Current approaches to prevent and treat GVHD after allogeneic stem cell transplantation

Anti-thymocyte globulin combined with post-transplantation cyclophosphamide reduce graft-versus-host disease in hematopoietic stem cell transplantation for pediatric leukemia

This retrospective analysis evaluated the use of anti-thymocyte globulin (ATG) with or without post-transplantation cyclophosphamide (PTCy) for graft-versus-host disease (GvHD) prophylaxis in children with acute leukemia undergoing hematopoietic stem cell transplantation (HSCT). The study included 57 children, with 35 in the ATG-PTCy group and 22 in the ATG group. While overall incidence of acute and chronic GvHD did not differ significantly between groups, the ATG-PTCy group had lower rates of grade II-IV acute GvHD (p = 0.013) and moderate-to-severe chronic GvHD (p = 0.001) compared to the ATG group. Importantly, ATG-PTCy significantly improved GvHD/relapse-free survival (GRFS) compared to ATG (65.71% vs. 36.63%; p = 0.003). There were no differences in engraftment, infection rates, immune reconstitution, overall survival, leukemia-free survival, relapse rate, or non-relapse mortality between the two groups. Combining ATG with PTCy may reduce moderate-to-severe GvHD and improve GRFS in children undergoing HSCT for acute leukemia.

Donor Lymphocyte Infusion (DLI) post allogeneic stem cell transplant (allo-SCT) in Acute Myeloid Leukemia (AML) and High-Grade Myelodysplastic Syndrome (MDS). A longitudinal retrospective study using peripheral blood (PB) CD34+ and CD3+ donor chimerism (DC) monitoring

INTRODUCTION

This longitudinal study was based on the outcomes of Donor Lymphocyte Infusion (DLI) for falling peripheral blood (PB) CD34+ and CD3+ donor chimerism (DC).

METHODS

From 2012 to 2018, data was collected from the BMT database and electronic medical records (EMR). The primary objective was to compare the indication for DLI based on falling PB CD34+ or CD3+ DC in patients post allo-SCT for AML and MDS and their overall survival (OS).

RESULTS

18/70 patients met the inclusion criteria. Indications for DLI were i) falling PB CD34+ DC ≤ 80 % with morphological relapse, ii) falling PB CD34+ DC ≤ 80 % without morphological relapse and iii) falling PB CD3+ DC ≤ 80 % without falling PB CD34+ DC. Log rank analysis showed falling PB CD34+ DC and morphological relapse had significantly lower OS. Linear regression demonstrated better OS post DLI if there was PB CD34+ and CD3+ chimerism response at 30 days (p = 0.029), GVHD (p = 0.032) and tapering immunosuppression at the time of falling DC (p = 0.042).

CONCLUSION

DLI for PB CD34+ DC values ≤ 80 % and morphological relapse had the lowest OS. In this study, full DC was achieved after DLI even with a PB CD3+DC value as low as 13 %, provided the PB CD34+ DC remained > 80 %. Further research is vital in CD34+ DC as a biomarker for disease relapse and loss of engraftment.

Calcineurin inhibition rescues alloantigen-specific central memory T cell subsets that promote chronic GVHD

Calcineurin inhibitors (CNIs) constitute the backbone of modern acute graft-versus-host disease (aGVHD) prophylaxis regimens but have limited efficacy in the prevention and treatment of chronic GVHD (cGVHD). We investigated the effect of CNIs on immune tolerance after stem cell transplantation with discovery-based single-cell gene expression and T cell receptor (TCR) assays of clonal immunity in tandem with traditional protein-based approaches and preclinical modeling. While cyclosporin and tacrolimus suppressed the clonal expansion of CD8+ T cells during GVHD, alloreactive CD4+ T cell clusters were preferentially expanded. Moreover, CNIs mediated reversible dose-dependent suppression of T cell activation and all stages of donor T cell exhaustion. Critically, CNIs promoted the expansion of both polyclonal and TCR-specific alloreactive central memory CD4+ T cells (TCM) with high self-renewal capacity that mediated cGVHD following drug withdrawal. In contrast to posttransplant cyclophosphamide (PT-Cy), CSA was ineffective in eliminating IL-17A-secreting alloreactive T cell clones that play an important role in the pathogenesis of cGVHD. Collectively, we have shown that, although CNIs attenuate aGVHD, they paradoxically rescue alloantigen-specific TCM, especially within the CD4+ compartment in lymphoid and GVHD target tissues, thus predisposing patients to cGVHD. These data provide further evidence to caution against CNI-based immune suppression without concurrent approaches that eliminate alloreactive T cell clones.

Hematopoietic Stem-Cell Transplantation: Exploring the Latest Advances and Gaps in Disparities, Psychosocial and Symptom Management Interventions, and Chronic Graft-Versus-Host Disease Care

Although allogeneic hematopoietic cell transplantation (HCT) offers a potential for cure for many patients with advanced hematologic malignancies and bone marrow failure or immunodeficiency syndromes, it is an intensive treatment and accompanied by short- and long-term physical and psychological symptoms requiring specialized care. With substantial advances in therapeutic approaches for HCT and supportive care, HCT survivors experience less morbidity and mortality. However, disparities in both HCT access and outcomes persist, and HCT survivors and their caregivers often lack access to much-needed psychosocial care. Additionally, more medical and psychosocial resources are needed to holistically care for HCT survivors with chronic graft-versus-host disease (GVHD). Hence, this chapter focuses on three areas pertaining to advances and gaps in HCT care: disparities in access to and outcomes of HCT, psychosocial and physical symptom management with supportive care interventions, and GVHD prevention and management.

The Role of Extracorporeal Photopheresis in the Management of Graft Versus Host Disease: Narrative Review

Hematopoietic stem cell donation is a method used to treat both blood-related and non-blood-related malignancies. Graft-versus-host disease is a potentially life-threatening complication that can occur following a stem cell transplant from a donor. This happens after the transplanted grafts attack the recipient's body as foreign cells, causing significant morbidity and mortality. Clinically, this condition can be classified as acute or chronic based on onset and pathophysiology. This review aims to provide an overview of recent studies on extracorporeal photopheresis as a treatment strategy option for graft-versus-host-diseased patients. It will explain how it treats graft-versus-host disease, summarize its promising effects, and provide future recommendations for its use in treating this illness. Extracorporeal photopheresis is used to treat graft-versus-host disease by collecting and separating white blood cells from the patient. This blood is fractionated into different parts, and white blood cells undergo treatment with 8-methoxy psoralen, a photoactivable drug, before exposure to ultraviolet light A. Lastly, the cells that have been treated are reinfused into the recipient's body. It prompts the programmed cell death of lymphocytes and the engulfment of cellular debris by host antigen-presenting, leading to a subsequent rise in T regulatory cells. However, more experimental and randomized controlled studies are required to identify the best patient selection requirements, environments, and treatment regimens for graft-versus-host disease.

