Not All Antibodies Are Created Equal: Factors That Influence Antibody Mediated Rejection

Pushing the Survival Bar Higher: Two Decades of Innovation in Lung Transplantation

Survival after lung transplantation has significantly improved during the last two decades. The refinement of the already existing extracorporeal life support (ECLS) systems, such as extracorporeal membrane oxygenation (ECMO), and the introduction of new techniques for donor lung optimization, such as ex vivo lung perfusion (EVLP), have allowed the extension of transplant indication to patients with end-stage lung failure after acute respiratory distress syndrome (ARDS) and the expansion of the donor organ pool, due to the better evaluation and optimization of extended-criteria donor (ECD) lungs and of donors after circulatory death (DCD). The close monitoring of anti-HLA donor-specific antibodies (DSAs) has allowed the early recognition of pulmonary antibody-mediated rejection (AMR), which requires a completely different treatment and has a worse prognosis than acute cellular rejection (ACR). As such, the standardization of patient selection and post-transplant management has significantly contributed to this positive trend, especially at high-volume centers. This review focuses on lung transplantation after ARDS, on the role of EVLP in lung donor expansion, on ECMO as a principal cardiopulmonary support system in lung transplantation, and on the diagnosis and therapy of pulmonary AMR.

Outcome-based Risk Assessment of Non-HLA Antibodies in Heart Transplantation: A Systematic Review

BACKGROUND

Current monitoring after heart transplantation (HT) employs repeated invasive endomyocardial biopsies (EMB). Although positive EMB confirms rejection, EMB fails to predict impending, subclinical, or EMB-negative rejection events. While non-human leukocyte antigen (non-HLA) antibodies have emerged as important risk factors for antibody-mediated rejection after HT, their use in clinical risk stratification has been limited. A systematic review of the role of non-HLA antibodies in rejection pathologies has the potential to guide efforts to overcome deficiencies of EMB in rejection monitoring.

METHODS

Databases were searched to include studies on non-HLA antibodies in HT recipients. Data collected included the number of patients, type of rejection, non-HLA antigen studied, association of non-HLA antibodies with rejection, and evidence for synergistic interaction between non-HLA antibodies and donor-specific anti-human leukocyte antigen antibody (HLA-DSA) responses.

RESULTS

A total of 56 studies met the inclusion criteria. Strength of evidence for each non-HLA antibody was evaluated based on the number of articles and patients in support versus against their role in mediating rejection. Importantly, despite previous intense focus on the role of anti-major histocompatibility complex class I chain-related gene A (MICA) and anti-angiotensin II type I receptor antibodies (AT1R) in HT rejection, evidence for their involvement was equivocal. Conversely, the strength of evidence for other non-HLA antibodies supports that differing rejection pathologies are driven by differing non-HLA antibodies.

CONCLUSIONS

This systematic review underscores the importance of identifying peri-HT non-HLA antibodies. Current evidence supports the role of non-HLA antibodies in all forms of HT rejection. Further investigations are required to define the mechanisms of action of non-HLA antibodies in HT rejection.

Microvascular activation and exocytosis after exposure to the serum from mismatched recipients by using donor microvascular cultures

BACKGROUND

Microvascular injury resulting from activation and exocytosis are early signs of tissue damage caused by allografting. However, humoral anti-graft reactions are not easily detectable in transplant biopsies. The aim of this study was to establish a bioassay to recapitulate this process in a prospective approach.

METHODS

The study was executed by using our previously established protocol to isolate and freeze the donors' microvascular endothelial cells (MVEC) at the transplantation (34 living-related donors and 26 cadaver donors); and to collect sera from the recipients before the transplantation, one-, three- and six-months after transplantation. The activation and exocytosis of the MVEC were determined by incubating the donors' cultures with the recipients' sera. We determined if there was any endothelial activation by quantifying the releases of monocyte chemotactic protein-1 (MCP-1) and interleukin 8 (IL-8) in supernatants and the expressions of membrane intercellular adhesion molecule-1 (CD54) and intercellular adhesion molecule-1 (CD106) by flow cytometry. Endothelial exocytosis was determined by quantifying soluble E-selectin (CD62E) and cytoplasmic von Willebrand Factor (vWF) in supernatants. Endothelial activation or exocytosis was considered positive when the fold change (≧1.5) of post-transplantation to pre-transplantation was reached. We also monitored serum PRA and cytokines using Luminex multiple-plex and cytometric bead-based assay respectively.

