Antibodies against MICA antigens and kidney-transplant rejection

Diminished Immune Cell Adhesion in Hypoimmune ICAM-1 Knockout Pluripotent Stem Cells

Hypoimmune gene edited human pluripotent stem cells (hPSCs) are a promising platform for developing reparative cellular therapies that evade immune rejection. Existing first-generation hypoimmune strategies have used CRISPR/Cas9 editing to modulate genes associated with adaptive (e.g., T cell) immune responses, but have largely not addressed the innate immune cells (e.g., monocytes, neutrophils) that mediate inflammation and rejection processes occurring early after graft transplantation. We identified the adhesion molecule ICAM-1 as a novel hypoimmune target that plays multiple critical roles in both adaptive and innate immune responses post-transplantation. In a series of studies, we found that ICAM-1 blocking or knock-out (KO) in hPSC-derived cardiovascular therapies imparted significantly diminished binding of multiple immune cell types. ICAM-1 KO resulted in diminished T cell proliferation responses in vitro and in longer in vivo retention/protection of KO grafts following immune cell encounter in NeoThy humanized mice. The ICAM-1 KO edit was also introduced into existing first-generation hypoimmune hPSCs and prevented immune cell binding, thereby enhancing the overall hypoimmune capacity of the cells. This novel hypoimmune editing strategy has the potential to improve the long-term efficacy and safety profiles of regenerative therapies for cardiovascular pathologies and a number of other diseases.

The role of anticomplement therapy in the management of the kidney allograft

As the number of patients living with kidney failure grows, the need also grows for kidney transplantation, the gold standard kidney replacement therapy that provides a survival advantage. This may result in an increased rate of transplantation from HLA-mismatched donors that increases the rate of antibody-mediated rejection (AMR), which already is the leading cause of allograft failure. Plasmapheresis, intravenous immunoglobulin therapy, anti-CD20 therapies (i.e., rituximab), bortezomib and splenectomy have been used over the years to treat AMR as well as to prevent AMR in high-risk sensitized kidney transplant recipients. Eculizumab and ravulizumab are monoclonal antibodies targeting the C5 protein of the complement pathway and part of the expanding field of anticomplement therapies, which is not limited to kidney transplant recipients, and also includes complement-mediated microangiopathic hemolytic anemia, paroxysmal nocturnal hemoglobinuria, and ANCA-vasculitis. In this narrative review, we summarize the current knowledge concerning the pathophysiological background and use of anti-C5 strategies (eculizumab and ravulizumab) and C1-esterase inhibitor in AMR, either to prevent AMR in high-risk desensitized patients or to treat AMR as first-line or rescue therapy and also to treat de novo thrombotic microangiopathy in kidney transplant recipients.

Advancing precision in histocompatibility and immunogenetics: a comprehensive review of the UCLA exchange program

Precise typing of human leukocyte antigens (HLA) is crucial for clinical hematopoietic stem cell and solid organ transplantations, transfusion medicine, HLA-related disease association, and drug hypersensitivity analysis. The UCLA Cell Exchange program has played a vital role in providing educational and proficiency testing surveys to HLA laboratories worldwide for the past 5 decades. This article highlights the significant contribution of the UCLA Cell and DNA Exchange Programs in advancing HLA antibody testing, genotyping, crossmatches, and, more recently, virtual crossmatches. Additionally, we discuss future directions of the UCLA Cell Exchange program to support histocompatibility testing to adapt to the fast-evolving field of immunotherapy, tolerance and xenotransplantation.

The Significance of Major Histocompatibility Complex Class I Chain-related Molecule A in Solid Organ and Hematopoietic Stem Cell Transplantation: A Comprehensive Overview

Improving long-term allograft survival and minimizing recipient morbidity is of key importance in all of transplantation. Improved matching of classical HLA molecules and avoiding HLA donor-specific antibody has been a major focus; however, emerging data suggest the relevance of nonclassical HLA molecules, major histocompatibility complex class I chain-related gene A (MICA) and B, in transplant outcomes. The purpose of this review is to discuss the structure, function, polymorphisms, and genetics of the MICA molecule and relates this to clinical outcomes in solid organ and hematopoietic stem cell transplantation. The tools available for genotyping and antibody detection will be reviewed combined with a discussion of their shortcomings. Although data supporting the relevance of MICA molecules have accumulated, key knowledge gaps exist and should be addressed before widespread implementation of MICA testing for recipients pre- or posttransplantation.

Heterogeneity in allospecific T cell function in transplant-tolerant hosts determines susceptibility to rejection following infection

Even when successfully induced, immunological tolerance to solid organs remains vulnerable to inflammatory insults, which can trigger rejection. In a mouse model of cardiac allograft tolerance in which infection with Listeria monocytogenes (Lm) precipitates rejection of previously accepted grafts, we showed that recipient CD4+ TCR75 cells reactive to a donor MHC class I-derived peptide become hypofunctional if the allograft is accepted for more than 3 weeks. Paradoxically, infection-induced transplant rejection was not associated with transcriptional or functional reinvigoration of TCR75 cells. We hypothesized that there is heterogeneity in the level of dysfunction of different allospecific T cells, depending on duration of their cognate antigen expression. Unlike CD4+ TCR75 cells, CD4+ TEa cells specific for a peptide derived from donor MHC class II, an alloantigen whose expression declines after transplantation but remains inducible in settings of inflammation, retained function in tolerant mice and expanded during Lm-induced rejection. Repeated injections of alloantigens drove hypofunction in TEa cells and rendered grafts resistant to Lm-dependent rejection. Our results uncover a functional heterogeneity in allospecific T cells of distinct specificities after tolerance induction and reveal a strategy to defunctionalize a greater repertoire of allospecific T cells, thereby mitigating a critical vulnerability of tolerance.

An Integrated Approach Using HLAMatchmaker and Pirche II for Epitopic Matching in Pediatric Kidney Transplant-A Romanian Single-Center Study

(1) Background: Renal transplantation (KT) is the most efficient treatment for chronic kidney disease among pediatric patients. Antigenic matching and epitopic load should be the main criteria for choosing a renal graft in pediatric transplantation. Our study aims to compare the integration of new histocompatibility predictive algorithms with classical human leukocyte antigen (HLA) matching regarding different types of pediatric renal transplants. (2) Methods: We categorized our cohort of pediatric patients depending on their risk level, type of donor and type of transplantation, delving into discussions surrounding their mismatching values in relation to both the human leukocyte antigen Matchmaker software (versions 4.0. and 3.1.) and the most recent version of the predicted indirectly identifiable HLA epitopes (PIRCHE) II score. (3) Results: We determined that the higher the antigen mismatch, the higher the epitopic load for both algorithms. The HLAMatchmaker algorithm reveals a noticeable difference in eplet load between living and deceased donors, whereas PIRCHE II does not show the same distinction. Dialysis recipients have a higher count of eplet mismatches, which demonstrates a significant difference according to the transplantation type. Our results are similar to those of four similar studies available in the current literature. (4) Conclusions: We suggest that an integrated data approach employing PIRCHE II and HLAMatchmaker algorithms better predicts histocompatibility in KT than classical HLA matching.

