Graft microvascular inflammation poses a significant challenge to successful kidney transplantation due to its heterogeneous clinical presentation. There is a critical need to unravel the clinical significance of newly defined allograft microvascular inflammation phenotypes in the Banff 2022 classification and assess the implications of these new phenotypes on kidney transplant precision diagnostics and patient risk stratification.

Antibody-mediated rejection is a major cause of graft failure in kidney transplant recipients, with allograft microvascular inflammation serving as the hallmark histological lesion of antibody-mediated graft injury. However, the frequent occurrence of graft microvascular inflammation in the absence of circulating anti-HLA donor-specific antibodies highlights the incomplete understanding of the mechanisms underlying this inflammation. This heterogenous presentation poses a significant challenge in the clinical setting, as current treatment strategies often prove ineffective, hindering the improvement of allograft and patient care. The Banff 2022 classification update has reappraised lesions of microvascular inflammation, identifying new diagnostic phenotypes of microvascular inflammation. However, the clinical significance of these phenotypes is yet to be determined.

The aims of this study are:

1. To determine the impact of the revised Banff 2022 Classification on the diagnostic classification of phenotypes related to microvascular inflammation, compared to previous Banff 2019 Classification.
2. To assess the association of microvascular inflammation phenotypes with kidney allograft survival.
3. To assess the association of microvascular inflammation phenotypes with disease progression, defined by transplant glomerulopathy occurrence (cg and subsequent antibody-mediated rejection episodes.

Inclusion Criteria:

• Kidney transplant recipients, with at least one kidney transplant biopsy performed, assessed with the Banff classification.

Exclusion Criteria:

• Missing data for a rejection-related diagnosis according to the 2019 and 2022 Banff classification.

Kidney transplant recipients of all sexes recruited in observational studies performed in Europe and United States, with at least one kidney biopsy performed with all the relevant data to provide a diagnosis according to the 2019 and 2022 Banff classification, including clinical data (recipient and donor's age, sex and transplant characteristics).

The data analyzed during the current study are available on reasonable request including standards for General Data Protection Regulation and Institutional Review Board approval.