Persistence of allogeneic cells in graft and host tissues after small bowel transplantation.

Small bowel transplantation is associated with a significant risk of graft versus host disease owing to the large amount of organized lymphoid tissue within the graft. This study assessed whether graft lymphoid cells could persist in the long term following fully allogeneic small bowel transplantation when graft rejection was prevented by cyclosporin immunosuppression. Transplantation was carried out between PVG and DA strains of rat. Cyclosporin (15 mg/kg) was given daily from transplantation, and groups of animals were studied at 28 and 56 days after grafting. The proportions of donor- and recipient-derived cells in the graft and in the host gut and lymphoid tissues were assessed using immunohistochemical tissue staining and monoclonal antibodies specific for cells expressing class I antigens from the two strains of rat. Results demonstrated a persisting population of graft-derived T cells which were capable of migration to the host. Therefore, there may be a long-term risk of graft versus host disease after small bowel transplantation under cyclosporin immunosuppression.     

Dynamics of virus‐specific T cell immunity in pediatric liver transplant recipients

Immunosuppression following solid organ transplantation (SOT) has a deleterious effect on cellular immunity leading to frequent and prolonged viral infections. To better understand the relationship between posttransplant immunosuppression and circulating virus‐specific T cells, we prospectively monitored the frequency and function of T cells directed to a range of latent (CMV, EBV, HHV6, BK) and lytic (AdV) viruses in 16 children undergoing liver transplantation for up to 1 year posttransplant. Following transplant, there was an immediate decline in circulating virus‐specific T cells, which recovered posttransplant, coincident with the introduction and subsequent routine tapering of immunosuppression. Furthermore, 12 of 14 infections/reactivations that occurred posttransplant were successfully controlled with immunosuppression reduction (and/or antiviral use) and in all cases we detected a temporal increase in the circulating frequency of virus‐specific T cells directed against the infecting virus, which was absent in 2 cases where infections remained uncontrolled by the end of follow‐up. Our study illustrates the dynamic changes in virus‐specific T cells that occur in children following liver transplantation, driven both by active viral replication and modulation of immunosuppression.     

Postdepletion Lymphocyte Reconstitution During Belatacept and Rapamycin Treatment in Kidney Transplant Recipients

Belatacept is used to prevent allograft rejection but fails to do so in a sizable minority of patients due to inadequate control of costimulation‐resistant T cells. In this study, we report control of costimulation‐resistant rejection when belatacept was combined with perioperative alemtuzumab‐mediated lymphocyte depletion and rapamycin. To assess the means by which the alemtuzumab, belatacept and rapamycin (ABR) regimen controls belatacept‐resistant rejection, we studied 20 ABR‐treated patients and characterized peripheral lymphocyte phenotype and functional responses to donor, third‐party and viral antigens using flow cytometry, intracellular cytokine staining and carboxyfluorescein succinimidyl ester–based lymphocyte proliferation. Compared with conventional immunosuppression in 10 patients, lymphocyte depletion evoked substantial homeostatic lymphocyte activation balanced by regulatory T and B cell phenotypes. The reconstituted T cell repertoire was enriched for CD28⁺ naïve cells, notably diminished in belatacept‐resistant CD28^? memory subsets and depleted of polyfunctional donor‐specific T cells but able to respond to third‐party and latent herpes viruses. B cell responses were similarly favorable, without alloantibody development and a reduction in memory subsets—changes not seen in conventionally treated patients. The ABR regimen uniquely altered the immune profile, producing a repertoire enriched for CD28⁺ T cells, hyporesponsive to donor alloantigen and competent in its protective immune capabilities. The resulting repertoire was permissive for control of rejection with belatacept monotherapy.

