Immunologic effector cells termed cytokine-induced killer (CIK) cells are generated in vitro from peripheral blood lymphocytes by addition of interferon-gamma, interleukin (IL)-2, IL-1 and an antibody against CD3. CIK cells have been shown to eradicate established tumors in a SCID mouse/human lymphoma model. CIK cells are dependent on exogenous cytokines such as IL-2, IL-7, or IL-12. We studied the effect of these cytokines in detail. Cellular proliferation was analyzed using an MTT proliferation assay, surface antigen expression via flow cytometry, cytotoxic activity using an LDH release assay, and apoptosis via flow cytometric analysis. IL-2, IL-7 and IL-12 led to significant growth of lymphocytes. Cells grown in IL-2 and IL-7 showed higher proliferation rates than cells grown in IL-12 according to the MTT assay. Concerning surface antigen expression, exogenous IL-7 led to a decrease in IL-7 receptor expression (4.8% from 60.4%) and exogenous IL-2 to a decrease in IL-2 receptor expression (61.2% from 73.2%). CD28 expression was higher in cells grown in IL-7 (77.3%) than in cells grown in IL-2 (62.5%). IL-12 led to a decrease in ICAM-1 adhesion molecule expression (57.7% from 76.7%) and an increase in CD56 expression compared with exogenous IL-7. IL-7 led to higher number of CD4-positive cells than IL-2 (53.0% vs 49.5%). No significant difference was found between IL-2, IL-7 and IL-12 in cytotoxic activity measured in an LDH release assay. Small amounts of apoptotic cells were found with all cytokines. However, the percentage of necrotic cells was higher with exogenous IL-12 than with IL-2 or IL-7. In summary, CIK cells can be generated using exogenous IL-2, IL-7 or IL-12. No difference in cytotoxic activity was found. However, significant differences were found in cell proliferation rates, antigen expression and percentage of necrotic cells.

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