Novel Biomarkers in Kidney Transplant: A Focus on Gene Expression Testing
Eurofins Transplant Genomics
Transplant Genomics improves organ transplant outcomes through molecular diagnostic tests.
Preliminary results are available from a study examining gene expression testing as a tool for managing immunosuppression?in organ transplant patients. Dr.?V. Ram Peddi, a nationally recognized leader in transplant clinical research, presented initial data in a November 2023 webinar. The findings, which include two case studies, suggest biomarker testing can guide clinicians in titrating immunosuppression medications. This can minimize long-term side effects and prevent acute transplant rejection.?
Board-certified in internal medicine and nephrology, Dr. Peddi is Director of Kidney Transplant Clinical Research at California Pacific Medical Center (CMPC) in San Francisco. CMPC's Kidney and Pancreas Transplant Program performs approximately 200 kidney transplants annually. Dr. Peddi also leads clinical trials and chairs scientific sessions on new directions in transplant medicine. ?
The webinar, Using Gene Expression Profile Biomarkers as an Immunosuppression Guide in Post-Transplant Care, was a panel-style discussion. It included Dr. John Friedewald, Professor of Medicine and Surgery at Northwestern Memorial Hospital and Dr. Michael Marvin, Transplant Surgeon at Geisinger Medical Center. The panelists reviewed case studies where gene expression profile tests detected immune system quiescence or activation, helping guide immunosuppression therapy.
Study Design
Dr. Peddi provided an overview of the study, which includes males and females aged 18 and older who received a transplant from a primary deceased or living donor. The first phase required participants to understand written informed consent and meet the following criteria for low immunological risk of acute rejection:
In addition, the study required participants to have a negative HLA crossmatch (virtual crossmatches accepted). Allografts from deceased donors required a Kidney Donor Profile Index (KDPI) score below 50%.
Patients were excluded from the study if they:
Dr. Peddi explained, "The idea was to pick low-risk transplant patients and treat them with thymoglobulin induction at about 3 mg/kg and plan for corticosteroid withdrawal at about 30 days posttransplant." He noted patients received weekly lab testing to determine eligibility for the second part of the study.?
Inclusion/Exclusion Criterianbsp;
Patients meeting the following criteria are enrolled in the second part of the study:
The criteria for excluding patients from the second part of the study are:
Study Methodology
Patients meeting the inclusion criteria are randomized into study and control groups at a 2:1 ratio. Participants in both groups received TruGraf blood testing at 3, 4, 5, 6, 7, 8, 9, and 12 months posttransplant. The results of the study group are available in real-time to guide immunosuppression therapy.
A negative TruGraf test, known as a TX result, suggests a patient is adequately immunosuppressed. Dr. Peddi explained, "If they have a TX result, their mycophenolate will be decreased when they're about 3 to 6 months posttransplant." He added, "If they continue to have TX, we will target tacrolimus lower in the 3 to 5 range ideally, but to a maximum of 6. If they're not-TX, we will not do any further reduction in the immunosuppression, and they will continue with monthly TruGraf testing for protocol."
TruGraf results for the control group will be held back until the end of the study. These patients receive?immunosuppression management according to each center's standard of care.
Study Enrollment
As of November 1, 2023, 69 patients were enrolled in the trial, and 61 have been randomized. There are 42 in the study group and 19 in the control group. Two more patients will be randomized into part 2 of the study once they're 3 months posttransplant. To date, 22 patients have completed the 12-month study.
Results: Assessing Immunosuppression Strategies
Dr. Peddi presented baseline data for 36 patients, noting that at the time of randomization (3 months posttransplant), patients in both the study and control arms were comparable.
The study group includes 25 patients:??
The control group includes 11 patients:
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As of November 1, 2023, 241 samples had been obtained from the 42 subjects in the study group. Dr. Peddi noted 87.6% of the samples were TX and 12.4% were not-TX. Eighteen of the 42 patients, or 43%, had one or more not-TX results, but not in consecutive months. Two patients, or 5%, had consecutive not-TX results in the study group.
Initial Study Findings
Dr. Peddi then presented results for the study and control groups.
3 Months Post-transplantation?
At randomization, the serum creatinine level, eGFR, tacrolimus level, and mycophenolate dose were comparable in both groups. In the study arm, the mycophenolate was 1,700 mg/day, and the tacrolimus level was 8.75 ng/mL. In the control arm, the mycophenolate was 1,818 mg/day, and the tacrolimus level was 9.16 ng/mL.
