Emerging biomarkers in kidney transplantation and challenge of clinical implementation

Biomarkers of Rejection in Kidney Transplantation

Alloimmune injury is a major cause of long-term kidney allograft failure whether due to functionally stable (subclinical) or overt clinical rejection. These episodes may be mediated by immune cells (cellular rejection) or alloantibody (antibody-mediated rejection). Early recognition of immune injury is needed for timely appropriate intervention to maintain graft functional viability. However, the conventional measure of kidney function (ie, serum creatinine) is insufficient for immune monitoring due to limited sensitivity and specificity for rejection. As a result, there is need for biomarkers that more sensitively detect the immune response to the kidney allograft. Recently, several biomarkers have been clinically implemented into the care of kidney transplant recipients. These biomarkers attempt to achieve multiple goals including (1) more sensitive detection of clinical and subclinical rejection, (2) predicting impending rejection, (3) monitoring for the adequacy of treatment response, and (4) facilitating personalized immunosuppression. In this review, we summarize the findings to date in commercially available biomarkers, along with biomarkers approaching clinical implementation. While we discuss the analytical and clinical validity of these biomarkers, we identify the challenges and limitations to widespread biomarker use, including the need for biomarker-guided prospective studies to establish evidence of clinical utility of these new assays.

Influence of gut flora on diabetes management after kidney transplantation

Post-transplant diabetes mellitus (PTDM) is a common complication following renal transplantation, and its incidence has been gradually increasing in recent years, posing a significant public health challenge. Managing PTDM is complex, as studies suggest that it involves changes in the microbial flora across multiple organs. Recent research highlights the critical role of gut flora metabolism in the development of diabetes among post-renal transplant patients. This paper reviews the alterations in gut flora observed in PTDM patients and explores how gut flora influences PTDM. These findings may offer new perspectives on targeting gut flora metabolites for the prevention and treatment of PTDM.

Very Low Frequency of Pathological Findings in One-year Protocol Biopsies of Uneventful Standard Risk Kidney Transplant Recipients: Results From the Nordic Protocol Biopsy Study

Background

The clinical significance of kidney transplant protocol biopsies has been debated. We studied the frequency of borderline changes and T cell-mediated rejection (TCMR) in 1-y protocol biopsies in standard risk kidney transplant recipients.

Methods

Consecutive non-HLA-sensitized recipients of kidney transplants between 2006 and 2017, who underwent a protocol biopsy at 1 y in 2 national transplant centers were studied retrospectively (N = 1546). Donor-specific HLA antibodies (DSAs), graft function (plasma creatinine), and proteinuria were measured at the time of 1-y protocol biopsy. The occurrence of subclinical acute TCMR (i2t2v0 or higher) or borderline changes suspicious of TCMR (i1t1v0 or higher) in the protocol biopsy was studied, together with frequency of findings causing changes in the composite score iBox.

Results

Subclinical acute TCMR was detected in 30 of 1546 (1.9%) of the protocol biopsies, and borderline or TCMR in 179 of 1546 (12%). Among patients with no history of acute rejection, and no proteinuria or DSA, TCMR was detected in only 1 of 974 (0.1%) and borderline or TCMR in only 48 of 974 (4.9%) patients at 1 y. In the absence of proteinuria (<30 mg/g, or equivalent as measured with a negative dipstick proteinuria) or DSA, or history of acute rejection, only 50 of 974 (5.1%) biopsies showed any lesions significant for the iBox score.

Conclusions

The likelihood of pathological findings in 1-y protocol biopsies in non-HLA-sensitized patients without previous immunological events is low. Clinical usefulness of protocol biopsies seems limited in these patients.

Long-term immunological outcomes of early subclinical inflammation on surveillance kidney allograft biopsies

The long-term impact of early subclinical inflammation (SCI) through surveillance biopsy has not been well studied. To do this, we recruited a prospective observational cohort that included 1000 sequential patients who received a kidney transplant from 2013-2017 at our center. A total of 586 patients who underwent a surveillance biopsy in their first year post-transplant were included after excluding those with clinical rejections, and those who were unable to undergo a surveillance biopsy. Patients were classified based on their biopsy findings: 282 with NSI (No Significant Inflammation) and 304 with SCI-T (SCI and Tubulitis) which was further subdivided into 182 with SC-BLR (Subclinical Borderline Changes) and 122 with SC-TCMR (Subclinical T Cell Mediated Rejection, Banff 2019 classification of 1A or more). We followed the clinical and immunological events including Clinical Biopsy Proven Acute Rejection [C-BPAR], long-term kidney function and death-censored graft loss over a median follow-up of five years. Episodes of C-BPAR were noted at a median of two years post-transplant. Adjusted odds of having a subsequent C-BPAR was significantly higher in the SCI-T group [SC-BLR and SC-TCMR] compared to NSI 3.8 (2.1-7.5). The adjusted hazard for death-censored graft loss was significantly higher with SCI-T compared to NSI [1.99 (1.04-3.84)]. Overall, SCI detected through surveillance biopsy within the first year post-transplant is a harbinger for subsequent immunological events and is associated with a significantly greater hazard for subsequent C-BPAR and death-censored graft loss. Thus, our study highlights the need for identifying patients with SCI through surveillance biopsy and develop strategies to prevent further alloimmune injuries.

Harnessing the B Cell Response in Kidney Transplantation - Current State and Future Directions

Despite dramatic improvement in kidney transplantation outcomes over the last decades due to advent of modern immunosuppressive agents, long-term outcomes remain poor. Antibody-mediated rejection (ABMR), a B cell driven process, accounts for the majority of chronic graft failures. There are currently no FDA-approved regimens for ABMR; however, several clinical trials are currently on-going. In this review, we present current mechanisms of B cell response in kidney transplantation, the clinical impact of sensitization and ABMR, the B cell response under current immunosuppressive regimens, and ongoing clinical trials for ABMR and desensitization treatment.