Treg-inducing microparticles promote donor-specific tolerance in experimental vascularized composite allotransplantation.

For individuals who sustain devastating composite tissue loss, vascularized composite allotransplantation (VCA; e.g., hand and face transplantation) has the potential to restore appearance and function of the damaged tissues. As with solid organ transplantation, however, rejection must be controlled by multidrug systemic immunosuppression with substantial side effects. As an alternative therapeutic approach inspired by natural mechanisms the body uses to control inflammation, we developed a system to enrich regulatory T cells (Tregs) in an allograft. Microparticles were engineered to sustainably release TGF-ß1, IL-2, and rapamycin, to induce Treg differentiation from naïve T cells. In a rat hindlimb VCA model, local administration of this Treg-inducing system, referred to as TRI-MP, prolonged allograft survival indefinitely without long-term systemic immunosuppression. TRI-MP treatment reduced expression of inflammatory mediators and enhanced expression of Treg-associated cytokines in allograft tissue. TRI-MP also enriched Treg and reduced inflammatory Th1 populations in allograft draining lymph nodes. This local immunotherapy imparted systemic donor-specific tolerance in otherwise immunocompetent rats, as evidenced by acceptance of secondary skin grafts from the hindlimb donor strain and rejection of skin grafts from a third-party donor strain. Ultimately, this therapeutic approach may reduce, or even eliminate, the need for systemic immunosuppression in VCA or solid organ transplantation.

Diagnostic performance of quantitative and qualitative parameters for the diagnosis of aortic graft infection using [18F]-FDG PET/CT.

PURPOSE: The aim of this study was the evaluation of quantitative and qualitative parameters for the diagnosis of aortic graft infection (AGI) using [18F]-FDG PET/CT. METHODS: PET/CT was performed in 50 patients with clinically suspected AGI. 12 oncological patients with aortic repair but without suspicion of AGI were included in the analysis to serve as control cohort. The [18F]-FDG uptake pattern around the graft was assessed using (a) a five-point visual grading scale (VGS), (b) SUVmax and (c) different graft-to-background ratios (GBRs). The diagnostic performance of VGS, SUVmax and GBRs was assessed and compared by ROC analysis. RESULTS: 28 infected and 34 uninfected grafts were identified by standard of reference. SUVmax and VGS were the most powerful predictors for the diagnosis of AGI according to the area under the curve (AUC 0.988 and 0.983, respectively) without a significant difference compared to GBRs. SUVmax and VGS showed congruent and accurate findings in 54 patients (i.e. either both positive or negative), yielding sensitivity and specificity (100%) in this subgroup of patients. CONCLUSION: Quantitative analysis by SUVmax and qualitative analysis by VGS are highly effective in the diagnosis of AGI and should be tested as an outcome measure in prospective trials.

Deletion of donor-reactive T cell clones after human liver transplant.

We recently developed a high throughput T cell receptor ß chain (TCRß) sequencing-based approach to identifying and tracking donor-reactive T cells. To address the role of clonal deletion in liver allograft tolerance, we applied this method in samples from a recent randomized study, ITN030ST, in which immunosuppression withdrawal was attempted within 2 years of liver transplantation. We identified donor-reactive T cell clones via TCRß sequencing following a pre-transplant mixed lymphocyte reaction and tracked these clones in the circulation following transplantation in 3 tolerant and 5 non-tolerant subjects. All subjects showed a downward trend and significant reductions in donor-reactive TCRß sequences were detected post-transplant in 6 of 8 subjects, including 2 tolerant and 4 non-tolerant recipients. Reductions in donor-reactive TCRß sequences were greater than those of all other TCRß sequences, including 3rd party-reactive sequences, in all 8 subjects, demonstrating an impact of the liver allograft after accounting for repertoire turnover. Although limited by patient number and heterogeneity, our results suggest that partial deletion of donor-reactive T cell clones may be a consequence of liver transplantation and does not correlate with success or failure of early immunosuppression withdrawal. These observations underscore the organ- and/or protocol-specific nature of tolerance mechanisms in humans.

