Non-invasive biomarkers to guide management following renal transplantation: the need for a multiplatform approach

Validation study of peripheral blood diagnostic test for acute rejection in kidney transplantation

BACKGROUND

Diagnosing acute rejection (AR) in kidney transplant recipients typically requires an invasive kidney biopsy. A previous study has suggested that expression of five genes in peripheral blood can indicate the presence of AR in American pediatric kidney transplant recipients. This study aims to validate if these five genes are also useful to diagnose AR in Korean adult kidney transplant patients.

METHODS

Blood samples were collected from 143 patients (39 biopsy-proven AR, 84 stable patients, and 20 other graft injuries) at an average of 9 months posttransplantation and performed real-time PCR for five-gene biomarkers (DUSP1, NKTR, MAPK9, PSEN1, and PBEF1).

RESULTS

Patients with acute cellular rejection (ACR) had a significantly decreased level of MAPK9 and a significantly increased level of PSEN1 when compared with controls and also with patients with other graft injury (OGI). In multivariate logistic regression analysis, for discrimination between ACR and OGI, an excellent diagnostic accuracy was observed in the gene sets but five-gene set generated a higher AUC than two-gene set. With clinical variables combined to these gene sets, the diagnostic accuracy increased in both five-gene set and two-gene set.

CONCLUSIONS

These results support the validity of 5 gene-set for the prediction of AR in Asian adult kidney transplant recipients and suggest the promising role of the peripheral blood gene test in the diagnosis of AR in kidney transplantation.

Acute kidney injury in kidney transplantation

PURPOSE OF REVIEW

Acute kidney injury (AKI) in transplant recipients is a prevalent condition with a broad list of potential inciting causes. This review highlights recent data describing the epidemiology and long-term consequences of transplant AKI, novel interventions in the management of delayed graft function (DGF), and noninvasive diagnostic strategies.

RECENT FINDINGS

The incidence and outcomes of nontransplant AKI are well documented, and similar data are emerging in the transplant setting with recent reports suggesting a high incidence rate and significant impact on long-term graft outcomes. DGF represents a 'pure' form of transplant AKI, and many interventional trials aiming to limit ischemia-reperfusion-induced injury have recently been reported or are currently ongoing. The search for accurate noninvasive predictors of DGF and acute rejection is ongoing and recent literature describes novel plasma and urine-based biomarkers as well as transcriptional profiling methods with high potential for clinical applicability.

SUMMARY

AKI in transplant recipients is a frequent occurrence with significant potential for poor long-term graft outcomes. Recent efforts to limit ischemia-reperfusion injury and diagnose transplant AKI via noninvasive methods may help to minimize the impact of AKI on future graft function.

Biomarkers of tolerance

PURPOSE OF REVIEW

As the induction and maintenance of donor-specific tolerance is a central aim in solid organ transplantation, it is essential that clinicians are able to identify and monitor tolerance accurately and reliably. This review highlights recent advances in defining sets of biomarkers in noninvasive samples that may guide minimization and withdrawal of immunosuppression in tolerant recipients.

RECENT FINDINGS

Recent studies in liver and kidney transplant recipients have identified distinct biomarker profiles that are associated with operational tolerance. Although there is some heterogeneity in the findings of these studies, these have suggested novel cellular mechanisms for the development of tolerance.

SUMMARY

Multiple platforms such as microarray gene expression analysis, flow cytometry, and immune cell functional assays have been used to discover and validate composite sets of biomarkers, which identify recipients with operational tolerance both in liver and kidney transplantation. These studies suggest that distinct cellular and molecular mechanisms lead to the development of tolerance in different transplanted organs. These putative biomarker profiles now need to be validated prospectively in trials of immunosuppression withdrawal and in novel approaches to induce transplant tolerance.

Epigenetic modulation of the immune function: a potential target for tolerance

Great efforts in the field of solid organ transplantation are being devoted to identifying biomarkers that allow a transplanted patient's immune status to be established. Recently, it has been well documented that epigenetic mechanisms like DNA methylation and histone modifications regulate the expression of immune system-related genes, modifying the development of the innate and adaptive immune responses. An in-depth knowledge of these epigenetic mechanisms could modulate the immune response after transplantation and to develop new therapeutic strategies. Epigenetic modifiers, such as histone deacetylase (HDAC) inhibitors have considerable potential as anti-inflammatory and immunosuppressive agents, but their effect on transplantation has not hitherto been known. Moreover, the detection of epigenetic marks in key immune genes could be useful as biomarkers of rejection and progression among transplanted patients. Here, we describe recent discoveries concerning the epigenetic regulation of the immune system, and how this knowledge could be translated to the field of transplantation.