Mini Review Banff 2022 Updated Classification of Renal Allograft Pathology.

Background: The 16th Banff Meeting for Allograft Pathology was held in Banff, Canada from September 19 to 23, 2022. The results were published in the American Journal of Transplantation in March this year as "The Banff 2022 Kidney Meeting Report: Reappraisal of Microvascular Inflammation and the Role of Biopsy-Based Transcript Diagnostics."

Summary: The changes in the Banff 2022 classification (Banff 2022) have four distinct features. The first was the modification of antibody-mediated rejection (AMR). The key points are microvascular inflammation/injury (MVI); the presence or absence of C4d deposition in the peritubular capillaries; and the presence or absence of donor-specific antibodies (DSAs). Even if the MVI is above the threshold, if C4d and DSA are negative, it is not classified as AMR but as "MVI, DSA-negative, and C4d-negative." Furthermore, if MVI is below the threshold, C4d is negative but DSA is positive, the patient is classified under "probable AMR." Second, patients with acute tubular injury (ATI) without other obvious causes such as ischemia are excluded from AMR. Third, the Banff cv score for "arterial intimal fibrosis of new onset" (AIFNO) is excluded from AMR when used alone. Fourth, non-human leukocyte antigen (HLA) antibodies, except for anti-blood group antibodies in ABO-incompatible kidney transplants, were excluded from DSA and included in the diagnostic criteria for AMR.

Key Messages: The changes in Banff 2022 are as follows: implementation of new terminology, such as MVI, DSA-negative, and C4d-negative and probable AMR, ATI, and AIFNO are excluded from AMR, and non-HLA antibodies are excluded from DSA.