6.4.1　What Is CIK?

Cytokine-induced killer cells, first discovered in 1991, are a heterogeneous population of CD8+ T cells, which are generated from human peripheral blood lymphocytes (PBLs) and simply expand ex vivo viaincubation with an anti-CD3 antibody, interferon-γ (IFN-γ), and interleukin (IL)-2.They can kill tumor cells mediated by FasL and perforin.According to the presence of cell surface molecule CD56, CIK cells are also divided into two main subsets: CD3+CD56+ T cells and CD3+CD56- T cells.CD3+CD56+ T cells, which are also called the natural killer T cells, are considered the major effector cells of CIK.Thus, CIK cells can lyse cancer cells in a MHC-unrestricted manner through activating NK cell receptors such as DNAX accessory molecule-1, NKp46, NKG2D, and NKp30.In addition to the direct killing effect of CIK on cancer cells, they can also regulate the immune function by secreting various cytokines.A lot of studies have indicated that after stimulation by tumor cells, the levels of pro-inflammatory cytokines such as tumor necrosis factor (TNF)-α, IFN-γ, and IL-2 secreted by CIK cells are significantly upregulated , and these cytokines further enhance systemic antitumor activity and induce a Th1 immune response [93-97].(https://www.daowen.com)