Novel role of immune-related non-coding RNAs as potential biomarkers regulating tumour immunoresponse via MICA/NKG2D pathway

Major histocompatibility complex class I related chain A (MICA) is an important and stress-induced ligand of the natural killer group 2 member D receptor (NKG2D) that is expressed in various tumour cells. Given that the MICA/NKG2D signalling system is critically embedded in the innate and adaptive immune responses, it is particularly involved in the surveillance of cancer and viral infections. Emerging evidence has revealed the important roles of non-coding RNAs (ncRNAs) including microRNAs (miRNAs), long noncoding RNAs (lncRNAs) and circular RNAs (circRNAs) in different cancer types. We searched for all relevant publications in the PubMed, Scopus and Web of Science database using the keywords ncRNA, MICA, NKG2D, cancer, and miRNAs. All relevant studies published from 2008 to the 2023 were retrieved and collated. Notably, we found that miRNAs can target to NKG2D mRNA and MICA mRNA 3'-untranslated regions (3'-UTR), leading to translation inhibition of NKG2D and MICA degradation. Several immune-related MICA/NKG2D pathways may be dysregulated in cancer with aberrant miRNA expressions. At the same time, the competitive endogenous RNA (ceRNA) hypothesis holds that circRNAs, lncRNAs, and mRNAs induce an abnormal MICA expression by directly targeting downstream miRNAs to mediate mRNA suppression in cancer. This review summarizes the novel mechanism of immune escape in the ncRNA-related MICA/NKG2D pathway mediated by NK cells and cancer cells. Moreover, we identified the miRNA-NKG2D, miRNA-MICA and circRNA/lncRNA/mRNA-miRNA-mRNA/MICA axis. Thus, we were particularly concerned with the regulation of mediated immune escape in the MICA/NKG2D pathway by ncRNAs as potential therapeutic targets and diagnostic biomarkers of immunity and cancer.

Autoantibodies against DNA topoisomerase I promote renal allograft rejection by increasing alloreactive T cell responses

Antibodies reactive to self-antigens are an important component of posttransplant immune responses. The generation requirements and functions of autoantibodies, as well as the mechanisms of their influence on alloimmune responses, still remain to be determined. Our study investigated the contribution of autoimmunity during rejection of renal allografts. We have previously characterized a mouse model in which the acute rejection of a life-supporting kidney allograft is mediated by antibodies. At rejection, recipient sera screening against >4000 potential autoantigens revealed DNA topoisomerase I peptide 205-219 (TI-I205-219) as the most prominent epitope. Subsequent analysis showed TI-I205-219-reactive autoantibodies are induced in nonsensitized recipients of major histocompatibility complex-mismatched kidney allografts in a T cell-dependent manner. Immunization with TI-I205-219 broke self-tolerance, elicited TI-I205-219 immunoglobin G autoantibodies, and resulted in acute rejection of allogeneic but not syngeneic renal transplants. The graft loss was associated with increased priming of donor-reactive T cells but not with donor-specific alloantibodies elevation. Similarly, passive transfer of anti-TI-I205-219 sera following transplantation increased donor-reactive T cell activation with minimal effects on donor-specific alloantibody levels. The results identify DNA topoisomerase I as a novel self-antigen in transplant settings and demonstrate that autoantibodies enhance activation of donor-reactive T cells following renal transplantation.

Case Report: Suspected Hyperacute Rejection During Living Kidney Transplantation

BACKGROUND

We report a case of suspected hyperacute rejection during living kidney transplantation.

CASE REPORT

A 61-year-old man underwent kidney transplantation in November 2019. Before the transplantation, immunologic tests revealed the presence of anti-HLA antibodies but not donor-specific HLA antibodies. The patient was intravenously administered 500 mg of methylprednisolone (MP) and basiliximab before perioperative blood flow reperfusion. After blood flow restoration, the transplanted kidney turned bright red and then blue. Hyperacute rejection was suspected. After the intravenous administration of 500 mg of MP and 30 g of intravenous immunoglobulin, the transplanted kidney gradually changed from blue to bright red. The initial postoperative urine output was good. On the 22nd day after the renal transplantation, the patient was discharged with a serum creatinine level of 2.38 mg/dL, and the function of the transplanted kidney gradually improved.

CONCLUSIONS

In this study, non-HLA antibodies may have been a cause of the hyperacute rejection, which was managed with additional perioperative therapies.

Protection of cell therapeutics from antibody-mediated killing by CD64 overexpression

Allogeneic cell therapeutics for cancer therapy or regenerative medicine are susceptible to antibody-mediated killing, which diminishes their efficacy. Here we report a strategy to protect cells from antibody-mediated killing that relies on engineered overexpression of the IgG receptor CD64. We show that human and mouse iPSC-derived endothelial cells (iECs) overexpressing CD64 escape antibody-dependent cellular cytotoxicity (ADCC) and complement-dependent cytotoxicity from IgG antibodies in vitro and in ADCC-enabled mice. When CD64 expression was combined with hypoimmune genetic modifications known to protect against cellular immunity, B2M-/-CIITA-/- CD47/CD64-transgenic iECs were resistant to both IgG antibody-mediated and cellular immune killing in vitro and in humanized mice. Mechanistic studies demonstrated that CD64 or its intracellularly truncated analog CD64t effectively capture monomeric IgG and occupy their Fc, and the IgG bind and occupy their target antigens. In three applications of the approach, human CD64t-engineered thyroid epithelial cells, pancreatic beta cells and CAR T cells withstood clinically relevant levels of graft-directed antibodies and fully evaded antibody-mediated killing.

Analysis of Antibodies Induced after SARS-CoV-2 Vaccination Using Antigen Coded Bead Array Luminex Technology

Objectives. Since the outbreak of SARS-CoV-2 in late 2019, nearly 12.2 billion doses of the COVID-19 vaccine have been administered worldwide; however, the humoral immune responses induced by different types of vaccines are yet to be fully validated. Methods. We analyzed antibody levels in 100 serum samples after vaccination with different types of COVID-19 vaccines and their reactivity against the RBD antigen of Delta and Omicron variants using a bead-based microarray. Results. Elevated levels of anti-wild-type (WT)-RBD IgG and anti-WT-NP IgG were detected in participants who received two doses of the inactivated vaccines (CoronaVac or BBIBP-CorV) and three doses of the recombinant spike protein vaccine (ZF2001), indicating that antibody responses to SARS-CoV-2 were generated regardless of the vaccine administered. We found highly correlated levels of serum anti-RBD IgG and anti-NP IgG (r = 0.432, p < 0.001). We observed that the antibodies produced in vivo after COVID-19 vaccination still reacted with variants of SARS-CoV-2 (p < 0.0001). Conclusions. Our results show that high levels of specific antibodies can be produced after completion of COVID-19 vaccination (two doses of the inactivated vaccines or three doses of ZF2001), with some degree of cross-reactivity to the RBD antigen of Delta and Omicron variants, and provide an accessible and practical experimental method for post-vaccination antibody detection.

Alloimmune risk assessment for antibody-mediated rejection in kidney transplantation: A practical proposal

Kidney transplantation is the treatment of choice for patients with end-stage renal disease. Although an improvement in graft survival has been observed in the last decades with the use of different immunosuppressive drugs, this is still limited in time with antibody-mediated rejection being a main cause of graft-loss. Immune monitoring and risk assessment of antibody-mediated rejection before and after kidney transplantation with useful biomarkers is key to tailoring treatments to achieve the best outcomes. Here, we provide a review of the rationale and several accessible tools for immune monitoring, from the most classic to the modern ones. Finally, we end up discussing a practical proposal for alloimmune risk assessment in kidney transplantation, including histocompatibility leukocyte antigen (HLA) and non-HLA antibodies, HLA molecular mismatch analysis and characterization of peripheral blood immune cells.

Unraveling complexity of antibody-mediated rejections, the mandatory way towards an accurate diagnosis and a personalized treatment

Antibody-mediated rejection (ABMR) remains one of the most challenging issues after organ transplantation and particularly after kidney transplantation. Despite many progresses during the last decade, ABMR is still the main cause of kidney graft loss and this all over the post- transplant period. In this review, we describe the recent knowledge about molecular and cellular mechanisms involved in ABMR. We focused our report on the role of the complement pathway in the process of ABMR and we give some insights into the role of inflammatory cells, NK lymphocytes and the role of endothelial cells. We further describe the potential role of non-HLA antibodies, of which the importance has been increasingly emphasized in recent years. Overall, this report could be of interest for all physicians who are working in the field of organ transplantation or who are working in the field of immunology. It gives essential information to understand new diagnosis advances and further therapeutic approaches. Antibody-mediated rejection (ABMR) is the leading cause of graft failure ([1,2]). In contrast to T-cell mediated rejection usually sensitive to steroids, active ABMR remains a therapeutic challenge. ABMR diagnosis relies on the presence of renal injuries and donor-specific antibodies (DSA) (HLA and non HLA antibodies) with sometimes the evidence of interaction between DSA and graft endothelium. Regularly revised during expert conferences, ABMR definition is currently categorized as active or chronic active. [3] The emergence of validated molecular assays targeting a better phenotyping of ABMR and the recent advances regarding the detrimental effect of DSA directed against minor antigens open the way to a better assessment of the heterogeneity of ABMR. In this review, we will address new aspects of ABMR regarding its mechanisms, diagnosis and treatments.