RESULTS

We found 41.2% recipients (14 out of 34, ranging from 1.5 to 5.2 folds, p < 0.05) exhibited positive MVEC activation in the first month after transplantation as determined by IL-8 levels; 26.5% recipients (9 out of 34, ranging from 1.5 to 11.8 folds, p < 0.05) by MCP-1 levels. In the group of three months post-transplantation, 70.6% patients were positive (12 out of 17, ranging from 1.8 to 87.1 folds, p < 0.05) by IL-8 increased levels; 24% recipients (4 out of 17, ranging from 1.8 to 50.5 folds, p < 0.05) measured by MCP-1 levels. However, these changes disappeared six months after transplantation. Flow cytometric data showed that a time-dependent of CD54+ and CD106+ expressions existed over the course of six months. Most CD54+ and CD106+ cells were CD31- (platelet-endothelial cell adhesion molecule-1), though CD31+/CD106+ (37.5%, 3 out of 8) and CD31+/CD106+ (25%. 2 out of 8) were seen. When comparing donor MVEC activation to their recipient's proinflammatory cytokine levels or PRA status, we could not draw a conclusion regarding the connections between them. The sera collected from recipients at either one- or three-months after allografting did not significantly induce the release of either soluble CD62E or vWF (p > 0.05), indicating exocytosis was not significantly involved in the acute phase of allografting.

CONCLUSIONS

This bioassay enables us to detect the activation and exocytosis of donor MVEC elicited by respective sera from mismatched kidney recipients.

Examining the impact of immunosuppressive drugs on antibody-dependent cellular cytotoxicity (ADCC) of human peripheral blood natural killer (NK) cells and gamma delta (γδ) T cells

BACKGROUND

Human natural killer (NK) cells and gamma delta (γδ) T cells may impact outcomes of solid organ transplantation (SOT) such as lung transplantation (LTx) following the differential engagement of an array of activating and inhibitory receptors. Amongst these, CD16 may be particularly important due to its capacity to bind IgG to trigger antibody-dependent cellular cytotoxicity (ADCC) and the production of proinflammatory cytokines. While the use of immunosuppressive drugs (ISDs) is an integral component of SOT practice, their relative impact on various immune cells, especially γδT cells and CD16-induced functional responses, is still unclear.

METHODS

The ADCC responses of peripheral blood NK cells and γδT cells from both healthy blood donors and adult lung transplant recipients (LTRs) were assessed by flow cytometry. Specifically, the degranulation response, as reflected in the expression of CD107a, and the capacity of both NK cells and γδT cells to produce IFN-γ and TNF-α was assessed following rituximab (RTX)-induced activation. Additionally, the effect of cyclosporine A (CsA), tacrolimus (TAC), prednisolone (Prdl) and azathioprine (AZA) at the concentration of 1 ng/ml, 10 ng/ml, 100 ng/ml, and 1000 ng/ml on these responses was also compared in both cell types.

RESULTS

Flow cytometric analyses of CD16 expresion showed that its expression on γδT cells was both at lower levels and more variable than that on peripheral blood NK cells. Nevertheless functional analyses showed that despite these differences, γδT cells like NK cells can be readily activated by engagement with RTX to degranulate and produce cytokines such as IFNg and TNF-a. RTX-induced degranulation by either NK cells or γδT cells from healthy donors was not impacted by co-culture with individual ISDs. However, CsA and TAC but not Prdl and AZA did inhibit the production of IFN-γ and TNF-α by both cell types. Flow cytometric analyses of RTX-induced activation of NK cells and γδT cells from LTRs suggested their capacity to degranulate was not markedly impacted by transplantation with similar levels of cells expressing CD107 pre- and post-LTx. However an impairment in the ability of NK cells to produce cytokines was observed in samples obtained post LTx whereas γδT cell cytokine responses were not significantly impacted.

CONCLUSIONS

In conclusion, the findings show that despite differences in the expression levels of CD16, γδT cells like NK cells can be readily activated by engagement with RTX and that in vitro exposure to CsA and TAC (calcineurin inhibitors) had a measurable effect on cytokine production but not degranulation by both NK cells and gdT cells from healthy donors. Finally the observation that in PBMC obtained from LTx recipients, NK cells but not γδT cells exhibited impaired cytokine reponses suggests that transplantation or chronic exposure to ISDs differentially impacts their potential to respond to the introduction of an allograft and/or transplant-associated infections.

