Background Heart transplantation allows for a long-term management of patients with end-stage heart failure. After the surgery, organ rejection is monitored with endomyocardial biopsy, which is an invasive, but not always informative procedure. Therefore, there is a pressing need for a new, safe, yet reliable, diagnostic method. Here, we present a pilot study confronting liquid biopsy based on donor-specific cell-free DNA with the protocol endomyocardial biopsy.

Methods The study was performed on 21 blood samples matched with endomyocardial biopsy (graded according to acute cellular rejection scale) from nine patients after heart transplantation. Genotyping was performed on genomic DNA from donors and recipients for 10 single-nucleotide polymorphisms (SNPs). Cell-free DNA isolated from plasma was analysed with digital droplet PCR to detect donor-specific alleles.

Results From 21 analysed endomyocardial biopsies, 4 were graded as 0R and 17 as 1R. Liquid biopsy was successfully performed in each sample for all informative SNPs (median of 3 per patient). We observed a high homogeneity of the results between SNPs in each sample (interclass correlation coefficient of >0.9).

Conclusions There is a undeniable need for an alternative, non-invasive diagnostic procedure of early transplant rejection and investigation of donor-derived cell-free DNA seems to be the promising choice. The very high sensitivity is particularly enticing to consider liquid biopsy as a potential screening tool. Its minimal invasiveness may allow for more frequent examination and, thus, tighter monitoring. The reliable assessment of its clinical utility requires an adequately powered and properly designed multicentre study.