     

Inflammatory activation and recovering BKV‐specific immunity correlate with self‐limited BKV replication after renal transplantation

As BKV‐associated nephropathy has emerged as an important cause of allograft failure, it has been of major importance to find immune mechanisms suitable to identify kidney transplant recipients (KTRs) at increased risk of BKV replication. We monitored 29 KTRs with seven measurements during the first year post‐transplantation. BKV‐specific T cells directed to 5 BKV proteins were analyzed in an interferon‐γ ELISPOT assay. BKV‐specific antibodies were measured using an ELISA. The extent of immunosuppression and inflammatory activation were quantified by measures of immune function including lymphocyte subpopulations, IP‐10, and adhesion molecule serum levels. All 5 BKV‐specific T cells increased significantly from diagnosis to resolution of BKV replication (P < 0.001). While antistructural T cells were significantly higher in KTRs with BKV replication (P < 0.05), no differences were observed for antismall t‐ and large T‐antigen‐directed T cells (P > 0.05). Interestingly, 65% of KTRs without BKV replication showed transient appearance of antismall t‐ and large T‐antigen‐directed T cells. Although no significant differences were observed for T‐cell subpopulations and adhesion molecules, IP‐10 levels increased significantly during BKV replication (P < 0.05). Assessment of BKV‐specific T cells identifies recovering BKV‐specific immunity in KTRs with BKV replication and suggests their protective ability in KTRs without BKV replication. Increases in IP‐10 levels stress the importance of infiltrating inflammatory leukocytes in the regulation of BKV replication and point to inflammatory activation in the pathogenesis of BKV replication.     

Complex role of tumor cell transforming growth factor (TGF)-βs on breast carcinoma progression

Growth inhibition by the TGF-s has been extensively studied in both normal and transformed mammary epithelial cells. It has been proposed that loss of autocrine TGF- mediated growth regulation is a critical event in breast tumorigenesis and several lines ofin vitro andin vivo data support this hypothesis. However, a positive association between the expression of TGF-s by tumor cells and the progression or maintenance of breast cancinoma cells has been observed in many studies inin vivo tumor models. Possible mechanisms for these growth enhancing effects of TGF- include immunosuppression mediated by tumor TGF-s, enhanced angiogenesis, increased peritumoral stroma formation, and cell adhesion. The net effect of tumor cell TGF- on the biology of breast carcinogenesis would depend on the balance between autocrine growth inhibition of mammary epithelial cells and these growth enhancing effects.     

Treatment with total lymphoid irradiation,cyclosporin A and a monoclonal anti-T-cell antibody in a hamster-to-rat heart transplantation model: Graft survival and morphological analysis

Treatment with preoperative total lymphoid irradiation and post-transplant cyclosporin A has been shown to have a synergistic effect on graft survival in allo-and xenotransplantation. Specific monoclonal antibodies against T cells and T cell subpopulations could offer new ways of preventing graft rejection in xenotransplantation. Graft survival and histology were examined after total lymphoid irradiation plus cyclosporin A treatment versus cyclosporin A plus a monoclonal antibody in a concordant, heterotopic, hamster-to-rat heart transplantation model. Preoperative total lymphoid irradiation was given at a dose of 1.25 Gy, 12 times over a period of 3 weeks. Cyclosporin A at a dose of 12.5 mg/kg per day was administered perorally and OX-19, a pan T cell monoclonal antibody, was given as intraperitoneal injections at doses of 100 g or 500 g/kg per day from day 0 until graft rejection. While total lymphoid irradiation alone prolonged graft survival to 9.4 days, total lymphoid irradiation plus cyclosporin A extended graft survival to a mean of 22 days. Cyclosporin alone or combined with the monoclonal antibody could not increase graft survival significantly when compared to untreated animals, which rejected their grafts within 3.7 days. Vascular rejection was the characteristic morphological finding, even after some weeks of excellent graft function. In conclusion, total lymphoid irradiation and cyclosporin A had a synergistic effect on graft survival in this concordant xenotransplantation model, although recent impressive results from other groups could not be reproduced. Total lymphoid irradiation combined with cyclosporin A appears to delay a primary humoral graft rejection, while the mechanism of rejection, judged by histology, stays the same.     