Novel JAK Inhibitors to Reduce Graft-Versus-Host Disease after Allogeneic Hematopoietic Cell Transplantation in a Preclinical Mouse Model

Allogeneic hematopoietic cell transplantation (allo-HCT) is a highly effective, well-established treatment for patients with various hematologic malignancies and non-malignant diseases. The therapeutic benefits of allo-HCT are mediated by alloreactive T cells in donor grafts. However, there is a significant risk of graft-versus-host disease (GvHD), in which the donor T cells recognize recipient cells as foreign and attack healthy organs in addition to malignancies. We previously demonstrated that targeting JAK1/JAK2, mediators of interferon-gamma receptor (IFNGR) and IL-6 receptor signaling, in donor T cells using baricitinib and ruxolitinib results in a significant reduction in GvHD after allo-HCT. Furthermore, we showed that balanced inhibition of JAK1/JAK2 while sparing JAK3 is important for the optimal prevention of GvHD. Thus, we have generated novel JAK1/JAK2 inhibitors, termed WU derivatives, by modifying baricitinib. Our results show that WU derivatives have the potential to mitigate GvHD by upregulating regulatory T cells and immune reconstitution while reducing the frequencies of antigen-presenting cells (APCs) and CD80 expression on these APCs in our preclinical mouse model of allo-HCT. In addition, WU derivatives effectively downregulated CXCR3 and T-bet in primary murine T cells. In summary, we have generated novel JAK inhibitors that could serve as alternatives to baricitinib or ruxolitinib.

Use of antithymocyte globulin (rabbit) in a patient with known alpha-gal syndrome undergoing allogenic stem cell transplantation

INTRODUCTION

Alpha-gal syndrome (AGS) is a hypersensitivity disorder in which tick bites-most commonly from the lone star tick (Ambylomma americanum)-trigger immunoglobulin E-mediated hypersensitivity reaction upon exposure to oligosaccharide galactosse-alpha-1,3-galactose (α-gal). α-gal is most notorious for being found in "red meat" products but is present in mammalian meats such as beef, pork, lamb, rabbit, and others. Manifestations of AGS hypersensitivity are variable. There is currently no in vivo data describing allergic reactions against rabbit products in patients with AGS.

CASE REPORT

Here, we describe a case of a 44-year-old male with myelodysplastic syndrome and a known history of AGS undergoing allogeneic hematopoietic cell transplantation (allo-HSCT) with the use of rabbit antithymocyte globulin (rATG) for graft-versus-host disease (GVHD) prophylaxis.

MANAGEMENT AND OUTCOME

The risk of cross-reactivity against rATG in our patient with AGS could not be ruled out and, therefore, a test dose was administered. The patient tolerated the test dose with no signs of anaphylaxis. After demonstrating tolerance to the test dose, rATG was utilized for GVHD prophylaxis.

DISCUSSION

Due to the heterogeneity of AGS manifestations in patients, the use of rATG in patients with known AGS should be considered on a case-by-case basis. The administration of a test dose may help predict the occurrence of severe hypersensitivity reactions. The limited data surrounding the risk of AGS with rabbit-containing products and the various indications for the use of rATG warrants more in-depth study of the reactivity of this medication in this population.

HIV-1 proviral DNA in purified peripheral blood CD34+ stem and progenitor cells in individuals with long-term HAART; paving the way to HIV gene therapy

Human immunodeficiency virus (HIV)-1 infection is an important public health problem worldwide. After primary HIV-1 infection, transcribed HIV-1 DNA is integrated into the host genome, serving as a reservoir of the virus and hindering a definite cure. Although highly active antiretroviral therapy suppresses active viral replication, resulting in undetectable levels of HIV RNA in the blood, a viral rebound can be detected after a few weeks of treatment interruption. This supports the concept that there is a stable HIV-1 reservoir in people living with HIV-1. Recently, a few individuals with HIV infection were reported to be probably cured by hematopoietic stem transplantation (HSCT). The underlying mechanism for this success involved transfusion of uninfected hematopoietic stem and progenitor cells (HSPCs) from CCR5-mutated donors who were naturally resistant to HIV infection. Thus, gene editing technology to provide HIV-resistant HSPC has promise in the treatment of HIV infections by HSCT. In this study, we aimed to find HIV-infected individuals likely to achieve a definite cure via gene editing HSCT. We screened for total HIV proviral DNA by Alu PCR in peripheral blood mononuclear cells (PBMCs) of 20 HIV-infected individuals with prolonged viral suppression. We assessed the amount of intact proviral DNA via a modified intact proviral DNA assay (IPDA) in purified peripheral CD34+ HSPCs. PBMCs from all 20 individuals were positive for the gag gene in Alu PCR, and peripheral CD34+ HSPCs were IPDA-negative for six individuals. Our results suggested that these six HIV-infected individuals could be candidates for further studies into the ability of gene editing HSCT to lead to a definite HIV cure.

Exopolysaccharide-Treated Dendritic Cells Effectively Ameliorate Acute Graft-versus-Host Disease

Graft-versus-host disease (GVHD) is a primary and often lethal complication of allogenic hematopoietic stem cell transplantation (HSCT). Prophylactic regimens for GVHD are given as standard pretransplantation therapy; however, up to 50% of these patients develop acute GVHD (aGVHD) and require additional immunosuppressive intervention. Using a mouse GVHD model, we previously showed that injecting mice with exopolysaccharide (EPS) from Bacillus subtilis prior to GVHD induction significantly increased 80-day survival after transplantation of complete allogeneic major histocompatibility complex-mismatched cells. To ask whether EPS might also inhibit GVHD in humans, we used humanized NSG-HLA-A2 mice and induced GVHD by i.v. injection of A2neg human peripheral blood mononuclear cells (PBMCs). Because we could not inject human donors with EPS, we transferred EPS-pretreated dendritic cells (DCs) to inhibit aGVHD. We derived these DCs from CD34+ human cord blood cells, treated them with EPS, and then injected them together with PBMCs into the NSG-HLA-A2 mice. We found that all mice that received untreated DCs were dead by day 35, whereas 25% of mice receiving EPS-treated DCs (EPS-DCs) survived. This DC cell therapy could be readily translatable to humans, because we can generate large numbers of human EPS-DCs and use them as an "off the shelf" treatment for patients undergoing HSCT.

