Immunologic risk stratification of pediatric heart transplant patients by combining HLA-EMMA and PIRCHE-II

Human leukocyte antigen (HLA) molecular mismatch is a powerful biomarker of rejection. Few studies have explored its use in assessing rejection risk in heart transplant recipients. We tested the hypothesis that a combination of HLA Epitope Mismatch Algorithm (HLA-EMMA) and Predicted Indirectly Recognizable HLA Epitopes (PIRCHE-II) algorithms can improve risk stratification of pediatric heart transplant recipients. Class I and II HLA genotyping were performed by next-generation sequencing on 274 recipient/donor pairs enrolled in the Clinical Trials in Organ Transplantation in Children (CTOTC). Using high-resolution genotypes, we performed HLA molecular mismatch analysis with HLA-EMMA and PIRCHE-II, and correlated these findings with clinical outcomes. Patients without pre-formed donor specific antibody (DSA) (n=100) were used for correlations with post-transplant DSA and antibody mediated rejection (ABMR). Risk cut-offs were determined for DSA and ABMR using both algorithms. HLA-EMMA cut-offs alone predict the risk of DSA and ABMR; however, if used in combination with PIRCHE-II, the population could be further stratified into low-, intermediate-, and high-risk groups. The combination of HLA-EMMA and PIRCHE-II enables more granular immunological risk stratification. Intermediate-risk cases, like low-risk cases, are at a lower risk of DSA and ABMR. This new way of risk evaluation may facilitate individualized immunosuppression and surveillance.

Precision transplant pathology

PURPOSE OF REVIEW

Transplant pathology contributes substantially to personalized treatment of organ allograft recipients. Rapidly advancing next-generation human leukocyte antigen (HLA) sequencing and pathology are enhancing the abilities to improve donor/recipient matching and allograft monitoring.

RECENT FINDINGS

The present review summarizes the workflow of a prototypical patient through a pathology practice, highlighting histocompatibility assessment and pathologic review of tissues as areas that are evolving to incorporate next-generation technologies while emphasizing critical needs of the field.

SUMMARY

Successful organ transplantation starts with the most precise pratical donor-recipient histocompatibility matching. Next-generation sequencing provides the highest resolution donor-recipient matching and enables eplet mismatch scores and more precise monitoring of donor-specific antibodies (DSAs) that may arise after transplant. Multiplex labeling combined with hand-crafted machine learning is transforming traditional histopathology. The combination of traditional blood/body fluid laboratory tests, eplet and DSA analysis, traditional and next-generation histopathology, and -omics-based platforms enables risk stratification and identification of early subclinical molecular-based changes that precede a decline in allograft function. Needs include software integration of data derived from diverse platforms that can render the most accurate assessment of allograft health and needs for immunosuppression adjustments.

Molecular events contributing to successful pediatric cardiac transplantation in HLA sensitized recipients

Antibodies to HLA resulting in positive cytotoxicity crossmatch are generally considered a contraindication for cardiac transplantation. However, cardiac transplantations have been performed in children by reducing the Abs and modifying immunosuppression. To identify mechanisms leading to allograft acceptance in the presence of Abs to donor HLA, we analyzed priming events in endothelial cells (EC) by incubating with sera containing low levels of anti-HLA followed by saturating concentration of anti-HLA. Pre-transplant sera were obtained from children with low levels of Abs to HLA who underwent transplantation. EC were selected for donor HLA and exposed to sera for 72 h (priming), followed by saturating concentrations of anti-HLA (challenge). Priming of EC with sera induced the phosphatidylinositol 3-kinase/Akt mediated by the BMP4/WNT pathway and subsequent challenge with panel reactive antibody sera increased survival genes Bcl2 and Heme oxygenase-1, decreased adhesion molecules, induced complement inhibitory proteins and reduced pro-inflammatory cytokines. In contrast, EC which did not express donor HLA showed decreased anti-apoptotic genes. Primed EC, upon challenge with anti-HLA, results in increased survival genes, decreased adhesion molecules, induction of complement inhibitory proteins, and downregulation of pro-inflammatory cytokines which may result in accommodation of pediatric cardiac allografts despite HLA sensitization.

Banff Lung Report: Current knowledge and future research perspectives for diagnosis and treatment of pulmonary antibody-mediated rejection (AMR)

The Lung session of the 2017 14th Banff Foundation for Allograft Pathology Conference, Barcelona focused on the multiple aspects of antibody-mediated rejection (AMR) in lung transplantation. Multidimensional approaches for AMR diagnosis, including classification, histological and immunohistochemical analysis, and donor- specific antibody (DSA) characterization with their current strengths and limitations were reviewed in view of recent research. The group also discussed the role of tissue gene expression analysis in the context of unmet needs in lung transplantation. The current best practice for monitoring of AMR and the therapeutic approach are summarized and highlighted in this report. The working group reached consensus of the major gaps in current knowledge and focused on the unanswered questions regarding pulmonary AMR. An important outcome of the meeting was agreement on the need for future collaborative research projects to address these gaps in the field of lung transplantation.