Efficacy and Safety of Steroid Therapy for Posttransplant Hyperbilirubinemia Caused by Early Allograft Dysfunction: A Randomized Controlled Trial.

BACKGROUND Hyperbilirubinemia is a common event that occurs after liver transplantation. Hyperbilirubinemia is usually caused by early allograft dysfunction. Glucocorticoid is widely used for immunosuppression, but few studies have analyzed the effects of steroid therapy on posttransplantation hyperbilirubinemia. The aim of this study was to assess whether glucocorticoid was beneficial in treating hyperbilirubinemia caused by early allograft dysfunction. MATERIAL AND METHODS Patients with postoperative hyperbilirubinemia (those with conditions such as biliary complications and rejections were excluded) were randomly assigned, in a 2: 1 ratio, to the steroid and control groups. Patients in the steroid group were treated with glucocorticoid combined with ursodeoxycholic acid, whereas patients in the control group were only treated with ursodeoxycholic acid. The primary endpoint was decrease in bilirubin and the secondary endpoint was safety. RESULTS From 1st June 2016 to 30th April 2018, 40 patients were enrolled into the steroid group, and 20 were enrolled into the control group. Donor, recipient, and operative data were similar between the 2 groups. The decrease in bilirubin levels in the steroid group was significantly greater than that in the control group on the first day after the intervention was finished (9.25±1.30 mg/dL vs. 3.11±1.45 mg/dL, p=0.005), and after 2 weeks (15.01±1.20 mg/dL vs. 8.88±1.98 mg/dL, p=0.007). The steroid group did not have a higher complication rate but it did have a shorter postoperative hospital stay than in the control group. CONCLUSIONS Low-dose steroid therapy was effective and safe for treating hyperbilirubinemia caused by early graft dysfunction, and it improved liver function.

Anti-Diabetogenic Properties of Mineralocorticoid Receptor Antagonists: Implications for Enhanced Safety and Efficacy of Post-Transplantation Pharmacotherapies.

Widespread usage of the calcineurin inhibitors tacrolimus and cyclosporine A as post-transplantation immunosuppressive agents is fraught with severe nephrotoxic and diabetogenic side effects. More recently, tapering of calcineurin inhibitor-based immunotherapies with concurrent administration of the mammalian target of rapamycin (mTOR) inhibitors sirolimus and everolimus has been employed within pharmacological regimens designed to achieve better safety and efficacy for preservation of allograft kidney function. Collected preclinical data and recent clinical study, however, indicate that usage of calcineurin inhibitors and/or mTOR blockers as immunosuppressive agents promotes equivalent diabetogenic side effects. Based on a wealth of validating preclinical studies, we contend that the favorable metabolic effects of mineralocorticoid receptor antagonists, such as spironolactone, support their inclusion in novel immunosuppressive strategies to inhibit new onset type II diabetic symptoms in post-transplantation patient populations.

Predictive Value of Indocyanine Green Plasma Disappearance Rate on Liver Function and Complications After Liver Transplantation.

BACKGROUND The aim of this study was to investigate the correlation between indocyanine green plasma disappearance rate (ICG-PDR) and allograft function as well as postoperative complications after liver transplantation. MATERIAL AND METHODS In this prospective study, 115 cases of adult liver transplantation performed from 1 June 2016 to 1 December 2016 were enrolled. These 115 patients were divided into a group of PDR <18%/min (50 cases) and a group of PDR ≥18%/min (65 cases). The rates of liver recovery, postoperative complications, and survival were compared between these 2 groups. RESULTS Among the total of 115 patients, 111 patients recovered well and were discharged, whereas 4 patients died during the first month after the operation. Between the 2 groups, significant differences were observed in terms of the model for end-stage liver disease (MELD) score, intraoperative bleeding volume, and the level of hemoglobin (Hb), pre-albumin (PA) and total bilirubin (TB) the first week after the operation. Overall, the incidence of hepatic arterial complications and pneumonia was much higher in the PDR<18%/min group (P<0.05). CONCLUSIONS The early postoperative value of ICG-PDR was closely related to graft function and could act as a good predictor for the incidence of postoperative arterial complications.