Evaluation of prolonged magnesium infusion after allogeneic hematopoietic cell transplant

PURPOSE

Calcineurin inhibitor use after allogeneic hematopoietic cell transplantation (allo-HCT) is associated with significant magnesium wasting. Utilization of a prolonged magnesium infusion is thought to lead to a lower serum peak concentration and therefore, decreased renal wasting of magnesium. In November 2017, our institution implemented a modification to our inpatient electrolyte replacement protocol for allo-HCT recipients that extended the magnesium infusion rate from 4 g/2 h to 4 g/4 h based on this theoretical advantage. The primary objective of this study was to compare the median magnesium requirements per day of admission between patients who received magnesium 4 g/2 h to patients who received magnesium 4 g/4 h. Secondary objectives included a comparison of the per-patient median serum magnesium concentration during admission, as well as the median incremental difference in serum magnesium concentration after intravenous replacement per patient per admission.

METHODS

Allo-HCT recipients who received prolonged infusion magnesium infusions were compared to a historical cohort of allo-HCT patients who received shorter IV magnesium infusions. Admissions were included if the patient had received an allo-HCT within 100 days prior, was admitted to the Transplant and Cellular Therapy Unit at WVU Medicine J.W. Ruby Memorial Hospital, and received at least one magnesium infusion and one dose of cyclosporine or tacrolimus. Admissions were excluded if the patient received oral magnesium, total parenteral nutrition, aminoglycosides, amphotericin, carboplatin, cisplatin, or foscarnet.

RESULTS

The pre-implementation group consisted of 81 admissions (n = 64 patients), while the post-implementation group consisted of 90 admissions (n = 60 patients). Median magnesium requirements per day of admission were not different between groups at 1.4 g of magnesium in the pre-implementation group and 1.9 g of magnesium in the post-implementation group (P = 0.25). Median serum magnesium concentrations and median incremental difference in serum magnesium concentration after intravenous replacement were also not different between groups: 1.65 mg/dL vs 1.60 mg/dL (P = 0.65) and 0.30 mg/dL vs 0.28 mg/dL (P = 0.67), respectively.

CONCLUSIONS

Prolonged infusion of magnesium in allo-HCT recipients receiving CNI therapy does not result in improvement in magnesium retention.

Mesenchymal stem cell-derived exosomes for managing graft-versus-host disease: An updated view

Graft-versus-host disease (GvHD) is the most common complication after stem cell transplantation, and also it is one of the primary limiting factors for the use of hematopoietic stem cell transplantation (HSCT) in the treatment of hematologic cancers. GvHD, a systemic inflammatory disease, is caused by donor T cells recognizing the recipient's foreign antigens. In addition, an immune dysregulation, caused by autoreactive immune cells, complicates potent inflammatory process following HSCT. While there is no one approved treatment method for GvHD, corticosteroids are the most common first-line treatment. Exosomes are biological vesicles between 30 and 120 nm in diameter, which carry various biologically active molecules. They are known to play a key role in the paracrine effect of mesenchymal stem cells with therapeutic and tissue repair effects, including an immunosuppressive potential. Exosomes are unable to replicate themselves but because of their small size and fluid-like structure, they can pass through physiological barriers. Exosome are relatively easy to prepare and they can be quickly sterilized by a filtration process. Administration of exosomes, derived from mesenchymal stem cells, effectively reduced GvHD symptoms and significantly increased HSCT recipients' survival. Mesenchymal stem cell-derived exosome therapy reduced clinical symptoms of GvHD in patients after HSCT. Studies in patients with GvHD described that that mesenchymal stem cell-derived exosomes inhibited the release of IFN-γ and TNF-α by activated natural killer (NK cells), thereby reducing the lethal function of NK cells and inflammatory responses. Current review provides a comprehensive overview about the use of mesenchymal stem cells and their derived exosomes for the treatment of GvHD.

Novel therapies for graft versus host disease with a focus on cell therapies

Graft versus host disease (GVHD) can occur at any period post allogeneic hematopoietic stem cell transplantation as a common clinical complication contributing to significant morbidity and mortality. Acute GVHD develops in approximately 30-50% of patients receiving transplants from matched related donors. High doses of steroids are used as first-line treatment, but are unsuccessful in around 40% of patients, resulting in the diagnosis of steroid-refractory acute GVHD. Consensus has yet to develop for the management of steroid-refractory acute GVHD, and prognosis at six months has been estimated at around 50%. Thus, it is critical to find effective treatments that increase survival of steroid-refractory acute GVHD. This article describes the currently known characteristics, pathophysiology, and treatments for GVHD, with a special focus on recent advances in cell therapies. In particular, a novel cell therapy using decidua stromal cells (DSCs) was recently shown to have promising results for acute GVHD, with improved effectiveness over previous treatments including mesenchymal stromal cells. At the Karolinska Institute, severe acute GVHD patients treated with placenta-derived DSCs supplemented with either 5% albumin or 10% AB plasma displayed a one-year survival rate of 76% and 47% respectively. Furthermore, patients with steroid-refractory acute GVHD, displayed survival rates of 73% with albumin and 31% with AB plasma-supplemented DSCs, compared to the 20% survival rate in the mesenchymal stromal cell control group. Adverse events and deaths were found to be attributed only to complications of hematopoietic stem cell transplant and GVHD, not to the study intervention. ASC Therapeutics, Inc, in collaboration with the Karolinska Institute, will soon initiate a phase 2 multicenter, open-label study to further assess the efficacy and safety of intravenous DSC treatment in sixty patients with Grade II-IV steroid-refractory acute GVHD. This novel cell therapy represents a promising treatment to combat the poor prognosis that steroid-refractory acute GVHD patients currently face.

Isavuconazole-tacrolimus drug-drug interactions in HSCT patients

OBJECTIVES

Because tacrolimus has a narrow therapeutic window and exhibits both intraindividual and interindividual variability, we attempted to establish the percentage of calcineurin inhibitor (CNI) dose reduction to prevent toxicity and ensure stem cell engraftment when using this immunosuppressant with the antifungal isavuconazole (ISA). By calculating the tacrolimus concentration/dose (C/D) ratio, we expected to demonstrate the magnitude of change in the C/D ratio from baseline after ISA administration.

METHODS

We evaluated the interaction between ISA, a new triazole antifungal used in prophylaxis for invasive fungal infections, and the CNI class of immunosuppressive drugs, specifically tacrolimus, in 11 blood samples from HSCT recipients.

RESULTS

The mean tacrolimus C/D ratio increased 1.44-fold from baseline 48 h after ISA administration (P = 0.001).

