Blood biomarkers of kidney transplant rejection, an endless search?

Characterization of immune phenotypes in peripheral blood of adult renal transplant recipients using mass cytometry (CyTOF)

Chronic immunosuppressive therapies are crucial in organ transplantation but can increase the risk of opportunistic infections and cancer over time. We investigated immune status changes in 10 kidney transplant patients and 11 age-matched healthy adults using broad in vitro stimulation of subject-derived peripheral blood mononuclear cells followed by mass cytometry by time of flight over 6 mo. Overall, the immune cells of transplant patients exhibited increased CD8+ T cell activation and differentiation compared with healthy donors, with elevated CD8+ CD57+, MIP-1β, and interferon γ production (P < 0.05, P < 0.05, and P < 0.01, respectively). CD107a and granzyme B expression were increased in CD8+ T cells and CD56bright natural killer cells (P < 0.05 and P < 0.01, respectively), while T regulatory cells had decreased interleukin-10 production (P < 0.05). These changes indicated a proinflammatory environment influenced by induction therapy and ongoing maintenance drugs. Additionally, transplant recipients displayed signs of immune modulation, including decreased tumor necrosis factor α, interferon γ, and MIP-1β expression in γδT cells (P < 0.05 and P < 0.01), and reduced interleukin-17 and granulocyte-macrophage colony-stimulating factor expression in CD8+ T memory cell subsets (P < 0.05). The diverse functional changes underscore the importance of comprehensive immune status profiling for optimizing individual treatment strategies and developing better immunosuppressants that specifically target activated cell populations.

Relationship Between CXCL11, CXCL13, CCL2, and CCL5 Gene Expression Levels and Allograft Function in Patients Undergoing Renal Transplant

OBJECTIVES

Chemokines are inflammatory mediators directly involved in immunological mechanisms that mediate alloimmune responses; recently, gene expression analysis studies have aroused great interest in the field of transplantation. We aimed to evaluate the predictive role of chemokine gene expression in rejection in renal transplant patients.

MATERIALS AND METHODS

Our study included 91 patients who underwent living-related renal transplant. Gene expression levels of chemokines were evaluated in urine samples collected preoperatively and postoperatively. Patients were followed up frequently in the clinic, and the relationship between chemokine levels and the development of acute rejection was investigated.

RESULTS

The CXCL11 and CXCL13 gene expression levels at day 1 (P = .018 and P = .037), day 7 (P = .021 and P = .041), and month 1 (P = .039 and P = .039) after renal transplant were significantly higher in patients with acute rejection. CCL2 gene expression level was significantly higher in the group with acute rejection on day 1 (P = .038) and day 7 (P = .014) posttransplant. CCL5 expression level was higher in the group with acute rejection only on day 7 posttransplant (P = .027).

CONCLUSIONS

Follow-up of allograft function after renal transplant is of utmost importance. CXCL11, CXCL13, CCL2, and CCL5 gene expression levels may have roles in immune monitoring as they seem to have a potential to predict rejection.

Peripheral blood immune cell profiling of acute corneal transplant rejection

Acute rejection (AR) of corneal transplants (CT) has a profound effect on subsequent graft survival but detailed immunological studies in human CT recipients are lacking. In this multi-site, cross-sectional study, clinical details and blood samples were collected from adults with clinically diagnosed AR of full-thickness (FT)-CT (n = 35) and posterior lamellar (PL)-CT (n = 21) along with Stable CT recipients (n = 177) and adults with non-transplanted corneal disease (n = 40). For those with AR, additional samples were collected 3 months later. Immune cell analysis was performed by whole-genome microarrays (whole blood) and high-dimensional multi-color flow cytometry (peripheral blood mononuclear cells). For both, no activation signature was identified within the B cell and T cell repertoire at the time of AR diagnosis. Nonetheless, in FT- but not PL-CT recipients, AR was associated with differences in B cell maturity and regulatory CD4⁺ T cell frequency compared to stable allografts. These data suggest that circulating B cell and T cell subpopulations may provide insights into the regulation of anti-donor immune response in human CT recipients with differing AR risk. Our results suggest that, in contrast to solid organ transplants, genetic or cellular assays of peripheral blood are unlikely to be clinically exploitable for prediction or diagnosis of AR.

T-cell Subset Profile in Kidney Recipients of Extended or Standard Donors

INTRODUCTION

The usage of extended-criteria donors (ECD) became a routinely accepted manner in the last decade. ECD is a potential risk factor for antibody-mediated rejection. Analysis of lymphocyte subsets might be a complementary diagnostic toolkit because there is limited knowledge about this term.

METHOD

Between May 12, 2016, and September 4, 2019, a total of 130 patients who had undergone kidney transplant were investigated. Patients were divided in ECD and standard criteria donor (SCD) groups. Blood samples were collected before the operation, then in the first week and after 30, 60, 180, and 365 days. Besides routine laboratory tests, multicolor flow cytometry was performed for lymphocyte subsets.

