KIR2DS2 and KIR2DS4 promoter hypomethylation patterns in patients undergoing hematopoietic cell transplantation (HCT)

The killer cell Ig-like receptor (KIR)-MHC class I pathway is an integral part of natural killer cell immunity, and its role in host protection from both cancer and infection is important. In addition, we have shown elevated KIR2DS2 and 2DS4 expression in PBMCs of patients undergoing hematopoietic cell transplantation (HCT) [1]. Since all inhibitory KIR promoters are known to be heavily methylated, the question asked here is how and when KIR2DS2 and 2DS4 promoters had changed their methylation profile in association with HCT. Genomic DNA, extracted from 20 KIR2DS2/4+ donor and recipient cells, was treated with sodium bisulfate that will modify the unmethylated cytosine into uracil. Sequencing chromatographs were examined for C/T double peak indicative of base conversion. A CpG island in KIR2DS2 promoter spans from -160 to +26 with six cytosine sites. In contrast, the KIR2DS4 promoter CpG island contains three cytosine sites. The noted increase of unmethylated sites was associated with increased KIR expression as measured by mRNA-cDNA Q-PCR. In addition, the frequency of unmethylated sites in the CpG island was increased after HCT. The mechanism through which hypomethylation occurs after HCT is not known but it suggests a linkage to NK clonal expansion during the process of NK education in response to transplant therapy or viral infection.