Cytokine-induced killer (CIK) cells are an ex vivo expanded heterogeneous population of natural killer (NK)-like T cells that can exert potent MHC-unrestricted antitumor activity. A number of pre-clinical and clinical studies have demonstrated that CIK cells can serve as a safe and potent immunotherapy of malignant tumors. N-acetylcysteine (NAC) has been demonstrated to enhance the T-cell functions by increasing their proliferation and cytokine production.