Abstract 1493: Improvement of the bispecific antibody ADCC platform by genetic insertion of IL-15 as a cross-linker to create NK cell reactive TriKEs

Natural killer (NK)-cell related anti-tumor surveillance is limited by the ability of the tumor to escape killing. Previously, we constructed a bispecific NK-cell engager (BiKE) consisting of two scFV against CD16 (FcγRIII) on NK cells and EpCAM on tumor cells (EpCAM16). Epithelial cell adhesion molecule (EpCAM) is a transmembrane protein with prevalent expression on carcinomas making it a valuable marker for cancer targeting. This BiKE facilitated ADCC and tumor elimination, but did not account for the cellular expansion required for the success of T CARs. To improve this, we incorporated a modified interleukin (IL)-15 crosslinker to create a trispecific construct (TriKE) to enhance activation, proliferation, and to prolong survival of NK-cells. IL-15 was chosen since it is an established immunostimulatory cytokine with known effects on NK cells and is recognized as a promising cancer cure drug in NIH guided review. TriKE was assembled, expressed in E.coli, extracted, refolded, and purified to >90% with a molecular weight of 68,860 daltons. To determine the functional activity of 1615EpCAM, its killing ability was measured in standard Cr-51 release assays with EpCAM+ HT-29 colorectal cancer cells. The 1615EpCAM TriKE induced the highest level of killing compared to BiKE and other controls. To determine if the effect of IL-15 in the drug correlated with NK-cell levels, donors were selected with different naturally occurring NK cell levels. Freshly isolated PBMCs were added to HT-29 cells at E:T ratios of 20:1, 6.6:1, and 2:1. Donors showed increasingly higher levels of Cr-51 kill with TriKE, but not with BiKE indicating that greater the presence of NK-cells, the greater the TriKE effect. In order to study lytic degranulation as a function of NK-cell activity, CD107a expression was measured. Cells treated with TriKE showed significantly elevated degranulation when co-cultivated with targets (p Citation Format: Daniel A. Vallera, Joerg U. Schmohl, Martin Felices, Jeffrey S. Miller. Improvement of the bispecific antibody ADCC platform by genetic insertion of IL-15 as a cross-linker to create NK cell reactive TriKEs. [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 1493.