Anti-glutathione S-transferase theta 1 antibodies correlate with graft loss in non-sensitized pediatric kidney recipients

Introduction

Immunity to Human leukocyte antigen (HLA) cannot explain all cases of ABMR, nor the differences observed in the outcome of kidney recipients with circulating DSAs endowed with similar biologic characteristics. Thus, increasing attention has recently been focused on the role of immunity to non-HLA antigenic targets.

Methods

We analyzed humoral auto- and alloimmune responses to the non-HLA antigen glutathione S-transferase theta 1 (GSTT1), along with development of de novo (dn)HLA-DSAs, in a cohort of 146 pediatric non-sensitized recipients of first kidney allograft, to analyze its role in ABMR and graft loss. A multiplex bead assay was employed to assess GSTT1 antibodies (Abs).

Results

We observed development of GSTT1 Abs in 71 recipients after transplantation, 16 with MFI &gt; 8031 (4th quartile: Q4 group). In univariate analyses, we found an association between Q4-GSTT1Abs and ABMR and graft loss, suggesting a potential role in inducing graft damage, as GSTT1 Abs were identified within ABMR biopsies of patients with graft function deterioration in the absence of concomitant intragraft HLA-DSAs. HLA-DSAs and GSTT1 Abs were independent predictors of graft loss in our cohort. As GSTT1 Ab development preceded or coincided with the appearance of dnHLA-DSAs, we tested and found that a model with the two combined parameters proved more fit to classify patients at risk of graft loss.

Discussion

Our observations on the harmful effects of GSTT1Abs, alone or in combination with HLA-DSAs, add to the evidence pointing to a negative role of allo- and auto-non-HLA Abs on kidney graft outcome.

Membrane attack complexes, endothelial cell activation, and direct allorecognition

Endothelial cells (ECs) form a critical immune interface regulating both the activation and trafficking of alloreactive T cells. In the setting of solid organ transplantation, donor-derived ECs represent sites where alloreactive T cells encounter major and minor tissue-derived alloantigens. During this initial encounter, ECs may formatively modulate effector responses of these T cells through expression of inflammatory mediators. Direct allorecognition is a process whereby recipient T cells recognize alloantigen in the context of donor EC-derived HLA molecules. Direct alloresponses are strongly modulated by human ECs and are galvanized by EC-derived inflammatory mediators.

Complement are immune proteins that mark damaged or foreign surfaces for immune cell activation. Following labeling by natural IgM during ischemia reperfusion injury (IRI) or IgG during antibody-mediated rejection (ABMR), the complement cascade is terminally activated in the vicinity of donor-derived ECs to locally generate the solid-phase inflammatory mediator, the membrane attack complex (MAC). Via upregulation of leukocyte adhesion molecules, costimulatory molecules, and cytokine trans-presentation, MAC strengthen EC:T cell direct alloresponses and qualitatively shape the alloimmune T cell response. These processes together promote T cell-mediated inflammation during solid organ transplant rejection.

In this review we describe molecular pathways downstream of IgM- and IgG-mediated MAC assembly on ECs in the setting of IRI and ABMR of tissue allografts, respectively. We describe work demonstrating that MAC deposition on ECs generates ‘signaling endosomes’ that sequester and post-translationally enhance the stability of inflammatory signaling molecules to promote EC activation, a process potentiating EC-mediated direct allorecognition. Additionally, with consideration to first-in-human xenotransplantation procedures, we describe clinical therapeutics based on inhibition of the complement pathway. The complement cascade critically mediates EC activation and improved understanding of relevant effector pathways will uncover druggable targets to obviate dysregulated alloimmune T cell infiltration into tissue allografts.

Pretransplant characteristics of kidney transplant recipients that predict posttransplant outcome

Better characterization of the potential kidney transplant recipient using novel biomarkers, for example, pretransplant plasma endotrophin, will lead to improved outcome after transplantation. This mini-review will focus on current knowledge about pretransplant recipients’ characteristics, biomarkers, and immunology. Clinical characteristics of recipients including age, obesity, blood pressure, comorbidities, and estimated survival scores have been introduced for prediction of recipient and allograft survival. The pretransplant immunologic risk assessment include histocompatibility leukocyte antigens (HLAs), anti-HLA donor-specific antibodies, HLA-DQ mismatch, and non-HLA antibodies. Recently, there has been the hope that pretransplant determination of markers can further improve the prediction of posttransplant complications, both short-term and long-term outcomes including rejections, allograft loss, and mortality. Higher pretransplant plasma endotrophin levels were independently associated with posttransplant acute allograft injury in three prospective European cohorts. Elevated numbers of non-synonymous single-nucleotide polymorphism mismatch have been associated with increased allograft loss in a multivariable analysis. It is concluded that there is a need for integration of clinical characteristics and novel molecular and immunological markers to improve future transplant medicine to reach better diagnostic decisions tailored to the individual patient.

Diseases association with the polymorphic major histocompatibility complex class I related chain a: MICA gene

The Major Histocompatibility Complex class I chain-related molecule A (MICA) genes encode a highly polymorphic glycoprotein among the cell surface antigens that trigger an immune response after allograft transplantation. It is encoded by the MICA gene, a member of the glycosylated MIC genes. Discovered in 1994, the MICA gene is located within the MHC class I region. Moreover, its biological function is achieved through the interaction with the NKG2D receptor. Unlike the classical HLA molecules, MICA protein is not associated with β2- microglobulin nor binds peptides. MICA gene expression may result in a cytotoxic response and IFN-γ secretion through the up-regulation by heat shock proteins in response to infection (Human Cytomegalovirus HCMV), mediated by NKG2D-expressing cells. Anti-MICA antibodies were identified as significant risk factors for antibody mediated rejection after being detected in sera of patients with graft rejection. In addition, soluble MICA proteins (sMICA) has been detected in the serum of transplant recipients with cancers. Furthermore, the association of MICA polymorphisms with infectious diseases, various autoimmune diseases, cancer, and allograft rejection or graft-versus-host disease (GVHD) has been studied. Moreover, numerous advanced disease studies centered on MICA polymorphism are independent of HLA association. In this review, we discussed the up-to-date data about MICA and the association of MICA polymorphism with infections, autoimmune diseases, graft-versus-host disease, and cancer.

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.

High-Throughput Sequencing of Complementarity Determining Region 3 in the Heavy Chain of B-Cell Receptor in Renal Transplant Recipients: A Preliminary Report

Background: Graft failure resulting from rejection or any other adverse event usually originates from an aberrant and/or exaggerated immune response and is often catastrophic in renal transplantation. So, it is essential to monitor patients’ immune status for detecting a rejection/graft failure early on. Methods: We monitored the sequence change of complementary determining region 3 (CDR3) in B-cell receptor (BCR) immunoglobulin heavy-chain (IGH) immune repertoire (iR) in 14 renal transplant patients using next-generation sequencing (NGS), correlating its diversity to various clinical events occurring after transplantation. BCR-IGH-CDR3 in peripheral blood mononuclear cells was sequenced along the post-transplantation course by NGS using the iRweb server. Results: Datasets covering VDJ regions of BCR-IGH-CDR3 indicated clonal diversity (D50) variations along the post-transplant course. Furthermore, principal component analysis showed the clustering of these sequence variations. A total of 544 shared sequences were identified before transplantation. D50 remained low in three patients receiving rituximab. Among them, one’s D50 resumed after 3 m, indicating graft tolerance. The D50 rapidly increased after grafting and decreased thereafter in four patients without rejection, decreased in two patients with T-cell-mediated rejection (TCMR) and exhibited a sharp down-sliding after 3 m in two patients receiving donations after cardiac death (DCD). In another two patients with TCMR, D50 was low just before individual episodes, but either became persistently low or returned to a plateau, depending on the failure or success of the immunosuppressive treatments. Shared CDR3 clonal expansions correlated to D50 changes. Agglomerative hierarchical clustering showed a commonly shared CDR3 sequence and at least two different clusters in five patients. Conclusions: Clonal diversity in BCR-IGH-CDR3 varied depending on clinical courses of 14 renal transplant patients, including B-cell suppression therapy, TCMR, DCD, and graft tolerance. Adverse events on renal graft failure might lead to different clustering of BCR iR. However, these preliminary data need further verification in further studies for the possible applications of iR changes as genetic expression biomarkers or laboratory parameters to detect renal graft failure/rejection earlier.

