Solid organ transplantation (SOT) is the only treatment option for patients with end stage organ failure. Yet transplantation is not a lifelong cure, in paediatric patients over half of recipients will not live over 25 years post transplantation. Short-term outcomes have improved with advances in surgery and immunosuppression, but medium- and long-term outcomes have not seen the same improvements due allograft rejection. Tissue biopsies are the gold standard for monitoring and detecting allograft rejection, which can allow for early intervention, but irreversible allograft damage may have already occurred by the time a biopsy is performed. The use of an alternative biomarker which can be performed more regularly to detect early sub-clinical rejection is if great interest. Research into the use of cell free DNA (cfDNA) as a non-invasive biomarker is expanding rapidly as a new test to detect allograft damage.
However, quantifying the low fraction of donor-derived cfDNA (ddcfDNA) is challenging requiring a highly sensitive technique. ddcfDNA detection through unique donor single nucleotide polymorphisms (SNPs) is a recent new approach, however there are limited data in paediatric SOT recipients. An assay using a combination of 61 SNPs was developed to accurately quantify ddcfDNA using a custom R script to model for both the patient and donor genotypes requiring only a single sample from the allograft recipient (a donor sample is not required). Performance of the assay was validated using genomic DNA (gDNA) , cfDNA and donor samples where available. 159 paediatric SOT recipients (kidney, heart and lung) were tested without the need for donor’s genotyping. Serial sampling was obtained from 82 patients. The R ‘’genotype-free’’ method gave results comparable to when using the known donor genotype, applicable to both related and unrelated pairs and can reliably measure ddcfDNA (limit of blank, below 0.12%; limit of detection, above 0.25%; limit of quantification 0.5% resulting in 84% accuracy, 99.65 %success rate). High levels of ddcfDNA were detected immediately post-transplantation (pTx) and also at acute rejection. This method can provide results in 48 hours at a low cost. Additional prospective studies are required to demonstrate its clinical validity in a larger cohort of paediatric SOT recipients.
Currently applying for funding for a national study (NIHR) Paper accepted for publication in Clinical Chemistry, currently with the publishers Abstract accepted for ISHLT annual conference 2020, but due to COVID did not go ahead. Poster for ITT Immunology meeting London, 2019 Poster for International Congress of Paediatric Nephrology, Venice, 2019