Intratumoral immunotherapy with anti-PD-1 and TLR9 agonist induces systemic antitumor immunity without accelerating rejection of cardiac allografts

Immune checkpoint inhibitors, such as programmed cell death 1 (PD-1) blockades, have revolutionized the field of cancer immunotherapy. However, there is a growing concern whether PD-1 inhibitors can be administered safely to transplant recipients with advanced cancer, as the T cells activated by checkpoint inhibitors may become reactive not only toward tumor antigens but also toward donor alloantigen, thereby resulting in allograft rejection. Here, immunotherapy with anti-PD-1/toll like receptor 9 agonist was administered to C57BL/6 mice bearing a cardiac allograft that were receiving maintenance immunosuppression or a PI4KIIIβ inhibitor-based tolerogenic regimen. Intratumoral (i.t.), but not systemic, immunotherapy promoted potent anti-tumor responses, but did not accelerate allograft rejection. This effect was associated with a pro-immunogenic effect induced by i.t. immunotherapy resulting in systemic cellular and humoral immune anti-tumor responses. Furthermore, when the tumor and cardiac allograft shared major histocompatibility complex (MHC) antigens, i.t. immunotherapy promoted immune responses directed against tumor and the cardiac allograft resulting in allograft rejection. The anti-tumor effect was compromised by maintenance immunosuppression with cyclosporin A, indicating that an optimal balance between enhanced anti-tumor immunity and decreased transplant immunoreactivity is critical. A clinically relevant approach could be to temporarily withdraw maintenance immunosuppression and/or replace it with a PI4KIIIβ inhibitor–based tolerance-inducing regimen to allow for effective immunotherapy to take place.     

Prognostic value of the immunomonitoring of patients with renal cell carcinoma under therapy with IL-2/IFN-α-2 in combination with 5-FU

After tumor nephrectomy, patients suffering from metastatic renal cell carcinoma (RCC) received interleukin-2 (IL-2), interferon (IFN)--2b and 5-fluorouracil (5-FU) in one to three treatment cycles over 8 weeks Using flow cytometry, we investigated the immunophenotype of peripheral blood lymphocytes from 22 patients during therapy. In all patients, we found an increase in the absolute number of T lymphocytes, especially of the CD4 type, and in the number of HLA-DR⁺, CD25⁺ T cells and natural killer (NK) cells. The mean number of B cells did not increase during therapy. The numbers of CD4⁺, CD8⁺ and CD25⁺ T cells correlated significantly with the clinical response. In addition, we found that the pretherapeutic number of T lymphocytes and B cells but not of NK cells was significantly higher in patients with a therapy-induced clinical response. In conclusion, we describe the predictive value of the number of lymphocytes from peripheral blood for the efficiency of IL-2/IFN--2b therapy in combination with 5-FU in patients with metastatic renal cell carcinoma.     

49. Refluxoesophagitis Operationstaktik beim Erwachsenen: Pexieverfahren

Zusammenfassung Mit der Fundophrenicopexie lassen sich fur den Verschlußapparat des UÖS wichtige mechanische Komponenten rekonstruieren. Prä- und postoperative elektronische Druckmessungen im Rahmen einer Studie (n = 52) ergaben einen signifikanten Druckanstieg von =20,1 mmHg auf =39,25 mmHg. Die Fundophrenicopexie bietet gegenüber der Fundoplikatio eine Reihe Op.-technischer Vorteile and weist weniger postoperative Komplikationen auf. Deswegen sollte, wenn die anatomischen Voraussetzungen gegeben sind, zur operativen Behandlung der Refluxkrankheit die Fundophrenicopexie gewählt werden.     

Modulation by interferon alpha of the decreased natural killer activity in patients with glioblastoma

Summary It is known that natural killer (NK) cells are involved in immunosurveillance against tumours. This study examines the NK activity of mononuclear cells (MNC) from the peripheral blood of patients with gliobalstoma. The cytotoxic inducer effect of interferonalpha (IFN-) upon these MNC has also been studied. A marked decrease in NK activity mediated by MNC from these patients was found. This functional defected in MNC is not due to a decrease in phenotypically defined NK cells. After long-term (5-day) incubation with IFN-, MNC from 5 out of 14 patients showed strong lytic activity against NK-sensitive target cells. In this system, IFN- failed to induce cytotoxic activity against NK-resistant target cells in MNC from all the patients studied. Thisin vitro induction of cytotoxic activity in MNC from some patients with glioblastoma by IFN- suggests a potential immunotherapeutic use of the lymphokine in these subjects.     

