P140 HLA match and donor-derived cell-free DNA levels in kidney transplant recipients

Abstract

Circulating cell-free DNA (cfDNA) has been correlated with allograft rejection in organ transplant recipients and is proposed as a biomarker to assess graft injury that may be reflective of allograft rejection or immunosuppression toxicity. We have validated a method for quantifying donor-derived cfDNA (dd-cfDNA) based on targeted amplification of SNPs and next-generation sequencing (NGS) that does not require genotyping of the donor or recipient (AlloSure®). The test measures alleles for 266 SNPs distributed across the genome and quantifies the proportion of dd-cfDNA present in the recipient’s plasma. The aim of this study was to identify relationships between levels of dd-cfDNA in kidney transplant patients and the degree of HLA mismatch with the donor, living or deceased donor type, and donor relationship to recipient. Testing was performed using cfDNA extracted from plasma collected in Streck Cell-Free DNA BCT blood collection tubes from kidney recipients enrolled in a multicenter observational study. Median values of dd-cfDNA were calculated from all visits for each recipient. Recipients were stratified by the total number of mismatches in HLA A, B and DR loci. Further stratifications were based on the donor type (living or deceased) as well as relationship to the donor (related or unrelated). Median dd-cfDNA levels were calculated from 208 recipients with 4 or more visits (median of 6 visits each). There were no statistically significant differences in median levels of dd-cfDNA associated with degree of donor HLA match. The between-patient variability trended higher for mismatched recipients compared to those with no mismatches to their donor and for recipients who received a kidney from a deceased donor compared to those recipients who received a kidney from a living donor, but the differences were not statistically significant. In samples collected on a surveillance schedule from study recipients, degree of HLA mismatch at HLA A, B, and DR were not predictive of dd-cfDNA overall nor when stratified by donor type and donor relationship. These results indicate that the level of dd-cfDNA in kidney recipients is independent of these variables and that these variables do not confound interpretation of the AlloSure results.