Kidney-induced cardiac allograft tolerance in miniature swine is dependent on MHC-matching of donor cardiac and renal parenchyma.

Kidney allografts possess the ability to enable a short course of immunosuppression to induce tolerance of themselves and of cardiac allografts across a full-MHC barrier in miniature swine. However, the renal element(s) responsible for kidney-induced cardiac allograft tolerance (KICAT) are unknown. Here we investigated whether MHC disparities between parenchyma versus hematopoietic-derived "passenger" cells of the heart and kidney allografts affected KICAT. Heart and kidney allografts were co-transplanted into MHC-mismatched recipients treated with high-dose tacrolimus for 12 days. Group 1 animals (n = 3) received kidney and heart allografts fully MHC-mismatched to each other and to the recipient. Group 2 animals (n = 3) received kidney and heart allografts MHC-matched to each other but MHC-mismatched to the recipient. Group 3 animals (n = 3) received chimeric kidney allografts whose parenchyma was MHC-mismatched to the donor heart. Group 4 animals (n = 3) received chimeric kidney allografts whose passenger leukocytes were MHC-mismatched to the donor heart. Five of six heart allografts in Groups 1 and 3 rejected <40 days. In contrast, heart allografts in Groups 2 and 4 survived >150 days without rejection (p < 0.05). These data demonstrate that KICAT requires MHC-matching between kidney allograft parenchyma and heart allografts, suggesting that cells intrinsic to the kidney enable cardiac allograft tolerance.

MicroRNA 26a prolongs skin allograft survival and promotes regulatory T cell expansion in mice.

MicroRNA 26a (Mir-26a) has been reported to play functions in cellular differentiation, cell growth, cell apoptosis, and metastasis. However, the role of Mir-26a in transplant rejection has never been investigated. Full-thickness skin grafts 1-2 cm in diameter were obtained from the tail-skin CBA/J donor mice and transplanted onto the back of wild-type C57Bl/6 recipient mice. Vectors encoding pre-Mir-26a (LV-26a) and an empty lentiviral vector (LV-Con) delivered approximately 2 × 10(7) transforming units of recombinant lentivirus were injected to mice once through the tail vein. Mir-26a overexpression results in prolonged skin allograft survival (MST = 9.5 days in LV-Con mice; MST = 22 days in LV-26a mice. P < 0.01) and promoted regulatory T cells (Tregs) expansion. The prolonged skin allograft survival induced by LV-26a was abrogated by depletion of Tregs with anti-CD25 antibodies. Mir-26a significantly promoted IL-10 expression and suppressed the expression of IL-6, IL-17, and IFN-γ. Furthermore, IL-6 overexpression led to complete suppression of the Mir-26a-induced upregulation of Foxp3. The prolonged allograft survival induced by LV-Mir-26a was also completely abrogated by IL-6 overexpression. In conclusion, Mir-26a prolongs skin allograft survival and promotes Tregs expansion in part through inhibition of IL-6 expression.

The purinergic system in allotransplantation.

The purine nucleotide adenosine triphosphate (ATP) is a universal source of energy for any intracellular reaction. Under specific physiological or pathological conditions, ATP can be released into extracellular spaces, where it binds and activates the purinergic receptors system (i.e. P2X, P2Y and P1 receptors). Extracellular ATP (eATP) binds to P2X or P2Y receptors in immune cells, where it mediates proliferation, chemotaxis, cytokine release, antigen presentation and cytotoxicity. eATP is then hydrolyzed by ectonucleotidases into adenosine diphosphate (ADP), which activates P2Y receptors. Ectonucleotidases also hydrolyze ADP to adenosine monophosphate and adenosine, which binds P1 receptors. In contrast to P2X and P2Y receptors, P1 receptors exert mainly an inhibitory effect on the immune response. In transplantation, a prominent role has been demonstrated for the eATP/P2X7R axis; the targeting of this pathway in fact is associated with long-term graft function and reduced graft versus host disease severity in murine models. Novel P2X receptor inhibitors are available for clinical use and are under assessment as immunomodulatory agents. In this review, we will focus on the relevance of the purinergic system and on the potential benefits of targeting this system in allograft rejection and tolerance.

