Objective: Heart transplantation remains the definitive treatment for patients with advanced heart failure, but post-transplant complications such as acute cellular rejection (ACR) continue to limit long-term outcomes. The current standard for ACR surveillance is endomyocardial biopsy, which is invasive and associated with procedural risks, variability in interpretation, high healthcare utilization costs, and poor patient tolerability. For these reasons, there is increasing interest in identifying non-invasive biomarkers that can reliably detect ACR. This review details the range of non-invasive methods for detecting ACR and to provide practical guidance for clinicians considering a transition to less invasive monitoring protocols following heart transplantation.

Methods: We conducted a narrative review of published literature focusing on non-invasive biomarkers for ACR in heart transplantation. We specifically focused on evaluating donor-derived cell-free DNA, gene expression profiling, plasma microRNA, metabolomics, cytokines and chemokines, and extracellular vesicle approaches, with emphasis on clinical applicability, diagnostic performance, and limitations.

Results: Our review identified several promising non-invasive biomarkers for ACR detection, with donor-derived cell-free DNA and gene expression profiling showing the most advanced clinical integration. Emerging approaches such as microRNA profiling, metabolomics, cytokine or chemokine panels, and extracellular vesicle analysis demonstrate potential in early-phase studies but require further validation. Most biomarkers exhibited high negative predictive value, though sensitivity and positive predictive values remained variable across platforms along with their applications in the early perioperative and late follow-up periods. None of the biomarker platforms distinguish ACR from antibody mediated rejection. Practical challenges including cost, assay standardization, and limited availability continue to impact widespread adoption.

Conclusion: Non-invasive blood-based biomarkers show promise for improving acute cellular rejection surveillance in heart transplant recipients. While markers such as dd-cfDNA, extracellular vesicles, and microRNAs have demonstrated encouraging early results, their clinical use remains limited by variable inadequate sensitivity, low positive predictive value, inability to distinguish ACR from AMR, and lack of standardization. Ongoing investigations are expected to refine their diagnostic performance and guide their integration into routine clinical care.

Acute cellular rejection, Non-invasive biomarkers, Transplantation immunology