Extracellular Vesicles Mediate Immune Responses to Tissue-Associated Self-Antigens: Role in Solid Organ Transplantations

Transplantation is a treatment option for patients diagnosed with end-stage organ diseases; however, long-term graft survival is affected by rejection of the transplanted organ by immune and nonimmune responses. Several studies have demonstrated that both acute and chronic rejection can occur after transplantation of kidney, heart, and lungs. A strong correlation has been reported between de novo synthesis of donor-specific antibodies (HLA-DSAs) and development of both acute and chronic rejection; however, some transplant recipients with chronic rejection do not have detectable HLA-DSAs. Studies of sera from such patients demonstrate that immune responses to tissue-associated antigens (TaAgs) may also play an important role in the development of chronic rejection, either alone or in combination with HLA-DSAs. The synergistic effect between HLA-DSAs and antibodies to TaAgs is being established, but the underlying mechanism is yet to be defined. We hypothesize that HLA-DSAs damage the transplanted donor organ resulting in stress and leading to the release of extracellular vesicles, which contribute to chronic rejection. These vesicles express both donor human leukocyte antigen (HLA) and non-HLA TaAgs, which can activate antigen-presenting cells and lead to immune responses and development of antibodies to both donor HLA and non-HLA tissue-associated Ags. Extracellular vesicles (EVs) are released by cells under many circumstances due to both physiological and pathological conditions. Primarily employing clinical specimens obtained from human lung transplant recipients undergoing acute or chronic rejection, our group has demonstrated that circulating extracellular vesicles display both mismatched donor HLA molecules and lung-associated Ags (collagen-V and K-alpha 1 tubulin). This review focuses on recent studies demonstrating an important role of antibodies to tissue-associated Ags in the rejection of transplanted organs, particularly chronic rejection. We will also discuss the important role of extracellular vesicles released from transplanted organs in cross-talk between alloimmunity and autoimmunity to tissue-associated Ags after solid organ transplantation.

Clinical Significances of Anti-Collagen Type I and Type III Antibodies in Antibody-Mediated Rejection

It is important to determine the clinical significance of non-human leukocyte antigen (HLA) antibodies and their association with antibody-mediated rejection (ABMR) of kidney allografts. We collected post-transplant sera from 68 ABMR patients, 67 T-cell mediated rejection (TCMR) patients, and 83 control subjects without rejection, and determined the titers of 39 non-HLA antibodies including antibodies for angiotensin II receptor type I and MICA. We compared all these non-HLA antibody titers among the study groups. Then, we investigated their association with the risk of death-censored graft failure in ABMR cases. Among the antibodies evaluated, anti-collagen type I (p = 0.001) and type III (p < 0.001) antibody titers were significantly higher in ABMR cases than in both TCMR cases and no-rejection controls. Both anti-collagen type I [per 1 standard deviation (SD), adjusted odds ratio (OR), 11.72 (2.73-76.30)] and type III [per 1 SD, adjusted OR, 6.22 (1.91-31.75)] antibodies were significantly associated with the presence of ABMR. Among ABMR cases, a higher level of anti-collagen type I [per 1 SD, adjusted hazard ratio (HR), 1.90 (1.32-2.75)] or type III per 1 SD, [adjusted HR, 1.57 (1.15-2.16)] antibody was associated with a higher risk of death-censored graft failure. In conclusion, post-transplant anti-collagen type I and type III antibodies may be novel non-HLA antibodies related to ABMR of kidney allografts.

Antigen and Cell-Based Assays for the Detection of Non-HLA Antibodies

To date, human leukocyte antigens (HLA) have been the major focus in the approach to acute and chronic antibody-mediated rejection (AMBR) in solid-organ transplantation. However, evidence from the clinic and published studies has shown that non-HLA antibodies, particularly anti-endothelial cell antibodies (AECAs), are found either in the context of AMBR or synergistically in the presence of donor-specific anti-HLA antibodies (DSA). Numerous studies have explored the influence of AECAs on clinical outcomes, yet the determination of the exact clinical relevance of non-HLA antibodies in organ transplantation is not fully established. This is due to highly heterogeneous study designs including differences in testing methods and outcome measures. Efforts to develop reliable and sensitive diagnostic non-HLA antibody tests are continuously made. This is essential considering the technical difficulties of non-HLA antibody assays and the large variation in reported incidences of antibodies. In addition, it is important to take donor specificity into account in order to draw clinically relevant conclusions from non-HLA antibody assays. Here, we provide an overview of non-HLA solid-phase and cell-based crossmatch assays for use in solid-organ transplantation that are currently available, either in a research setting or commercially.

Donor–Recipient Non-HLA Variants, Mismatches and Renal Allograft Outcomes: Evolving Paradigms

Despite significant improvement in the rates of acute allograft rejection, proportionate improvements in kidney allograft longevity have not been realized, and are a source of intense research efforts. Emerging translational data and natural history studies suggest a role for anti-donor immune mechanisms in a majority of cases of allograft loss without patient death, even when overt evidence of acute rejection is not identified. At the level of the donor and recipient genome, differences in highly polymorphic HLA genes are routinely evaluated between donor and recipient pairs as part of organ allocation process, and utilized for patient-tailored induction and maintenance immunosuppression. However, a growing body of data have characterized specific variants in donor and recipient genes, outside of HLA loci, that induce phenotypic changes in donor organs or the recipient immune system, impacting transplant outcomes. Newer mechanisms for “mismatches” in these non-HLA loci have also been proposed during donor–recipient genome interactions with transplantation. Here, we review important recent data evaluating the role of non-HLA genetic loci and genome-wide donor-recipient mismatches in kidney allograft outcomes.

The MHC class I MICA gene is a histocompatibility antigen in kidney transplantation

The identity of histocompatibility loci, besides human leukocyte antigen (HLA), remains elusive. The major histocompatibility complex (MHC) class I MICA gene is a candidate histocompatibility locus. Here, we investigate its role in a French multicenter cohort of 1,356 kidney transplants. MICA mismatches were associated with decreased graft survival (hazard ratio (HR), 2.12; 95% confidence interval (CI): 1.45–3.11; P < 0.001). Both before and after transplantation anti-MICA donor-specific antibodies (DSA) were strongly associated with increased antibody-mediated rejection (ABMR) (HR, 3.79; 95% CI: 1.94–7.39; P < 0.001; HR, 9.92; 95% CI: 7.43–13.20; P < 0.001, respectively). This effect was synergetic with that of anti-HLA DSA before and after transplantation (HR, 25.68; 95% CI: 3.31–199.41; P = 0.002; HR, 82.67; 95% CI: 33.67–202.97; P < 0.001, respectively). De novo-developed anti-MICA DSA were the most harmful because they were also associated with reduced graft survival (HR, 1.29; 95% CI: 1.05–1.58; P = 0.014). Finally, the damaging effect of anti-MICA DSA on graft survival was confirmed in an independent cohort of 168 patients with ABMR (HR, 1.71; 95% CI: 1.02–2.86; P = 0.041). In conclusion, assessment of MICA matching and immunization for the identification of patients at high risk for transplant rejection and loss is warranted.

