Abstract 5811: Ultralong CDR3 engineered interleukin-15 antibody fusion for T and NK cell expansion

Abstract

Abstract Interleukin (IL)-15 is a promising immunotherapeutic cytokine for cancer treatment because it can stimulate the proliferation and cytotoxicity of CD8+ T lymphocytes and nature killer (NK) cells, similar to the action of IL-2, which has been used to treat metastatic melanoma and renal cancer. IL-15 may have improved pharmacologic properties over IL-2 because it doesn’t cause vascular leak syndrome or stimulate regulatory T cells. However, IL-15 is difficult to express as a stable soluble protein and has a short half-life in vitro and in vivo. To solve the problem, we designed an IL-15 ultralong CDR3 humanized bovine antibody fusion. Bovine ultralong CDR3 antibodies have a unique “stalk and knob” structure in which two antiparallel β-strands support a disulfide bonded knob protruding out of the antibody surface and forms a mini antigen binding domain. By replacing the knob domain with IL-15, we have created a chimeric CDR3-IL-15 IgG which functions as IL-15 in vitro and in vivo but can be easily produced in mammalian cells with increased stability. Thus, the CDR3 can stabilize IL-15 in the absence of its high affinity receptor α (Rα) chain. Furthermore, as IL-15 utilizes Rα for increased trans signaling to the receptor β and γ subunits, one variant candidate (CDR3-IL-15_Rα) was produced by co-expressing Rα sushi domain with the chimeric IgG. Both constructs have been demonstrated to be highly active in stimulating proliferation of NK cells and CD8+ T cells in vitro as well as in stimulating proliferation of NK cells and CD8+ T cells in rats and non-human primates (NHP). Although the CDR3-IL-15_Rα exhibited higher in vitro signaling activity than CDR3-IL-15, both were equally potent in stimulating the proliferation of NK cells and CD4+ and CD8+ T cells in NHP without any immunogenicity detected. Moreover, in vivo studies in NHP indicated that CDR3-IL-15 acted faster than CDR3-IL-15_Rα in stimulating the proliferation of these lymphocytes. CDR3-IL-15 is the first thermodynamically stabilized variant of IL-15 produced in the absence of its Rα chain, is highly active in vivo, and has multiple potential cancer applications as an T and NK cell stimulating agent. Citation Format: Ruiqi Huang, Duncan McGregor, Vaughn Smider. Ultralong CDR3 engineered interleukin-15 antibody fusion for T and NK cell expansion [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5811.