Incidence, characterization, and impact of newly detected donor-specific anti-HLA antibody in the first year after pediatric heart transplantation: A report from the CTOTC-04 study

Data on the clinical importance of newly detected donor-specific anti-HLA antibodies (ndDSAs) after pediatric heart transplantation are lacking despite mounting evidence of the detrimental effect of de novo DSAs in solid organ transplantation. We prospectively tested 237 pediatric heart transplant recipients for ndDSAs in the first year posttransplantation to determine their incidence, pattern, and clinical impact. One-third of patients developed ndDSAs; when present, these were mostly detected within the first 6 weeks after transplantation, suggesting that memory responses may predominate over true de novo DSA production in this population. In the absence of preexisting DSAs, patients with ndDSAs had significantly more acute cellular rejection but not antibody-mediated rejection, and there was no impact on graft and patient survival in the first year posttransplantation. Risk factors for ndDSAs included common sensitizing events. Given the early detection of the antibody response, memory responses may be more important in the first year after pediatric heart transplantation and patients with a history of a sensitizing event may be at risk even with a negative pretransplantation antibody screen. The impact on late graft and patient outcomes of first-year ndDSAs is being assessed in an extended cohort of patients.

Pediatric heart transplantation across a positive crossmatch: First year results from the CTOTC-04 multi-institutional study

Sensitization is common in pediatric heart transplant candidates and waitlist mortality is high. Transplantation across a positive crossmatch may reduce wait time, but is considered high risk. We prospectively recruited consecutive candidates at eight North American centers. At transplantation, subjects were categorized as nonsensitized or sensitized (presence of ≥1 HLA antibody with MFI ≥1000 using single antigen beads). Sensitized subjects were further classified as complement-dependent cytotoxicity crossmatch (CDC-crossmatch) positive or negative and as donor-specific antibodies (DSA) positive or negative. Immunosuppression was standardized. CDC-crossmatch-positive subjects also received perioperative antibody removal, maintenance corticosteroids, and intravenous immunoglobulin. The primary endpoint was the 1 year incidence rate of a composite of death, retransplantation, or rejection with hemodynamic compromise. 317 subjects were screened, 290 enrolled and 240 transplanted (51 with pretransplant DSA, 11 with positive CDC-crossmatch). The incidence rates of the primary endpoint did not differ statistically between groups; nonsensitized 6.7% (CI: 2.7%, 13.3%), sensitized crossmatch positive 18.2% (CI: 2.3%, 51.8%), sensitized crossmatch negative 10.7% (CI: 5.7%, 18.0%), P = .2354. The primary endpoint also did not differ by DSA status. Freedom from antibody-mediated and cellular rejection was lower in the crossmatch positive group and/or in the presence of DSA. Follow-up will determine if acceptable outcomes can be achieved long-term.

Isolated vascular "v" lesions in liver allografts: How to approach this unusual finding

According to the Banff criteria for kidney allografts, isolated vascular or "v" lesions are defined as intimal inflammation, age-inappropriate fibro-intimal hyperplasia, or both, without the presence of associated interstitial T cell-mediated rejection (TCMR). In general, these lesions portend a worse outcome for kidney allografts, particularly in those where the "v" lesions are identified in patients with coexistent donor specific antibodies (DSA) or later after transplantation. Although affected arteries are rarely sampled in liver allograft biopsies, we identified nine patients at a mean of 1805 days posttransplantation and compared these to matched controls. Almost half (4 of 9) of the study patient biopsies showed inflammatory arteritis associated with focal or diffuse C4d positivity, which was not observed in matched controls. One "v" lesion patient progressed to rejection-related graft failure and two developed moderate/severe TCMR in subsequent biopsies, whereas only one rejection episode occurred in follow-up biopsies, and no rejection-related deaths or graft failures were detected in controls. In conclusion, patients with liver allograft isolated "v" lesions should undergo further evaluation and closer follow-up for impending TCMR and/or underlying co-existent chronic antibody-mediated rejection (AMR).

