Gene expression signature of tolerance and lymphocyte subsets in stable renal transplants: Results of a cross-sectional study

A Machine Learning Analysis of Prognostic Genes Associated With Allograft Tolerance After Renal Transplantation

In this study, we aimed to identify transplantation tolerance (TOL)-related gene signature and use it to predict the different types of renal allograft rejection performances in kidney transplantation. Gene expression data were obtained from the Gene Expression Omnibus (GEO) database, differently expressed genes (DEGs) were performed, and the gene ontology (GO) function enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis were also conducted. The machine learning methods were combined to analyze the feature TOL-related genes and verify their predictive performance. Afterward, the gene expression levels and predictive performances of TOL-related genes were conducted in the context of acute rejection (AR), chronic rejection (CR), and graft loss through heatmap plots and the receiver operating characteristic (ROC) curves, and their respective immune infiltration results were also performed. Furthermore, the TOL-related gene signature for graft survival was conducted to discover gene immune cell enrichment. A total of 25 TOL-related DEGs were founded, and the GO and KEGG results indicated that DEGs mainly enriched in B cell-related functions and pathways. 7 TOL-related gene signature was constructed and performed delightedly in TOL groups and different types of allograft rejection. The immune infiltration analysis suggested that gene signature was correlated with different types of immune cells. The Kaplan-Meier (KM) survival analysis demonstrated that BLNK and MZB1 were the prognostic TOL-related genes. Our study proposed a novel gene signature that may influence TOL in kidney transplantation, providing possible guidance for immunosuppressive therapy in kidney transplant patients.

Effect of Kidney Transplantation on Accelerated Immunosenescence and Vascular Changes Induced by Chronic Kidney Disease

Kidney transplantation is the best option for patients with end-stage renal disease. Despite the improvement in cardiovascular burden (leading cause of mortality among patients with chronic kidney disease), cardiovascular adverse outcomes related to the inflammatory process remain a problem. Thus, the aim of the present study was to characterize the immune profile and microvesicles of patients who underwent transplantation. We investigated the lymphocyte phenotype (CD3, CD4, CD8, CD19, and CD56) and monocyte phenotype (CD14, CD16, CD86, and CD54) in peripheral blood, and endothelium-derived microvesicles (annexin V+CD31+CD41–) in plasma of patients with advanced chronic kidney disease (n = 40), patients with transplantation (n = 40), and healthy subjects (n = 18) recruited from the University Hospital “12 de Octubre” (Madrid, Spain). Patients with kidney transplantation had B-cell lymphopenia, an impairment in co-stimulatory (CD86) and adhesion (CD54) molecules in monocytes, and a reduction in endothelium-derived microvesicles in plasma. The correlations between those parameters explained the modifications in the expression of co-stimulatory and adhesion molecules in monocytes caused by changes in lymphocyte populations, as well as the increase in the levels of endothelial-derived microvesicles in plasma caused by changes in lymphocyte and monocytes populations. Immunosuppressive treatment could directly or indirectly induce those changes. Nevertheless, the particular characteristics of these cells may partly explain the persistence of cardiovascular and renal alterations in patients who underwent transplantation, along with the decrease in arteriosclerotic events compared with advanced chronic kidney disease. In conclusion, the expression of adhesion molecules by monocytes and endothelial-derived microvesicles is related to lymphocyte alterations in patients with kidney transplantation.

B cells in transplant tolerance and rejection: friends or foes?

Our understanding of the role of B cells in organ transplantation remains incomplete and continues to grow. The majority of research has focused on the detrimental role of antibodies that drive the development of pathogenesis of the transplanted organ. However, it has been shown that not all donor-specific antibodies are harmful and in some circumstances can even promote tolerance through the mechanism of accommodation. Furthermore, B cells can have effects on transplanted organs through their interaction with T cells, namely antigen presentation, cytokine production, and costimulation. More recently, the role and importance of Bregs was introduced to the field of transplantation. Due to this functional and ontogenetic heterogeneity, targeting B cells in transplantation may bring undesired immunologic side effects including increased rejection. Therefore, the selective control of B cells that contribute to the humoral response against donor antigens will continue to be an important and challenging area of research and potentially lead to improved long-term transplant outcomes.

