Background: There is increasing interest in the use of noninvasive biomarkers to reduce the risks posed by invasive biopsy for monitoring of solid organ transplants (SOTs). One such promising marker is the presence of donor-derived cell-free DNA (dd-cfDNA) in the urine or blood of transplant recipients.
Methods: We systematically reviewed the published literature investigating the use of cfDNA in monitoring of graft health after SOT. Electronic databases were searched for studies relating cfDNA fraction or levels to clinical outcomes, and data including measures of diagnostic test accuracy were extracted. Narrative analysis was performed.
Results: Ninety-five articles from 47 studies met the inclusion criteria (18 kidneys, 7 livers, 11 hearts, 1 kidney-pancreas, 5 lungs, and 5 multiorgans). The majority were retrospective and prospective cohort studies, with 19 reporting diagnostic test accuracy data. Multiple techniques for measuring dd-cfDNA were reported, including many not requiring a donor sample. dd-cfDNA falls rapidly within 2 weeks, with baseline levels varying by organ type. Levels are elevated in the presence of allograft injury, including acute rejection and infection, and return to baseline after successful treatment. Elevation of cfDNA levels is seen in advance of clinically apparent organ injury. Discriminatory power was greatest for higher grades of T cell-mediated and antibody-mediated acute rejection, with high negative predictive values.
Conclusions: Cell-free DNA is a promising biomarker for monitoring the health of SOTs. Future studies will need to define how it can be used in routine clinical practice and determine clinical benefit with routine prospective monitoring.