6 Months Post-Transplantation
At 6 months posttransplant, there was an intentional difference, as the mycophenolate dose was decreased for patients with TX. Mycophenolate was 1,500 mg/day in the study group and 1750 mg/day in the control group. Tacrolimus levels were similar at 7.41 ng/mL in the study group and 7.17 ng/mL in the control group.
9 Months Post-Transplantation
There was a pronounced difference at 9 months posttransplant. Mycophenolate dosages were 1,083 mg/day in the study group and 1,813 mg/day in the control group. A gap was also appearing in tacrolimus levels, which were 6.97 ng/mL in the study group and 7.68 ng/mL in the control group.
12 Months Post-Transplantation
By 12 months posttransplant, the mycophenolate dose in the study group was 1,076 mg/day, about half of the dose in the control group, which was 2,000 mg/day. Tacrolimus was also lower in the study group at 5.99 ng/mL, compared to 8.02 ng/mL in the control group.
The serum creatinine levels were comparable in the study and control groups at 1.23 mg/dL and 1.42 mg/dL respectively. Similarly, eGFR was comparable at 69.83 mL/min in the study arm and 63.33 mL/min in the control arm.
Case Study #1
Dr. Peddi then presented two case studies demonstrating how TruGraf testing can inform patient care. In the first, a 57-year-old who had end-stage renal disease from polycystic kidney disease received a 29% KDPI kidney transplant. In the early posttransplant period, she had neutropenia. Her MMF dose was held, and she was only on tacrolimus for a few days. Her creatinine was consistently in the 0.7 to 0.9 range.
However, her TruGraf came back as positive, or not-TX, at 3, 4, and 5 months posttransplant. "I sent off a DSA and sure enough, she now has a DSA against B44 and also BW4," said Dr. Peddi. He explained, "We did a biopsy and [found] some interstitial infiltrate, but … it didn't quite meet the criteria for borderline rejection. I increased her immunosuppression and went back to a thousand BID on the mycophenolate and ramped up her tacrolimus. She changed to TX, and the creatinine levels have been stable in the 0.7 to 0.9 range. She's now over a year posttransplant."
Case Study #2
The patient in the second case study was one of the first five patients enrolled: a 33-year-old male with end-stage renal disease due to chronic glomerulonephritis. He had hypertension, proteinuria, and chronic renal failure diagnosed when he was 27. His biopsy showed advanced changes with ischemic glomeruli and interstitial fibrosis.
The patient had a good urine output at the time of transplant and proteinuria — about 500 to 700 milligrams per day. He was mildly sensitized with a calculated Panel Reactive Antibody (cPRA) of 31%. He had no DSA and received a kidney from a 12% KDPI acute kidney injury donor. There was delayed graft function in the immediate posttransplant period.
The patient's TruGraf remained TX at 3 and 4 months. His creatinine dropped to about 1.0 and then started going up to 1.3 to 1.6 on multiple measurements. He had no DSA or BK viruria, and his tacrolimus was around 8.0. His MMF was decreased for 500 BID for neutropenia, but he had worsening proteinuria.
"I was concerned that he may have antibody-mediated rejection," explained Dr. Peddi. "We had a transplant kidney biopsy and there was no rejection. And he had normal glomerular structure on the biopsy. It was thought his proteinuria was probably coming from his native kidneys."
The patient remains stable. His creatinine is 1.26, and he does not have significant proteinuria anymore. Dr. Peddi noted the patient had a TX at months 3 and 4, which is highly correlated to adequate immunosuppression. This was confirmed by the biopsy.
Implications and Future Research
Based on the study's preliminary results, immunosuppression minimization may be feasible in patients who have TruGraf TX results. The study will be completed in mid-2025.
These findings have significant implications for kidney transplant patients. One of the challenges for transplant doctors is to manage immunosuppression. Allograft recipients who are?under-immunosuppressed are at risk of organ rejection. If they're over-immunosuppressed, they may experience adverse side effects over time, such as fungal infections and cancers.?
Used as a tool for surveilling patients, gene expression profiling can provide early detection of an immune system response against the transplanted organ, even before cellular or clinical graft injury. As TX results are correlated to adequate immunosuppression, doctors can optimize immunosuppressive medications in an informed way.
Research is also underway regarding the use of donor-derived cell-free DNA (dd-cfDNA) for monitoring organ transplant rejection. The percentage of dd-cfDNA?in a patient's plasma strongly suggests allograft injury. Together, these two novel biomarkers can provide a clearer picture of transplant kidney health. Gene expression profiling?can detect potential immune activation and dd-cfDNA can identify allograft injury, offering a promising alternative to organ biopsies.
Transplant Genomics aims to improve transplant outcomes for recipients through noninvasive treatment options. Learn more today.