Analysis of a multicenter cohort of kidney transplants shows that mismatches in the MICA locus and the presence of anti-MICA donor-specific antibodies are associated with reduced graft survival and increased rejection.

Innate (and Innate-like) Lymphoid Cells: Emerging Immune Subsets With Multiple Roles Along Transplant Life

Transplant immunology is currently largely focused on conventional adaptive immunity, particularly T and B lymphocytes, which have long been considered as the only cells capable of allorecognition. In this vision, except for the initial phase of ischemia/reperfusion, during which the role of innate immune effectors is well established, the latter are largely considered as "passive" players, recruited secondarily to amplify graft destruction processes during rejection. Challenging this prevalent dogma, the recent progresses in basic immunology have unraveled the complexity of the innate immune system and identified different subsets of innate (and innate-like) lymphoid cells. As most of these cells are tissue-resident, they are overrepresented among passenger leukocytes. Beyond their role in ischemia/reperfusion, some of these subsets have been shown to be capable of allorecognition and/or of regulating alloreactive adaptive responses, suggesting that these emerging immune players are actively involved in most of the life phases of the grafts and their recipients. Drawing upon the inventory of the literature, this review synthesizes the current state of knowledge of the role of the different innate (and innate-like) lymphoid cell subsets during ischemia/reperfusion, allorecognition, and graft rejection. How these subsets also contribute to graft tolerance and the protection of chronically immunosuppressed patients against infectious and cancerous complications is also examined.

MHC Class I Related Chain A (MICA) Antibodies - A Potential Cause of Renal Allograft Rejection

MHC class I related chain A (MICA) antibodies, especially those directed against the donor in absence of donor-specific anti-HLA antibodies have been reported to be possibly associated with renal allograft rejection in sensitized recipients. We are the first ones to present a case series of five patients who underwent primary live related donor renal transplantation in non-sensitized recipients either in the presence of donor-specific MICA antibodies (MICA-DSA) or developed de novo. Four of them presented characteristics of either accelerated, acute or chronic antibody-mediated rejection (AMR) attributable to the presence of MICA DSA. This case series emphasizes that AMR due to MICA-DSA is amenable to treatment with conventional regimens for treatment of AMR and there is a need for screening of MICA antibodies especially those directed against the donor on case to case basis.

Emerging monitoring technologies in kidney transplantation

Non-invasive technologies to monitor kidney allograft health utilizing high-throughput assays of blood and urine specimens are emerging out of the research realm and slowly becoming part of everyday clinical practice. HLA epitope analysis and eplet mismatch score determination promise a more refined approach to the pre-transplant recipient-donor HLA matching that may lead to reduced rejection risk. High-resolution HLA typing and multiplex single antigen bead assays are identifying potential new offending HLA antibody subtypes. There is increasing recognition of the deleterious role non-HLA antibodies play in post-transplant outcomes. Donor-derived cell-free DNA detected by next-generation sequencing is a promising biomarker for kidney transplant rejection. Multi-omics techniques are shedding light on discrete genomic, transcriptomic, proteomic, and metabolomic signatures that correlate with and predict allograft outcomes. Over the next decade, a comprehensive approach to optimize kidney matching and monitor transplant recipients for acute and chronic graft dysfunction will likely involve a combination of those emerging technologies summarized in this review.

Current Desensitization Strategies in Heart Transplantation

Heart transplant candidates sensitized to HLA antigens wait longer for transplant, are at increased risk of dying while waiting, and may not be listed at all. The increasing prevalence of HLA sensitization and limitations of current desensitization strategies underscore the urgent need for a more effective approach. In addition to pregnancy, prior transplant, and transfusions, patients with end-stage heart failure are burdened with unique factors placing them at risk for HLA sensitization. These include homograft material used for congenital heart disease repair and left ventricular assist devices (LVADs). Moreover, these risks are often stacked, forming a seemingly insurmountable barrier in some cases. While desensitization protocols are typically implemented uniformly, irrespective of the mode of sensitization, the heterogeneity in success and post-transplant outcomes argues for a more tailored approach. Achieving this will require progress in our understanding of the immunobiology underlying the innate and adaptive immune response to these varied allosensitizing exposures. Further attention to B cell activation, memory, and plasma cell differentiation is required to establish methods that durably abrogate the anti-HLA antibody response before and after transplant. The contribution of non-HLA antibodies to the net state of sensitization and the potential implications for graft longevity also remain to be comprehensively defined. The aim of this review is to first bring forth select issues unique to the sensitized heart transplant candidate. The current literature on desensitization in heart transplantation will then be summarized providing context within the immune response. Building on this, newer approaches with therapeutic potential will be discussed emphasizing the importance of not only addressing the short-term pathogenic consequences of circulating HLA antibodies, but also the need to modulate alloimmune memory.

Establishment of HLA class I and MICA/B null HEK-293T panel expressing single MICA alleles to detect anti-MICA antibodies

Pre- and post-transplantation anti-MICA antibody detection development are associated with an increased rejection risk and low graft survival. We previously generated HLA class I null HEK-293T using CRISPR/Cas9, while MICA and MICB genes were removed in this study. A panel of 11 cell lines expressing single MICA alleles was established. Anti-MICA antibody in the sera of kidney transplant patients was determined using flow cytometric method (FCM) and the Luminex method. In the 44 positive sera, the maximum FCM value was 2879 MFI compared to 28,135 MFI of Luminex method. Eleven sera (25%) were determined as positive by FCM and 32 sera (72%) were positive by the Luminex method. The sum of total MICA antigens, MICA*002, *004, *009, *019, and *027 correlation showed a statistically significant between the two methods (P = 0.0412, P = 0.0476, P = 0.0019, P = 0.0098, P = 0.0467, and P = 0.0049). These results demonstrated that HEK-293T-based engineered cell lines expressing single MICA alleles were suitable for measuring specific antibodies against MICA antigens in the sera of transplant patients. Studies of antibodies to MICA antigens may help to understand responses in vivo and increase clinical relevance at the cellular level such as complement-dependent cytotoxicity.

Association of non-HLA antibodies against endothelial targets and donor-specific HLA antibodies with antibody-mediated rejection and graft function in pediatric kidney transplant recipients

BACKGROUND

Non-HLA antibodies against endothelial targets have been implicated in the pathogenesis of antibody-mediated rejection (ABMR), but data in pediatric patients are scarce.

METHODS

We retrospectively analyzed a carefully phenotyped single-center (University Children's Hospital Heidelberg, Germany) cohort of 62 pediatric kidney transplant recipients (mean age at transplantation, 8.6 ± 5.0 years) at increased risk of graft function deterioration. Patients had received their transplant between January 1, 1999, and January 31, 2010. We examined at time of late index biopsies (more than 1-year post-transplant, occurring after January 2004) the association of antibodies against the angiotensin II type 1 receptor (AT₁R), the endothelin type A receptor (ET_AR), the MHC class I chain-like gene A (MICA), and vimentin in conjunction with overall and complement-binding donor-specific HLA antibodies (HLA-DSA) with graft histology and function.

RESULTS

We observed a high prevalence (62.9%) of non-HLA antibody positivity. Seventy-two percent of HLA-DSA positive patients showed additional positivity for at least one non-HLA antibody. Antibodies against AT₁R, ET_AR, and MICA were associated with the histological phenotype of ABMR. The cumulative load of HLA-DSA and non-HLA antibodies in circulation was related to the degree of microinflammation in peritubular capillaries. Non-HLA antibody positivity was an independent non-invasive risk factor for graft function deterioration (adjusted hazard ratio 6.38, 95% CI, 2.11-19.3).

CONCLUSIONS

Our data indicate that the combined detection of antibodies to HLA and non-HLA targets may allow a more comprehensive assessment of the patients' immune responses against the kidney allograft and facilitates immunological risk stratification.

