Urinary soluble HLA-DR is a potential biomarker for acute renal transplant rejection

Renal graft function in transplanted patients correlates with CD45RC T cell phenotypic signature

Biomarkers that could predict the evolution of the graft in transplanted patients and that could allow to adapt the care of the patients would be an invaluable tool. Additionally, certain biomarkers can be target of treatments and help to stratify patients. Potential effective biomarkers have been identified but still need to be confirmed. CD45RC, one of the splicing variants of the CD45 molecule, a tyrosine phosphatase that is critical in negatively or positively regulating the TCR and the BCR signaling, is one marker already described. The frequency of CD8+ T cells expressing high levels of CD45RC before transplantation is increased in patients with an increased risk of acute rejection. However, single biomarkers have limited predictive reliability and the correlation of the expression levels of CD45RC with other cell markers was not reported. In this study, we performed a fluorescent-based high dimensional immunophenotyping of T cells on a cohort of 69 kidney transplant patients either with stable graft function or having experienced acute transplant rejection during the first year after transplantation or at the time of rejection. We identified combinations of markers and cell subsets associated with activation/inflammation or Tregs/tolerance (HLA-DR, PD-1, IFNγ, CD28) as significant biomarkers associated to transplant outcome, and showed the importance of cell segregation based on the CD45RC marker to identify the signature of a stable graft function. Our study highlights potential reliable biomarkers in transplantation to predict and/or monitor easily graft-directed immune responses and adapt immunosuppression treatments to mitigate adverse effects.

Soluble HLA peptidome: A new resource for cancer biomarkers

Using circulating molecular biomarkers to screen for cancer and other debilitating disorders in a high-throughput and low-cost fashion is becoming increasingly attractive in medicine. One major limitation of investigating protein biomarkers in body fluids is that only one-fourth of the entire proteome can be routinely detected in these fluids. In contrast, Human Leukocyte Antigen (HLA) presents peptides from the entire proteome on the cell surface. While peptide-HLA complexes are predominantly membrane-bound, a fraction of HLA molecules is released into body fluids which is referred to as soluble HLAs (sHLAs). As such peptides bound by sHLA molecules represent the entire proteome of their cells/tissues of origin and more importantly, recent advances in mass spectrometry-based technologies have allowed for accurate determination of these peptides. In this perspective, we discuss the current understanding of sHLA-peptide complexes in the context of cancer, and their potential as a novel, relatively untapped repertoire for cancer biomarkers. We also review the currently available tools to detect and quantify these circulating biomarkers, and we discuss the challenges and future perspectives of implementing sHLA biomarkers in a clinical setting.

A novel approach reveals that HLA class 1 single antigen bead-signatures provide a means of high-accuracy pre-transplant risk assessment of acute cellular rejection in renal transplantation

BACKGROUND

Acute cellular rejection (ACR) is associated with complications after kidney transplantation, such as graft dysfunction and graft loss. Early risk assessment is therefore critical for the improvement of transplantation outcomes. In this work, we retrospectively analyzed a pre-transplant HLA antigen bead assay data set that was acquired by the e:KID consortium as part of a systems medicine approach.

RESULTS

The data set included single antigen bead (SAB) reactivity profiles of 52 low-risk graft recipients (negative complement dependent cytotoxicity crossmatch, PRA < 30%) who showed detectable pre-transplant anti-HLA 1 antibodies. To assess whether the reactivity profiles provide a means for ACR risk assessment, we established a novel approach which differs from standard approaches in two aspects: the use of quantitative continuous data and the use of a multiparameter classification method. Remarkably, it achieved significant prediction of the 38 graft recipients who experienced ACR with a balanced accuracy of 82.7% (sensitivity = 76.5%, specificity = 88.9%).

CONCLUSIONS

The resultant classifier achieved one of the highest prediction accuracies in the literature for pre-transplant risk assessment of ACR. Importantly, it can facilitate risk assessment in non-sensitized patients who lack donor-specific antibodies. As the classifier is based on continuous data and includes weak signals, our results emphasize that not only strong but also weak binding interactions of antibodies and HLA 1 antigens contain predictive information.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00724022 . Retrospectively registered July 2008.

Novel non-invasive biomarkers diagnostic of acute rejection in renal transplant recipients: A systematic review

BACKGROUND AND OBJECTIVES

Acute rejection is a significant complication detrimental to kidney transplant function. Current accepted means of diagnosis is percutaneous renal biopsy, a costly and invasive procedure. There is an urgent need to detect and validate non-invasive biomarkers capable of replacing the biopsy.