Engraftment of human HSCs in nonirradiated newborn NOD-scid IL2rγ null mice is enhanced by transgenic expression of membrane-bound human SCF.

Immunodeficient mice engrafted with human HSCs support multidisciplinary translational experimentation, including the study of human hematopoiesis. Heightened levels of human HSC engraftment are observed in immunodeficient mice expressing mutations in the IL2-receptor common γ chain (IL2rg) gene, including NOD-scid IL2rγ(null) (NSG) mice. Engraftment of human HSC requires preconditioning of immunodeficient recipients, usually with irradiation. Such preconditioning increases the expression of stem cell factor (SCF), which is critical for HSC engraftment, proliferation, and survival. We hypothesized that transgenic expression of human membrane-bound stem cell factor Tg(hu-mSCF)] would increase levels of human HSC engraftment in nonirradiated NSG mice and eliminate complications associated with irradiation. Surprisingly, detectable levels of human CD45(+) cell chimerism were observed after transplantation of cord blood-derived human HSCs into nonirradiated adult as well as newborn NSG mice. However, transgenic expression of human mSCF enabled heightened levels of human hematopoietic cell chimerism in the absence of irradiation. Moreover, nonirradiated NSG-Tg(hu-mSCF) mice engrafted as newborns with human HSCs rejected human skin grafts from a histoincompatible donor, indicating the development of a functional human immune system. These data provide a new immunodeficient mouse model that does not require irradiation preconditioning for human HSC engraftment and immune system development.

Membrane-bound human SCF/KL promotes in vivo human hematopoietic engraftment and myeloid differentiation.

In recent years, advances in the humanized mouse system have led to significantly increased levels of human hematopoietic stem cell (HSC) engraftment. The remaining limitations in human HSC engraftment and function include lymphoid-skewed differentiation and inefficient myeloid development in the recipients. Limited human HSC function may partially be attributed to the inability of the host mouse microenvironment to provide sufficient support to human hematopoiesis. To address this problem, we created membrane-bound human stem cell factor (SCF)/KIT ligand (KL)-expressing NOD/SCID/IL2rgKO (hSCF Tg NSG) mice. hSCF Tg NSG recipients of human HSCs showed higher levels of both human CD45(+) cell engraftment and human CD45(+)CD33(+) myeloid development compared with NSG recipients. Expression of hSCF/hKL accelerated the differentiation of the human granulocyte lineage cells in the recipient bone marrow. Human mast cells were identified in bone marrow, spleen, and gastrointestinal tissues of the hSCF Tg NSG recipients. This novel in vivo humanized mouse model demonstrates the essential role of membrane-bound hSCF in human myeloid development. Moreover, the hSCF Tg NSG humanized recipients may facilitate investigation of in vivo differentiation, migration, function, and pathology of human mast cells.

Stable mixed hematopoietic chimerism permits tolerance of vascularized composite allografts across a full major histocompatibility mismatch in swine.