Continuous function of 80 primary renal allografts for 30-47 years with maintenance prednisone and azathioprine/mycophenolate mofetil therapy: A clinical mosaic of long-term successes

Eighty primary renal allograft recipients, 61 living-related and 19 deceased donor, transplanted from 1963 through 1984 had continuous graft function for 30-47 years. They were treated with three different early immunosuppression programs (1963-1970: thymectomy, splenectomy, high oral prednisone; 1971-1979: divided-dose intravenous methylprednisolone; and 1980-1984: antilymphocyte globulin) each with maintenance prednisone and azathioprine, and no calcineurin inhibitor. Long-term treatment often included the anti-platelet medication, dipyridamole. Although both recipient and donor ages were young (27.2 ± 9.5 and 33.1 ± 12.0 years, respectively), six recipients with a parent donor had >40-year success. At 35 years, death-censored graft survival was 85.3% and death with a functioning graft 84.2%; overall graft survival was 69.5% (Kaplan-Meier estimate). Biopsy-documented early acute cellular and highly probable antibody-mediated rejections were reversed with divided-dose intravenous methylprednisolone. Complications are detailed in an integrated timeline. Hypogammaglobulinemia identified after 20 years doubled the infection rate. An association between a monoclonal gammopathy of undetermined significance and non-plasma-cell malignancies was identified. Twenty-seven azathioprine-treated patients tested after 37 years had extremely low levels of T1/T2 B lymphocytes representing a "low immunosuppression state of allograft acceptance (LISAA)". The lifetime achievements of these patients following a single renal allograft and low-dose maintenance immunosuppression are remarkable. Their success evolved as a clinical mosaic.

Development and validation of the first consensus gene-expression signature of operational tolerance in kidney transplantation, incorporating adjustment for immunosuppressive drug therapy

BACKGROUND

Kidney transplant recipients (KTRs) with "operational tolerance" (OT) maintain a functioning graft without immunosuppressive (IS) drugs, thus avoiding treatment complications. Nevertheless, IS drugs can influence gene-expression signatures aiming to identify OT among treated KTRs.

METHODS

We compared five published signatures of OT in peripheral blood samples from 18 tolerant, 183 stable, and 34 chronic rejector KTRs, using gene-expression levels with and without adjustment for IS drugs and regularised logistic regression.

FINDINGS

IS drugs explained up to 50% of the variability in gene-expression and 20-30% of the variability in the probability of OT predicted by signatures without drug adjustment. We present a parsimonious consensus gene-set to identify OT, derived from joint analysis of IS-drug-adjusted expression of five published signature gene-sets. This signature, including CD40, CTLA4, HSD11B1, IGKV4-1, MZB1, NR3C2, and RAB40C genes, showed an area under the curve 0⋅92 (95% confidence interval 0⋅88-0⋅94) in cross-validation and 0⋅97 (0⋅93-1⋅00) in six months follow-up samples.

INTERPRETATION

We advocate including adjustment for IS drug therapy in the development stage of gene-expression signatures of OT to reduce the risk of capturing features of treatment, which could be lost following IS drug minimisation or withdrawal. Our signature, however, would require further validation in an independent dataset and a biomarker-led trial.

FUNDING

FP7-HEALTH-2012-INNOVATION-1 [305147:BIO-DrIM] (SC,IR-M,PM,DSt); MRC [G0801537/ID:88245] (MPH-F); MRC [MR/J006742/1] (IR-M); Guy's&StThomas' Charity [R080530]&[R090782]; CONICYT-Bicentennial-Becas-Chile (EN-L); EU:FP7/2007-2013 [HEALTH-F5-2010-260687: The ONE Study] (MPH-F); Czech Ministry of Health [NV19-06-00031] (OV); NIHR-BRC Guy's&StThomas' NHS Foundation Trust and KCL (SC); UK Clinical Research Networks [portfolio:7521].

