Human leukocyte antigen (HLA) matching evaluates the degree of compatibility between donors and organ transplant recipients and assesses broad antigen differences that may influence immune responses post-transplant. A refined HLA matching method based on examining clusters of amino acids on HLA molecules, named eplets, has been recently developed. This method identifies immunogenic discrepancies that may not be apparent through traditional HLA matching. In recent years, assessment of HLA eplet mismatches has emerged as a promising strategy to improve immune risk stratification in kidney transplantation, which is crucial for kidney recipients' management and maximizing allograft longevity. Despite its potential, the prognostic value and clinical relevance of HLA eplet mismatches for predicting long-term kidney allograft failure has not been robustly demonstrated.

In this study, the investigators aim to investigate whether HLA eplet mismatches may represent a relevant clinical tool for patient risk stratification and prediction of long-term allograft failure beyond standard clinical, histological and immunological parameters for monitoring in kidney transplant recipients.

Inclusion Criteria:

• Living or deceased donor kidney recipients transplanted after 2004
• Kidney recipients older than 18 years of age
• Kidney recipients with available HLA genotyping data

Exclusion Criteria:

• Combined transplantation

Kidney transplant recipients from seven European referral centers