Cell subsets responding to purified hepatocytes and evidence of indirect recognition of hepatocyte major histocompatibility complex class I antigen. II. In vitro-generated "memory" cells to class I+ class II- hepatocytes.

Purified hepatocytes stimulate the development of L3T4-, Ly2+ allospecific cytolytic T cells from naive splenocytes after 5 days in primary mixed lymphocyte-hepatocyte culture (MLHC). Previous studies indicate that the immunogenicity of purified hepatocytes relates to the expression of MHC class I antigen. The purpose of the following experiments was to identify the cell subsets that specifically recognize hepatocyte MHC class I antigen. We employed primed lymphocyte testing (PLT) in order to test for a "second set" response. Cells from primary MLHC reverted to a functionally quiescent state when they were grown in culture for an additional 7-9 days. The cells were then tested for cytotoxicity or rechallenged with allogeneic, syngeneic, or "third party" hepatocytes and tested for proliferation. Allocytotoxicity was low on day 12 in MLHC, but the sensitized cell population demonstrated peak proliferation in response to allogeneic hepatocytes 48 hr after restimulation. When bulk PLT cells were immunodepleted, both L3T4+, Ly2- and L3T4-, Ly2+ T cell subsets demonstrated a "second set" response to allogeneic hepatocytes consistent with specific recognition of and retention of "memory" for hepatocyte MHC class I alloantigen.     

T-cell inhibition does not aggravate bacterial translocation from rat small bowel

BACKGROUND: T-cell mediated immunity has been proposed to have an important function in the defence against translocating microbes from the gastrointestinal tract. After small bowel transplantation massive T-cell immunosuppression is necessary to avoid rejection. As a consequence, infections with intestinal bacteria are the main contributors to mortality in this setting. This could further imply that T cells are important in limiting bacterial translocation. In a model for bacterial translocation from small bowel in the rat we examined the outcome of T-cell inactivation. METHODS: The studies were performed in a model of bacterial translocation from a Thiry-Vella loop of small bowel in the rat. The animals were treated with an anti-alpha/beta T-cell receptor monoclonal antibody (R73). Inhibition of T-cell activation was also made using the immunosuppressive drug cyclosporin A. All animals were sacrificed on day 3 postoperatively and translocation to the mesenteric lymph nodes, liver, spleen, lung and blood was evaluated. RESULTS: Treatment with R73 resulted in an almost complete labelling of T cells but did not result in any increased bacterial translocation compared to animals treated with saline. Neither did immunosuppression with cyclosporin A. CONCLUSIONS: In the model of bacterial translocation from a defunctionalised loop of small bowel the inhibition of T cells does not increase bacterial translocation to mesenteric lymph nodes or promote the systemic spread of the translocating bacteria. This indicates that T cells do not have any important protective function against translocating microbes from defunctionalised small bowel.     

Changes in T-cell receptor subsets after cardiac surgery in children

T cells are divided into two subsets, αβ and γδ, according to the T-cell receptor (TCR) expressed. Recent findings indicate that γδ T cells serve as the first defense against microbial pathogens, and represent a link between innate and acquired immunity. We conducted a study to investigate the changes in circulating TCR subsets after cardiac surgery in children. Blood samples from 24 children who underwent cardiac surgery with cardiopulmonary bypass (CPB) were collected serially to analyze TCR subsets by flow cytometry. The αβ T cells reached a nadir on postoperative day (POD) 1, but recovered to pre-CPB levels on POD 3. On the other hand, the γδ T cells decreased after CPB and did not recover to pre-CPB levels even after POD 7. The αβ/γδ T-cell ratio was increased after POD 3. In children, γδ T cells recover more slowly than αβ T cells after cardiac surgery. These changes in TCR subsets may contribute to postoperative immunosuppression. Received: August 23, 1999 / Accepted: May 30, 2000     

Glomerular filtration rate after liver transplantation with a low-dose cyclosporin protocol

