The Banff 2024 Kidney Meeting Report: Rejection as a spectrum of phenotypes and focus on differential diagnostic reasoning.

The XVIIth Banff meeting for transplant pathology was held in Paris, France, from September 16, 2024 to September 20, 2024, hosted by the Paris Institute for Transplantation & Organ Regeneration. The Banff 2024 meeting resulted in no changes to the Banff kidney classification. Important outputs of the meeting were a reaffirmation of the clinical usefulness of the clinical reasoning framework and flowchart for cases with microvascular inflammation/antibody-mediated rejection introduced at the Banff 2022 meeting and the introduction of a similar flowchart for tubulointerstitial inflammation and intimal arteritis (v lesion). The meeting highlighted the complexity of the immunologic processes (alloimmune and others) that lead to allograft inflammation and the need to strengthen the Banff system for differential diagnostic reasoning. Guidance is put in place for cases with incomplete/mixed phenotypes, which acknowledges the limits of our understanding. A proposal for potential future implementation of activity and chronicity indices was discussed, as well as digital and biopsy-based molecular tools that have the potential to help transform the classification into a probabilistic tool reflective of the underlying immunologic processes. Finally, guidelines for reporting of glomerular disease in the posttransplant setting were developed.