Clinical Pharmacology and Translational Considerations in the Development of CRISPR-Based Therapies

Genome editing holds the potential for curative treatments of human disease, however, clinical realization has proven to be a challenging journey with incremental progress made up until recently. Over the last decade, advances in clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein (Cas) systems have provided the necessary breakthrough for genome editing in the clinic. The progress of investigational CRISPR therapies from bench to bedside reflects the culmination of multiple advances occurring in parallel, several of which intersect with clinical pharmacology and translation. Directing the CRISPR therapy to the intended site of action has necessitated novel delivery platforms, and this has resulted in special considerations for the complete characterization of distribution, metabolism, and excretion, as well as immunogenicity. Once at the site of action, CRISPR therapies aim to make permanent alterations to the genome and achieve therapeutically relevant effects with a single dose. This fundamental aspect of the mechanism of action for CRISPR therapies results in new considerations for clinical translation and dose selection. Early advances in model-informed development of CRISPR therapies have incorporated key facets of the mechanism of action and have captured hallmark features of clinical pharmacokinetics and pharmacodynamics from phase I investigations. Given the recent emergence of CRISPR therapies in clinical development, the landscape continues to evolve rapidly with ample opportunity for continued innovation. Here, we provide a snapshot of selected topics in clinical pharmacology and translation that has supported the advance of systemically administered in vivo and ex vivo CRISPR-based investigational therapies in the clinic.

Afucosylation of HLA-specific IgG1 as a potential predictor of antibody pathogenicity in kidney transplantation

Antibody-mediated rejection (AMR) is the leading cause of graft failure. While donor-specific antibodies (DSAs) are associated with a higher risk of AMR, not all patients with DSAs develop rejection, suggesting that the characteristics of alloantibodies determining their pathogenicity remain undefined. Using human leukocyte antigen (HLA)-A2-specific antibodies as a model, we apply systems serology tools to investigate qualitative features of immunoglobulin G (IgG) alloantibodies including Fc-glycosylation patterns and FcγR-binding properties. Levels of afucosylated anti-A2 antibodies are elevated in seropositive patients, especially those with AMR, suggesting potential cytotoxicity via FcγRIII-mediated mechanisms. Afucosylation of both glycoengineered monoclonal and naturally glycovariant polyclonal serum IgG specific to HLA-A2 drives potentiated binding to, slower dissociation from, and enhanced signaling through FcγRIII, a receptor widely expressed on innate effector cells, and greater cytotoxicity against HLA-A2+ cells mediated by natural killer (NK) cells. Collectively, these results suggest that afucosylated DSA may be a biomarker of AMR and contribute to pathogenesis.

Non-HLA Antibodies in Kidney Transplantation: Immunity and Genetic Insights

The polymorphic human leukocyte antigen (HLA) system has been considered the main target for alloimmunity, but the non-HLA antibodies and autoimmunity have gained importance in kidney transplantation (KT). Apart from the endothelial injury, secondary self-antigen exposure and the presence of polymorphic alloantigens, respectively, auto- and allo- non-HLA antibodies shared common steps in their development, such as: antigen recognition via indirect pathway by recipient antigen presenting cells, autoreactive T cell activation, autoreactive B cell activation, T helper 17 cell differentiation, loss of self-tolerance and epitope spreading phenomena. Both alloimmunity and autoimmunity play a synergic role in the formation of non-HLA antibodies, and the emergence of transcriptomics and genome-wide evaluation techniques has led to important progress in understanding the mechanistic features. Among them, non-HLA mismatches between donors and recipients provide valuable information regarding the role of genetics in non-HLA antibody immunity and development.

Off-the-Shelf Chimeric Antigen Receptor Immune Cells from Human Pluripotent Stem Cells

Autologous chimeric antigen receptor (CAR) T cells have expanded the scope and therapeutic potential of anti-cancer therapy. Nevertheless, autologous CAR-T therapy has been challenging due to labor some manufacturing processes for every patient, and the cost due to the complexity of the process. Moreover, T cell dysfunction results from the immunosuppressive tumor microenvironment in certain patients. Considering technical challenges in autologous donors, the development of safe and efficient allogeneic CAR-T therapy will address these issues. Since the advent of the generation of immune cells from pluripotent stem cells (PSCs), numerous studies focus on the off-the-shelf generation of CAR-immune cells derived from the universal donor PSCs, which simplifies the manufacturing process and standardizes CAR-T products. In this review, we will discuss advances in the generation of immune cells from PSCs, together with the potential and perspectives of CAR-T, CAR-macrophages, and CAR-natural killer (NK) cells in cancer treatment. The combination of PSC-derived immune cells and CAR engineering will pave the way for developing next-generation cancer immunotherapy.