Cyclosporin nephrotoxicity is a well-known complication in organ transplantation. In successful liver transplantation, a moderate degree of renal impairment is accepted. Whether this impairment is continuously progressive, stabilizes with time, or is reversible is not known. We have prospectively evaluated the glomerular filtration rate (GFR) using ⁵¹CrEDTA plasma clearance in 29 liver transplant patients (11 males and 18 females) with a mean age of 49 years (range 22–62 years). The ⁵¹CrEDTA plasma clearance measurements were performed preoperatively and at 3, 6, 12, 24, and 36 months after the liver transplantation. All but six patients were given sequential, quadruple drug therapy with antithymocyte globulin, azathioprine, steroids, and cyclosporin. Intravenous cyclosporin was avoided and oral cyclosporin started when renal function was stable. Cyclosporin was started in a dose of 8 mg/kg body weight, aiming at whole blood trough levels (specific monoclonal technique) of 200 g/l in the postoperative period; thereafter, the dosage was rapidly tapered down, aiming at whole blood trough levels of less than 100 g/l at 3 months (1.5–2 mg/kg body weight). From a mean preoperative GFR of 89±3 ml/min per 1.73 m², all patients declined in renal function after transplantation to a mean of 64±4 ml/min per 1.73 m² 3 months after transplantation, and starting in the 3rd month the renal function was stable at about 70% of the preoperative value. No correlations were found between cyclosporin weak level or accumulated cyclosporin dose and renal impairment. We conclude that liver transplantation with cyclosporin immunosuppression will induce renal impairment even if cyclosporin blood levels are carefully monitored and kept low. However, with a low-dose regimen, a progressive decline can be avoided.     

After discontinuation of calcineurin inhibitors, tapering of mycophenolate mofetil further impairs donor-directed cytotoxicity

Abstract: Background: Recently, we described a significant decrease in donor‐specific cytotoxic T‐lymphocyte precursor frequency (CTLpf) after discontinuation of calcineurin inhibitors (CNI), while the proliferative capacity in mixed lymphocyte culture (MLC), and the number of interferon‐γ (IFN‐γ) producing cells (pc) in Elispot remained unchanged. Methods: We tested T‐cell reactivity in CNI free patients with stable renal graft function, on mycophenolate mofetil (MMF) or azathioprine (AZA) plus prednisone, who were tapered to 50% of their MMF or AZA dose. Results: Furthermore, tapering of the MMF or AZA dose resulted in a decrease of donor‐reactive CTLpf in all patients with detectable CTLpf. Detectable numbers decreased from a median of 32 to 8 CTLp/10⁶ peripheral blood mononuclear cell (PBMC). No effect on third‐party reactive CTLpf was found, while the T‐cell reactivity to donor and third‐party cells as tested in MLC and in IFN‐γ Elispot was not affected either by tapering of immunosuppression. Third‐party reactivity was significantly higher than donor‐specific reactivity in all tests. A control group showed no changes in any of the in vitro assays. Conclusion: Both withdrawal of CNI and tapering of MMF or AZA dose decreases the donor‐specific CTLpf. Our data suggest that reduction of immunosuppression results in a specific decrease of donor‐directed cytotoxic capacity of immunocompetent cells, while their proliferation and cytokine production capacity remained unchanged. Immunosuppression hinders development of cytotoxic non‐responsiveness.     

Suppressive effects of fisetin on mice T lymphocytes in vitro and in vivo

Background

Most of the immunosuppressive drugs have satisfactory therapeutic effects on organ transplantation and autoimmune disease. However, their clinical application is limited by side effects. Therefore, new and safe immunosuppressive drugs against acute and chronic rejections are eagerly awaited. Fisetin, a flavonoid present in various types of vegetables and fruits, has few side effects and low level of toxicity, which would be a desirable clinical feature. In the present study, we investigated the immunosuppressive effects and underlying mechanisms of fisetin against T-cell activation in vitro and in vivo.

Methods

We measured the effect of fisetin on T-lymphocyte proliferation, T-cell subsets, cell cycle progression, cytokine production, and nuclear factor activation in vitro, as well as its influence on T cell–mediated delayed-type hypersensitivity reaction in vivo.