Validation Study of an Operational Tolerance Signature in Korean Kidney Transplant Recipients

Operational tolerance (OT), defined as maintaining stable graft function without immunosuppression after transplant surgery, is an ideal goal for kidney transplant recipients (KTRs). Recent investigations have demonstrated the distinctive features of B cells, T cells, and dendritic cell-related gene signatures and the distributions of circulating lymphocytes in these patients; nonetheless, substantial heterogeneities exist across studies. This study was conducted to determine whether previously reported candidate gene biomarkers and the profiles of lymphocyte subsets of OT could be applied in Korean KTRs. Peripheral blood samples were collected from 153 patients, including 7 operationally tolerant patients. Quantitative real-time PCR and flow cytometry were performed to evaluate gene expression and lymphocyte subsets, respectively. Patients with OT showed significantly higher levels of B cell-related gene signatures (IGKV1D-13 and IGKV4-1), while T cell-related genes (TOAG-1) and dendritic cell-related genes (BNC2, KLF6, and CYP1B1) were not differentially expressed across groups. Lymphocyte subset analyses also revealed a higher proportion of immature B cells in this group. In contrast, the distributions of CD4⁺ T cells, CD8⁺ T cells, mature B cells, and memory B cells showed no differences across diagnostic groups. An OT signature, generated by the integration of IGKV1D-13, IGKV4-1, and immature B cells, effectively discriminated patients with OT from those in other diagnostic groups. Finally, the OT signature was observed among 5.6% of patients who had stable graft function for more than 10 years while on immunosuppression. In conclusion, we validated an association of B cells and their related signature with OT in Korean KTRs.

Steroid regulation: An overlooked aspect of tolerance and chronic rejection in kidney transplantation

Steroid conversion (HSD11B1, HSD11B2, H6PD) and receptor genes (NR3C1, NR3C2) were examined in kidney-transplant recipients with "operational tolerance" and chronic rejection (CR), independently and within the context of 88 tolerance-associated genes. Associations with cellular types were explored. Peripheral whole-blood gene-expression levels (RT-qPCR-based) and cell counts were adjusted for immunosuppressant drug intake. Tolerant (n = 17), stable (n = 190) and CR patients (n = 37) were compared. Healthy controls (n = 14) were used as reference. The anti-inflammatory glucocorticoid receptor (NR3C1) and the cortisol-activating HSD11B1 and H6PD genes were up-regulated in CR and were lowest in tolerant patients. The pro-inflammatory mineralocorticoid gene (NR3C2) was downregulated in stable and CR patients. NR3C1 was associated with neutrophils and NR3C2 with T-cells. Steroid conversion and receptor genes, alone, enabled classification of tolerant patients and were major contributors to gene-expression signatures of both, tolerance and CR, alongside known tolerance-associated genes, revealing a key role of steroid regulation and response in kidney transplantation.

B cells in operational tolerance

Transplantation is currently the therapy of choice for endstage organ failure even though it requires long-term immunosuppresive therapy, with its numerous side effects, for acceptance of the transplanted organ. In rare cases however, patients develop operational tolerance, that is, graft survival without immunosuppression. Studies conducted on these patients reveal genetic, phenotypic, and functional signatures. They provide a better understanding of the immunological mechanisms involved in operational tolerance and define biomarkers that could be used to adapt immunosuppressive treatment to the individual, safely reduce immunosuppression doses, and ideally and safely guide immunosuppression withdrawal. This review summarizes studies that suggest a role for B cells as biomarkers of operational tolerance and discusses the use of B cells as a predictive tool for immunologic risk.

Messengers of tolerance

The use of immunosuppressant drugs after organ transplantation has brought great success in the field of organ transplantation with respect to short-term outcome. However, major challenges (i.e., limited improvement of long-term survival, immunosuppressant toxicity, infections and carcinoma) demand alternate treatment approaches that minimizes the use of immunosuppressants. Interestingly, few studies have identified groups of transplant patients who developed operational tolerance and thereby keep their allograft without complications in absence of immunosuppressants. These rare groups of patients are of particular interest as study subjects for understanding mechanisms of graft tolerance that could be leveraged in future for inducing tolerance and for understanding mechanisms involved in improving long-term allograft outcomes. Also, biomarkers from these studies could benefit the larger transplant population by their application in immunosuppressant tailoring and identification of tolerant patients among patients with stably functioning allografts. This review compiles several gene expression studies performed in samples from tolerant patients in different solid organ transplantations to identify key genes and associated molecular pathways relevant to tolerance. This review is aimed at putting forth all this important work done thus far and to identify research gaps that need to be filled, in order to achieve the greater purpose of these studies.