Allogeneic Chimeric Antigen Receptor Therapy in Lymphoma

The therapeutic armamentarium has significantly expanded since the approval of various CD19-targeting chimeric antigen receptor T cell (CAR-T) therapies in non-Hodgkin lymphoma (NHL). These CAR-Ts are patient-specific and require a complex, resource, and time-consuming process. While this appears promising, autologous CAR-Ts are limited due to the lack of accessibility, manufacturing delays, and variable product quality. To overcome these, allogeneic (allo) CARs from healthy donors appear appealing. These can be immediately available as “off the shelf” ready-to-use products of standardized and superior quality exempt from the effects of an immunosuppressive tumor microenvironment and prior treatments, and potentially with lower healthcare utilization using industrialized scale production. Allogeneic CARs, however, are not devoid of complications and require genomic editing, especially with αβ T cells to avoid graft versus host disease (GvHD) and allo-rejection by the recipient’s immune system. Tools for genomic editing such as TALEN and CRISPR provide promise to develop truly “off the shelf” universal CARs and further advance the field of cellular immunotherapy. Several allogeneic CARs are currently in early phase clinical trials, and preliminary data is encouraging. Longer follow-up is required to truly assess the feasibility and safety of these techniques in the patients. This review focuses on the strategies for developing allogeneic CARs along with cell sources and clinical experience thus far in lymphoma.

Approaching the sensitized lung patient: risk assessment for donor acceptance

The presence of HLA antibodies is widely recognized as a barrier to solid organ transplantation, and for lung transplant candidates, it has a significant negative impact on both waiting time and waiting list mortality. Although HLA antibodies have been associated with a broad spectrum of allograft damage, precise characterization of these antibodies in allosensitized candidates may enhance their accessibility to transplant. The introduction of Luminex-based single antigen bead (SAB) assays has significantly improved antibody detection sensitivity and specificity, but SAB alone is not sufficient for risk-stratification. Functional characterization of donor-specific antibodies (DSA) is paramount to increase donor accessibility for allosensitized lung candidates. We describe here our approach to evaluate sensitized lung transplant candidates. By employing state-of-the-art technologies to assess histocompatibility and determine physiological properties of circulating HLA antibodies, we can provide our Clinical Team a better risk assessment for lung transplant candidates and facilitate a "road map" to transplant. The cases presented in this paper illustrate the "individualized steps" taken to determine calculated panel reactive antibodies (cPRA), titer and complement-fixing properties of each HLA antibody present in circulation. When a donor is considered, we can better predict the risk associated with potentially crossing HLA antibodies, thereby allowing the Clinical Team to approach allosensitized lung patients with an individualized medicine approach. To facilitate safe access of sensitized lung transplant candidates to potential donors, a synergy between the histocompatibility laboratory and the Clinical Team is essential. Ultimately, donor acceptance is a decision based on several parameters, leading to a risk-stratification unique for each patient.

Increased Autoantibodies Against Ro/SS-A, CENP-B, and La/SS-B in Patients With Kidney Allograft Antibody-mediated Rejection

Supplemental Digital Content is available in the text.

Antibody-mediated rejection (AMR) causes more than 50% of late kidney graft losses. In addition to anti-human leukocyte antigen (HLA) donor-specific antibodies, antibodies against non-HLA antigens are also linked to AMR. Identifying key non-HLA antibodies will improve our understanding of AMR.

Effects of serum from mismatched patients with solid organ transplantation on the activation of microvascular cultures isolated from adipose tissues

BACKGROUND

Aggregating the human leukocyte antigen (HLA) Class I antigens on the endothelial membrane has been known to elicit an activation, an underlying mechanism of chronic rejection in organ transplant recipients. The current study aims at examining the endothelial responses using HLA typed microvascular cultures from human adipose tissues upon exposure to the serum that contain corresponding antibodies collected from mismatched transplant recipients.

METHODS

We have successfully cultured 30 microvascular cultures and typed their HLAs. They are functionally competent to respond to inflammatory TNF-α stimulation and the aggregating monoclonal antibody against HLA Class I. The post-transplantation serum was collected either from the recipients with pathologically diagnosed chronic rejection or from the recipients without rejection. We determined their activation either by double-staining the endothelial cells in crude cultures with flow cytometry or by quantifying cytokine releases in purified endothelial cells using ELISA.

RESULTS

Under our current protocol, adipose tissue cultures are functionally intact in regard to its responses to TNF-alpha and anti-HLA Class I antibody. We observed that the post-transplantation serum with rejection contained the pathogenic antibodies and led to proinflammatory activation, as demonstrated by not only increased CD54+/CD31+ and CD106+/CD31+ cell counts but also inflammatory cytokine releases including MCP-1, IL-8 and RANTES.

CONCLUSION

This methodological study provides the feasibility of examining the pathogenicity of the alloantibodies in mis-transplant serum. Potentially, the endothelial activation elicited as a result of exposure can be used as an alternative readout for chronic rejection.