Leveraging NKG2D Ligands in Immuno-Oncology

Immune checkpoint inhibitors (ICI) revolutionized the field of immuno-oncology and opened new avenues towards the development of novel assets to achieve durable immune control of cancer. Yet, the presence of tumor immune evasion mechanisms represents a challenge for the development of efficient treatment options. Therefore, combination therapies are taking the center of the stage in immuno-oncology. Such combination therapies should boost anti-tumor immune responses and/or target tumor immune escape mechanisms, especially those created by major players in the tumor microenvironment (TME) such as tumor-associated macrophages (TAM). Natural killer (NK) cells were recently positioned at the forefront of many immunotherapy strategies, and several new approaches are being designed to fully exploit NK cell antitumor potential. One of the most relevant NK cell-activating receptors is NKG2D, a receptor that recognizes 8 different NKG2D ligands (NKG2DL), including MICA and MICB. MICA and MICB are poorly expressed on normal cells but become upregulated on the surface of damaged, transformed or infected cells as a result of post-transcriptional or post-translational mechanisms and intracellular pathways. Their engagement of NKG2D triggers NK cell effector functions. Also, MICA/B are polymorphic and such polymorphism affects functional responses through regulation of their cell-surface expression, intracellular trafficking, shedding of soluble immunosuppressive isoforms, or the affinity of NKG2D interaction. Although immunotherapeutic approaches that target the NKG2D-NKG2DL axis are under investigation, several tumor immune escape mechanisms account for reduced cell surface expression of NKG2DL and contribute to tumor immune escape. Also, NKG2DL polymorphism determines functional NKG2D-dependent responses, thus representing an additional challenge for leveraging NKG2DL in immuno-oncology. In this review, we discuss strategies to boost MICA/B expression and/or inhibit their shedding and propose that combination strategies that target MICA/B with antibodies and strategies aimed at promoting their upregulation on tumor cells or at reprograming TAM into pro-inflammatory macrophages and remodeling of the TME, emerge as frontrunners in immuno-oncology because they may unleash the antitumor effector functions of NK cells and cytotoxic CD8 T cells (CTL). Pursuing several of these pipelines might lead to innovative modalities of immunotherapy for the treatment of a wide range of cancer patients.

The Problem of Subclinical Antibody-mediated Rejection in Kidney Transplantation

Defined as histologic evidence of rejection on a protocol biopsy in the absence of kidney dysfunction, subclinical rejection has garnered attention since the 1990s. The major focus of much of this research, however, has been subclinical T cell-mediated rejection (TCMR). Herein, we review the literature on subclinical antibody-mediated rejection (AMR), which may occur with either preexisting donor-specific antibodies (DSA) or upon the development of de novo DSA (dnDSA). In both situations, subsequent kidney function and graft survival are compromised. Thus, we recommend protocol biopsy routinely within the first year with preexisting DSA and at the initial detection of dnDSA. In those with positive biopsies, baseline immunosuppression should be maximized, any associated TCMR treated, and adherence stressed, but it remains uncertain if antibody-reduction treatment should be initiated. Less invasive testing of blood for donor DNA or gene profiling may have a role in follow-up of those with negative initial biopsies. If a protocol biopsy is positive in the absence of detectable HLA-DSA, it also remains to be determined whether non-HLA-DSA should be screened for either in particular or on a genome-wide basis and how these patients should be treated. Randomized controlled trials are clearly needed.

Prevalence and impact of HLA and MICA allele mismatching on donor-specific antibodies induction in kidney transplant rejection

AIM

Donor-recipient antigen mismatching for anti-human leucocyte antigen (HLA) and MICA is one of the risk factors for antibody induction leading to graft rejection. Our aim was to analyze the incidence and specificity of the different DSAs developing and to investigate the impact of HLA and MICA allele mismatches on antibody production in kidney transplant patients experiencing antibody-mediated rejection (AMR).

METHODS

We retrospectively reviewed 253 consecutive recipients of kidney transplant who were diagnosed as experiencing AMR.

RESULTS

Our results showed that around 27% of our patients were positive for DSAs over a median follow-up period of 24 months. Antibody to HLA-DQ7 was the most prevalent DSA detected. The allele mismatch number was significantly lower for DQ loci than -A and -B loci (DQ vs. A, p < .001; DQ vs. B, p = .002). Considering each HLA antigen, the incidence rate of DQ-DSA [41.9 (32.92-51.46; 95%CI)] was much higher than the rate observed for DSA directed to -A, -DR and -B loci. Half of the recipients in the DQ-DSA-only group, and the DQ-DSA together with non-DQ group, had MFI > 5000. Only one case developed de novo MICA-DSA (MICA002).

CONCLUSION

Our study indicates that mismatching for HLA and MICA alleles leads to the development of HLA and MICA antibodies in some kidney transplant recipients. We have also demonstrated that DSA to the DQ locus is the most prevalent in kidney transplant patients with AMR. Thus, matching the DQ locus in kidney allocation algorithms may reduce post-transplant development of DSA.

The emerging field of non-human leukocyte antigen antibodies in transplant medicine and beyond

The major medical advances in our knowledge of the human leukocyte antigen (HLA) system have allowed us to uncover several gaps in our understanding of alloimmunity. Although the non-HLA system has long sparked the interest of the transplant community, recognition of the role of immunity to non-HLA antigenic targets has only emerged recently. In this review, we will provide a comprehensive summary of the paradigm-changing concept of immunity to the non-HLA angiotensin II type 1 receptor (AT1R), discovered by Duška Dragun et al., that began from careful bedside clinical observations, to validated detection of anti-AT1R antibodies and lead to clinical intervention. This scientific approach has also allowed the recognition of broader pathogenicity of anti-AT1R antibodies across multiple organ transplants and in other human diseases, the integration of both non-HLA and HLA systems to understand their immunologic effects on organ allografts, and the identification of future directions for therapeutic intervention to modulate immunity to AT1R. Rationally designed successful interventions to target AT1R system provide an exemplar for other non-HLA antibodies to cross borders between medical specialties, will generate new avenues in translational research beyond transplantation, and will foster the development of new and reliable tools to improve our understanding of non-HLA immunity and ultimately allow us to improve patient care.

Histologic Antibody-Mediated Kidney Allograft Rejection in the Absence of Donor Specific HLA Antibodies

Histologic antibody-mediated rejection (hAMR) is defined as a kidney allograft biopsy satisfying the first 2 Banff criteria for diagnosing antibody-mediated rejection (AMR): tissue injury and evidence of current/recent antibody interaction with the endothelium. In approximately one-half of such cases, circulating HLA donor specific antibodies (DSA) are not detectable by current methodology at the time of biopsy. Some studies indicated a better prognosis for HLA-DSA-negative cases of hAMR compared to those with detectable HLA-DSA, whereas others found equally poor survival compared to hAMR-negative cases. We reviewed the literature regarding the pathophysiology of HLA-DSA-negative hAMR. We find 3 nonmutually exclusive possibilities: 1) HLA-DSA are involved, but just not detected; 2) non-HLA DSA (allo- or autoantibodies) are pathogenically involved; and/or 3) antibody-independent NK cell activation is mediating the process through "missing self" or other activating mechanisms. These possibilities are discussed in detail. Recommendations regarding the approach to such patients are made. Clearly, more research is necessary regarding the measurement of non-HLA antibodies, recipient/donor NK cell genotyping, and the use of antibody reduction therapy or other immunosuppression in any subset of patients with HLA-DSA-negative hAMR.

