Demonstrate the relationship between DD-cfDNA levels and HLA antibodies in blood, and the Molecular Microscope® (MMDx) Diagnostic System results in indication biopsies.

There is a need for better screening of kidney transplant patients for rejection. Patients with kidney transplants are routinely tested (creatinine, urine protein, histology and donor specific antibody (DSA) as standard of care to detect rejection, but these tests are not adequate. Rejection is often missed by these tests (false negatives) and other processes such as acute kidney injury can produce false-positive results. Moreover, histology has a high interobserver disagreement diagnosing rejection, and cannot accurately assess acute injury. A definitive molecular assessment of rejection and injury in kidney biopsies has emerged - the Molecular Microscope® Diagnostic System (MMDx) - developed by the Alberta Transplant Applied Genomics Centre, University of Alberta. Now a new screening test is being introduced: the monitoring of donor-derived cell-free DNA (DD-cfDNA) released in the blood by the kidney during rejection. The Natera Inc DD-cfDNA Prospera® test is based on the massively multiplex PCR that targets 13,392 single nucleotide polymorphisms and targeted sequences are quantified by Next Generation Sequencing. The Prospera® test done on kidney transplant recipients detected "active rejection" and differentiated it from borderline rejection and no rejection. It is likely, however, that DD-cfDNA test may miss some T cell-mediated rejection (TCMR) cases and the distinction between early and fully developed antibody-mediated rejection (ABMR) was not tested. No study has actually examined the DD-cfDNA results in kidney transplants with acute or chronic kidney disease (AKI and CKD). DD-cfDNA measurements have only been correlated with histology, a flawed standard. DD-cf-DNA test must now be calibrated against MMDx that is based on global gene expression, the new standard for biopsy interpretation. The present study will calibrate centrally measured (Natera Inc) DD-cfDNA levels obtained at the time of an indication biopsy against the MMDx measurements of TCMR, and ABMR (early-stage, fully-developed, and late-stage), AK, and atrophy-fibrosis. We will compare blood DD-cfDNA measurements in 600 samples at the time of 300 indication biopsies to the MMDx results, as well as central assessment of HLA antibody (One Lambda) in 300 blood samples, interpreted centrally as DSA based on the tissue typing results. This study is an extension of the INTERCOMEX ClinicalTrials.gov Identifier: NCT01299168. Investigators have collected 1195 kidney biopsies, 1103 blood samples for DD-cfDNA test and 1150 blood samples for One Lamba test, and will extend this study to the total of 1400 biopsies and 2800 blood samples.

Inclusion Criteria:

• All kidney transplant recipients undergoing a kidney biopsy for clinical indications, as determined by their physician or surgeon, will be eligible to enroll in the study.

Exclusion Criteria:

• Patients will be excluded from the study if they decline participation or are unable to give informed consent or multiple organ recipients.

The study population includes patients with a functioning kidney transplant undergoing a biopsy for clinical indications as standard of care to determine the cause of their graft dysfunction (deterioration in graft function, delayed graft function, proteinuria).