SIGNIFICANCE

We prototype an ex vivo model that enables us to examine whether allogenic antibodies from the recipient can functionally activate microvascular endothelial cells from the donor adipose tissues. This system can be further developed as crossmatch using cellular responses as readouts for chronic rejection for post-transplant surveillance.

HLA Desensitization in Solid Organ Transplantation: Anti-CD38 to Across the Immunological Barriers

The presence of anti-human leucocyte antigen (HLA) antibodies in the potential solid organ transplant recipient's blood is one of the main barriers to access to a transplantation. The HLA sensitization is associated with longer waitlist time, antibody mediated rejection and transplant lost leading to increased recipient's morbidity and mortality. However, solid organ transplantation across the HLA immunological barriers have been reported in recipients who were highly sensitized to HLA using desensitization protocols. These desensitization regimens are focused on the reduction of circulating HLA antibodies. Despite those strategies improve rates of transplantation, it remains several limitations including persistent high rejection rate and worse long-term outcomes when compare with non-sensitized recipient population. Currently, interest is growing in the development of new desensitization approaches which, beyond targeting antibodies, would be based on the modulation of alloimmune pathways. Plasma cells appears as an interesting target given their critical role in antibody production. In the last decade, CD38-targeting immunotherapies, such as daratumumab, have been recognized as a key component in the treatment of myeloma by inducing an important plasma cell depletion. This review focuses on an emerging concept based on targeting CD38 to desensitize in the field of transplantation.

The early impact of preformed angiotensin II type 1 receptor antibodies on graft function in a low immunological risk cohort of kidney transplant recipients

Intruduction and aim: Angiotensin II type 1 receptor antibodies (AT1R-Ab) are associated with graft rejection and poor graft outcomes in kidney transplantation (KT). We aimed to assess the frequency of preformed AT1R-Ab and their impact on graft function and survival at 1 year after KT in a low immunological risk cohort.

METHODS

We performed a prospective, observational cohort study in 67 adult KT recipients, transplanted between 2018 and 2019. A cut-off value >10 U/ml was used for AT1R-Ab detection.

RESULTS

The frequency of preformed AT1R-Ab was 10.4% and the median value of their level was 8.4 U/ml (IQR: 6.8-10.4). Donor-specific anti-human leukocyte antigen antibodies (HLA-DSA) were absent, no case of biopsy-proven rejection was reported and the incidence of graft failure was 7.5%. Estimated glomerular filtration rate (eGFR) was significantly reduced in the AT1R-Ab group [35 (29.8-55.2) vs 56.1 (41.3-66.5) ml/min, p = 0.02] at 1 year after KT. After multivariate linear regression analysis, preformed AT1R-Ab were found as an independent determinant of eGFR at 1 year after KT (β: -15.395; 95% CI: -30.49 - -0.30; p = 0.04). By Cox multivariate regression analysis, preformed AT1R-Ab were not associated with graft failure (HR: 1.36; 95% CI:0.10-14.09; p = 0.80).

CONCLUSION

Preformed AT1R-Ab are an independent determinant of graft function but do not impact graft survival at 12 months after transplantation in a prospective low immunological risk cohort of KT recipients.

The Future of Regulatory T Cell Therapy: Promises and Challenges of Implementing CAR Technology

Cell therapy with polyclonal regulatory T cells (Tregs) has been translated into the clinic and is currently being tested in transplant recipients and patients suffering from autoimmune diseases. Moreover, building on animal models, it has been widely reported that antigen-specific Tregs are functionally superior to polyclonal Tregs. Among various options to confer target specificity to Tregs, genetic engineering is a particularly timely one as has been demonstrated in the treatment of hematological malignancies where it is in routine clinical use. Genetic engineering can be exploited to express chimeric antigen receptors (CAR) in Tregs, and this has been successfully demonstrated to be robust in preclinical studies across various animal disease models. However, there are several caveats and a number of strategies should be considered to further improve on targeting, efficacy and to understand the in vivo distribution and fate of CAR-Tregs. Here, we review the differing approaches to confer antigen specificity to Tregs with emphasis on CAR-Tregs. This includes an overview and discussion of the various approaches to improve CAR-Treg specificity and therapeutic efficacy as well as addressing potential safety concerns. We also discuss different imaging approaches to understand the in vivo biodistribution of administered Tregs. Preclinical research as well as suitability of methodologies for clinical translation are discussed.