Humoral Acute Rejection in a Kidney Transplant Recipient with Idiopathic Thrombocytopenic Purpura

A 47-year-old male was diagnosed with chronic kidney disease (CKD) in 2011; idiopathic thrombocytopenic purpura (ITP) was also diagnosed in 2011 refractory to medical treatment and finally treated with splenectomy (2017) without relapses since that date, 5 blood transfusions, and 4 platelet apheresis in 2017. Renal transplant from a living related donor (brother), ABO compatible, crossmatch were negative, sharing 1 haplotype. Donor-specific anti-HLA antibody was negative. Graft function was stable until the 5th day and graft biopsy on the 6th day; thrombotic microangiopathy (TMA), C4D negative and inflammatory infiltration of polymorphonuclear leukocytes inside peritubular capillary, and anti-MICA antibodies were positive. The treatment used were plasmapheresis, intravenous immunoglobulin, and rituximab. Serum creatinine began to decrease since the 14th day, and by day 33, post-RT graft function was restored.

KDIGO Clinical Practice Guideline on the Evaluation and Management of Candidates for Kidney Transplantation

The 2020 Kidney Disease: Improving Global Outcomes (KDIGO) Clinical Practice Guideline on the Evaluation and Management of Candidates for Kidney Transplantation is intended to assist health care professionals worldwide who evaluate and manage potential candidates for deceased or living donor kidney transplantation. This guideline addresses general candidacy issues such as access to transplantation, patient demographic and health status factors, and immunological and psychosocial assessment. The roles of various risk factors and comorbid conditions governing an individual's suitability for transplantation such as adherence, tobacco use, diabetes, obesity, perioperative issues, causes of kidney failure, infections, malignancy, pulmonary disease, cardiac and peripheral arterial disease, neurologic disease, gastrointestinal and liver disease, hematologic disease, and bone and mineral disorder are also addressed. This guideline provides recommendations for evaluation of individual aspects of a candidate's profile such that each risk factor and comorbidity are considered separately. The goal is to assist the clinical team to assimilate all data relevant to an individual, consider this within their local health context, and make an overall judgment on candidacy for transplantation. The guideline development process followed the Grades of Recommendation Assessment, Development, and Evaluation (GRADE) approach. Guideline recommendations are primarily based on systematic reviews of relevant studies and our assessment of the quality of that evidence, and the strengths of recommendations are provided. Limitations of the evidence are discussed with differences from previous guidelines noted and suggestions for future research are also provided.

Pretransplant Calculated Panel Reactive Antibody in the Absence of Donor-Specific Antibody and Kidney Allograft Survival

BACKGROUND AND OBJECTIVES

Panel reactive antibody informs the likelihood of finding an HLA-compatible donor for transplant candidates, but has historically been associated with acute rejection and allograft survival because testing methods could not exclude the presence of concomitant donor-specific antibodies. Despite new methods to exclude donor-specific antibodies, panel reactive antibody continues to be used to determine the choice of induction and maintenance immunosuppression. The study objective was to determine the clinical relevance of panel reactive antibody in the absence of donor-specific antibodies.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Retrospective observational study of kidney allograft survival among 4058 zero HLA-A-, B-, DR-, and DQB1-mismatched transplant recipients without antibodies to donor kidney antigens encoded by these HLA gene loci.

RESULTS

Among 4058 first and repeat transplant recipients, patients with calculated panel reactive antibody (cPRA) 1%-97% were not at higher risk of transplant failure, compared with patients with cPRA of 0% (death censored graft loss: hazard ratio, 1.07; 95% confidence interval, 0.82 to 1.41). Patients with cPRA ≥98% had a higher risk of graft loss from any cause including death (hazard ratio, 1.39; 95% confidence interval, 1.08 to 1.79) and death censored allograft failure (hazard ratio, 1.78; 95% confidence interval, 1.27 to 2.49). In stratified analyses, the higher risk of graft loss among patients with cPRA ≥98% was only observed among repeat, but not first, transplant recipients. In subgroup analysis, there was no association between cPRA and graft loss among living related transplant recipients.

CONCLUSIONS

Calculated panel reactive antibody is poorly associated with post-transplant immune reactivity to the allograft in the absence of donor-specific antibody.

PODCAST

This article contains a podcast at https://www.asn-online.org/media/podcast/CJASN/2021_01_25_CJN13640820_final.mp3.

Precision Medicine in Kidney Transplantation: Just Hype or a Realistic Hope?

Desirable outcomes including rejection- and infection-free kidney transplantation are not guaranteed despite current strategies for immunosuppression and using prophylactic antimicrobial medications. Graft survival depends on factors beyond human leukocyte antigen matching such as the level of immunosuppression, infections, and management of other comorbidities. Risk stratification of transplant patients based on predisposing genetic modifiers and applying precision pharmacotherapy may help improving the transplant outcomes. Unlike certain fields such as oncology in which consistent attempts are being carried out to move away from the "error and trial approach," transplant medicine is lagging behind in implementing personalized immunosuppressive therapy. The need for maintaining a precarious balance between underimmunosuppression and overimmunosuppression coupled with adverse effects of medications calls for a gene-based guidance for precision pharmacotherapy in transplantation. Technologic advances in molecular genetics have led to increased accessibility of genetic tests at a reduced cost and have set the stage for widespread use of gene-based therapies in clinical care. Evidence-based guidelines available for precision pharmacotherapy have been proposed, including guidelines from Clinical Pharmacogenetics Implementation Consortium, the Pharmacogenomics Knowledge Base National Institute of General Medical Sciences of the National Institutes of Health, and the US Food and Drug Administration. In this review, we discuss the implications of pharmacogenetics and potential role for genetic variants-based risk stratification in kidney transplantation. A single score that provides overall genetic risk, a polygenic risk score, can be achieved by combining of allograft rejection/loss-associated variants carried by an individual and integrated into practice after clinical validation.

Circulating NKG2A-NKG2D+ CD56dimCD16+ Natural Killer (NK) Cells as Mediators of Functional Immunosurveillance in Kidney Transplant Recipients

Background

Recently, in patients with long-term functioning allografts, we showed that high NKG2D+ NK cell numbers in the peripheral blood were associated with a higher glomerular filtration rate, whereas high NKG2A+ NK cells were associated with a lower glomerular filtration rate. Both NK cell determinants react with ligands (MIC A/B, HLA-E) expressed on stressed cells, such as virus-infected cells, tumor cells, or cells activated during graft rejection. In the present study, we attempted to characterize these 2 NK cell subsets further.

Material/Methods

Using flow cytometry, NK cell subsets were analyzed in whole-blood samples of 35 stable kidney transplant recipients (serum creatinine mean±SD: 1.44±0.45 mg/dl). Blood was obtained 95–3786 days after transplant (mean±SD: 1168±1011 days after transplant).

Results

High proportions of NKG2A–NKG2D+ NK cells were strongly associated with high numbers of CD56dimCD16+ (p=0.001) NK cells co-expressing CD107 (P=0.001) and granzyme B (P=0.045), suggesting that NKG2A–NKG2D+ NK cells are predominantly cytotoxic. In contrast, high numbers of NKG2A+NKG2D− NK cells were strongly associated with low numbers of CD56dimCD16+ NK cells expressing CD107 (P=0.026), CD25 (p=0.008), TGF-βR (P=0.028), and TGF-β (P=0.005), suggesting that patients with high proportions of NKG2A+NKG2D− NK cells have low proportions of NK cell subsets with cytotoxic phenotype.

Conclusions

A high proportion of NKG2A+NKG2D− NK cells is associated with decreased counts of NKG2A–NKG2D+ CD56dimCD16+ cytotoxic NK cells in the circulation. This may result in impaired immunosurveillance. We would like to hypothesize that NKG2A–NKG2D+ CD56dimCD16+ cytotoxic NK cells eliminate MIC A/B-expressing stressed cells which possess a potential to harm the transplant. Further studies will have to evaluate whether the proportion of NKG2A–NKG2D+ CD56dimCD16+ cytotoxic NK cells is a useful biomarker for the prediction of an uncomplicated postoperative course in kidney transplant recipients.

