Detection and quantification of donor cell-free dna in the circulation of organ transplant recipients

A method of quantifying the amount of donor DNA in a cell-free blood sample of a recipient of a transplanted organ from a donor without genotyping a sample obtained from said donor, the method comprising:

• (a) identifying that one or more SNPs of a panel of SNPs preselected to have a minor allele frequency of 0.4 or greater across human populations are homozygous in the recipient;
• (b) performing targeted DNA sequencing to quantify the one or more SNPs identified in (a), in a cfDNA preparation from a blood sample from which cells have been removed obtained from the recipient following transplantation of donor tissue to the recipient, to detect the level of an alternative allele to the allele present in the recipient, wherein detecting the level of the alternative allele comprises counting the DNA molecules that comprise the alternative allele compared to those that comprise the allele present in the recipient;
• wherein the amount of donor DNA in the cell-free cell sample is quantified without genotyping a donor specific sample