Intragraft Molecular Pathways Associated with Tolerance Induction in Renal Transplantation

The modern immunosuppression regimen has greatly improved short-term allograft outcomes but not long-term allograft survival. Complications associated with immunosuppression, specifically nephrotoxicity and infection risk, significantly affect graft and patient survival. Inducing and understanding pathways underlying clinical tolerance after transplantation are, therefore, necessary. We previously showed full donor chimerism and immunosuppression withdrawal in highly mismatched allograft recipients using a bioengineered stem cell product (FCRx). Here, we evaluated the gene expression and microRNA expression profiles in renal biopsy samples from tolerance-induced FCRx recipients, paired donor organs before implant, and subjects under standard immunosuppression (SIS) without rejection and with acute rejection. Unlike allograft samples showing acute rejection, samples from FCRx recipients did not show upregulation of T cell- and B cell-mediated rejection pathways. Gene expression pathways differed slightly between FCRx samples and the paired preimplantation donor organ samples, but most of the functional gene networks overlapped. Notably, compared with SIS samples, FCRx samples showed upregulation of genes involved in pathways, like B cell receptor signaling. Additionally, prediction analysis showed inhibition of proinflammatory regulators and activation of anti-inflammatory pathways in FCRx samples. Furthermore, integrative analyses (microRNA and gene expression profiling from the same biopsy sample) identified the induction of regulators with demonstrated roles in the downregulation of inflammatory pathways and maintenance of tissue homeostasis in tolerance-induced FCRx samples compared with SIS samples. This pilot study highlights the utility of molecular intragraft evaluation of pathways related to FCRx-induced tolerance and the use of integrative analyses for identifying upstream regulators of the affected downstream molecular pathways.

Immune monitoring in renal transplantation: The search for biomarkers

It is now widely accepted that in order to improve long-term graft function and survival, a more personalized immunosuppressive treatment of transplant patients according to the individual anti-donor immune response status is needed. This applies to the identification of potentially "high-risk" patients likely to develop acute rejection episodes or display an accelerated decline of graft function, patients who might need immunosuppression intensification, and operationally tolerant patients suitable for immunosuppression minimization or weaning off. Such a patient stratification would benefit from biomarkers, which enable categorization into low and high risk or, ideally, identification of operational tolerant patients. Here, we report on recent developments regarding identification and performance analysis of noninvasive biomarkers such as mRNA and miRNA expression profiles, chemokines, or changes in immune cell subsets in either blood or urine of renal transplant patients. We will also discuss which future steps are needed to accelerate their clinical implementation.

Operational tolerance in kidney transplantation and associated biomarkers

In the 1960s, our predecessors won a historical battle against acute rejection and ensured that transplantation became a common life-saving treatment. In parallel with this success, or perhaps because of it, we lost the battle for long-lived transplants, being overwhelmed with chronic immune insults and the toxicities of immunosuppression. It is likely that current powerful treatments block acute rejection, but at the same time condemn the few circulating donor cells that would have been able to elicit immunoregulatory host responses towards the allograft. Under these conditions, spontaneously tolerant kidney recipients - i.e. patients who maintain allograft function in the absence of immunosuppression - are merely accidents; they are scarce, mysterious and precious. Several teams pursue the goal of finding a biomarker that would guide us towards the 'just right' level of immunosuppression that avoids rejection while leaving some space for donor immune cells. Some cellular assays are attractive because they are antigen-specific, and provide a comprehensive view of immune responses toward the graft. These seem to closely follow patient regulatory capacities. However, these tests are cumbersome, and require abundant cellular material from both donor and recipient. The latest newcomers, non-antigen-specific recipient blood transcriptomic biomarkers, offer the promise that a practicable and simple signature may be found that overcomes the complexity of a system in which an infinite number of individual cell combinations can lead possibly to graft acceptance. Biomarker studies are as much an objective - identifying tolerant patients, enabling tolerance trials - as a means to deciphering the underlying mechanisms of one of the most important current issues in transplantation.

