Abstract 1497: Development of a novel TCR-like bi-specific T-cell engager targeting endogenous PR1/HLA-A2 leukemia antigen

Abstract

Abstract PR1 (VLQELNVTV) is a HLA-A2 restricted peptide derived from endogenous tumor associated antigens proteinase-3 and neutrophil elastase that are aberrantly expressed in myeloid leukemia blasts. Previously, we have developed a high affinity T-cell receptor-like monoclonal antibody (h8F4) specific for PR1/HLA-A2, and demonstrated the effective killing of myeloid leukemia blasts via antibody dependent cellular cytotoxicity (ADCC). To improve the therapeutic efficacy of h8F4, we adopted a novel antibody engineering strategy, bi-specific T-cell engaging (BiTE) antibody that can bring T cells in close proximity to leukemia blasts through the binding of both PR1/HLA-A2 and CD3, resulting in T-cell mediated cytolysis of leukemia blasts. Here we successfully generated h8F4-BiTE proteins using a eukaryotic expression system and investigated binding characteristics, target specificities, and subsequent T-cell activation with the h8F4-BiTE. The h8F4 BiTE showed binding affinities in the nM range for PR1/HLA-A2 and CD3 moiety of T cells. Within 18 hours of h8F4-BiTE engagement with PR1 pulsed T2 cells, polyclonal T cells from healthy donors up-regulated surface expression of CD69 and down-regulated CD3 in a PR1/HLA-A2 specific and concentration dependent manner, suggesting successful T-cell activation. In conclusion, we developed a novel h8F4 BiTE antibody that recognizes both the CD3 on T cells and endogenous PR1/HLA-A2 complexes on myeloid leukemia, and demonstrated high affinity bindings and subsequent T cell activation. We envision our novel TCR-like BiTE antibody will provide a safer and more potent treatment option for patients with aggressive myeloid leukemias that will improve upon currently available highly toxic standard therapies. Citation Format: Amanda Cernosek Herrmann, Jin S. Im, Sijie Lu, Anna Sergueeva, Jeffrey Molldrem. Development of a novel TCR-like bi-specific T-cell engager targeting endogenous PR1/HLA-A2 leukemia antigen. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1497.