RESULTS

ECD grafts were transplanted to older recipients. The number of CD4+ cells increased in the SCDs from the first week to until the end of first month, and then decreased. The number of CD4+ cells decreased from the beginning of the study until the end of first year to 66% of its original value in ECDs. At the first month, the number of CD19+ cells was higher in SCD compared with ECD cases; the number then decreased in both groups. T-regulatory cells had a drop at the first week that lasted until the first month. A bigger increase in SCD and a moderate increase in ECD group were then observed. The kinetics of CD19+ and CD19+ naive cells are similar in the ECD and SCD groups. In the SCD group, cell count decreased in both CD19+ (13%) and CD19+ naive (12%) between third and sixth month. The count of CD19+ cells decreased by 9%, but the count of CD19+ naive cells increased by 11% between the sixth month and first year.

DISCUSSION

The prolonged postoperative uremic state caused by the poorer initial function, together with an aging immune system, explains the weaker immune response in ECD patients, which may be the cause of the decreased number of memory and regulatory T cells. Older patients with an ECD graft need a tailored, personalized, and less aggressive immunosuppressive treatment.

The Role of Prognostic and Predictive Biomarkers for Assessing Cardiovascular Risk in Chronic Kidney Disease Patients

Chronic kidney disease (CKD) is currently defined as the presence of proteinuria and/or an eGFR < 60 mL/min/1.73m² on the basis of the renal diagnosis. The global dimension of CKD is relevant, since its prevalence and incidence have doubled in the past three decades worldwide. A major complication that occurs in CKD patients is the development of cardiovascular (CV) disease, being the incidence rate of fatal/nonfatal CV events similar to the rate of ESKD in CKD. Moreover, CKD is a multifactorial disease where multiple mechanisms contribute to the individual prognosis. The correct development of novel biomarkers of CV risk may help clinicians to ameliorate the management of CKD patients. Biomarkers of CV risk in CKD patients are classifiable as prognostic, which help to improve CV risk prediction regardless of treatment, and predictive, which allow the selection of individuals who are likely to respond to a specific treatment. Several prognostic (cystatin C, cardiac troponins, markers of inflammation, and fibrosis) and predictive (genes, metalloproteinases, and complex classifiers) biomarkers have been developed. Despite previous biomarkers providing information on the pathophysiological mechanisms of CV risk in CKD beyond proteinuria and eGFR, only a minority have been adopted in clinical use. This mainly depends on heterogeneous results and lack of validation of biomarkers. The purpose of this review is to present an update on the already assessed biomarkers of CV risk in CKD and examine the strategies for a correct development of biomarkers in clinical practice. Development of both predictive and prognostic biomarkers is an important task for nephrologists. Predictive biomarkers are useful for designing novel clinical trials (enrichment design) and for better understanding of the variability in response to the current available treatments for CV risk. Prognostic biomarkers could help to improve risk stratification and anticipate diagnosis of CV disease, such as heart failure and coronary heart disease.

Optimizing Detection of Kidney Transplant Injury by Assessment of Donor-Derived Cell-Free DNA via Massively Multiplex PCR

Standard noninvasive methods for detecting renal allograft rejection and injury have poor sensitivity and specificity. Plasma donor-derived cell-free DNA (dd-cfDNA) has been reported to accurately detect allograft rejection and injury in transplant recipients and shown to discriminate rejection from stable organ function in kidney transplant recipients. This study used a novel single nucleotide polymorphism (SNP)-based massively multiplexed PCR (mmPCR) methodology to measure dd-cfDNA in various types of renal transplant recipients for the detection of allograft rejection/injury without prior knowledge of donor genotypes. A total of 300 plasma samples (217 biopsy-matched: 38 with active rejection (AR), 72 borderline rejection (BL), 82 with stable allografts (STA), and 25 with other injury (OI)) were collected from 193 unique renal transplant patients; dd- cfDNA was processed by mmPCR targeting 13,392 SNPs. Median dd-cfDNA was significantly higher in samples with biopsy-proven AR (2.3%) versus BL (0.6%), OI (0.7%), and STA (0.4%) (p < 0.0001 all comparisons). The SNP-based dd-cfDNA assay discriminated active from non-rejection status with an area under the curve (AUC) of 0.87, 88.7% sensitivity (95% CI, 77.7⁻99.8%) and 72.6% specificity (95% CI, 65.4⁻79.8%) at a prespecified cutoff (>1% dd-cfDNA). Of 13 patients with AR findings at a routine protocol biopsy six-months post transplantation, 12 (92%) were detected positive by dd-cfDNA. This SNP-based dd-cfDNA assay detected allograft rejection with superior performance compared with the current standard of care. These data support the feasibility of using this assay to detect disease prior to renal failure and optimize patient management in the case of allograft injury.