Steroid free immunosuppression is associated with enhanced Th1 transcripts in kidney transplantation

BACKGROUND

Steroid avoidance in immunosuppression in kidney transplantation offers several metabolic advantages, however it is associated with higher early acute rejection rate. Cellular and molecular mechanisms of this phenomenon remain poorly understood.

METHODS

In this single center observational study, low-risk kidney transplant recipients randomized into large multicenter prospective ADVANCE trial with steroid avoidance/early withdrawal and center standard of care treated patients were monitored for 12months. The expressions of 28 transcripts, associated with alloimmune response and operational tolerance, were evaluated in the peripheral blood using RT-qPCR at 0, 7, 14, 90 and 365 postoperative days (POD) and in the protocol graft biopsy at 3months while lymphocyte subpopulations were analyzed by flow-cytometry within the follow-up.

RESULTS

Both steroid avoidance and withdrawal regimens were associated with significantly higher granzyme B (GZMB) transcript at POD 14 and perforin 1 (PRF1) transcript at POD 7. The higher interleukin 2 (IL-2) expression at POD 7 was detected only in the steroid avoidance group. Initial steroids decreased the expression SH2D1B transcript at POD14 and there were no further differences in other operational tolerance transcripts among groups. The statistically significant decrease in absolute numbers of peripheral NK cells in the first 14days was observed in the standard of care group only. There were no differences in analyzed intrarenal transcripts in 3-month biopsies among groups.

CONCLUSIONS

The enhanced expression of some of Th1 associated transcripts and limited effects on NK cells of steroid avoidance immunosuppression suggest higher susceptibility for early acute rejection.

Regulatory B cells: Phenotype, function and role in transplantation

While B cells are traditionally known for their roles in antibody production, antigen presentation and cytokine production, recent studies have highlighted the existence of B cells with regulatory properties, which have been termed Bregs, analogous to regulatory T cells (Tregs). Bregs have been found to play a role in autoimmune disease, malignancies, infections, and may also be involved in solid organ transplantation. Their main mechanism of action is by promoting the development of Tregs while suppressing effector CD4⁺ and CD8⁺ T cells, primarily by IL-10 secretion. In the field of transplantation evidence for an active role of Bregs is scarce. While the presence of Bregs has been associated with improved graft survival and operational tolerance in kidney transplant recipients, these findings are not without controversy. Since the majority of fundamental research on Bregs has been performed in the fields in autoimmunity and infectious diseases, we will first focus on what these fields taught us on basic Breg biology, after which the relevance for the transplant setting is discussed.

Application of Operational Tolerance Signatures Are Limited by Variability and Type of Immunosuppression in Renal Transplant Recipients: A Cross-Sectional Study

Supplemental digital content is available in the text.

Background

Renal transplant recipients (RTR) frequently develop complications relating to chronic immunosuppression. Identifying RTR who could safely reduce immunosuppression is therefore highly desirable. We hypothesized that “signatures” described in RTR who have stopped immunosuppression but maintained stable graft function (“operational tolerance”) may enable identification of immunosuppressed RTR who are candidates for immunosuppression minimization. However, the effect of immunosuppression itself on these signatures and circulating B-cell populations is currently unknown.

Methods

We undertook a cross-sectional study of 117 RTR to assess the effect of immunosuppression upon circulating B cell populations, humoral alloresponse and 2 previously published “signatures” of operational tolerance.

Results

Immunosuppression associated with alterations in both published “signatures.” Azathioprine associated with a decrease in transitional and naive B-cell numbers and calcineurin inhibition associated with an increase in the number of circulating plasmablasts. However, only azathioprine use associated with the presence of donor-specific anti-HLA IgG antibodies. Calcineurin inhibition associated with an increase in total serum IgM but not IgG. Data were corrected for age, time since last transplant, and other immunosuppression.

