Monitoring of Donor‐Derived Cell‐Free DNA by Short Tandem Repeats: Concentration of Total Cell‐Free DNA and Fragment Size for Acute Rejection Risk Assessment in Liver Transplantation

Monitoring of graft function is essential during the first months after liver transplantation (LT), but current liver function tests (LFTs) lack the specificity and sensitivity to ensure an efficient diagnosis of acute rejection (AR). Recently, donor‐derived cell‐free DNA (ddcfDNA) has emerged as a noninvasive biomarker to assess graft integrity. This study evaluated the feasibility of measuring the ddcfDNA through short tandem repeat (STR) analysis by quantitative fluorescent‐polymerase chain reaction (QF‐PCR) and to assess the role of the concentration and fragment size of total cfDNA as AR biomarkers. The total concentration and fragment size of cfDNA and the ddcfDNA percentage were monitored in plasma of 20 patients without rejection and 7 patients with T‐cell–mediated AR during the first 3 months after LT. The median ddcfDNA percentage was 3‐fold higher before AR diagnosis (34.8%; P