CONCLUSIONS

Although further investigation is needed, the results of this study suggest that a reduction of 18% in tacrolimus may be recommended.

Association between busulfan exposure and survival in patients undergoing a CD34+ selected stem cell transplantation

Busulfan is an alkylating drug routinely used in conditioning regimens for allogeneic hematopoietic cell transplantation (allo-HCT). A myeloablative conditioning regimen, including busulfan, is commonly used in patients undergoing T-cell depletion (TCD) and allo-HCT, but data on optimal busulfan pharmacokinetic (PK) exposure in this setting are limited. Between 2012 and 2019, busulfan PK was performed to target an area under the curve exposure between 55 and 66 mg × h/L over 3 days using a noncompartmental analysis model. We retrospectively re-estimated busulfan exposure following the published population PK (popPK) model (2021) and correlated it with outcomes. To define optimal exposure, univariable models were performed with P splines, wherein hazard ratio (HR) plots were drawn, and thresholds were found graphically as the points at which the confidence interval crossed 1. Cox proportional hazard and competing risk models were used for analyses. 176 patients were included, with a median age of 59 years (range, 2-71). Using the popPK model, the median cumulative busulfan exposure was 63.4 mg × h/L (range, 46.3-90.7). The optimal threshold was at the upper limit of the lowest quartile (59.5 mg × h/L). 5-year overall survival (OS) with busulfan exposure ≥59.5 vs <59.5 mg × h/L was 67% (95% CI, 59-76) vs 40% (95% CI, 53-68), respectively (P = .02), and this association remained in a multivariate analyses (HR, 0.5; 95% CI, 0.29; 0.88; P = .02). In patients undergoing TCD allo-HCT, busulfan exposure is significantly associated with OS. The use of a published popPK model to optimize exposure may significantly improve the OS.

Cytomegalovirus reactivation under pre-emptive therapy following allogeneic hematopoietic stem cell transplant: Pattern, survival, and risk factors in the Republic of Korea

INTRODUCTION

Pre-emptive therapy for cytomegalovirus (CMV) reactivation has been used in allogeneic hematopoietic stem cell transplantation (allo-HSCT). It is unclear if this strategy has poorer clinical outcomes in CMV-endemic areas and if more aggressive prophylaxis is required.

METHODS

We retrospectively analyzed the patterns and survival after CMV reactivation in patients undergoing pre-emptive therapy following allo-HSCT and assessed high-risk patients who could benefit from aggressive CMV prophylaxis in endemic areas.

RESULTS

Of the 292 patients who underwent allo-HSCT, 70.5% (donor+ or recipient+) were CMV seropositive. CMV reactivation occurred in 139 patients (47.6%), with a median of 31.5 days from day 0 of allo-HSCT. The overall survival of patients with CMV reactivation who received pre-emptive therapy did not differ from those without reactivation. Of the 139 patients with CMV reactivation, 78 (56.1%) underwent ≥2 rounds of pre-emptive therapy. In multivariate analysis, the risk of CMV reactivation was higher in patients with multiple myeloma, with CMV seropositivity of the recipient and donor, administered with a higher dose of anti-thymocyte globulin (ATG), and with acute graft-versus-host disease (aGVHD) ≥ grade 2.

CONCLUSION

Although half of the patients with allo-HSCT were administered with pre-emptive therapy for CMV, CMV reactivation did not affect their survival, indicating the advantages of pre-emptive therapy, even in CMV-endemic areas. The cost-effectiveness of more aggressive CMV prophylaxis should be re-evaluated in patients at a high risk for CMV reactivation.

Acute Graft-versus-Host Disease: An Update on New Treatment Options

Acute graft-versus-host disease (GVHD) occurs in approximately 50% of patients and remains a primary driver of non-relapse and transplant-related mortality. The best treatment remains prevention with either in vivo or ex vivo T-cell depletion, with multiple strategies used worldwide based on factors such as institution preference, ability to perform graft manipulation, and ongoing clinical trials. Predicting patients at high risk for developing severe acute GVHD based on clinical and biomarker-based criteria allows for escalation or potential de-escalation of therapy. Modern therapies for treatment of the disease include JAK/STAT pathway inhibitors, which are standard of care in the second-line setting and are being investigated for upfront management of non-severe risk based on biomarkers. Salvage therapies beyond the second-line remain suboptimal. In this review, we will focus on the most clinically used GVHD prevention and treatment strategies, including the accumulating data on JAK inhibitors in both settings.

Impact of anti-thymocyte globulin on survival outcomes in female-to-male allogeneic hematopoietic stem cell transplantation

Allogeneic hematopoietic cell transplantation between female donors and male recipients (female-to-male allo-HCT) is a well-established risk factor for inferior survival outcomes due to a higher incidence of graft-versus-host disease (GVHD). However, a clinical significance of anti-thymocyte globulin (ATG) in the female-to-male allo-HCT has not been elucidated. In this study, we retrospectively evaluated male patients who underwent allo-HCT between 2012 and 2019 in Japan. In the female-to-male allo-HCT cohort (n = 828), the use of ATG was not associated with a decreased risk of GVHD (HR of acute GVHD 0.691 [95% CI: 0.461-1.04], P = 0.074; HR of chronic GVHD 1.06 [95% CI: 0.738-1.52], P = 0.76), but was associated with favorable overall survival (OS) and a decreased risk of non-relapse mortality (NRM) (HR of OS 0.603 [95% CI: 0.400-0.909], P = 0.016; HR of NRM 0.506 [95% CI: 0.300-0.856], P = 0.011). The use of ATG in female-to-male allo-HCT resulted in survival outcomes that were almost equivalent to those in the male-to-male allo-HCT group. Therefore, GVHD prophylaxis with ATG might overcome the inferiority of survival outcomes in female-to-male allo-HCT.

