P33. NK-92 cellular immunotherapy as an alternative to donor derived peripheral blood NK cells

Abstract

<h3>INTRODUCTION</h3> Hypermethylation of the promoter region of the <i>hMLH1</i> gene is associated with absent expression of MLH1 protein in sporadic colorectal cancers with microsatellite instability (MSI+), and it has been proposed that methylation may be a mechanism of inactivation in Knudson9s hypothesis. The incidence of hypermethylation of the<i>hMLH1</i> promoter in hereditary non-polyposis colorectal cancer (HNPCC) versus MSI+ sporadic colorectal cancer was investigated and compared. <h3>METHODS</h3> DNA was available from 10 HNPCC colorectal cancers (median age 58 years, range 39-67) with germline mutations in <i>hMLH1 </i>and 10 MSI+ sporadic colorectal cancers (mean age 79 years, range 41-85). MSI was determined by amplification of BAT26 and TGF-β RII. The methylation status of the <i>hMLH1</i> promoter was studied by the polymerase chain reaction (PCR) based<i>Hpa</i>II restriction enzyme assay technique. Evidence of allelic loss at <i>hMLH1 </i>was searched for in the HNPCC colorectal cancers. <h3>RESULTS</h3> All cases were confirmed to be MSI+. The promoter region of <i>hMLH1 </i>was hypermethylated in seven of 10 MSI+ sporadic cancers versus 0 of 10 HNPCC cancers (p&lt;0.002). Evidence of loss of heterozygosity at<i>hMLH1 </i>was observed in eight of the 10 HNPCC colorectal cancers. <h3>CONCLUSION</h3> While mutations and allelic loss are responsible for the MSI+ phenotype in HNPCC cancers, the majority of MSI+ sporadic cancers are hypermethylated in the promoter region of <i>hMLH1.</i> These data further support our argument that tumours from HNPCC patients, which almost always acquire a raised mutation rate, mostly follow a different pathway from MSI+ sporadic tumours.