This study tested the hypothesis that vascularized composite allografts (VCA) could be accepted in a robust model of hematopoietic chimerism by injecting allogeneic bone marrow cells (BMC) into swine fetuses. Outbred Yorkshire sows and boars were screened to ensure the absence of the major histocompatibility (MHC) allele SLA(cc) of inbred MGH miniature swine and then mated. Bone marrow harvested from an SLA(cc) swine donor was T-cell depleted and injected intravenously into the fetuses between days 50-55 of gestation. After birth, the piglets were studied with flow cytometry to detect donor cells and mixed lymphocyte reactions (MLR) and cell-mediated lympholysis (CML) assays to assess their response to donor. Donor-matched VCAs from SLA(cc) donors were performed on four chimeric and two nonchimeric swine. The results showed donor cell engraftment and multilineage macrochimerism after the in utero transplantation of adult BMC, and chimeric animals were unresponsive to donor antigens in vitro. Both control VCAs were rejected by 21 days and were alloreactive. Chimeric animals accepted the VCAs and never developed antidonor antibodies or alloreactivity to donor. These results confirm that the intravascular, in utero transplantation of adult BMC leads to donor cell chimerism and donor-specific tolerance of VCAs across a full MHC barrier in this animal model.

[Proteasomes on thyroid tissue allotransplantation under induction of donor specific tolerance in rats].

The proteasomes in the liver of August rats (RT1C) were investigated 30 days after the allotransplantation of Wistar rat (RT1u) thyroid tissue under renal capsule with/without induction of donor specific tolerance by donor splenocyte intraportal administration. The level of the total proteasome pool, immune proteasomes containing the LMP2 and/or LMP7 subunits, proteasome 19S- and 11S-regulators was defined. The intact and sham-operated August rats were used as control groups. The level of all immune proteasome forms and 11S regulator increased while the level of the total proteasome pool and 19S regulator decreased in the liver of experimental animals compared to the control groups that indicated changes of liver functional state after transplantation. The 19S/11S ratio increased in the liver of non-tolerated rats compared to tolerated animals. In the liver of tolerated rats with survived transplants, the quantity of mononuclear cells, expressing the immune subunit LMP2, greatly increased in comparison with control and non-tolerated animals. Study of the survived transplants showed the increase of the ratio of LMP2/LMP7 immune subunits and 19S/11S regulators in them compared to the tissue replacing the rejected transplants. In the control intact thyroid tissue, the immune proteasomes were almost not revealed, while 19S/11S ratio was maximal. Thus, the development of the immune reaction or its suppression is accompanied by change of the balance between different proteasome forms. The immune subunit LMP7 and 11S regulator are connected with the response against donor tissue. On the contrary, the immune subunit LMP2 and 19S regulator are likely to be important for the immune tolerance development and survived tissue functioning. The low content of the immune proteasomes in the follicle cells was found by immunofluorescence assay. The formation of antigens for major histocompatibility complex class I molecules was impaired by low immune proteasome content that led to immunological tolerance to hormone-producing follicle cells.

Mutated major histocompatibility complex class II transactivator up-regulates interleukin-33-dependent differentiation of Th2 subset through Nod2 binding for NLR (NOD-like receptor) signaling initiation.

Dominant-negative mutants of class II transactivator (mCIITAs) with N-terminal depletion have been used to repress the transcription of class II genes in xenotransplantation. Here, we report that mCIITA overexpressing myeloid cell line Ana-1 (Ana-1-mCIITA) derived from a C57BL/6 mouse was able to down-regulate the MHC class II expression and reverse immune responses from Th1 (IL-2(+)IFN-γ(+)STAT4(+)) to Th2 (IL-4(+)IL-5(+)IL-10(+)IL-13(+)STAT6(+)) when cocultured with T cells. Mechanism analysis indicated that the mCIITA protein is able to initiate a NOD-like receptor-related signaling pathway via binding of the cytoplasmic Nod2 protein, which was followed by activating RIP2, caspase 1, and IKK-α/ß. This ensures the expression of the genes encoding the cytokines IL-33, IL-1ß, and TNF-α; however, only the highly expressed IL-33 is responsible for inducing the type 2 response, with a skewed Th2 cytokine secretion (IL-4(+)IL-5(+)IL-10(+)IL-13(+)IL-2(-)IFN-γ(-)), which was completely prevented by the deactivation of the Nod2 gene with siRNA or by the blockage of the IL-33-related signaling using the mAb ST2L against the IL-33 receptor. mCIITA-mediated Th2 conversion was also successfully induced in vivo in a mCIITA-transgenic C57BL/6 mouse model. These results indicate that the Th1/Th2 balance could be regulated by an N terminus-depleted CIITA molecule via NOD-like receptor-related signaling, a property valuable for disease control, especially for inducing transplantation tolerance via the repression of class II expression and the attenuation of a Th1-dominant response.

