Epigenetic biomarkers indicate islet cell death in xenotransplantation

Background: Xenotransplantation of porcine islets has emerged in recent decades as a potential treatment for type 1 diabetes (T1D). Current methods of detection, indicative of successful engraftment, occur downstream of actual islet death. Epigenetic biomarkers can be detected in circulating cell-free DNA (cfDNA) to provide an earlier indication of graft dysfunction. Aims: The present study identified a biomarker of islet death using differential methylation of the insulin gene, INS, originating from β-cells in porcine islets. Materials & Methods: Pyrosequencing primers specific for porcine INS were designed to quantify hypomethylation along 12 cysteine-guanine dinucleotide (CpG) sites, including three sites in the cyclic adenosine monophosphate (cAMP) response element (CRE) binding protein 2 (CRE2) binding region of the 5′ untranslated region (UTR) and nine sites within intron 2. Results: PCR amplification of bisulfite-converted DNA combined with pyrosequencing data support the conclusion that hypomethylated porcine INS is specific to islet origin. Conclusion: Moreover, the results of this study indicate a highly specific epigenetic biomarker, capable of detecting a single islet, supporting the measurement of cfDNA as a biomarker for transplanted islet death. Defining the epigenetic characteristics of porcine-derived islets within cfDNA will be crucial to develop a better understanding of graft survival immunology for transplantation.