Conclusions

Current signatures of operational tolerance may be significantly affected by immunosuppressive regimen, which may hinder use in their current form in clinical practice. Calcineurin inhibition may prevent the development of long-lasting humoral alloresponses, whereas azathioprine therapy may be associated with donor specific antibody development.

Biomarkers of Tolerance in Kidney Transplantation: Are We Predicting Tolerance or Response to Immunosuppressive Treatment?

We and others have previously described signatures of tolerance in kidney transplantation showing the differential expression of B cell-related genes and the relative expansions of B cell subsets. However, in all of these studies, the index group-namely, the tolerant recipients-were not receiving immunosuppression (IS) treatment, unlike the rest of the comparator groups. We aimed to assess the confounding effect of these regimens and develop a novel IS-independent signature of tolerance. Analyzing gene expression in three independent kidney transplant patient cohorts (232 recipients and 14 tolerant patients), we have established that the expression of the previously reported signature was biased by IS regimens, which also influenced transitional B cells. We have defined and validated a new gene expression signature that is independent of drug effects and also differentiates tolerant patients from healthy controls (cross-validated area under the receiver operating characteristic curve [AUC] = 0.81). In a prospective cohort, we have demonstrated that the new signature remained stable before and after steroid withdrawal. In addition, we report on a validated and highly accurate gene expression signature that can be reliably used to identify patients suitable for IS reduction (approximately 12% of stable patients), irrespective of the IS drugs they are receiving. Only a similar approach will make the conduct of pilot clinical trials for IS minimization safe and hence allow critical improvements in kidney posttransplant management.

Fingerprints of transplant tolerance suggest opportunities for immunosuppression minimization

HLA incompatible organ transplant tolerance is the holy grail of transplantation. Stable engraftment of an HLA mismatched allograft and life-long tolerance induction, though feasible in highly selected cohorts with depletional protocols, is not ready for generalized application to the entire transplant recipient pool. It has thus been important to harness biomarkers that can uncover mechanisms and tools for monitoring HLA mismatched recipients that develop a state of operational tolerance, during accidental immunosuppression withdrawal secondary to problems of over-immunosuppression (infection or malignancy) or toxicity (mostly cosmetic or cardiovascular). A restricted and unpredictable group of patients can demonstrate a clinical state of operational tolerance, manifested by state of stable graft function of a graft with HLA mismatches between recipient and donor, intact immune responses to third party antigens and no measurable immunosuppression. These patients have served as the basis for the discovery of clinically correlative biomarkers, in distal biofluids (mainly blood), that can define the existing state of operational clinical tolerance. Operationally tolerant patients are rare, as withdrawal of immunosuppression most often results in rejection and graft loss. Nevertheless, operationally tolerant kidney, liver and heart allograft recipients have been reported. The presence of similar biomarker signature profiles in HLA mismatched transplant recipients on immunosuppression, suggests the feasibility of utilizing these biomarkers for educated immunosuppression minimization with a view to retaining immunological quiescence, while reducing the maintenance immunosuppression burden to a "safe" alloimmune threshold. Though clinical operational tolerance is rare, as immunosuppression cessation most often results in increased alloimmunity and rejection, the biomarker profile studies that have harnessed whole genome profiling suggest that the frequency of this state may be ~8% in kidney allograft recipients, and even more frequent in pediatric recipients and in liver transplantation: 25% in adult liver allograft recipients and ~60% in pediatric liver allograft recipients. In this review we discuss putative molecular mechanisms, cellular players and correlative biomarkers that have been developed through clinically associative studies of tolerant and non-tolerant patients. Through mechanisms of carefully constructed and monitored randomized, prospective clinical trials, the transplant community stands at the cusp of improved quality of recipient life through educated immunosuppression minimization.

