Objective: To study the effect of thymoglobulin (TG) on proliferation, immune cell phenotype and cytotoxicity of cytokine-induced killer (CIK) cells in a clinical-grade culture protocol.
Methods: Peripheral blood mononuclear cells (PBMCs) isolated from 11 healthy donors were primed with IFN-γ on day 0 and treated with either TG or CD3 mAb on day 1. Thereafter, the cells were fed with IL-2 every 3 days until day 21. Aliquots of cells were harvested weekly. The cell number and viability were measured using trypan blue exclusion. The expressions of CD3, CD4, CD8, CD16/CD56, NK activating/inhibitory receptor, and the CD25⁺ Foxp3⁺ regulatory T cells (Tregs) were analyzed with flow cytometry. The cytotoxicity of CIK cells against K562 cells were determined by lactate dehydrogenase (LDH) release assay on day 16 and day 21.
Results: Both TG and CD3 mAb stimulated the growth of CIK cells. However, the effect of CD3 mAb was weaker than that of TG. Flow cytometric analysis showed that the percentages of CD3⁺ CD16⁺ CD56⁺ cells and CD3⁻ CD16⁺ CD56⁺ cells and the expression of NK activating/inhibitory receptor recovered and increased continuously until the end of culture (day 21) following a transient decrease at day 7. Noticeably, on day 7, 14 and 21, the percentages of CD3⁺ CD 16⁺ CD56⁺ cells and CD3⁻ CD16⁺ CD56⁺ cells as well as the expression of NK activating/inhibitory receptor were higher in TG-induced CIK cells than those in CD3 mAb-induced CIK cells (P<0.05); Moreover, LDH release assay revealed that the cytotoxicity of CIK cells against K562 cells in TG-induced CIK cells was significantly higher than that of CD3 mAb-induced CIK cells (P<0.05). In both CD3 mAb-induced CIK cell culture system and TG-induced CIK cell culture system, Treg increased transiently at day 7; moreover, the percentage of Treg in TG-induced CIK cells was significantly higher than that of CD3 mAb-induced CIK cells (P<0.05). In addition, both CD3 mAb and TG reduced the percentage of CD3⁺ CD4⁺ cells continuously, meanwhile increased the percentage of CD3⁺ CD8⁺ cells. There was no significant difference in the changes of CD3⁺ CD4⁺ cells and CD3⁺ CD8⁺ cells between the two CIK cell culture systems.
Conclusion: Compared with CD3 mAb, TG more selectively expanded CD3⁺ CD16⁺ CD56⁺ cells and CD3⁻ CD16⁺ CD56⁺ cells (CIK effector cells) and promoted the differentiation and maturation of these CIK effector cells with more powerful cytotoxic activity. Therefore, it is feasible for TG to substitute CD3 mAb to prepare the clinical grade products of CIK cells. Both CD3 mAb and TG increased negative regulatory cells, Tregs, transiently in CIK culture system and depleting or reducing Tregs might be helpful for increasing the production efficacy of the main effector cells in CIK cells.