has been identified to be essential in T cell activation; however, the role of TIRC7 in aGVHD remains unclear. The purpose of this study was to measure the expression of TIRC7 and T helper (Th) cells in patients with aGVHD before and after treatment. We showed that TIRC7 levels in aGVHD patients were higher than those of healthy controls and markedly declined after treatment. The levels of IFN-γ (Th1), IL-17 (Th17), and IL-22 (Th22) were in accordance with the grade of aGVHD. In addition, TIRC7 levels were also associated with the severity of aGVHD. In conclusion, TIRC7 might be involved in the pathogenesis of aGVHD and TIRC7 level might be an indicator to evaluate the response of patients with aGVHD to treatment.

Tc17 Cells in Immunity and Systemic Autoimmunity

Tc17 cells-a subset of CD8(+)T cells-have recently been identified that are characterized by the production of interleukin (IL)-17. Cytokines IL-6 and transforming growth factor-beta 1 (TGF-β1) and transcription factors signaling transducers and activators of transcription (STAT)3, retinoic acid receptor-related orphan nuclear receptor gamma (RORγt), and interferon regulatory factor (IRF)4 are necessary for differentiation of Tc17 cells, controlling expression of molecules essential for Tc17 cell trafficking and function. Current human researches have determined the significance of CD161 expression as either a marker of Tc17 cells or as an effector and regulator of Tc17 cell function. Noncytotoxic Tc17 cells possess a high plasticity to convert into IFN-γ producing cells, which exhibit strong cytotoxic activity. The importance of in vivo plasticity of Tc17 cells for the induction of autoimmune diseases has been demonstrated and Tc17 cells potentially represent novel therapeutic targets in autoimmune diseases. The involvement of interleukin (IL)-17-producing CD8(+)T cells (Tc17) in various conditions, such as infection, cancer, and autoimmune inflammation, has been documented in both humans and mice; however, Tc17 cells have received only marginal attention. Here, we provide an overview of the cytokines and chemokines that characterize the murine and human Tc17 cells. Moreover, we discuss signaling pathways, molecular interactions, and transcriptional events that contribute to Tc17 differentiation and acquisition of effector functions. Also considered is the basis of Tc17 cell plasticity toward the Tc1 lineage, and we suggest that in vivo plasticity of Tc17 cells may be a key feature of Tc17 cell biology in autoimmune diseases. Furthermore, current human researches have revealed that Tc17 cells are different than that in mice because all of them express CD161 and exclusively originate from CD161 precursors present in umbilical cord blood. Finally, we focus on the recent evidence for long-lived Tc17 memory cell populations in mouse models and humans, and their functional roles in mediating disease memory. Hopefully, the information obtained will benefit for developing novel therapeutic strategies.

Kinetics of IFN-γ and IL-17 Production by CD4 and CD8 T Cells during Acute Graft-versus-Host Disease

Graft-versus-host disease (GVHD) is a fatal complication that occurs after allogeneic hematopoietic stem cell transplantation. To understand the dynamics of CD4 and CD8 T cell production of IFN-γ and IL-17 during GVHD progression, we established a GVHD model by transplanting T cell-depleted bone marrow (TCD-BM) and purified T cells from B6 mice into irradiated BALB.B, creating an MHC-matched but minor histocompatibility (H) antigen-mismatched transplantation (B6 → BALB.B GVHD). Transplantation-induced GVHD was confirmed by the presence of the appropriate compositional changes in the T cell compartments and innate immune cells in the blood and the systemic secretion of inflammatory cytokines. Using this B6 → BALB.B GVHD model, we showed that the production of IFN-γ and IL-17 by CD4 T cells preceded that by CD8 T cells in the spleen, mesenteric lymph node, liver, and lung in the BALB.B GVHD host, and Th1 differentiation predated Th17 differentiation in all organs during GVHD progression. Such changes in cytokine production were based on changes in cytokine gene expression by the T cells at different time points during GVHD development. These results demonstrate that both IFN-γ and IL-17 are produced by CD4 and CD8 T cells but with different kinetics during GVHD progression.

Prevention of acute graft-versus-host disease by humanized anti-CD26 monoclonal antibody

CD26 (DPP4) is a T cell costimulatory molecule as well as T cell activation marker, and CD26(+) T cells are accumulated in inflamed tissues, such as rheumatoid synovitis and autoimmune thyroiditis. In the present study, we found accumulation of CD26(+) T cells in graft-versus-host disease (GVHD) target organs. To expand our in vitro findings to an in vivo system, we examined CD26-dependent organ injury in a xenogeneic GVHD (x-GVHD) murine model. Following intraperitoneal injection of human peripheral blood mononuclear cells into non-obese diabetic severe combined immunodeficiency/γ(c) (-/-) mice (hu-PBL-NOG mice), the mice exhibited the onset of GVHD symptoms associated with the presence of CD26(high) human lymphocytes in the peripheral blood and GVHD target tissues. Administration of humanized anti-human CD26 monoclonal antibody (mAb) decreased x-GVHD severity and prolonged survival in hu-PBL-NOG mice without loss of engraftment of human T cells, while increasing doses of CTLA4- immunoglobulin fusion protein diminished engraftment of human lymphocytes. Importantly, anti-CD26 mAb treatment preserved the graft-versus-leukaemia effects in studies using cotransplantation of P815 murine leukaemic cells. In addition, CD26(+) lymphocytes infiltrated the GVHD patients' target tissues. Altogether, our data indicate a role for CD26 in the regulation of GVHD and point to CD26 as a novel target for therapeutic intervention in this disease.