Key Points of the Banff 2019 Classification of Renal Allograft Pathology

The Banff 2019 Kidney Meeting Report was published following the 15th Banff Conference for Allograft Pathology, which was held in Pittsburgh on September 23-28, 2019. The diagnosis of renal transplant rejection based on the Banff 2019 classification is globally utilized. The Banff 2019 classification of renal allograft pathology includes several changes. This mini-review summarizes the key points and issues of the Banff 2019 classification. The criteria for borderline change have been reverted to ≥ i1, the t-IFTA score has been incorporated into the classification, the histological classification of polyoma virus nephropathy has been adopted, and a category was added for chronic (inactive) antibody-mediated rejection. In addition, whether the spread is diffuse or focal should now be noted in the presence of peritubular capillaritis. One of the issues with the Banff 2019 classification is the continuing lack of clarity regarding the definition of the t score, which is used to evaluate tubulitis not only in non-scarred areas but also in moderately atrophic tubules that are assumed to be present in scarred areas, which constitutes a contradiction in the definition.

Outcomes of paediatric kidney transplant recipients using the updated 2013/2017 Banff histopathological classification for antibody-mediated rejection

BACKGROUND

After the major changes with regard to acute and chronic ABMR in the Banff classification initiated in 2013, there has been an improvement in diagnosing antibody-mediated rejection (ABMR) in adult studies but no data have been published in the paediatric population.

METHODS

We assessed 56 paediatric kidney transplant biopsies due to kidney dysfunction in patients with donor-specific antibodies (DSA) in a retrospective single-centre study between January 2006 and March 2012. The results were compared with 2003/2007 Banff classification noting the subsequent 2017 and 2019 modifications do not change the 2013 Banff classification with regard to acute antibody-mediated rejection (apart from the addition of gene transcripts/classifiers that do not affect our analysis).

RESULTS

Following the 2013 Banff classification, there were seven cases (12.5%) diagnosed with ABMR that would have been misclassified when applying the 2003/2007 classification. Evaluating the histological features of all ABMR-related cases, we report the importance of v- (intimal arteritis) and t- (tubulitis) lesions: absence of v- and t- lesions in the biopsy is related to significantly higher kidney allograft survival (OR 7.3, 95%CI 1.1-48.8, p = 0.03 and OR 5.3, 95%CI 1.2-25.5, p = 0.04 respectively). Moreover, absence of t- lesions was associated with significantly fewer rejection episodes the year after the initial biopsy (OR 5.1, 95%CI 1.4-19.8, p = 0.01).

CONCLUSIONS

Our study supports that the updated 2013 Banff classification shows superior clinicopathological correlation in identifying ABMR in paediatric kidney transplant recipients. Our results can be extrapolated to the recently updated 2019 Banff classification.

Anti-mitochondria antibody-related tubulointerstitial nephritis accompanied by severe hypokalemic paralysis

A 47-year-old man presented with severe hypokalemic paralysis and respiratory failure. A large amount of potassium was administered along with providing intensive care, and his condition improved. Hypokalemia was attributed to increased urinary potassium excretion. A kidney biopsy was performed to make a definitive histological diagnosis. It revealed acute tubulointerstitial nephritis (TIN). After the diagnosis, prednisolone was administered, and the TIN gradually improved. From the clinical course and laboratory findings, the TIN was presumed to be an autoimmune disorder. Further specific autoantibody tests were positive for anti-mitochondrial antibody (AMA), which has been gaining increasing attention in regard to TIN. In addition, all previous cases of TIN associated with AMA have affected females. The detailed pathogenetic mechanisms are as yet unclear and require further investigation.