The incidence of donor white blood cell survival (transfusion-associated microchimerism) in Australian pediatric patients

Introduction: Donor leucocyte survival following red blood cell (RBC) transfusion, known as transfusion-associated microchimerism (TAM), can occur in some patients. In Australia, despite the introduction of leucocyte filtration (leucodepletion) during RBC manufacture, TAM has been detected in adult trauma patients. However, the incidence of TAM in Australian pediatric patients has not been analyzed. Methods: Patients aged 0-16 years were recruited across two cohorts. Retrospective participants had RBC transfusion between January 1, 2002 and November 15, 2017 and prospective participants received RBC transfusion between December 1, 2016 and November 25, 2020. Twelve bi-allelic insertion/deletion (InDel) polymorphisms were used to detect microchimerism amplification patterns using real-time PCR (RT-PCR) and droplet digital PCR (ddPCR). Results: Of the retrospective cohort (n = 40), six patients showed amplification of InDel sequences indicating potential microchimerism. For three patients, minor InDel sequences were detected using RT-PCR only, two patients had minor InDel amplification using ddPCR only, and one patient had minor InDel amplification that was confirmed using both techniques. Amplification of minor sequences occurred in three patients who had received a bone marrow transplant in addition to RBC transfusion. In the prospective cohort (n = 25), no InDel amplification indicating potential microchimerism was detected using RT-PCR. Discussion: Cell-based therapies had been administered in three patients where microchimerism amplification patterns were detected. Three patients have microchimerism that may be attributed to RBC transfusion. In prospective patients, who received leucodepleted and gamma-irradiated RBC units, no potential microchimerism amplification were detected. ddPCR may be a suitable technique for TAM analysis but requires further evaluation.