Factors Affecting Day-to-Day Variations in Tacrolimus Concentration among Children and Young Adults Undergoing Allogeneic Hematopoietic Stem Cell Transplantation

Tacrolimus is widely used as prophylaxis for graft-versus-host disease (GVHD) in allogeneic stem cell transplantation (allo-HSCT). It has a narrow therapeutic index range; high tacrolimus concentrations are associated with toxicity, whereas low concentrations are associated with an increased risk of GVHD. Although dose adjustments based on therapeutic drug monitoring are performed, unexpected large variations in tacrolimus concentration are sometimes encountered. The available evidence suggests that the factors affecting tacrolimus concentration are not fully understood. This study was aimed primarily at investigating the factors affecting day-to-day variations in tacrolimus concentration in children and young adults who received continuous tacrolimus infusion after allo-HSCT. The secondary objective was to identify the factors causing large variations (>20%) in tacrolimus concentrations. This retrospective cohort study comprised 123 consecutive pediatric and young adult patients (age <25 years) who received continuous i.v. tacrolimus infusion after allo-HSCT at Shinshu University Hospital, Matsumoto, Japan, between January 2009 and December 2021. To compare day-to-day variations in tacrolimus concentration without consideration of the tacrolimus dose, 2 consecutive days when the tacrolimus dose was not changed were selected from between the first post-allo-HSCT day of a tacrolimus concentration >7 ng/mL and day 28 post-allo-HSCT. Subsequently, information for the subsequent 24 hours was collected along with the tacrolimus concentrations and hematocrit values. Tacrolimus concentration was determined using whole blood samples. Tacrolimus concentrations were significantly higher in patients who received red blood cell concentrate (RCC) transfusions (P < .0001) and methotrexate (P = .0162), patients with persistent fever (P = .0056), and patients with a decline in fever (P = .0003). In contrast, tacrolimus concentrations were significantly lower in patients who received platelet concentrate (PC) transfusions (P < .0001), who redeveloped fever (P = .0261), and who had a replaced tacrolimus administration route set (P = .0008). Variations in tacrolimus concentration were significantly correlated with variations in hematocrit (r = .556; P < .0001). Body weight (P < .0001), RCC transfusion (P < .0001), methotrexate use (P = .0333), persistent fever (P = .0150), and decline in fever (P = .0073) were associated with a sharp increase in tacrolimus concentration. In contrast, body weight (P < .0001), PC transfusion (P = .0025), and replacement of the tacrolimus administration route set (P = .0025) were associated with a sharp decrease in tacrolimus concentration. RCC and PC transfusions, fever, methotrexate administration, and replacement of the tacrolimus administration route set were independent factors affecting day-to-day variations in tacrolimus concentration. In addition to these factors, low body weight was a risk factor for both sharp increases and decreases in tacrolimus concentration. These findings suggest the need for better control of tacrolimus concentration using whole blood samples.

International society for cell & gene therapy stem cell engineering committee: Cellular therapies for the treatment of graft-versus-host-disease after hematopoietic stem cell transplant

BACKGROUND AIMS

Allogeneic hematopoietic stem cell transplant is a curative approach for many malignant and non-malignant hematologic conditions. Despite advances in its prevention and treatment, the morbidity and mortality related to graft-versus-host disease (GVHD) remains. The mechanisms by which currently used pharmacologic agents impair the activation and proliferation of potentially alloreactive T cells reveal pathways essential for the detrimental activities of these cell populations. Importantly, these same pathways can be important in mediating the graft-versus-leukemia effect in recipients transplanted for malignant disease. This knowledge informs potential roles for cellular therapies such as mesenchymal stromal cells and regulatory T cells in preventing or treating GVHD. This article reviews the current state of adoptive cellular therapies focused on GVHD treatment.

METHODS

We conducted a search for scientific literature in PubMed® and ongoing clinical trials in clinicaltrial.gov with the keywords "Graft-versus-Host Disease (GVHD)," "Cellular Therapies," "Regulatory T cells (Tregs)," "Mesenchymal Stromal (Stem) Cells (MSCs)," "Natural Killer (NK) Cells," "Myeloid-derived suppressor cells (MDSCs)," and "Regulatory B-Cells (B-regs)." All the published and available clinical studies were included.

RESULTS

Although most of the existing clinical data focus on cellular therapies for GVHD prevention, there are observational and interventional clinical studies that explore the potential for cellular therapies to be safe modalities for GVHD treatment while maintaining the graft-versus-leukemia effect in the context of malignant diseases. However, there are multiple challenges that limit the broader use of these approaches in the clinical scenario.

CONCLUSIONS

There are many ongoing clinical trials to date with the promise to expand our actual knowledge on the role of cellular therapies for GVHD treatment in an attempt to improve GVHD-related outcomes in the near future.

Engineering T cells to suppress acute GVHD and leukemia relapse after allogeneic hematopoietic stem cell transplantation

Acute graft-versus-host disease (aGVHD) limits the therapeutic benefit of allogeneic hematopoietic stem cell transplantation (allo-HSCT) and requires immunosuppressive prophylaxis that compromises antitumor and antipathogen immunity. OX40 is a costimulatory receptor upregulated on circulating T cells in aGVHD and plays a central role in driving the expansion of alloreactive T cells. Here, we show that OX40 is also upregulated on T cells infiltrating GVHD target organs in a rhesus macaque model, supporting the hypothesis that targeted ablation of OX40+ T cells will mitigate GVHD pathogenesis. We thus created an OX40-specific cytotoxic receptor that, when expressed on human T cells, enables selective elimination of OX40+ T cells. Because OX40 is primarily upregulated on CD4+ T cells upon activation, engineered OX40-specific T cells mediated potent cytotoxicity against activated CD4+ T cells and suppressed alloreactive T-cell expansion in a mixed lymphocyte reaction model. OX40 targeting did not inhibit antiviral activity of memory T cells specific to Epstein-Barr virus, cytomegalovirus, and adenoviral antigens. Systemic administration of OX40-targeting T cells fully protected mice from fatal xenogeneic GVHD mediated by human peripheral blood mononuclear cells. Furthermore, combining OX40 targeting with a leukemia-specific chimeric antigen receptor in a single T cell product provides simultaneous protection against leukemia and aGVHD in a mouse xenograft model of residual disease posttransplant. These results underscore the central role of OX40+ T cells in mediating aGVHD pathogenesis and support the feasibility of a bifunctional engineered T-cell product derived from the stem cell donor to suppress both disease relapse and aGVHD following allo-HSCT.

Synthetic Biology Technologies And Genetically Engineering Strategies For Enhanced Cell Therapeutics

Stem cell therapy mainly uses natural stem cells for transplantation, and the use of genetic engineering to optimize stem cell products is a very important process. This article reviews successful gene modification methods in the field of immune cell therapy and summarizes some attempts at stem cell gene editing in current research. Cell bridging is an innovative cutting-edge strategy that includes the specific recognition and signal transduction of artificial receptors. The "off-the-shelf" cell strategies mainly introduce the advantages of allogeneic cell therapy and how to overcome issues such as immunogenicity. Gene regulatory systems allow us to manipulate cells with small molecules to control cellular phenotypes. In addition, we also summarize some important genes that can provide a reference for cell genetic engineering. In conclusion, we summarize a variety of technical strategies for gene editing cells to provide useful ideas and experiences for future stem cell therapy research.

