Purpose: The selective elimination of cancer stem cells (CSCs) in tumor patients is a crucial goal because CSCs cause drug refractory relapse. To improve the current conventional bispecific immune-engager platform, a 16133 bispecific natural killer (NK) cell engager (BiKE), consisting of scFvs binding FcγRIII (CD16) on NK cells and CD133 on carcinoma cells, was first synthesized and a modified interleukin (IL)-15 crosslinker capable of stimulating NK effector cells was introduced.
Materials and methods: DNA shuffling and ligation techniques were used to assemble and synthesize the 1615133 trispecific NK cell engager (TriKE). The construct was tested for its specificity using flow cytometry, cytotoxic determinations using chromium release assays, and lytic degranulation. IL-15-mediated expansion was measured using flow-based proliferation assays. The level of interferon (IFN)-γ release was measured because of its importance in the anti-cancer response.
Results: 1615133 TriKE induced NK cell-mediated cytotoxicity and NK expansion far greater than that achieved with BiKE devoid of IL-15. The drug binding and induction of cytotoxic degranulation was CD133+ specific and the anti-cancer activity was improved by integrating the IL-15 cross linker. The NK cell-related cytokine release measured by IFN-γ detection was higher than that of BiKE. NK cytokine release studies showed that although the IFN-γ levels were elevated, they did not approach the levels achieved with IL-12/IL-18, indicating that release was not at the supraphysiologic level.
Conclusion: 1615133 TriKE enhances the NK cell anti-cancer activity and provides a self-sustaining mechanism via IL-15 signaling. By improving the NK cell performance, the new TriKE represents a highly active drug against drug refractory relapse mediated by CSCs.
Keywords: Antibody-dependent cell cytotoxicity; CD133; Interleukin-15; Natural killer cell engager; Neoplastic stem cells.