DESIGN, SETTING, PARTICIPANTS AND MEASUREMENTS

Comprehensive literature searches of Medline, EMBASE and Cochrane Central Register of Controlled Trials databases were performed. Eligible studies were included as per inclusion criteria and assessed for quality using the GRADE quality of evidence tool. Outcomes evaluated included biomarker diagnostic performance, number of patients/samples, mean age and gender ratio, immunosuppression regime, in addition to clinical applications of the biomarker(s) tested. PRISMA guidelines were followed. Where possible, statistical analysis of comparative performance data was performed.

RESULTS

23 studies were included in this review, including 19 adult, 3 paediatric and 1 mixed studies. A total of 2858 participants and 50 candidate non-invasive tests were identified. Sensitivity, specificity and area under the curve performance values ranged 36%-100%, 30%-100% and 0.55-0.98, respectively.

CONCLUSIONS

Although larger, more robust multi-centre validation studies are needed before non-invasive biomarkers can replace the biopsy, numerous candidate tests have demonstrated significant promise for various facets of postoperative management. Suggested uses include: ruling out patients with a low risk of acute rejection to avoid the need for biopsy, non-invasive testing where the biopsy is contraindicated and a prompt diagnosis is needed, and integration into a serial blood monitoring protocol in conjunction with serum creatinine.

Soluble HLA-DR serum levels are associated with smoking but not with acute coronary syndrome

BACKGROUND & AIMS

Elevated soluble HLA-DR (sHLA-DR) serum levels have been reported in HLA class II-associated inflammatory disorders. We have previously shown that the HLA class II allele HLA-DRB1*01 may predispose to acute coronary syndromes (ACS). To our knowledge, sHLA-DR serum levels have not been studied in ACS.

METHODS

sHLA-DR serum levels were measured in 477 ACS patients as cases and 475 area- and sex-matched controls by sandwich enzyme-linked immunosorbent assay. Binary logistic regression and ordinal logistic regression analyses adjusted for clinical parameters were conducted to evaluate the associations of sHLA-DR levels.

RESULTS

ACS patients had lower sHLA-DR serum levels compared to controls (OR = 0.837; 95% CI = 0.704-0.994; p = 0.043). After adjustment for smoking status, this association was no longer significant. This was explained by the notion that current smoking was inversely associated with sHLA-DR levels both in cases (OR = 0.592; 95% CI = 0.553-0.908; p = 0.016) and in controls (OR = 0.356; 95% CI = 0.226-0.563; p = 0.000010). A similar effect was not seen with other cardiovascular risk factors.

CONCLUSIONS

The results indicate, for the first time, that lower sHLA-DR levels are associated with smoking, but not with ACS. This is an important finding because previous studies of sHLA-DR have not accounted for the possible associations between smoking and sHLA-DR levels. Further studies are required to confirm these novel results and explore the mechanisms behind the observed associations.

Subclinical Rejection in Renal Transplantation: Reappraised

Short-term outcomes in renal transplantation have improved significantly in the past few years. However, the improvement in long-term outcomes has been modest. The reasons for graft failure beyond the first year of transplantation have been attributed to several different factors. We believe that subclinical rejection (SCR) may be 1 of the factors that contribute to graft loss in the long run. We also believe that there are data to suggest that SCR leads to progressive fibrosis and loss of graft function. This has been demonstrated even in patients who have mild degrees of subclinical inflammation. This review outlines the major studies that have been published on this important topic. It also outlines potential risk factors for the development of SCR. The current approach and diagnostic methods are discussed as well as their pros and cons. Newer noninvasive methods of diagnosis as well as molecular diagnostics and their merits and shortcomings are also discussed in some depth. Thus, the proposed state of the art review on SCR will create a renewed interest at all levels including transplant clinicians, transplant researchers, pharmaceutical industries as well as regulatory organizations.

A LASSO Method to Identify Protein Signature Predicting Post-transplant Renal Graft Survival

Identifying novel biomarkers to predict renal graft survival is important in post-transplant clinical practice. Serum creatinine, currently the most popular surrogate biomarker, offers limited information of the underlying allograft profiles. It is known to perform unsatisfactorily to predict renal function. In this paper, we apply a LASSO machine-learning algorithm in the Cox proportional hazards model to identify promising proteins that are associated with the hazard of allograft loss after renal transplantation, motivated by a clinical pilot study that collected 47 patients receiving renal transplants at the University of Michigan Hospital. We assess the association of 17 proteins previously identified by Cibrik et al. [5] with allograft rejection in our regularized Cox regression analysis, where the LASSO variable selection method is applied to select important proteins that predict the hazard of allograft loss. We also develop a post-selection inference to further investigate the statistical significance of the proteins on the hazard of allograft loss, and conclude that two proteins KIM-1 and VEGF-R2 are important protein markers for risk prediction.

