CIK cells, Cytokine-Induced Killer (CIK), are a new type of immunologically active cells with strong proliferative capacity, cytotoxic effects, and certain immunological properties. Because the cells express both CD3 and CD56 membrane protein molecules, they are also known as NK cell (natural killer cell)-like T lymphocytes, which have both the powerful anti-tumor activity of T lymphocytes and the non-MMC-restricted tumor-killing advantage of NK cells. The cells have a strong ability to recognize tumor cells and act as “cellular missiles” that can precisely “point and shoot” tumor cells without harming “innocent” normal cells. CIK cells are especially effective in post-operative or post-radiotherapy patients, eliminating small metastatic lesions, preventing the spread and recurrence of cancer cells, and improving the body’s immunity. CIK cells (cytokine-inducedkiller) are immunologically active cells that effectively kill leukemia cells. Under in vitro conditions, certain single nucleated cells in human peripheral blood are induced to become CIK cells after co-stimulation with various cytokines (e.g. IFN-γ, IL-1,IL-2, anti-CD3mAb), and their main effector cells have surface markers of both T cells (TCR-α/β, CD3) and NK cells (CD56). Compared with lymphokine-activatedkiller (LAK) and tumor-infiltrating lymphocytes (TIL), which have been used in the past for secondary immunotherapy, CIK has a stronger proliferative capacity and more potent anti-leukemic cell effects, and CIK has become a new approach to leukemia biotherapy because of its stronger proliferative capacity and more potent anti-leukemia cellular effects with minimal toxic side effects, which can meet the requirements for effector cells in over-the-top immunotherapy. Cell therapy can directly kill leukemia cells without damaging the structure and function of the body’s immune system, and regulate and enhance the body’s immune function, restoring the normal growth and regulation of cells to the greatest extent possible, providing a new means to completely remove residual leukemia cells and thus cure leukemia. Clinical statistics show that about 50% to 70% of leukemia patients can relapse after chemotherapy, because the residual leukemia cells in the body are prone to resurgence. In the human body, lymphocytes have the potential to attack leukemia cells, but they are “inert”; cytokines can expand a large number of lymphocytes in a short period of time and activate them, which have powerful leukemia cell killing activity. CIK cell therapy is based on this principle, in which cells that can be induced to become CIK cells are harvested from the human body, specially cultivated and expanded in large numbers to become “cell missiles” that specifically attack and kill leukemia cells. This “cell missile” can precisely “target” leukemia cells without harming the “innocent”, thus achieving a complete cure for the patient.