SERGEEVA et al PR1/HLA-A2 ANTIBODY MEDIATES AML STEM CELL LYSIS IMMUNOBIOLOGY An anti-PR1/HLA-A2 T cell receptor-like antibody mediates complement dependent cytotoxicity against acute myeloid leukemia progenitor cells

PR1 (VLQELNVTV) is an HLA-A2-restricted leukemia-associated peptide from proteinase 3 and neutrophil elastase that is recognized by PR1-specific cytotoxic T lymphocytes that contribute to cytogenetic remission of myeloid leukemia. We report a novel T cell receptor (TCR)-like IgG2a antibody (8F4) with high specific binding affinity (KD=9.9nM) for a combined epitope of the PR1/HLA-A2 complex. Flow cytometry and confocal microscopy of 8F4-labeled cells showed significantly higher PR1/HLA-A2 expression on AML blasts compared with normal leukocytes (p=0.046). 8F4 mediated complement dependent cytolysis of AML blasts and Lin-CD34+CD38− leukemia stem cells (LSC), but not normal leukocytes (p<0.005). Although PR1 expression was similar on LSC and hematopoietic stem cells, 8F4 inhibited AML progenitor cell growth, but not normal colony-forming units from healthy donors (p<0.05). This study shows that 8F4, a novel TCR-like antibody, binds to a conformational epitope of the PR1/HLA-A2 complex on the cell surface and mediates specific lysis of AML, including LSC. Therefore, this antibody warrants further study as a novel approach to target leukemia-initiating cells in patients with myeloid leukemia. For personal use only. on October 31, 2017. by guest www.bloodjournal.org From