Identification of a protein signature in renal allograft rejection

PURPOSE

Serum creatinine functions as a poor surrogate marker of renal allograft dysfunction and long-term graft survival. By measuring multiple proteins simultaneously in the serum of transplant patients, we can identify unique protein signatures of graft dysfunction.

EXPERIMENTAL DESIGN

We utilized training and validation cohorts composed of healthy and volunteer subjects, stable renal transplant patients, and renal transplant patients experiencing acute allograft rejection. Utilizing our antibody microarray, we measured 108 proteins simultaneously in these groups.

RESULTS

Using Mann-Whitney tests with Bonferroni correction, we identified ten serum proteins from 19 renal transplant patients with stable renal function, which are differentially expressed, compared to healthy control subjects. In addition, we identified 17 proteins that differentiate rejecting renal transplant recipients from stable renal transplant. Validation cohorts substantiated these findings.

CONCLUSION AND CLINICAL RELEVANCE

Our preliminary results support that a specific pattern of protein expression or "protein signature" may be able to differentiate between stable transplant patients from those with rejection. Future studies will focus on other etiologies of renal allograft dysfunction and the effect of treatment on protein expression and long-term outcome.

Biomarkers in native and transplant kidneys: opportunities to improve prediction of outcomes in chronic kidney disease

PURPOSE OF REVIEW

Predicting the outcomes of patients with chronic kidney disease (CKD) is important from both patient and healthcare system perspectives. This review examines the current state of conventional and nonconventional biomarkers as noninvasive tools to improve risk-stratification and outcome prediction in CKD.

RECENT FINDINGS

Conventional biomarkers (serum creatinine, urine albumin, and clinical variables such as sex, age, and diabetes) have been the cornerstone of most prediction models for CKD progression to end-stage renal disease (ESRD), and adverse cardiovascular outcomes including death. With better understanding of the pathophysiology of CKD and the evolution of molecular diagnostics, numerous novel or nonconventional markers have emerged. They have been examined individually and in combination to predict specific outcomes. We highlight these markers and studies, conducted primarily in patients with native kidneys. In those with transplant kidneys, markers of both acute and chronic kidney dysfunction have been examined, although to a lesser extent. Similarities and differences in knowledge derived from these two populations are highlighted.

SUMMARY

Improving prediction of outcomes in CKD patients with either native or transplant kidneys remains an important goal. Increasingly sophisticated biomarkers may potentially identify targets for clinical research, improve the nature and timing of therapeutic interventions, and guide resource allocation.

Serum neopterin as an indicator of increased risk of renal allograft rejection

Acute rejection remains associated with poor graft outcome. An early predictor of acute renal transplant rejection is the long sought after goal for transplant immunologists. In this study we measured levels of serum neopterin at day 5 post-transplant in a cohort of 216 consecutive renal allograft recipients, and compared this with serum creatinine and acute rejection episodes during the first year post transplant. We compared serum neopterin in recipients from living donors (LD), donors after brain death (DBD) and donors after cardiac death (DCD). In all cases higher neopterin levels were correlated with acute rejection in the first year post transplant, but this was only significant in recipients of DCD kidneys who suffered acute cellular or vascular rejection (p=0.04, odds ratio 1.08, 95% CI 1.003-1.012). The neopterin/creatinine ratio, which takes into account the effect of kidney function on circulating neopterin levels, was significantly higher for all recipients who suffered biopsy proven cellular or vascular rejection in the first year post transplant, compared to all other patients (p=0.001, for an increase of 0.1, odds ratio=1.64, 95% CI 1.21-2.20). The ability to use non-invasive biomarkers in the transplant recipient has the potential to increase transplant survival for these patients.

Analysis of urine sediment for cytology and antigen expression in acute renal allograft rejection: an alternative to renal biopsy

Acute rejection in renal transplant recipients is diagnosed by renal biopsy at an advanced disease stage. There is no modality for sequential monitoring of graft status. We studied the role of urine cytology in predicting acute cellular rejection (ACR) and its ability to correctly diagnose ACR and differentiate it from drug toxicity (DT). Urine samples from 203 renal transplant recipients were studied to determine the cellular composition using cytology and immunocytochemistry for HLA-DR, intercellular adhesion molecule (ICAM)-1, and interleukin (IL)-2R. In a 3-month follow-up period, there were 36 episodes of graft dysfunction, of which 28 occurred due to ACR and 8 due to DT. The cytology results showed a significantly increased percentage of lymphocytes and polymorphonuclear cells in samples obtained before and during the clinical manifestations of ACR. A greater level of expression of antigens was observed before and during ACR. The use of IL2-R-, ICAM-1-, and HLA class II-specific monoclonal antibodies gave very high specificity, sensitivity, and positive predictive values in diagnosing rejection through urine cytology, suggesting that routine cytology along with immunocytochemistry of urine sediment has clinical potential for early diagnosis and management of ACR and DT.