The Influence of Race and Common Genetic Variations on Outcomes After Pediatric Heart Transplantation

Significant racial disparity remains in the incidence of unfavorable outcomes following heart transplantation. We sought to determine which pediatric posttransplantation outcomes differ by race and whether these can be explained by recipient demographic, clinical, and genetic attributes. Data were collected for 80 black and 450 nonblack pediatric recipients transplanted at 1 of 6 centers between 1993 and 2008. Genotyping was performed for 20 candidate genes. Average follow-up was 6.25 years. Unadjusted 5-year rates for death (p = 0.001), graft loss (p = 0.015), acute rejection with severe hemodynamic compromise (p = 0.001), late rejection (p = 0.005), and late rejection with hemodynamic compromise (p = 0.004) were significantly higher among blacks compared with nonblacks. Black recipients were more likely to be older at the time of transplantation (p < 0.001), suffer from cardiomyopathy (p = 0.004), and have public insurance (p < 0.001), and were less likely to undergo induction therapy (p = 0.0039). In multivariate regression models adjusting for age, sex, cardiac diagnosis, insurance status, and genetic variations, black race remained a significant risk factor for all the above outcomes. These clinical and genetic variables explained only 8-19% of the excess risk observed for black recipients. We have confirmed racial differences in survival, graft loss, and several rejection outcomes following heart transplantation in children, which could not be fully explained by differences in recipient attributes.

Proteasome Inhibitor Carfilzomib-Based Therapy for Antibody-Mediated Rejection of the Pulmonary Allograft: Use and Short-Term Findings

We present this observational study of lung transplant recipients (LTR) treated with carfilzomib (CFZ)-based therapy for antibody-mediated rejection (AMR) of the lung. Patients were considered responders to CFZ if complement-1q (C1q)-fixing ability of their immunodominant (ID) donor-specific anti-human leukocyte antibody (DSA) was suppressed after treatment. Treatment consisted of CFZ plus plasma exchange and immunoglobulins. Fourteen LTRs underwent CFZ for 20 ID DSA AMR. Ten (71.4%) of LTRs responded to CFZ. DSA IgG mean fluorescence intensity (MFI) fell from 7664 (IQR 3230-11 874) to 1878 (653-7791) after therapy (p = 0.001) and to 1400 (850-8287) 2 weeks later (p = 0.001). DSA C1q MFI fell from 3596 (IQR 714-14 405) to <30 after therapy (p = 0.01) and <30 2 weeks later (p = 0.02). Forced expiratory volume in 1s ( FEV₁ ) fell from mean 2.11 L pre-AMR to 1.92 L at AMR (p = 0.04). FEV₁ was unchanged after CFZ (1.91 L) and subsequently rose to a maximum of 2.13 L (p = 0.01). Mean forced expiratory flow during mid forced vital capacity (25-75) (FEF_25-75 ) fell from mean 2.5 L pre-AMR to 1.95 L at AMR (p = 0.01). FEF_25-75 rose after CFZ to 2.54 L and reached a maximum of 2.91 L (p = 0.01). Responders had less chronic lung allograft dysfunction or progression versus nonresponders (25% vs. 83%, p = 0.04). No deaths occurred within 120 days and 7 patients died post CFZ therapy of allograft failure. Larger prospective interventional studies are needed to further describe the benefit of CFZ-based therapy for pulmonary AMR.

The Banff 2015 Kidney Meeting Report: Current Challenges in Rejection Classification and Prospects for Adopting Molecular Pathology

The XIII Banff meeting, held in conjunction the Canadian Society of Transplantation in Vancouver, Canada, reviewed the clinical impact of updates of C4d-negative antibody-mediated rejection (ABMR) from the 2013 meeting, reports from active Banff Working Groups, the relationships of donor-specific antibody tests (anti-HLA and non-HLA) with transplant histopathology, and questions of molecular transplant diagnostics. The use of transcriptome gene sets, their resultant diagnostic classifiers, or common key genes to supplement the diagnosis and classification of rejection requires further consensus agreement and validation in biopsies. Newly introduced concepts include the i-IFTA score, comprising inflammation within areas of fibrosis and atrophy and acceptance of transplant arteriolopathy within the descriptions of chronic active T cell-mediated rejection (TCMR) or chronic ABMR. The pattern of mixed TCMR and ABMR was increasingly recognized. This report also includes improved definitions of TCMR and ABMR in pancreas transplants with specification of vascular lesions and prospects for defining a vascularized composite allograft rejection classification. The goal of the Banff process is ongoing integration of advances in histologic, serologic, and molecular diagnostic techniques to produce a consensus-based reporting system that offers precise composite scores, accurate routine diagnostics, and applicability to next-generation clinical trials.