Kidney Transplantation Among the Elderly: Challenges and Opportunities to Improve Outcomes

Elderly patients (>65 years old) represent the fastest growing population among the ESRD patients and those awaiting kidney transplantation. There is ample evidence to suggest that kidney transplant in the elderly population offers the best chance of survival and improves health-related quality of life compared to remaining on dialysis. Although all these emerging facts are encouraging, this population brings with them complex medical problems including frailty, cognitive impairment, and multiple comorbidities. These issues can be barriers to transplantation and threaten the well-being of the patients after transplantation. Furthermore, aging results in changes to the immune system and affects the pharmacokinetics of immunosuppressants. All these changes can increase risk of complications such as infections and malignancy. Because death with a functioning graft is a common cause of graft loss, the new kidney allocation system has been implemented in an attempt to maximize allograft utilization and minimize unrealized graft years. This may result in longer wait-times for the elderly. In this review, we will highlight the barriers to kidney transplant, characterize transplant-related issues in the elderly, and propose alternative strategies under the new allocation system.

CD8+ Immunosenescence Predicts Post-Transplant Cutaneous Squamous Cell Carcinoma in High-Risk Patients

Most morbidity associated with malignancy in long-term renal transplant recipients is due to cutaneous squamous cell carcinoma (SCC). Previously identified measures to stratify SCC risk have limited use, however. We hypothesized that an increased proportion of senescent, terminally differentiated CD8(+) T cells would identify renal transplant recipients at elevated SCC risk. Peripheral blood lymphocytes were isolated from 117 stable transplant recipients at high risk of SCC and analyzed phenotypically by flow cytometry. Participants were followed up prospectively for SCC development. The predictive value of variables was assessed using Cox regression. Age at transplant and enrollment, dialysis duration, and previous disease were predictive of SCC development during follow-up. Previously published clinical phenotype-based risk scores lost predictive value with the removal of age as a covariate. The percentage of CD57-expressing CD8(+) T cells was the strongest immunologic predictor of future SCC and correlated with increasing CD8(+) T cell differentiation. We dichotomized participants into those with a majority (CD57hi) and a minority (CD57lo) of CD8(+) T cells expressing CD57; CD57hi participants were more likely to develop SCC during follow-up (hazard ratio, 2.9; 95% confidence interval, 1.0 to 8.0), independent of potential confounders, and tended to develop earlier recurrence. The CD57hi phenotype was stable with time and associated with increasing age and cytomegalovirus seropositivity. Our results show that the CD57hi phenotype is a strong predictor of SCC development and recurrence in this cohort of long-term, high-risk renal transplant recipients. This information may allow identification of recipients who may benefit from intensive dermatologic screening and immunosuppression reduction.

Tolerance signatures in transplant recipients

PURPOSE OF REVIEW

The intent of this review was to describe biomarkers that predict or identify individuals who exhibit tolerance to a transplanted organ. The identification of tolerance biomarkers would spare some individuals the toxicity of immunosuppressive agents, enhance the safety of studies to induce tolerance, and provide insights into mechanisms of tolerance that may aid in designing new regimens.

RECENT FINDINGS

Studies of tolerant kidney transplant recipients have revealed an association with B cells. More recent studies have suggested that these B cells may be less mature than from those in nontolerant recipients, and especially suited to suppress alloimmune responses. Biomarkers in tolerant liver transplant patients appear to be distinct from those associated renal tolerance. Most reports have identified an association with natural killer and/or γδ T cells rather than B cells. Recent data indicate biomarkers associated with iron homeostasis within the transplanted liver more accurately predict the tolerant state than do biomarkers expressed in the blood, suggesting that the renal allograft itself, which is infrequently sampled, would be informative.

SUMMARY

Given the encouraging progress in identifying tolerance biomarkers, it will be important to validate these markers in larger studies of transplant recipients undergoing prospective minimization or withdrawal of immunosuppression.

Circulating biomarkers of tolerance

On the basis of reviewed literature here we describe models of tolerance and summarize the evidence of circulating biomarkers suitable for the assessment of immunological risk in organ transplantation. We focused on results of evaluation of specific peripheral immune cell populations and transcripts in peripheral blood of operationally tolerant liver and kidney transplant recipients. Validation of described markers to define potentially tolerant patients before their use in clinical trials is critical.