The objective of this study is to determine whether cell-free DNA (cf-DNA) measurement can be used as a biomarker for successful treatment of an acute rejection (AR) episode after kidney transplantation.

A fall in donor cf-DNA level may be a biomarker for successful AR treatment. The goal is to do an exploratory study to determine, in recipients with biopsy-proven AR, whether persistence or elevated levels of donor cf-DNA are associated with ongoing inflammation at the time of exit biopsy; and whether fall in donor cf-DNA level is associated with successful AR treatment.

Measurement of cf-DNA has recently been started for kidney transplant recipients. There will be two groups of patients eligible for this study:

1. those who have had sequential measurement of cf-DNA prior to graft dysfunction leading to a biopsy, and
2. those who have not had previous measurement of cf-DNA

Significance of Research Question/Purpose:

A kidney transplant biopsy is the gold standard for making a diagnosis at the time of graft dysfunction. However, there are risks associated with a transplant biopsy (e.g., hematuria, clots within the collecting system, bleeding, hematoma within the kidney, urine leak, and rarely AKI and/or graft loss). Recently, a blood test has been developed which distinguishes donor and recipient circulating cf-DNA. Using this methodology, circulating cf-DNA is amplified, then using a panel of markers, 2 DNA peaks can be observed - a high peak for the recipient DNA and a very low peak for the donor (importantly, this is not genetic testing; only high and low peaks are identified). When cf-DNA is measured at the time of a kidney biopsy for graft dysfunction, an elevated donor cf-DNA level - compared to that seen in a cohort without inflammation - can be seen in recipients with an acute rejection (AR) episode. Data, to date, suggests that if >1% of cf-DNA is donor derived, there is likely graft inflammation.

Currently, there are ongoing studies to determine if sequential measurement of cf-DNA in the same recipient will show elevated donor cf-DNA levels earlier than a serum creatinine rise, thus potentially allowing earlier detection and treatment of AR episodes.

Serum creatinine level is used as a marker for successful treatment of an acute rejection episode. However, creatinine level is an insensitive marker of response to treatment of both cellular and antibody mediated rejection. Studies in which biopsies are done at the end of "presumed" successful rejection treatment show that some patients whose creatinine level returned to baseline have ongoing inflammation. Unless additional anti-rejection treatment is given, this incomplete treatment leads to increased risk for donor-specific antibody formation and graft failure.

As a consequence, the investigators (the U of MN Kidney Transplant Program) are now doing routine "exit" biopsies for patients treated for acute rejection episodes and whose serum creatinine level returns to baseline. The investigators have always done biopsies in patients whose creatinine level did not return to baseline. The "exit" biopsy is done at ~6 weeks after completion of rejection treatment. If the exit biopsy shows ongoing inflammation, additional rejection treatment is considered.

It would be ideal to have a noninvasive marker for successful rejection treatment. The objective of this study is to determine whether cell-free DNA (cf-DNA) measurement can be used as a biomarker for successful treatment of an acute rejection (AR) episode after kidney transplantation.

The addition of cf-DNA testing would have two potential benefits:

1. Serum creatinine may return to baseline (pre-rejection level), but ongoing allograft injury may be occurring as creatinine is an insensitive marker of subtle allograft dysfunction. This inflammation is known to create antigenic presentation that results in DSA production which is major cause of long-term allograft loss
2. Serum creatinine may not return to baseline as there is irreparable allograft loss or intensification of CNI dosing. This would result in a biopsy that does not change management, but would put the patient through an unnecessary and potentially harmful procedure. If a non-invasive marker decreases with treatment and correlates with complete resolution of rejection episode, this would be useful for monitoring purposes.

Preliminary Data:

1. The University of MN Transplant Program participated in the original studies showing an association between cf-DNA and acute rejection. The investigators have experience with the methodology and with working with the company that does the cf-DNA assay
2. Since starting to do exit biopsies the investigators, like others, have found that some patients with presumed successful rejection treatment have evidence of ongoing inflammation seen in the biopsy.

Inclusion Criteria:

• Adult kidney transplant recipients undergoing transplant biopsy between 1 and 12 months post-transplant because of graft dysfunction.

Exclusion Criteria:

• <1 months post-transplant
• >12 months post-transplant

Adult kidney transplant recipients undergoing transplant biopsy between 1 and 12 months post-transplant because of graft dysfunction.