This observational cohort study aims to compile routinely collected clinical, histological and outcome data of kidney transplant recipients, to evaluate risk factors for post-transplant injury, phenotypes of injury, and impact on outcome of such injury, in order to provide clinicians more accurate, less biased and faster tools for diagnosis, clinical management and treatment decisions with regard to kidney transplant rejection.

The following data/features are collected prospectively and structured in the electronic medical records:

Demographics:

• Date of transplantation
• Date of graft failure
• Last date of follow-up
• Time after transplantation of survival (number of days);
• kidney survival;
• recipient death;
• recipient gender;
• recipient age at time of transplantation;
• recipient weight at time of transplantation;
• recipient BMI at time of transplantation;
• recipient race;
• recipient diabetes prior to transplantation;
• the Belgian Index for Multiple Deprivation (BIMD);
• combined vs single transplant (we included only single transplants);
• repeat transplant vs. first transplant;
• diagnosis of the original kidney disease (prior to transplantation);
• donor type (living vs. deceased);
• donor gender;
• donor age in years;
• donor diabetes yes vs no;
• HLA genotype of donors and recipients, number of HLA A mismatches between donor and recipient (0-2); number of HLA B mismatches between donor and recipient (0-2); number of HLA DR mismatches between donor and recipient (0-2); number of total HLA mismatches between donor and recipient (0-6); high-resolution genotyping of donors and recipients HLA genes (11 loci);
• cold ischemia time
• warm ischemia time
• operation time

Graft functional data:

• Serum creatinine values from day of transplantation onwards;
• Proteinuria values from day of transplantation onwards

Data on DSA:

DSA data collected in clinical routine, from the day of listing for transplantation onwards (clinically measured at the Histocompatibility laboratory of the Red Cross, Motstraat, Mechelen, and reported in the clinical patient records).

Biopsy data:

Both clinically indicated and protocol biopsies were performed in this cohort. On average, 3.2 biopsies per patient.

• The following data are collected from the clinical records and transferred to a pseudonymized database: Date of the kidney biopsy; Indication biopsy = at time of graft dysfunction; protocol = prespecified biopsy per protocol; pretransplant = biopsy prior to transplantation (in the donor); post-transplant = biopsy after transplantation; time point (indication vs. Protocol biopsy time points); tubulitis (0-3); interstitial inflammation (0-3); vasculitis (0-3); glomerulitis (0-3); peritubular capillaritis (0-3); thrombi (0-3); C4d deposition in peritubular capillaries (0-3); C4d deposition in glomerular capillaries (0-3); transplant glomerulopathy (0-3); interstitial fibrosis (0-3); tubular atrophy (0-3); vascular intimal thickening (0-3); mesangial matrix increase (0-3); arteriolar hyalinosis (0-3); glomerulosclerosis (%); microcirculatory inflammation (0-6) = g + ptc; diagnosis of antibody-mediated rejection yes vs no according to current international consensus, calculated from g, ptc, cg, thrombi, C4d_ptc and v; diagnosis of T-cell mediated rejection yes vs no according to current international consensus (0 = absent, 1 = borderline; 1=present); diagnosis of IFTA grade (0-3) according to current international consensus: calculated from ci and ct
• Next to pseudonymized clinical data, also histological slides are retrieved from the biobank of the Department of Pathology of the University Hospitals Leuven and whole slide images made available for image analysis.

Inclusion Criteria:

* All adult kidney transplant recipients transplanted at the University Hospitals Leuven between 01/03/2004 and 01/06/2022, without restrictions with regard to age, sex, underlying kidney disease etc.

Exclusion Criteria:

* Patients with combined transplantations (e.g. heart + kidney, liver + kidney, lung + kidney)

All renal allograft recipients transplanted at the University Hospitals Leuven between 01/03/2004 and 01/06/2022 are included in this study, without restrictions with regard to age, sex, underlying kidney disease etc.

Individual participant data can only be made available to other researchers with a dedicated data transfer agreement.