Complement-activated interferon-γ-primed human endothelium transpresents interleukin-15 to CD8+ T cells

Alloantibodies in presensitized transplant candidates deposit complement membrane attack complexes (MACs) on graft endothelial cells (ECs), increasing risk of CD8+ T cell-mediated acute rejection. We recently showed that human ECs endocytose MACs into Rab5+ endosomes, creating a signaling platform that stabilizes NF-κB-inducing kinase (NIK) protein. Endosomal NIK activates both noncanonical NF-κB signaling to synthesize pro-IL-1β and an NLRP3 inflammasome to process and secrete active IL-1β. IL-1β activates ECs, increasing recruitment and activation of alloreactive effector memory CD4+ T (Tem) cells. Here, we report that IFN-γ priming induced nuclear expression of IL-15/IL-15Rα complexes in cultured human ECs and that MAC-induced IL-1β stimulated translocation of IL-15/IL-15Rα complexes to the EC surface in a canonical NF-κB-dependent process in which IL-15/IL-15Rα transpresentation increased activation and maturation of alloreactive CD8+ Tem cells. Blocking NLRP3 inflammasome assembly, IL-1 receptor, or IL-15 on ECs inhibited the augmented CD8+ Tem cell responses, indicating that this pathway is not redundant. Adoptively transferred alloantibody and mouse complement deposition induced IL-15/IL-15Rα expression by human ECs lining human coronary artery grafts in immunodeficient mice, and enhanced intimal CD8+ T cell infiltration, which was markedly reduced by inflammasome inhibition, linking alloantibody to acute rejection. Inhibiting MAC signaling may similarly limit other complement-mediated pathologies.

Hyperacute graft dysfunction in an orthotopic heart transplant in the presence of non-HLA antibodies

Antibody-mediated rejection (AMR) in heart transplants in the absence of anti-HLA donor-specific antibody (DSA) is not well studied or documented. This case reviews hyperacute fulminant graft dysfunction suspected to be mediated by non-HLA antibodies. After cross clamp removal, the patient developed severe pulmonary edema, profound coagulopathy, and biventricular failure. The patient's presumed AMR, cardiogenic shock, and coagulopathy were treated with extracorporeal membrane oxygenation (ECMO), plasmapheresis, intravenous immunoglobulin (IVIG), multiple blood products, and prothrombin complex concentrate. The recipient was 0% panel-reactive antibody (PRA), ABO, and crossmatch compatible. Intraoperative biopsy sample revealed a thrombotic process suggestive of a coagulation pathway activated by AMR; however, no C4d deposition was detected. Postmortem biopsies also suggested AMR. Retrospective testing of the patient's pretransplant serum revealed strong antiangiotensin II type 1 receptor (AT1R) antibodies and a strongly positive endothelial cell crossmatch. Anti-AT1R antibodies are known to be AT1 receptor agonists and may trigger inflammation and activate the extrinsic coagulation pathway. Given the potential effects of signaling through the AT1R, the patient's preexisting anti-AT1R antibodies and procoagulant therapy may have adversely affected the patient's clinical course.

HLA expression levels of unstimulated and cytokine stimulated human umbilical vein endothelial cells

Transplant rejection occurs following recipient recognition of mismatched HLA on donor tissue, but active rejection is dependent not only upon the severity of the T cell or alloantibody response, but also upon the cell surface expression of target HLA molecules. To investigate the variation in HLA expression using a model of endothelium, human umbilical vein endothelial cell (HUVEC) cultures were generated from 48 umbilical cords donated consecutively following planned caesarean section. HUVECs were stimulated using the cytokines tumour necrosis factor alpha and interferon gamma and HLA expression of unstimulated and stimulated cells determined using flow cytometry. HLA-A2, HLA-A3 and HLA-C antigens all showed a modest increase in expression for 12 hours post cell activation, followed by a more pronounced response over the next 24 to 36 hours. Each of these antigens increased by up to 40 times over unstimulated levels and in addition cells homozygous for specific HLA antigens on average had twice the amount of antigen expressed compared with cells heterozygous for that antigen, both when unstimulated and following cytokine stimulation. Cell activation is an important consideration in the assessment of transplant risk and may help progress towards understanding why rejection does not always occur in the presence of significant donor specific antibody. This data also confirms guidelines for transplantation, which recommend doubling the specific antibody level when considering immunological risk for homozygous donors.