The XIIIth Banff Conference on Allograft Pathology: The Banff 2015 Heart Meeting Report: Improving Antibody-Mediated Rejection Diagnostics: Strengths, Unmet Needs, and Future Directions

The 13th Banff Conference on Allograft Pathology was held in Vancouver, British Columbia, Canada from October 5 to 10, 2015. The cardiac session was devoted to current diagnostic issues in heart transplantation with a focus on antibody-mediated rejection (AMR) and small vessel arteriopathy. Specific topics included the strengths and limitations of the current rejection grading system, the central role of microvascular injury in AMR and approaches to semiquantitative assessment of histopathologic and immunophenotypic indicators, the role of AMR in the development of cardiac allograft vasculopathy, the important role of serologic antibody detection in the management of transplant recipients, and the potential application of new molecular approaches to the elucidation of the pathophysiology of AMR and potential for improving the current diagnostic system. Herein we summarize the key points from the presentations, the comprehensive, open and wide-ranging multidisciplinary discussion that was generated, and considerations for future endeavors.

2016 Comprehensive Update of the Banff Working Group on Liver Allograft Pathology: Introduction of Antibody-Mediated Rejection

The Banff Working Group on Liver Allograft Pathology reviewed and discussed literature evidence regarding antibody-mediated liver allograft rejection at the 11th (Paris, France, June 5-10, 2011), 12th (Comandatuba, Brazil, August 19-23, 2013), and 13th (Vancouver, British Columbia, Canada, October 5-10, 2015) meetings of the Banff Conference on Allograft Pathology. Discussion continued online. The primary goal was to introduce guidelines and consensus criteria for the diagnosis of liver allograft antibody-mediated rejection and provide a comprehensive update of all Banff Schema recommendations. Included are new recommendations for complement component 4d tissue staining and interpretation, staging liver allograft fibrosis, and findings related to immunosuppression minimization. In an effort to create a single reference document, previous unchanged criteria are also included.

C1 Inhibitor in Acute Antibody-Mediated Rejection Nonresponsive to Conventional Therapy in Kidney Transplant Recipients: A Pilot Study

Complement inhibitors have not been thoroughly evaluated in the treatment of acute antibody-mediated rejection (ABMR). We performed a prospective, single-arm pilot study to investigate the potential effects and safety of C1 inhibitor (C1-INH) Berinert added to high-dose intravenous immunoglobulin (IVIG) for the treatment of acute ABMR that is nonresponsive to conventional therapy. Kidney recipients with nonresponsive active ABMR and acute allograft dysfunction were enrolled between April 2013 and July 2014 and received C1-INH and IVIG for 6 months (six patients). The primary end point was the change in eGFR at 6 months after inclusion (M+6). Secondary end points included the changes in histology and DSA characteristics and adverse events as evaluated at M+6. All patients showed an improvement in eGFR between inclusion and M+6: from 38.7 ± 17.9 to 45.2 ± 21.3 mL/min/1.73 m(2) (p = 0.0277). There was no change in histological features, except a decrease in the C4d deposition rate from 5/6 to 1/6 (p = 0.0455). There was a change in DSA C1q status from 6/6 to 1/6 positive (p = 0.0253). One deep venous thrombosis was observed. In a secondary analysis, C1-INH patients were compared with a similar historical control group (21 patients). C1-INH added to IVIG is safe and may improve allograft function in kidney recipients with nonresponsive acute ABMR.

Elevated ST2 Distinguishes Incidences of Pediatric Heart and Small Bowel Transplant Rejection

Elevated serum soluble (s) suppressor of tumorigenicity-2 is observed during cardiovascular and inflammatory bowel diseases. To ascertain whether modulated ST2 levels signify heart (HTx) or small bowel transplant (SBTx) rejection, we quantified sST2 in serially obtained pediatric HTx (n = 41) and SBTx recipient (n = 18) sera. At times of biopsy-diagnosed HTx rejection (cellular and/or antibody-mediated), serum sST2 was elevated compared to rejection-free time points (1714 ± 329 vs. 546.5 ± 141.6 pg/mL; p = 0.0002). SBTx recipients also displayed increased serum sST2 during incidences of rejection (7536 ± 1561 vs. 2662 ± 543.8 pg/mL; p = 0.0347). Receiver operator characteristic (ROC) analysis showed that serum sST2 > 600 pg/mL could discriminate time points of HTx rejection and nonrejection (area under the curve [AUC] = 0.724 ± 0.053; p = 0.0003). ROC analysis of SBTx measures revealed a similar discriminative capacity (AUC = 0.6921 ± 0.0820; p = 0.0349). Quantitative evaluation of both HTx and SBTx biopsies revealed that rejection significantly increased allograft ST2 expression. Pathway and Network Analysis of biopsy data pinpointed ST2 in the dominant pathway modulated by rejection and predicted tumor necrosis factor-α and IL-1β as upstream activators. In total, our data indicate that alloimmune-associated pro-inflammatory cytokines increase ST2 during rejection. They also demonstrate that routine serum sST2 quantification, potentially combined with other biomarkers, should be investigated further to aid in the noninvasive diagnosis of rejection.

