Antibody-mediated rejection in the Banff classifications of 2007 and 2017: A comparison of renal graft loss prediction capability

Applications of Transcriptomics in the Research of Antibody-Mediated Rejection in Kidney Transplantation: Progress and Perspectives

Antibody-mediated rejection (ABMR) is the major cause of chronic allograft dysfunction and loss in kidney transplantation. The immunological mechanisms of ABMR that have been featured in the latest studies indicate a highly complex interplay between various immune and nonimmune cell types. Clinical diagnostic standards have long been criticized for being arbitrary and the lack of accuracy. Transcriptomic approaches, including microarray and RNA sequencing of allograft biopsies, enable the identification of differential gene expression and the continuous improvement of diagnostics. Given that conventional bulk transcriptomic approaches only reflect the average gene expression but not the status at the single-cell level, thereby ignoring the heterogeneity of the transcriptome across individual cells, single-cell RNA sequencing is rising as a powerful tool to provide a high-resolution transcriptome map of immune cells, which allows the elucidation of the pathogenesis and may facilitate the development of novel strategies for clinical treatment of ABMR.

Proposed Definitions of Antibody-Mediated Rejection for Use as a Clinical Trial Endpoint in Kidney Transplantation

Antibody-mediated rejection (AMR) is caused by antibodies that recognize donor human leukocyte antigen (HLA) or other targets. As knowledge of AMR pathophysiology has increased, a combination of factors is necessary to confirm the diagnosis and phenotype. However, frequent modifications to the AMR definition have made it difficult to compare data and evaluate associations between AMR and graft outcome. The present paper was developed following a Broad Scientific Advice request from the European Society for Organ Transplantation (ESOT) to the European Medicines Agency (EMA), which explored whether updating guidelines on clinical trial endpoints would encourage innovations in kidney transplantation research. ESOT considers that an AMR diagnosis must be based on a combination of histopathological factors and presence of donor-specific HLA antibodies in the recipient. Evidence for associations between individual features of AMR and impaired graft outcome is noted for microvascular inflammation scores ≥2 and glomerular basement membrane splitting of >10% of the entire tuft in the most severely affected glomerulus. Together, these should form the basis for AMR-related endpoints in clinical trials of kidney transplantation, although modifications and restrictions to the Banff diagnostic definition of AMR are proposed for this purpose. The EMA provided recommendations based on this Broad Scientific Advice request in December 2020; further discussion, and consensus on the restricted definition of the AMR endpoint, is required.

Single antigen testing to reduce early antibody-mediated rejection risk in female recipients of a spousal donor kidney

Female recipients of a spousal donor kidney transplant are at greater risk of donor-specific pre-immunization, which may increase the risk of acute antibody-mediated rejection (ABMR). We assessed the incidence of early ABMR (within two weeks after transplantation), risk factors for ABMR and graft function in 352 complement-dependent cytotoxicity test-negative LURD transplant recipients, transplanted between 1997 and 2014 at the Leiden University Medical Center in The Netherlands. Risk factors for immunization were retrieved from the health records. As methods to screen for preformed donor-specific antibodies (pDSA) have developed through time, we retrospectively screened those with ABMR for pDSA using pooled-antigen bead (PAB) and single-antigen bead (SAB) assays. The cumulative incidence of rejection in the first six months after transplantation was 18% (TCMR 15%; early ABMR 3%). Early ABMR resulted in inferior graft survival and was more common in women who received a kidney from their spouse (10%) than in other women (2%) and men (<1%). The SAB assay retrospectively identified pDSA in seven of nine cases of early ABMR (78%), while the PAB detected pDSA in only three cases (33%). Seeing that early ABMR occurred in 10% of women who received a kidney from their spouse, a SAB assay should be included in the pre-transplant assessment of this group of women, regardless of the result of the PAB assay.

Differences in Pathologic Features and Graft Outcomes of Rejection on Kidney Transplant

BACKGROUND

Rejection is still a barrier to long-term allograft survival, but there are not many reports of clinical outcomes according to rejection types. The purpose of this study was to investigate differences in pathologic features and graft outcomes of rejection on kidney transplant (KT).

MATERIALS AND METHODS

We retrospectively analyzed 139 kidney transplant recipients diagnosed to rejection by allograft biopsy results between 2006 and 2018. We divided kidney transplant recipients into 3 groups as follows: T cell-mediated rejection (TCMR), antibody-mediated rejection, and mixed rejection. We investigated clinical characteristics, pathologic findings, death-censored graft survival rates, and patient survival rates among the 3 groups.

RESULTS

Mean follow-up duration was 113.5 (SD, 80.6) months. The mixed rejection group was the youngest significantly. There were no significant differences of the proportion of sex, KT type, KT number, number of HLA mismatches, induction immunosuppressant, and maintenance immunosuppressant among the 3 groups. In pathologic findings, microvascular inflammation and C4d were significantly different among the 3 groups. Death-censored graft survival of mixed rejection was the least. In multivariate analysis, recipient age, TCMR, and positive C4d were the risk factors associated with graft failure. However, patient survival rates showed no significant differences among the 3 groups.

CONCLUSIONS

Our study showed that mixed rejection had poor prognosis in comparison with TCMR and antibody-mediated rejection groups, and TCMR and positive C4d were the most important risk factors for graft survival. Therefore, constant monitoring through allograft biopsy and early treatment for rejection are very important in post-transplant clinical outcomes.