'Off-the-shelf' allogeneic CAR T cells: development and challenges

Autologous chimeric antigen receptor (CAR) T cells have changed the therapeutic landscape in haematological malignancies. Nevertheless, the use of allogeneic CAR T cells from donors has many potential advantages over autologous approaches, such as the immediate availability of cryopreserved batches for patient treatment, possible standardization of the CAR-T cell product, time for multiple cell modifications, redosing or combination of CAR T cells directed against different targets, and decreased cost using an industrialized process. However, allogeneic CAR T cells may cause life-threatening graft-versus-host disease and may be rapidly eliminated by the host immune system. The development of next-generation allogeneic CAR T cells to address these issues is an active area of research. In this Review, we analyse the different sources of T cells for optimal allogeneic CAR-T cell therapy and describe the different technological approaches, mainly based on gene editing, to produce allogeneic CAR T cells with limited potential for graft-versus-host disease. These improved allogeneic CAR-T cell products will pave the way for further breakthroughs in the treatment of cancer.

Impact of low tacrolimus exposure and high tacrolimus intra-patient variability on the development of de novo anti-HLA donor-specific antibodies in kidney transplant recipients

Introduction: De novo donor-specific antibodies (dnDSA) directed against HLA are a major contributing factor to the chronic deterioration of renal allograft function. Several factors, including the degree of HLA matching, younger recipient age, and past sensitization events have been shown to increase the risk for the development of dnDSA. The development of dnDSA is also strongly associated with modifications in the immunosuppressive regimen, non-adherence, and under-immunosuppression.Areas covered: Tacrolimus is widely used after solid organ transplantation (SOT) and in recent years, both a high intra-patient variability in tacrolimus exposure and low tacrolimus exposure have been found to be associated with a higher risk of dnDSA development in kidney transplant recipients. This article provides an overview of current findings published in the recent 5 years regarding the relationship between tacrolimus exposure and variation therein and the development of dnDSA.Expert opinion: In this review, we describe how combining data on tacrolimus intra-patient variability and mean pre-dose concentration may be an effective tool to identify kidney transplant recipients who are at higher risk of developing dnDSA.

Safety and efficacy of eculizumab for the prevention of antibody-mediated rejection after deceased-donor kidney transplantation in patients with preformed donor-specific antibodies

The presence of preformed donor-specific antibodies in transplant recipients increases the risk of acute antibody-mediated rejection (AMR). Results of an open-label single-arm trial to evaluate the safety and efficacy of eculizumab in preventing acute AMR in recipients of deceased-donor kidney transplants with preformed donor-specific antibodies are reported. Participants received eculizumab as follows: 1200 mg immediately before reperfusion; 900 mg on posttransplant days 1, 7, 14, 21, and 28; and 1200 mg at weeks 5, 7, and 9. All patients received thymoglobulin induction therapy and standard maintenance immunosuppression including steroids. The primary end point was treatment failure rate, a composite of biopsy-proved grade II/III AMR (Banff 2007 criteria), graft loss, death, or loss to follow-up, within 9 weeks posttransplant. Eighty patients received transplants (48 women); the median age was 52 years (range 24-70 years). Observed treatment failure rate (8.8%) was significantly lower than expected for standard care (40%; P < .001). By 9 weeks, 3 of 80 patients had experienced AMR, and 4 of 80 had experienced graft loss. At 36 months, graft and patient survival rates were 83.4% and 91.5%, respectively. Eculizumab was well tolerated and no new safety concerns were identified. Eculizumab has the potential to provide prophylaxis against injury caused by acute AMR in such patients (EudraCT 2010-019631-35).

Importance of HLA typing, PRA and DSA tests for successful parathyroid allotransplantation

Parathyroid allotransplantation is increasingly practiced for patients who have permanent hypoparathyroidsm. Parathyroid allotransplantation success is varied, and no defined criteria about immunologic monitoring for pre-/post-transplantation follow-up. This study sought to evaluate the possible role of immunological tests. Four unrelated recipients and one living donor who have chronic kidney disease were evaluated for HLA-typing, PRA, CXM tests to conduct parathyroid allotransplantation. Parathyroid glands were obtained and resected from the donor, then cells were isolated and cryopreserved. Upon histologic examination, cells were cultivated and injected into muscle of four recipients. Recipient's were followed for parathormone and calcium levels for four years. PRA screening were monitored and de novo DSA was evaluated as well. In two of the recipients, allografts continued to be functional more than four years. In one recipient, allograft remained functional for two years and another recipient lost function after one year. Two out four were negative for de novo DSA and three out of four of the recipients remained negative for PRA. Neither HLA-matching nor de novo DSA positivity and PRA screenings seems significant for successfull parathyroid allotransplantation. This study has considerable potential for immunological monitoring of parathyroid allotransplantation.

