Effects of interleukin-2 concentration and administration method on proliferation and function of cytokine-induced killer cells

Cytokine-induced killer cells (CIKs) adoptive cell transfer (ACT) is a common malignant tumor treatment method. Interleukin-2 (IL-2) is one of the essential cytokines for CIKs cultures. In different phase of CIKs (quiescent and exponential growth), due to different active states and IL-2R expression of the CIKs surface, different doses of IL-2 are required. However, most studies, only addressed the effects of IL-2 concentrations on the function of CIKs, and the differences between varied administration methods of IL-2 have not been explored.This study established a novel sequential administration methods for IL-2. Different concentrations of IL-2 were added during different CIKs induction phases. Then, the proliferation ability of CIKs was evaluated using cell proliferation curves. The immune phenotype was analyzed by flow cytometry (FCM), and IFN-γ secretion ability and cytotoxicity were detected using enzyme-linked immunosorbent assay (ELISA) kits and cell counting kit-8, respectively. Multiple comparisons were conducted between each group to compare the function of CIKs in 12 experimental groups.As the IL-2 concentration increased, the number of CIKs continued to increase in each group, but the function of CIKs was not positively related to its number: CD3+ CD56+ subpopulation ratio, INF-γ secretion ability, and cytotoxicity showed irregular changes. During the quiescent and exponential growth phases, adding 300 and 1,000 U/mL IL-2 respectively achieved powerful CIKs (cell numbers of day 16: (384.37±2.05)×106/mL, proliferation: 128.12, CD3+ CD56+ subpopulation ratio: 40.9%, INF-γ secretion ability: 542 pg/mL, cytotoxicity: 40:1, 74.22).Different concentrations of IL-2 had a greater influence on the biological function of CIKs in different growth phases, and it is better to add IL-2 sequentially during the quiescent and exponential growth phases of CIKs.