Opportunities for Treg cell therapy for the treatment of human disease

Regulatory T (Treg) cells are essential for maintaining peripheral tolerance, preventing autoimmunity, and limiting chronic inflammatory diseases. This small CD4+ T cell population can develop in the thymus and in the peripheral tissues of the immune system through the expression of an epigenetically stabilized transcription factor, FOXP3. Treg cells mediate their tolerogenic effects using multiple modes of action, including the production of inhibitory cytokines, cytokine starvation of T effector (e.g., IL-2), Teff suppression by metabolic disruption, and modulation of antigen-presenting cell maturation or function. These activities together result in the broad control of various immune cell subsets, leading to the suppression of cell activation/expansion and effector functions. Moreover, these cells can facilitate tissue repair to complement their suppressive effects. In recent years, there has been an effort to harness Treg cells as a new therapeutic approach to treat autoimmune and other immunological diseases and, importantly, to re-establish tolerance. Recent synthetic biological advances have enabled the cells to be genetically engineered to achieve tolerance and antigen-specific immune suppression by increasing their specific activity, stability, and efficacy. These cells are now being tested in clinical trials. In this review, we highlight both the advances and the challenges in this arena, focusing on the efforts to develop this new pillar of medicine to treat and cure a variety of diseases.

Multi-faceted role of LRP1 in the immune system

Graft versus host disease (GVHD) represents the major complication after allogeneic hematopoietic stem cell transplantation (Allo-SCT). GVHD-prone patients rely on GVHD prophylaxis (e.g. methotrexate) and generalized anti-GVHD medical regimen (glucocorticoids). New anti-GVHD therapy strategies are being constantly explored, however there is an urgent need to improve current treatment, since GVHD-related mortality reaches 22% within 5 years in patients with chronic GVHD. This review is an attempt to describe a very well-known receptor in lipoprotein studies - the low-density lipoprotein receptor related protein 1 (LRP1) - in a new light, as a potential therapeutic target for GVHD prevention and treatment. Our preliminary studies demonstrated that LRP1 deletion in donor murine T cells results in significantly lower GVHD-related mortality in recipient mice with MHC (major histocompatibility complex) -mismatched HSCT. Given the importance of T cells in the development of GVHD, there is a significant gap in scientific literature regarding LRP1's role in T cell biology. Furthermore, there is limited research interest and publications on this classical receptor molecule in other immune cell types. Herein, we endeavor to summarize existing knowledge about LRP1's role in various immune cells to demonstrate the possibility of this receptor to serve as a novel target for anti-GVHD treatment.

The oral histopathological and immunological characteristics of a xenogeneic mouse chronic graft-versus-host disease model

BACKGROUND

Oral lesions are important clinical manifestations of chronic graft-verse-host disease (cGVHD). However, the oral characteristics of cGVHD mouse model are not yet clear. This study aims to demonstrate oral histopathological and immunological characteristics of a xenogeneic cGVHD mouse model.

MATERIALS AND METHODS

2.5 × 10⁶ , 5.0 × 10⁶ , 7.5 × 10⁶ , and 10.0 × 10⁶  human peripheral blood mononuclear cells (hPBMCs) were intravenously transplanted into NCG mice to induce cGVHD. After transplantation, clinical observations were recorded. Tissue samples from salivary glands and oral mucosa were stained with H&E, Masson Trichrome, and immunofluorescence, and the histopathology of oral tissues was scored according to our modified criteria.

RESULTS

NCG mice showed signs of cGVHD onset after transplantation. The oral histopathological lesion incidences in each group were 37.50%, 50.00%, 62.50%, and 75.00%, respectively. Oral histopathological lesion incidence and histopathological scores were positively correlated with the amount of infused hPBMCs. Epithelial atrophy, epithelial cells vacuolar degeneration, and basal cells liquefaction denaturation were observed in oral mucosa, and acinar destruction and collagen deposition were observed in the salivary glands. Human CD45⁺ , CD4⁺ , CD8⁺ , IL-17⁺ , and FoxP3⁺ cells infiltrated into oral tissues. In the 5.0 × 10⁶  hPBMCs group, oral histopathological changes mainly began between days 30 and 45 post-transplantation, and became more severe after day 45. The oral histopathological scores also gradually increased.

CONCLUSION

Inflammation in oral mucosa epithelium and salivary glands, and CD4⁺ and CD8⁺ T cells dominating infiltration are the main oral features in the xenogeneic cGVHD mouse model. The severity of oral histopathological lesions shows a dose and time correlation. These may be helpful to oral cGVHD research.

Immunometabolic Therapeutic Targets of Graft-versus-Host Disease (GvHD)

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is a curative option in the treatment of aggressive malignant and non-malignant blood disorders. However, the benefits of allo-HSCT can be compromised by graft-versus-host disease (GvHD), a prevalent and morbid complication of allo-HSCT. GvHD occurs when donor immune cells mount an alloreactive response against host antigens due to histocompatibility differences between the donor and host, which may result in extensive tissue injury. The reprogramming of cellular metabolism is a feature of GvHD that is associated with the differentiation of donor CD4+ cells into the pathogenic Th1 and Th17 subsets along with the dysfunction of the immune-suppressive protective T regulatory cells (Tregs). The activation of glycolysis and glutaminolysis with concomitant changes in fatty acid oxidation metabolism fuel the anabolic activities of the proliferative alloreactive microenvironment characteristic of GvHD. Thus, metabolic therapies such as glycolytic enzyme inhibitors and fatty acid metabolism modulators are a promising therapeutic strategy for GvHD. We comprehensively review the role of cellular metabolism in GvHD pathogenesis, identify candidate therapeutic targets, and describe potential strategies for augmenting immunometabolism to ameliorate GvHD.

Comparative effects of fluconazole, posaconazole, and isavuconazole upon tacrolimus and cyclosporine serum concentrations

INTRODUCTION

Calcineurin inhibitors are commonly used in hematopoietic stem cell transplant (HSCT) patients to prevent graft versus host disease, but as CYP3A4 substrates they are frequently involved in drug-drug interactions. The purpose of this study is to characterize the effects of isavuconazole, fluconazole, and posaconazole on tacrolimus and cyclosporine serum concentrations and dose adjustments in allogeneic HSCT patients.

METHODS

This retrospective study included patients admitted to Oregon Health and Science University between April 2008 and December 2018 who underwent hematopoietic stem cell transplantation and received concomitant tacrolimus or cyclosporine and fluconazole, isavuconazole or posaconazole therapy. Data on patient characteristics, drug dosing, and serum drug concentrations were collected through chart review, and descriptive statistics were used to summarize the results.