Chronic Active Antibody-Mediated Rejection with Linear IgG Deposition on Glomerular Capillaries in a Kidney Transplant Recipient

Glomerular IgG deposition is rarely observed in antibody-mediated rejection. Here, we report chronic active antibody-mediated rejection with linear IgG deposition on glomerular capillary walls in a pediatric kidney transplant recipient. A 6-year-old boy with bilateral renal hypoplasia underwent preemptive deceased-donor kidney transplantation. Five years after the transplantation, an allograft biopsy revealed chronic active antibody-mediated rejection with diffuse linear IgG deposition on glomerular capillaries. Anti-glomerular basement membrane antibody, donor-specific anti-human leukocyte antigen (HLA) antibodies, and anti-angiotensin II type 1 receptor antibody were negative. A multiplex antibody assay identified anti-major histocompatibility complex class I chain-related molecule A antibody. Additionally, a single-antigen bead assay identified autoantibodies to 12 non-HLA antigens, including vimentin and glutathione S-transferase theta-1. To investigate whether IgG autoantibodies in the patient's serum bind to antigens on glomerular capillaries, we incubated the patient's serum with 0-h biopsy specimens of tissue donated to the patient and a control subject, both obtained immediately after nephrectomy from respective donors. IgG signals were observed in neither patient nor control samples. Nevertheless, linear IgG deposition may be explained by the binding of autoantibodies to non-HLA antigens that are usually hidden and only exposed via severe endothelial cell injury. Further studies are needed to confirm the significance of non-HLA antibodies in glomerular IgG deposition.

Noninvasive biomarkers for prediction and diagnosis of heart transplantation rejection

For most patients with end-stage heart failure, heart transplantation is the treatment of choice. Allograft rejection is one of the major post-transplantation complications affecting graft outcome and survival. Recent advancements in science and technology offer an opportunity to integrate genomic and other omics-based biomarkers into clinical practice, facilitating noninvasive evaluation of allograft for diagnostic and prognostic purposes. Omics, including gene expression profiling (GEP) of blood immune cell components and donor-derived cell-free DNA (dd-cfDNA) are of special interest to researchers. Several studies have investigated levels of dd-cfDNA and miroRNAs in blood as potential markers for early detection of allograft rejection. One of the achievements in the field of transcriptomics is AlloMap, GEP of peripheral blood mononuclear cells (PBMC), which can identify 11 differentially expressed genes and help with detection of moderate and severe acute cellular rejection in stable heart transplant recipients. In recent years, the utilization of GEP of PBMC for identifying differentially expressed genes to diagnose acute antibody-mediated rejection and cardiac allograft vasculopathy has yielded promising results. Advancements in the field of metabolomics and proteomics as well as their potential implications have been further discussed in this paper.

Genetic background and transplantation outcomes: insights from genome-wide association studies

PURPOSE OF REVIEW

The current review summarizes recent advances in the genetic studies of transplantation outcomes, including new genome-wide association studies for acute rejection, allograft survival, pharmacogenomics, and common transplant comorbidities.

RECENT FINDINGS

Genetic studies of kidney transplantation outcomes have begun to address the question of genetic compatibility beyond human leukocyte antigens, including the role of genome-wide mismatches in missense variants, and the 'genomic collision' hypothesis under which the risk of rejection may be increased in recipients homozygous for loss-of-function variants with grafts from nonhomozygous donors. In recent pilot studies, missense mismatch scores for transmembrane and secreted proteins were associated with antibodies against the mismatched peptides and reduced allograft survival. A 'genomic collision' at the LIMS1 locus involving a common deletion near LIMS1 gene was associated with anti-LIMS1 antibody response and increased risk of rejection. Additional genetic factors under active investigation include genome-wide polygenic risk scores for renal function and apolipoprotein L1 risk genotypes in African-American kidney donors. Due to the heterogeneity and complexity of clinical outcomes, new genome-wide association studies for rejection, allograft survival, and specific transplant comorbidities will require larger multicenter meta-analyses.

SUMMARY

Genetic compatibilities between donor and recipient represent an important determinant of rejection and long-term allograft survival. Genetic background of transplant donors may be additionally predictive of allograft function, while recipient's genomes are likely determinant of a wide range of transplantation outcomes, from rejection susceptibility to pharmacogenetics and various comorbidities related to prolonged immunosuppression.

Influence of pretransplant class I and II non-donor-specific anti-HLA immunization on immunologic outcome and graft survival in kidney transplant recipients

BACKGROUND

Anti-HLA immunization determined by Panel Reactive Antibody (PRA) is known to have a negative impact on patient and graft survival. The predictive value of peak PRA (pPRA) on immunologic outcome, however, and the individual effects of anti-HLA class I and II antibodies remain uncertain.

METHODS

The influence of HLA immunization on immunologic outcome parameters and graft survival was investigated in 1150 adult patients without pretransplant donor-specific antibodies (DSA) and in a subgroup of elderly kidney recipients aged ≥ 65 (n = 264). Anti-HLA immunization was defined as a pPRA > 0%. We investigated the influence of class I and II pPRA by dividing all kidney recipients into four pPRA groups (0%, 1-20%, 21-80%, >80%).

RESULTS

Patients with non-donor-specific pretransplant anti-HLA immunization were at a higher risk for developing de novo DSA (49.9% vs. 18.7% p < 0.001), antibody mediated rejections (ABMR) (15.7% vs. 5.1%; p < 0.001), had a poorer death censored graft survival (69.2% vs. 86.2%; p < 0.001) and a higher decline of the calculated GFR. In elderly patients anti-HLA immunization only had a significant influence on the development of DSA (40.5% vs. 27.4%; p = 0.004). A multivariate model adjusted for all relevant factors revealed only class I but not class II pretransplant HLA immunization as a significant independent risk factor for de novo DSA, ABMR and death censored graft loss (HR 2.76, p < 0.001, HR 4.16, p < 0.001 and HR 2.07, p < 0.001, respectively).

CONCLUSION

Mainly non-donor-specific pretransplant HLA class I immunization is an independent risk factor for the development of de novo DSA, ABMR and graft loss.

Endothelin Type A Receptor Antibodies Are Associated With Angiotensin II Type 1 Receptor Antibodies, Vascular Inflammation, and Decline in Renal Function in Pediatric Kidney Transplantation

Introduction

Autoantibody to angiotensin II type 1 receptor (AT1R-Ab) has been recognized as a non-human leukocyte antigen (HLA) antibody relevant in transplantation. Endothelin type A receptor antibody (ETAR-Ab) has been strongly associated with AT1R-Ab, but the data in kidney transplantation are scarce.

Methods

We examined the relationship of ETAR-Ab and AT1R-Ab with clinical outcomes, biopsy findings, inflammatory cytokines, and HLA donor-specific antibody (DSA) in a cohort of pediatric renal transplant recipients. Sixty-five patients were longitudinally monitored for ETAR-Ab, AT1R-Ab, HLA DSA, interleukin (IL)-8, tumor necrosis factor-α, IL-1β, interferon-γ, IL-17, IL-6, renal dysfunction, hypertension, rejection, and allograft loss during the first 2 years post-transplant.

Results

Fifteen patients (23%) had AT1R-Ab alone, 1 (2%) had ETAR-Ab alone, 23 (35%) had both ETAR-Ab and AT1R-Ab, and 26 (40%) were negative for both antibodies at all timepoints. Having both ETAR-Ab and AT1R-Ab was associated with >30% decline in estimated glomerular filtration rate (P = 0.024), arteritis (P = 0.016), and elevated IL-8 levels (P = 0.010), but not rejection, HLA DSA, or allograft loss. Having both antibodies resulted in greater increases in IL-8 compared with AT1R-Ab alone, even when controlled for additional clinical factors, including HLA DSA (P = 0.012).

Conclusion

Our study demonstrates that, in pediatric kidney transplantation, ETAR-Ab is highly associated with AT1R-Ab, but there are a subset of patients with AT1R-Ab alone. Having both antibodies is significantly associated with arteritis, elevated IL-8, and decline in renal function, and our results suggest possible interaction effects. Better understanding of this interaction may be informative in developing protocols for testing, treatment, and prevention of allograft injury.