Composite tissue allotransplantation in newborns: a swine model.

BACKGROUND: Management of congenital limb aplasia or facial malformations could be improved by composite tissue allotransplantation (CTA), a technique that has never been performed in newborns. For this, however, the induction of donor-specific tolerance would be mandatory, as long-term immunosuppression is not acceptable in this non-lifesaving procedure. Induction of tolerance has been shown to be possible in a newborn CTA rat model but has never been tested in large-animal models. Our goals were to establish a model of CTA in newborn swine to see if tolerance could be obtained without immunosuppression and to assess rejection or tolerance properties via clinical and histologic examinations. MATERIALS AND METHODS: We applied a CTA heterotopic knee swine model. We performed two series of surgical procedures: Series 1 was 20 autografts in 6-day-old (1-10) 2,544 kg (1,140-4,060 kg) piglets; Series 2 was 10 allografts without immunosuppression between outbred animals aged 7.8 d (6-10) and weighing 2,770 kg (2,200-3,550 kg). RESULTS: In Series 1, six early deaths and two cases of vascular failure were observed. In Series 2, no spontaneous deaths were observed and all piglets presented clinical and histologic rejection. CONCLUSIONS: Our findings strongly suggest that newborn immunologic status is not sufficient for the development of tolerance in large animals without immunologic intervention. Complications and animal death after transplantation correlate with age and weight. Low rates for both vascular failure and postoperative death permit the use of this model in piglets weighing over 2 kg and aged more than 6 d for research on newborn CTA.

Induction of allograft tolerance by monoclonal CD3 antibodies: a matter of timing.

Despite remarkable progress in organ transplantation through the development of a wealth of immunosuppressive drugs highly effective at controlling acute rejection, two major problems still remain, the loss of transplants due to chronic rejection and the growing number of sensitized recipients due to previous transplants, transfusions or pregnancies. Induction of immune tolerance appears to be the only way to curb this complex situation. Here we describe that a therapy, already successfully used to restore immune tolerance to self-antigens in overt autoimmunity, is effective at promoting transplant tolerance. We demonstrate that a short low-dose course with CD3 antibodies started after transplantation, at the time of effector T cell priming to alloantigens, induces permanent acceptance of fully mismatched islet allografts. Mechanistic studies revealed that antigen-specific regulatory and effector T cells are differentially affected by the treatment. CD3 antibody treatment preferentially induces apoptosis of activated alloreactive T cells which is mandatory for tolerance induction. In contrast, regulatory T cells are relatively spared from CD3 antibody-induced depletion and can transfer antigen-specific tolerance thus arguing for their prominent role in sustaining long-term graft survival.

Ultrasound renal resistive index is not an organ-specific predictor of allograft outcome.

BACKGROUND: Ultrasound-measured renal resistive index (RRI) has been suggested to predict allograft survival in renal transplant recipients. Based on experimental and clinical data, we objected to the theory that RRI specifically mirrors allograft characteristics. Instead, we hypothesized that RRI rather represents a marker of systemic vascular damage than an organ-specific marker. In order to refute this hypothesis, RRI should override the resistive index measured in other abdominal parenchymatous organs-such as the spleen-as predictor of allograft outcome. We therefore set out to simultaneously measure renal and splenic ultrasound resistive index in kidney allograft recipients. METHODS: Eighty-seven stable transplant recipients were recruited. We measured RRI, splenic resistive index (SRI) and an established marker of systemic vascular damage, namely common carotid intima-media thickness (IMT). During a follow-up of 4.9 ± 0.5 years, the occurrence of the combined primary end point, defined as a decrease of ≥ 50% in estimated glomerular filtration rate (eGFR), need for dialysis treatment or death, was recorded. RESULTS: At baseline, both RRI and SRI correlated with common carotid IMT [RRI: r = 0.203 (P = 0.006); SRI: r = 0.315 (P < 0.001)], but not with allograft-specific markers such as eGFR or proteinuria. Elevated RRI was a weak non-significant predictor of the combined primary end point. Notably, RRI did not surpass SRI as outcome predictor. When analysing individual components of the combined primary end point separately, elevated RRI failed to predict strictly renal events (decrease of ≥ 50% in eGFR/need for dialysis treatment), while it predicted total mortality. CONCLUSIONS: Our findings support the notion that RRI is not a specific indicator of allograft damage. Similar to SRI, RRI is rather associated with systemic vascular damage markers and mortality.