RESULTS

A total of 139 patients were included in this study. We found fluconazole initiation leads to a 25% reduction in both tacrolimus and cyclosporine doses in order to maintain goal serum concentrations. Posaconazole and isavuconazole initiation requires tacrolimus dose reductions by 53% and 21%, respectively.

CONCLUSIONS

Based on our experience, FLC, POS, and ISA initiation may require CNI dose reductions and close monitoring of CNI levels to ensure levels remain within goal serum concentrations. Larger studies are needed to fully quantify the percentage in CNI dose reductions and characterize differences among these antifungals.

Impact of the combination of donor age and HLA disparity on the outcomes of unrelated bone marrow transplantation

Impact of donor age considering HLA disparity on hematopoietic cell transplantation (HCT) outcomes has not been fully evaluated. We evaluated 8486 patients who received unrelated bone marrow transplantation (UR-BMT) from 8/8 or 7/8 HLA-matched donors. Compared to 8/8 HLA-matched younger donors (<40 years), 8/8 HLA-matched older donors (subdistribution hazard ratio [SHR], 1.16; 95% CI, 0.97-1.38) and 7/8 HLA-matched younger donors (SHR, 1.33; 95% CI, 1.11-1.58) were associated with increased risk of grade III-IV acute graft-versus-host disease (aGVHD). 7/8 HLA-matched older donors had further increased risk (SHR, 2.00; 95% CI, 1.68-2.38) due to interaction between donor age and HLA disparity (p for interaction = 0.038). Progression-free survival (PFS) after UR-BMT with 8/8 HLA-matched younger donors was comparable to that after UR-BMT with 8/8 HLA-matched older donors, whereas UR-BMT with 7/8 HLA-matched younger or older donors was significantly associated with lower PFS than UR-BMT with 8/8 HLA-matched younger donors (younger donor; HR, 1.12; 95% CI, 1.04-1.21, older donor; HR, 1.28; 95% CI, 1.17-1.40; p for interaction = 0.079). In conclusion, adverse effect of increased donor age requires attention, especially in HLA-mismatched UR-BMT due to interaction between donor age and HLA disparity. Intensive aGVHD prophylaxis may be required to improve outcomes after HCT with mismatched older donors.

Decreased Mortality in 1-Year Survivors of Umbilical Cord Blood Transplant vs. Matched Related or Matched Unrelated Donor Transplant in Patients with Hematologic Malignancies

Allogeneic hematopoietic stem cell transplantation (HCT) has the potential to cure hematologic malignancies but is associated with significant morbidity and mortality. Although deaths during the first year after transplantation are often attributable to treatment toxicities and complications, death after the first year may be due to sequelae of accelerated aging caused by cellular senescence. Cytotoxic therapies and radiation used in cancer treatments and conditioning regimens for HCT can induce aging at the molecular level; HCT patients experience time-dependent effects, such as frailty and aging-associated diseases, more rapidly than people who have not been exposed to these treatments. Consistent with this, recipients of younger cells tend to have decreased markers of aging and improved survival, decreased graft-versus-host disease, and lower relapse rates. Given that umbilical cord blood (UCB) is the youngest donor source available, we studied the outcomes after the first year of UCB transplantation versus matched related donor (MRD) and matched unrelated donor (MUD) transplantation in patients with hematologic malignancies over a 20-year period. In this single-center, retrospective study, we examined the outcomes of all adult patients who underwent their first allogeneic HCT through the Duke Adult Bone Marrow Transplant program from January 1, 1996, to December 31, 2015, to allow for at least 3 years of follow-up. Patients were excluded if they died or were lost to follow-up before day 365 after HCT, received an allogeneic HCT for a disease other than a hematologic malignancy, or received cells from a haploidentical or mismatched adult donor. UCB recipients experienced a better unadjusted overall survival than MRD/MUD recipients (log rank P = .03, median overall survival: UCB not reached, MRD/MUD 7.4 years). After adjusting for selected covariates, UCB recipients who survived at least 1 year after HCT had a hazard of death that was 31% lower than that of MRD/MUD recipients (hazard ratio, 0.69; 95% confidence interval, 0.47-0.99; P = .049). This trend held true in a subset analysis of subjects with acute leukemia. UCB recipients also experienced lower rates of moderate or severe chronic graft-versus-host disease (GVHD) and nonrelapse mortality, and slower time to relapse. UCB and MRD/MUD recipients experienced similar rates of grade 2-4 acute GVHD, chronic GHVD, secondary malignancy, and subsequent allogeneic HCT. UCB is already widely used as a donor source in pediatric HCT; however, adult outcomes and adoption have historically lagged behind in comparison. Recent advancements in UCB transplantation such as the implementation of lower-intensity conditioning regimens, double unit transplants, and ex vivo expansion have improved early mortality, making UCB an increasingly attractive donor source for adults; furthermore, our findings suggest that UCB may actually be a preferred donor source for mitigating late effects of HCT.

Cyclosporine A-related neurotoxicity after haploidentical hematopoietic stem cell transplantation in children with hematopathy

Background

To evaluate cyclosporine A (CSA)-related neurotoxicity after haploidentical hematopoietic stem cell transplantation (HID-HSCT) in children with hematopathy.

Methods

This retrospective case series study included children with hematopathy who underwent HID-HSCT at Fujian Medical University Union Hospital between February 2013 and January 2017.

Results

Fifty-one children (39 males) were included in the study with a median age of 8 (range, 1.1–18) years. Seven patients (13.7%) developed CSA-related neurotoxicity after a median 38 (range, − 3 to 161) days from HID-HSCT. Hypertension (5/7, 71%) was the most common prodrome. Brain magnetic resonance imaging showed posterior reversible encephalopathy syndrome in six patients and atypical abnormalities in one patient. One patient died from grade IV graft-versus-host disease (GvHD) on day + 160, and six patients were alive at the last follow-up. Four patients (71.4%) achieved complete remission, while two patients developed secondary epilepsy and exhibited persistent MRI and electroencephalogram abnormalities at the 5-year follow-up. Hypertension after CSA was more common in patients with CSA-related neurotoxicity than in those without (71% vs. 11%, P = 0.002). Five-year overall survival did not differ significantly between patients with CSA-related neurotoxicity (85.7 ± 13.2%) and those without (65.8 ± 7.2%).

Conclusions

The incidence of CSA-related neurotoxicity in children with hematopathy undergoing HID-HSCT is relatively high.

