Cytokine-induced killer cells efficiently kill stem-like cancer cells of nasopharyngeal carcinoma via the NKG2D-ligands recognition

// Fang Wei 1, 6, * , Xiao-Xiang Rong 3, * , Rao-Ying Xie 1, * , Li-Ting Jia 5 , Hui-Yan Wang 1 , Yu-Juan Qin 1 , Lin Chen 1 , Hong-Fen Shen 1 , Xiao-Lin Lin 1 , Jie Yang 1 , Sheng Yang 1 , Wei-Chao Hao 1 , Yan Chen 1 , Sheng-Jun Xiao 5 , Hui-Rong Zhou 5 , Tao-Yan Lin 1 , Yu-Shuang Chen 1 , Yan Sun 4 , Kai-Tai Yao 1 , Dong Xiao 1, 2 1 Cancer Research Institute, Southern Medical University, Guangzhou 510515, China 2 Institute of Comparative Medicine & Laboratory Animal Center, Southern Medical University, Guangzhou 510515, China 3 Department of Oncology, Nanfang Hospital, Southern Medical University, Guangzhou 510515, China 4 Children's Hospital Boston, Harvard Medical School, Boston, Massachusetts 02115, USA 5 Department of Pathology, Guilin Medical College, Guilin 541001, China 6 Guangzhou Digestive Disease Center, Guangzhou First People's Hospital, Guangzhou Medical University, Guangzhou 510180, China * These authors have contributed equally to this work Correspondence to: Dong Xiao, e-mail: Xiao_d@hotmail.com Kai-Tai Yao, e-mail: yao.kaitai@hotmail.com Keywords: nasopharyngeal carcinoma, cytokine-induced killer cells, cancer stem cells, promoter-reporter gene strategy, time-lapse imaging Received: May 27, 2015      Accepted: September 04, 2015      Published: September 16, 2015 ABSTRACT Cancer stem cells (CSCs) are considered to be the root cause for cancer treatment failure. Thus, there remains an urgent need for more potent and safer therapies against CSCs for curing cancer. In this study, the antitumor activity of cytokine-induced killer (CIK) cells against putative CSCs of nasopharyngeal carcinoma (NPC) was fully evaluated in vitro and in vivo . To visualize putative CSCs in vitro by fluorescence imaging, and image and quantify putative CSCs in tumor xenograft-bearing mice by in vivo bioluminescence imaging, NPC cells were engineered with CSC detector vector encoding GFP and luciferase (Luc) under control of Nanog promoter. Our study reported in vitro intense tumor-killing activity of CIK cells against putative CSCs of NPC, as revealed by percentage analysis of side population cells, tumorsphere formation assay and Nanog-promoter-GFP-Luc reporter gene strategy plus time-lapse recording. Additionally, time-lapse imaging firstly illustrated that GFP-labeled or PKH26-labeled putative CSCs or tumorspheres were usually attacked simultaneously by many CIK cells and finally killed by CIK cells, suggesting the necessity of achieving sufficient effector-to-target ratios. We firstly confirmed that NKG2D blockade by anti-NKG2D antibody significantly but partially abrogated CIK cell-mediated cytolysis against putative CSCs. More importantly, intravenous infusion of CIK cells significantly delayed tumor growth in NOD/SCID mice, accompanied by a remarkable reduction in putative CSC number monitored by whole-body bioluminescence imaging. Taken together, our findings suggest that CIK cells demonstrate the intense tumor-killing activity against putative CSCs of NPC, at least in part, by NKG2D-ligands recognition. These results indicate that CIK cell-based therapeutic strategy against CSCs presents a promising and safe approach for cancer treatment.