Results

In vitro, the results showed that fisetin significantly suppressed mouse splenocytes proliferation, Th1 and Th2 cytokine production, cell cycle and the ratio of CD4⁺/CD8⁺ T cells. Furthermore, fisetin exerts an immunosuppressive effect in mouse T lymphocytes through the suppression of nuclear factor kappa B activation and nuclear factor of activated T cells signaling in a dose-dependent manner. In vivo, fisetin treatment also significantly inhibited the dinitrofluorobenzene-induced delayed-type hypersensitivity reactions in mice.

Conclusions

Fisetin had strong immunosuppressive activity in vitro and in vivo, suggesting a potential role for fisetin as an immunosuppressive agent.     

262. Immunologische Probleme bei der Knochenmarktransplantation

Zusammenfassung Die Transplantation von hämopoetischen Zellen bietet besondere Probleme and Moglichkeiten. Die Probleme. Im Gegensatz zur Organtransplantation werden bei der Knochenmarktransplantation immunkompetente Zellen des Spenders auf den Empfanger übertragen, die bei Gewebsunverträglichkeit den Empfanger attackieren. Diese Transplantat-gegen-Wirt-Reaktion verursacht ein Syndrom, dal unter dem Begriff der Sekundarkrankheit bekannt ist and vor allem in einer Atrophic des lymphatischen Gewebes, in Leberzellnekrosen and Veränderungen an Haut and MagenDarmtrakt besteht. Die nicht selten letal endende Sekundarkrankheit wurde eingehend an tierexperimentellen Modellen (Nager, Hunde, Affe) analysiert. Die Moglichkeiten. Eine erfolgreiche Knochenmarktransplantation induziert im Knochenmarkempfänger eine Toleranz nicht nur gegennber Spenderknochenmark, sondern gegennber allen Geweben and Organen des Knochenmarkspenders. Es handelt sick dabei um die einzige bisher bekannte Möglichkeit einer Toleranz gegenüber stark histoinkompatiblen Geweben zu induzieren. Sic ist dauerhaft and spezifisch, d. h. ihre Aufrechterhaltung bedarf keiner weiteren Immunsuppression.Es wird der Stand der Knochenmarktransplantation and der Überwindung ihrer immunologischen Komplikationen unter Berücksichtigung der immunologischen Spenderauswahl and der chemischen and biologischen Immunsuppression diskutiert.

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Immunological problems in the transplant of bone marrow

Summary The transplantation of haemopoetic cells involves special problems and opens up new possibilities. The Problems. In contrast to organ transplantation, in bone marrow transplantation immune-competent cells of the donor are transmitted to the recipient, which in the case of tissue incompatibility, attack the recipient. This transplantagainst-host reaction produces a syndrome which is known by the term secondary disease and consists mainly of an atrophy of the lymphatic tissue, liver-cell necrosis and changes in the skin and gastro-intestinal tract. This secondary disease which quite often ends fatally, has been thoroughly analysed with the aid of animal trials with rodents, dogs and apes. The Possibilities. A successful bone-marrow transplantation induces in the recipient a tolerance not only to the bone-marrow but also to all tissues and organs of the donor. We are dealing here with the only possibility which is known at present of inducing a tolerance to strongly histoincompatible tissues. The tolerance is permanent and specific, that is, its maintenance does not require further immunosuppression.The present state of bone-marrow transplantation and ways of overcoming its immunological complications are discussed, with special consideration to the immunological selection of donors and chemical and biological immunosuppression.