Should HLA mismatch acceptability for sensitized transplant candidates be determined at the high-resolution rather than the antigen level?

Defining HLA mismatch acceptability of organ transplant donors for sensitized recipients has traditionally been based on serologically defined HLA antigens. Now, however, it is well accepted that HLA antibodies specifically recognize a wide range of epitopes present on HLA antigens and that molecularly defined high resolution alleles corresponding to the same low resolution antigen can possess different epitope repertoires. Hence, determination of HLA compatibility at the allele level represents a more accurate approach to identify suitable donors for sensitized patients. This approach would offer opportunities for increased transplant rates and improved long term graft survivals.

Immunologic challenges in small bowel transplantation

Since the introduction of tacrolimus, small-bowel and multivisceral transplantion has increased to 100-200/year in the United States. The intestine carries more passenger lymphocytes than other organs, and bidirectional trafficking of lymphocytes and other immunocytes begins as soon as the vascular clamp is released. Because of ischemia-reperfusion injury and exposure to ligands for Toll-like receptors from the lumen, the innate immune system of the graft is activated, causing inflammation which must be brought under control by regulatory cells. Inclusion of the liver in the allograft favors graft acceptance, but the mechanism of this effect has not been determined. Anti-HLA and other anti-donor antibodies clearly play a major role in determining the long-term fate of the graft, as reflected in 5-year graft survival. Development of new (de novo) HLA antibodies and/or increases in their titers or function-especially the ability to bind C1q and activate complement increase the risk of graft loss. Monitoring antidonor antibody production and the use of new therapies including complement inhibitors will contribute to increasing success of SBT.

Immunologic challenges in small bowel transplantation

Since the introduction of tacrolimus, small-bowel and multivisceral transplantion has increased to 100-200/year in the United States. The intestine carries more passenger lymphocytes than other organs, and bidirectional trafficking of lymphocytes and other immunocytes begins as soon as the vascular clamp is released. Because of ischemia-reperfusion injury and exposure to ligands for Toll-like receptors from the lumen, the innate immune system of the graft is activated, causing inflammation which must be brought under control by regulatory cells. Inclusion of the liver in the allograft favors graft acceptance, but the mechanism of this effect has not been determined. Anti-HLA and other anti-donor antibodies clearly play a major role in determining the long-term fate of the graft, as reflected in 5-year graft survival. Development of new (de novo) HLA antibodies and/or increases in their titers or function-especially the ability to bind C1q and activate complement increase the risk of graft loss. Monitoring antidonor antibody production and the use of new therapies including complement inhibitors will contribute to increasing success of SBT.

Preformed and de novo donor specific antibodies in visceral transplantation: long-term outcome with special reference to the liver

Despite improvement in early outcome, rejection particularly chronic allograft enteropathy continues to be a major barrier to long-term visceral engraftment. The potential role of donor specific antibodies (DSA) was examined in 194 primary adult recipients. All underwent complement-dependent lymphocytotoxic crossmatch (CDC-XM) with pre- and posttransplant solid phase HLA-DSA assay in 156 (80%). Grafts were ABO-identical with random HLA-match. Liver was included in 71 (37%) allografts. Immunosuppression was tacrolimus-based with antilymphocyte recipient pretreatment in 150 (77%). CDC-XM was positive in 55 (28%). HLA-DSA was detectable before transplant in 49 (31%) recipients with 19 continuing to have circulating antibodies. Another 19 (18%) developed de novo DSA. Ninety percent of patients with preformed DSA harbored HLA Class-I whereas 74% of recipients with de novo antibodies had Class-II. Gender, age, ABO blood-type, cold ischemia, splenectomy and allograft type were significant DSA predictors. Preformed DSA significantly (p < 0.05) increased risk of acute rejection. Persistent and de novo HLA-DSA significantly (p < 0.001) increased risk of chronic rejection and associated graft loss. Inclusion of the liver was a significant predictor of better outcome (p = 0.004, HR = 0.347) with significant clearance of preformed antibodies (p = 0.04, OR = 56) and lower induction of de novo DSA (p = 0.07, OR = 24). Innovative multifaceted anti-DSA strategies are required to further improve long-term survival particularly of liver-free allografts.