Abstract 4294: Cancer immunotherapeutic potential of NKTT320, a novel human invariant natural killer T-cell activating monoclonal antibody
Authors: Das Rupali , Scheuplein Felix , Guan Peng , Schaub Robert , Nichols Kim E. 
Published: August 2015

Invariant natural killer T cells (iNKTs) directly kill tumor cells and trans-activate the anti-tumor functions of dendritic cells (DC), natural killer (NK), T and B cells. As such, iNKTs serve as a powerful tool for use in cell-based cancer immunotherapy. iNKT cell activation commonly requires engagement of the invariant T cell receptor (iTCR) by CD1d presenting glycolipid antigen. However, transformed cells often down-regulate CD1d expression, which results in a reduction of iNKT cell anti-tumor functions. One approach to circumvent this critical barrier to iNKT cell activation is to develop an agonistic antibody that binds directly to the iTCR without the requirement for CD1d-mediated antigen presentation. Towards this end, we characterized the iNKT cell stimulatory properties of NKTT320, a novel recombinant humanized monoclonal antibody that binds selectively and with high affinity to the human iTCR. Strikingly, both soluble and immobilized NKTT320 induced a dose-dependent iNKT cell activation (upregulation of activation markers [CD25, CD69]), proliferation (by measuring CFSE dilution), degranulation (measured by exposure of CD107 on the cell surface) and activation of bystander immune cells. Additionally, iNKT cells stimulated by plate-bound NKTT320 also robustly secreted Th1 (IL-1β, IFN-γ, TNF-α, IL-2, IL-6) and Th2-type (IL-4, IL-5, IL-10) cytokines as well as chemokines. Our in vitro studies are consistent with in vivo data in Vα24 transgenic mice, which express the human iTCR alpha chain. Dosing of NKTT320 in these animals led to iNKT cell activation and IFN-γ production, as well as incorporation of BRDU indicating in vivo iNKT cell proliferation. Similarly, NKT14m (a murine iNKT-agonistic antibody) induced murine iNKT cell activation, cytokine production, and degranulation in vitro. Consistently, treatment of C57BL/6 (B6) mice with NKT14m led to rapid and robust iNKT cell activation and IFN-γ production. Furthermore, in vivo injection of NKT 14m in B6 mice induced robust T, B, and NK cell activation as well as DC maturation (as assessed by increased expression of MHC class II and co-stimulatory molecules [CD80 and CD86]). Importantly, treatment of T-lymphoma-bearing B6 mice with a single dose of NKT14m substantially repressed the growth of subcutaneous tumors. Taken together, these data suggest that iNKT-activating antibodies hold great potential for use in cell-based cancer immunotherapy. Studies are underway to examine whether treatment with NKT14m in combination with interleukin-12 (a potent iNKT and NK cell activating cytokine) can further augment iNKT cell activation in vivo. These studies are significant, as they provide a framework by which iNKT cell anti-cancer functions could be enhanced for therapeutic purposes.

Citation Format: Rupali Das, Felix Scheuplein, Peng Guan, Robert Schaub, Kim E. Nichols. Cancer immunotherapeutic potential of NKTT320, a novel human invariant natural killer T-cell activating monoclonal antibody. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4294. doi:10.1158/1538-7445.AM2015-4294