Hypoxia increases membranal and secreted HLA-DR in endothelial cells, rendering them T-cell activators

Transplantation involves preoperative ischemic periods that contribute to endothelial cell (EC) dysfunction and T-cell activation, leading to graft rejection. As hypoxia is a major constituent of ischemia, we evaluated its effect on the ability of ECs to express HLA-DR, which is required for presentation of antigens to T cells, and by itself serves as an important target for allogeneic T cells. Primary human umbilical vein ECs (HUVEC) and the human endothelial cell line EaHy926 were incubated in normoxia or hypoxia (PO(2) < 0.3%). Hypoxia increased the membranal expression (by 4-6 fold, P < 0.01) and secretion (by sixfold, P < 0.05) of HLA-DR protein, without influencing the accumulation of its mRNA. Alternative splicing, attenuated trafficking, or shedding from the plasma membrane were not observed, but the lysosomal inhibitor bafilomycin A1 reduced HLA-DR secretion. Hypoxia-induced endothelial HLA-DR elevated and diminished the secretion of IL-2 and IL-10, respectively, from co-cultured allogeneic CD4(+) T cells in a HLA-DR-dependent manner, as demonstrated by the use of monoclonal anti-HLA-DR. Our results indicate a yet not fully understood post-translational mechanism(s), which elevate both membranal and soluble HLA-DR expression. This elevation is involved in allogeneic T-cell activation, highlighting the pivotal role of ECs in ischemia/hypoxia-associated injury and graft rejection.

Identifying biomarkers as diagnostic tools in kidney transplantation

There is a critical need for biomarkers for early diagnosis, treatment response, and surrogate end point and outcome prediction in organ transplantation, leading to a tailored and individualized treatment. Genomic and proteomic platforms have provided multiple promising new biomarkers during the last few years. However, there is still no routine application of any of these markers in clinical transplantation. This article will discuss the existing gap between biomarker discovery and clinical application in the kidney transplant setting. Approaches to implementing biomarker monitoring into clinical practice will also be discussed.

Review: Serum and urine biomarkers of kidney disease: A pathophysiological perspective

The use of reliable biomarkers is becoming increasingly important for the improved management of patients with acute and chronic kidney diseases. Recent developments have identified a number of novel biomarkers in serum or urine that can determine the potential risk of kidney damage, distinguish different types of renal injury, predict the progression of disease and have the potential to assess the efficacy of therapeutic intervention. Some of these biomarkers can be used independently while others are more beneficial when used in combination with knowledge of other clinical risk factors. Advances in gene expression analysis, chromatography, mass spectrometry and the development of sensitive enzyme-linked immunosorbent assays have facilitated accurate quantification of many biomarkers. This review primarily focuses on describing new and established biomarkers, which identify and measure the various pathophysiological processes that promote kidney disease. It provides an overview of some of the different classes of renal biomarkers that can be assessed in serum/plasma and urine, including markers of renal function, oxidative stress, structural and cellular injury, immune responses and fibrosis. However, it does not explore the current status of these biomarkers in terms of their clinical validation.

Serum and Urinary Biomarkers Determination and Their Significance in Diagnosis of Kidney Diseases

Chronic kidney disease (CKD) is becoming a major public health problem worldwide due to the epidemic increase of patients on renal replacement therapy and their high cardiovascular morbidity and mortality. The only effective approach to this problem is prevention and early detection of CKD. In addition, despite significant improvements in therapeutics, the mortality and morbidity associated with acute kidney injury (AKI) remain high. A major reason for this is the lack of early markers for AKI, and hence an unacceptable delay in initiating therapy. Therefore, there is a pressing need to develop biomarkers (proteins and other molecules in the blood or urine) for renal disease, which might assist in diagnosis and prognosis and might provide endpoints for clinical trials of drugs designed to slow the progression of renal insufficiency. Besides serum creatinine, promising novel biomarkers for AKI include a plasma panel (neutrophil gelatinase-associated lipocalin-NGAL and cystatin C) and a urine panel (NGAL, kidney injury molecule-1, interleukin-18, cystatin C, alpha 1-microglobulin, Fetuin-A, Gro-alpha, and meprin). For CKD, these include a similar plasma panel and a urine panel (NGAL, asymmetric dimethylarginine, and liver-type fatty acid-binding protein). Increased plasma and urinary TGF-β1 levels might contribute to the development of chronic tubulointerstitial disease, indicating the possible therapeutic implications. Furthermore, to differentiate lower urinary tract infection and pyelonephritis interleukin-6 and serum procalcitonin levels were introduced. It will be important in future studies to validate the sensitivity and specificity of these biomarker panels in clinical samples from large cohorts and in multiple clinical situations.