Factors affecting HLA expression: A review

The detection and semiquantitative measurement of circulating human leucocyte antigen (HLA)-specific antibodies is essential for the management of patients before and after transplantation. In addition, the pretransplant cross-match to assess the reactivity of recipient HLA antibody against donor lymphocytes has long been the gold standard to prevent hyperacute rejection. Whilst both of these tests assume that recipient HLA-specific antibody is the only variable in the assessment of transplant risk, this is not the case. Transplant immunologists recognize that some HLA antigens are expressed at levels a magnitude lower than others (e.g., HLA-C, HLA-DQ), but within loci, and between different cell types there are many factors that influence HLA expression in both resting and activated cells. HLA is not usually expressed without the specific promoter proteins NLRC5, for HLA class I, and CIITA, for class II. The quantity of HLA protein production is then affected by factors including promoter region polymorphisms, alternative exon splice sites, methylation and microRNA-directed degradation. Different loci are influenced by multiple combinations of these control mechanisms making prediction of HLA regulation difficult, but an ability to measure the cellular expression of each HLA antigen, in conjunction with knowledge of circulating HLA-specific antibody, would lead to a more informed algorithm to assess transplant risk.

B Cell Activating Factor, Renal Allograft Antibody-Mediated Rejection, and Long-Term Outcome

Antibody-mediated rejection (ABMR) of renal allograft lacks typical phenotypes and clinical manifestations, always resulting in delayed diagnosis and treatment. It has been considered to be an elemental factor influencing the improvement of the long-term outcome of renal allograft. The B cell activating factor (BAFF) signal plays a fundamental function in the process of antibody-mediated immune response. Data from recipients and the nonhuman primate ABMR model suggest that the BAFF signal participates in the ABMR of renal allograft, while there are objections. The challenges in the diagnosis of ABMR, different study population, and details of research may explain the discrepancy. Large quantities of dynamic, credible data of BAFF ligands and their association with renal allograft pathological characteristics would constitute a direct proof of the role of BAFF in the progression of renal allograft ABMR.

The European Society for Blood and Marrow Transplantation (EBMT) Consensus Guidelines for the Detection and Treatment of Donor-specific Anti-HLA Antibodies (DSA) in Haploidentical Hematopoietic Cell Transplantation

Haploidentical donors are now increasingly considered for transplantation in the absence of HLA-matched donors or when an urgent transplant is needed. Donor-specific anti-HLA antibodies (DSA) have been recently recognized as an important barrier against successful engraftment of donor cells, which can affect transplant survival. DSA appear more prevalent in this type of transplant due to higher likelihood of alloimmunization of multiparous females against offspring's HLA antigens, and the degree of mismatch. Here we summarize the evidence for the role of DSA in the development of primary graft failure in haploidentical transplantation and provide consensus recommendations from the European Society for Blood and Marrow Transplant Group on testing, monitoring, and treatment of patients with DSA receiving haploidentical hematopoietic progenitor cell transplantation.

Novel Non-Histocompatibility Antigen Mismatched Variants Improve the Ability to Predict Antibody-Mediated Rejection Risk in Kidney Transplant

Transplant rejection is the critical clinical end-point limiting indefinite survival after histocompatibility antigen (HLA) mismatched organ transplantation. The predominant cause of late graft loss is antibody-mediated rejection (AMR), a process whereby injury to the organ is caused by donor-specific antibodies, which bind to HLA and non-HLA (nHLA) antigens. AMR is incompletely diagnosed as donor/recipient (D/R) matching is only limited to the HLA locus and critical nHLA immunogenic antigens remain to be identified. We have developed an integrative computational approach leveraging D/R exome sequencing and gene expression to predict clinical post-transplant outcome. We performed a rigorous statistical analysis of 28 highly annotated D/R kidney transplant pairs with biopsy-confirmed clinical outcomes of rejection [either AMR or T-cell-mediated rejection (CMR)] and no-rejection (NoRej), identifying a significantly higher number of mismatched nHLA variants in AMR (ANOVA—p-value = 0.02). Using Fisher’s exact test, we identified 123 variants associated mainly with risk of AMR (p-value < 0.001). In addition, we applied a machine-learning technique to circumvent the issue of statistical power and we found a subset of 65 variants using random forest, that are predictive of post-tx AMR showing a very low error rate. These variants are functionally relevant to the rejection process in the kidney and AMR as they relate to genes and/or expression quantitative trait loci (eQTLs) that are enriched in genes expressed in kidney and vascular endothelium and underlie the immunobiology of graft rejection. In addition to current D/R HLA mismatch evaluation, additional mismatch nHLA D/R variants will enhance the stratification of post-tx AMR risk even before engraftment of the organ. This innovative study design is applicable in all solid organ transplants, where the impact of mitigating AMR on graft survival may be greater, with considerable benefits on improving human morbidity and mortality and opens the door to precision immunosuppression and extended tx survival.