     

PD‐1 Analysis on CD28−CD27− CD4 T Cells Allows Stimulation‐Independent Assessment of CMV Viremic Episodes in Transplant Recipients

Expression of the inhibitory receptor programmed death 1 (PD‐1) on cytomegalovirus (CMV)‐specific CD4 T cells defines a phenotype associated with CMV viremia in transplant recipients. Moreover, CD28^?CD27^? double negativity is known as a typical phenotype of CMV‐specific CD4 T cells. Therefore, the co‐expression of inhibitory receptors on CD28^?CD27^? CD4 T cells was assessed as a rapid, stimulation‐independent parameter for monitoring CMV complications after transplantation. Ninety‐three controls, 67 hemodialysis patients and 81 renal transplant recipients were recruited in a cross‐sectional and longitudinal manner. CMV‐specific CD4 T cell levels quantified after stimulation were compared to levels of CD28^?CD27^? CD4 T cells. PD‐1 and cytotoxic T lymphocyte–associated antigen 4 (CTLA‐4) expression on CD28^?CD27^? CD4 T cells were related to viremia. A percentage of ≥0.44% CD28^?CD27^? CD4 T cells defined CMV seropositivity (93.3% sensitivity, 97.1% specificity), and their frequencies correlated strongly with CMV‐specific CD4 T cell levels after stimulation (r = 0.73, p < 0.0001). Highest PD‐1 expression levels on CD28^?CD27^? CD4 T cells were observed in patients with primary CMV viremia and reactivation (p < 0.0001), whereas CTLA‐4 expression was only elevated during primary CMV viremia (p < 0.05). Longitudinal analysis showed a significant increase in PD‐1 expression in relation to viremia (p < 0.001), whereas changes in nonviremic patients were nonsignificant. In conclusion, increased PD‐1 expression on CD28^?CD27^? CD4 T cells correlates with CMV viremia in transplant recipients and may serve as a specific, stimulation‐independent parameter to guide duration of antiviral therapy.

     

An Anti‐CD154 Domain Antibody Prolongs Graft Survival and Induces Foxp3+ iTreg in the Absence and Presence of CTLA‐4 Ig

The use of monoclonal antibodies targeting the CD154 molecule remains one of the most effective means of promoting graft tolerance in animal models, but thromboembolic complications during early clinical trials have precluded their use in humans. Furthermore, the role of Fc‐mediated deletion of CD154‐expressing cells in the observed efficacy of these reagents remains controversial. Therefore, determining the requirements for anti‐CD154‐induced tolerance will instruct the development of safer but equally efficacious treatments. To investigate the mechanisms of action of anti‐CD154 therapy, two alternative means of targeting the CD40–CD154 pathway were used: a nonagonistic anti‐CD40 antibody and an Fc‐silent anti‐CD154 domain antibody. We compared these therapies to an Fc‐intact anti‐CD154 antibody in both a fully allogeneic model and a surrogate minor antigen model in which the fate of alloreactive cells could be tracked. Results indicated that anti‐CD40 mAbs as well as Fc‐silent anti‐CD154 domain antibodies were equivalent to Fc‐intact anti‐CD154 mAbs in their ability to inhibit alloreactive T cell expansion, attenuate cytokine production of antigen‐specific T cells and promote the conversion of Foxp3⁺ iTreg. Importantly, iTreg conversion observed with Fc‐silent anti‐CD154 domain antibodies was preserved in the presence of CTLA4‐Ig, suggesting that this therapy is a promising candidate for translation to clinical use.

     

Outstanding questions in transplantation: B cells,alloantibodies, and humoral rejection

Over the past three decades, improved immunosuppression has significantly reduced T cell–mediated acute rejection rates, but long‐term graft survival rates have seen only marginal improvement. The cause of late graft loss has been under intense investigation, and chronic antibody‐mediated rejection (AMR) has been identified as one of the leading causes, thus providing a strong rationale for basic science investigation into donor‐specific B cells and antibodies in transplantation and ways to mitigate their pathogenicity. In 2018, the American Society of Transplantation launched a community‐wide online discussion of Outstanding Questions in Transplantation, and the topic of B cell biology and donor‐specific antibody prevention emerged as a major area of interest to the community, leading to a highly engaged dialogue, with comments from basic and translational scientists as well as physicians ( http://community.myast.org/communities/community-home/digestviewer ). We have summarized this discussion from a bedside to bench perspective and have organized this review into outstanding questions within the paradigm that AMR is a leading cause of graft loss in the clinic, and points of view that challenge aspects of this paradigm. We also highlight opportunities for basic and translational scientists to contribute to the resolution of these questions, mapping important future directions for the transplant research field.