P2X7 receptor antagonism increases regulatory T cells and reduces clinical and histological graft-versus-host disease in a humanised mouse model

Graft-versus-host disease (GVHD) is a severe inflammatory response arising from allogeneic haematopoietic stem cell transplantation. Previous studies revealed that antagonism of the P2X7 receptor with Brilliant Blue G (BBG) reduced liver GVHD but did not alter clinical GVHD in a humanised mouse model. Therefore, the present study aimed to trial a modified injection regime using more frequent dosing of BBG to improve outcomes in this model of GVHD. NOD-scid IL2Rγnull (NSG) mice were injected intraperitoneally (i.p.) with 10 × 106 human peripheral blood mononuclear cells (hPBMCs) (day 0), then daily with BBG (50 mg/kg) or saline (days 0-10). BBG significantly reduced clinical score, mortality and histological GVHD compared with saline treatment (endpoint). BBG significantly increased proportions of human regulatory T cells (Tregs) and human B cells and reduced serum human interferon-γ compared with saline treatment prior to development of clinical GVHD (day 21). To confirm the therapeutic benefit of P2X7 antagonism, NSG mice were injected i.p. with 10 × 106 hPBMCs (day 0), then daily with pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid (PPADS) (300 mg/kg) or saline (days 0-10). PPADS increased human Treg proportions compared with saline treatment (day 21), but potential clinical benefits were confounded by increased weight loss with this antagonist. To investigate the role of P2X7 antagonism on Treg survival, hPBMCs were cultured in reduced serum conditions to promote cell death. BBG increased proportions of Tregs (and B cells) compared with saline under these conditions. In conclusion, P2X7 antagonism reduces clinical and histological GVHD in a humanised mouse model corresponding to an increase in human Tregs.

Immune Reconstitution after Haploidentical Donor and Umbilical Cord Blood Allogeneic Hematopoietic Cell Transplantation

Allogeneic hematopoietic cell transplantation (HCT) is the only potentially curative therapy for a variety of hematologic diseases. However, this therapeutic platform is limited by an initial period when patients are profoundly immunocompromised. There is gradual immune recovery over time, that varies by transplant platform. Here, we review immune reconstitution after allogeneic HCT with a specific focus on two alternative donor platforms that have dramatically improved access to allogeneic HCT for patients who lack an HLA-matched related or unrelated donor: haploidentical and umbilical cord blood HCT. Despite challenges, interventions are available to mitigate the risks during the immunocompromised period including antimicrobial prophylaxis, modified immune suppression strategies, graft manipulation, and emerging adoptive cell therapies. Such interventions can improve the potential for long-term overall survival after allogeneic HCT.

Current Prophylaxis and Treatment Approaches for Acute Graft-Versus-Host Disease in Haematopoietic Stem Cell Transplantation for Children With Acute Lymphoblastic Leukaemia

Acute graft-versus-host disease (aGvHD) continues to be a leading cause of morbidity and mortality following allogeneic haematopoietic stem cell transplantation (HSCT). However, higher event-free survival (EFS) was observed in patients with acute lymphoblastic leukaemia (ALL) and grade II aGvHD vs. patients with no or grade I GvHD in the randomised, controlled, open-label, international, multicentre Phase III For Omitting Radiation Under Majority age (FORUM) trial. This finding suggests that moderate-severity aGvHD is associated with a graft-versus-leukaemia effect which protects against leukaemia recurrence. In order to optimise the benefits of HSCT for leukaemia patients, reduction of non-relapse mortality-which is predominantly caused by severe GvHD-is of utmost importance. Herein, we review contemporary prophylaxis and treatment options for aGvHD in children with ALL and the key challenges of aGvHD management, focusing on maintaining the graft-versus-leukaemia effect without increasing the severity of GvHD.

Tolerance to Bone Marrow Transplantation: Do Mesenchymal Stromal Cells Still Have a Future for Acute or Chronic GvHD?

Mesenchymal Stromal Cells (MSCs) are fibroblast-like cells of mesodermal origin present in many tissues and which have the potential to differentiate to osteoblasts, adipocytes and chondroblasts. They also have a clear immunosuppressive and tissue regeneration potential. Indeed, the initial classification of MSCs as pluripotent stem cells, has turned into their identification as stromal progenitors. Due to the relatively simple procedures available to expand in vitro large numbers of GMP grade MSCs from a variety of different tissues, many clinical trials have tested their therapeutic potential in vivo. One pathological condition where MSCs have been quite extensively tested is steroid resistant (SR) graft versus host disease (GvHD), a devastating condition that may occur in acute or chronic form following allogeneic hematopoietic stem cell transplantation. The clinical and experimental results obtained have outlined a possible efficacy of MSCs, but unfortunately statistical significance in clinical studies has only rarely been reached and effects have been relatively limited in most cases. Nonetheless, the extremely complex pathogenetic mechanisms at the basis of GvHD, the fact that studies have been conducted often in patients who had been previously treated with multiple lines of therapy, the variable MSC doses and schedules administered in different trials, the lack of validated potency assays and clear biomarkers, the difference in MSC sources and production methods may have been major factors for this lack of clear efficacy in vivo. The heterogeneity of MSCs and their different stromal differentiation potential and biological activity may be better understood through more refined single cell sequencing and proteomic studies, where either an “anti-inflammatory” or a more “immunosuppressive” profile can be identified. We summarize the pathogenic mechanisms of acute and chronic GvHD and the role for MSCs. We suggest that systematic controlled clinical trials still need to be conducted in the most promising clinical settings, using better characterized cells and measuring efficacy with specific biomarkers, before strong conclusions can be drawn about the therapeutic potential of these cells in this context. The same analysis should be applied to other inflammatory, immune or degenerative diseases where MSCs may have a therapeutic potential.

Extracellular Vesicle-Dependent Communication Between Mesenchymal Stromal Cells and Immune Effector Cells

Mesenchymal stem/stromal cells (MSCs) are multipotent cells residing in the stromal tissues of the body and capable of promoting tissue repair and attenuating inflammatory processes through their immunomodulatory properties. Preclinical and clinical observations revealed that not only direct intercellular communication mediates MSC properties; in fact, a pivotal role is also played by the release of soluble and bioactive factors, such as cytokines, growth factor and extracellular vesicles (EVs). EVs are membrane-coated vesicles containing a large variety of bioactive molecules, including lipids, proteins, and nucleic acids, such as RNA. EVs release their contents into target cells, thus influencing cell fate through the control of intracellular processes. In addition, MSC-derived EVs can mediate modulatory effects toward different effector cells belonging to both innate and adaptive immunity. In this review, we will discuss the literature data concerning MSC-derived EVs, including the current standardized methods for their isolation and characterization, the mechanisms supporting their immunoregulatory properties, and their potential clinical application as alternative to MSC-based therapy for inflammatory reactions, such as graft-versus-host disease (GvHD).