Multiple Cytotoxic Factors Involved in IL-21 Enhanced Antitumor Function of CIK Cells Signaled through STAT-3 and STAT5b Pathways

Background/
Objectives: Maintenance of cellular function in culture is vital for transfer and developmentfollowing adoptive immunotherapy. Dual properties of IL-21 in activating T cells and reducing activation inducedcell death led us to explore the mechanism of action of IL-21 enhanced proliferation and cytotoxic potential ofCIK cells.
Method: CIK cells cultured from PBMCs of healthy subjects were stimulated with IL-21 and cellularviability and cytotoxicity to K562 cells were measured. To elucidate the mechanism of action of IL-21, mRNAexpression of cytotoxic factors was assessed by RT-PCR and protein expression of significantly importantcytotoxic factors and cytokine secretion were determined through flow cytometry and ELISA. Western blottingwas performed to check the involvement of the JAK/STAT pathway following stimulation.
Results: We found thatIL-21 did not enhance in vitro proliferation of CIK cells, but did increase the number of cells expressing the CD3+/CD56+ phenotype. Cytotoxic potential was increased with corresponding increase in perforin (0.9831±0.1265to 0.7592±0.1457), granzyme B (0.4084±0.1589 to 0.7319±0.1639) and FasL (0.4015±0.2842 to 0.7381±0.2568).Interferon gamma and TNF-alpha were noted to increase (25.8±6.1 ng/L to 56.0±2.3 ng/L; and 5.64±0.61 μg/Lto 15.14±0.93 μg/L, respectively) while no significant differences were observed in the expression of granzyme A,TNF-alpha and NKG2D, and NKG2D. We further affirmed that IL-21 signals through the STAT-3 and STAT-5b signaling pathway in the CIK cell pool.
Conclusion: IL-21 enhances cytotoxic potential of CIK cells throughincreasing expression of perforin, granzyme B, IFN-gamma and TNF-alpha. The effect is brought about by theactivation of STAT-3 and STAT-5b proteins.