Tolerance in clinical transplantation: progress, challenge or just a dream?

INTRODUCTION: The achievement of clinical operational tolerance (COT) is still considered a major goal in the academic field of solid organ transplantation. Even COT is feasible and safe in selected cases after liver transplantation, in the clinical arena of solid organ transplantation, tolerance remains, for the most part, a concept rather than a reality. CHALLENGES: Although modern immunosuppression regimens have effectively handled acute rejection, nearly all organs except the liver commonly suffer chronic immunologic damage that impairs organ function, threatening patient and allograft survival. Strong arguments in favour of conducting clinical tolerance trials are the high number of grafts still lost due to chronic rejection, the burden of serious adverse effects from immunosuppressants which causes considerable cardiovascular morbidity and mortality, respectively, and the fact that sporadic tolerance can be observed in rare cases where non-adherence to immunosuppressive regimens is linked with a state of long-lasting organ tolerance. Whereas molecule-based regimens have been largely ineffective, cell-based tolerance protocols have delivered some encouraging results to achieve COT. DISCUSSION: In combination with donor bone marrow-derived stem cells, some encouraging results in COT development were reported lately for renal transplantation as well. However, less toxic conditioning protocols and more experience by use of cell products with regulatory properties in combination with synergizing immunosuppressive drugs is required to launch future tolerance trials for a broader spectrum of potential transplant candidates. New methods in immunomonitoring including biomarkers, microarray-based genetic tolerance signatures and functional assays may pave the way to achieve COT in upcoming clinical trials.

Gut microbes enlarged the protective effect of transplanted regulatory B cells on rejection of cardiac allografts.

BACKGROUND: Regulatory B cells (Bregs) play an important role in maintaining immune homeostasis and have the potential to induce tolerance. Previous work has found that Breg cells are involved in heart transplantation tolerance. However, the effect of Breg on the transplantation tolerance and the underlying mechanisms remain to be clarified. METHODS: Using a within-species heart transplantation model, we aimed to investigate the role of CD19+CD5+CD1dhigh Bregs isolated from transplanted mice in preventing transplant rejection in vivo. We also explored the effects of CD40 and tumor necrosis factor receptor-associated factor 6 (TRAF6) ubiquitin ligase on Breg-mediated prolongation of survival in heart transplant (HT) mice, and the regulatory effects of downstream Cdk4 and Cdk6 proteins on dendritic cells (DCs), which clarified the function and molecular mechanism of Breg cells in HT mice. RESULTS: Our data suggest that adoptive transfer of the transplanted Bregs served as an effective tolerance-inducing mechanism in HT mice and was involved in the CD40-TRAF6 signaling pathway in DCs. Moreover, DCs collected from the Breg treated HT mice also prolonged the survival of HT mice. Furthermore, DC-specific knockout of TRAF6 diminished Breg-mediated prolongation of survival in HT mice. Interestingly, gut microbes from donors increased the survival of cardiac allografts both in both the absence and presence of Bregs but were not implicated in CD40-TRAF6 signaling. CONCLUSIONS: These findings reveal a role of Breg cells in the induction of transplantation tolerance through the blockade of the CD40-TRAF6 signaling pathway, which might be used in the treatment of HT in the clinic.