[Effect of Special Structure Bi-Specific Chimeric Antigen Receptor T Cell on Tumor Cells].

Objective: To explore and design a novel bi-specific chimeric antigen receptor (CAR) structure. To obtain the corresponding CAR-T cells and verify killing effects on tumor cells in vitro and in vivo.
Methods: Five kinds of bi-specific CAR structures including humanized CD19 scFv and CD79b scFv, CD8 hinge & TM-4-1BB-CD3ζ and/or CD3ε chain intracellular regions were constructed and prepared. CAR-19-79b cells were obtained. Five kinds of CAR-T cells were co-incubated with the 3M-CD19-CD79b-Luc target cells. Luciferase assay and ELISA were used to detecte the killing ability of these five groups of CAR-T cells and the secretion of cytokines and compared. The optimal structure of CAR-T cells was used to treat the leukemia mouse model constructed by Daudi-Luc cells. And the treatment efficacy was evaluated. At the same time, other targets were used in this structure. With the same methods, the stability and effectiveness of the structure were verified.
Results: CAR-19-79b-T cells were cultured for 7 days, the expression rates of CAR-19 and CAR-79b were 21.6%-36.3% and 21.7%-37.8%, respectively. The killing rates of 5 kinds of CAR-19-79b-T cells prepared by T cells from 3 healthy donors on 3M-CD19-CD79b-Luc cells were significantly higher than those of the T cell control group at the effect-target ratio of 10∶1. Among them, the killing rates of CAR-19-79b-T cells with No. III and No. IV structures were the strongest. After co-incubation with 3M-CD19-CD79b-Luc target cells, the amount of IFN-γ and TNF-α secreted by CAR-T cells with CAR IV and CARV structures was the lowest. And there was no significance between the two groups ( P >0.05). CAR IV cells with remarkable killing effect and low secretion factor had obvious therapeutic effect on Daudi-Luc leukemia mice, extending the survival period of mice to 64 days. And all mice in the T cell control group died at 41.0±2.4 days. The CAR-19-BCMA-T and CAR-19-22-T with the same structure showed significant killing ability and low cytokine expression levels.
Conclusion: A novel bi-specific CAR structures was successfully designed, which could efficiently kill the corresponding tumor cells and secrete less cytokines (such as TNF-α, IFN-γ). Moreover, it shows obvious therapeutic effect on Daudi lymphoma mouse model. The bi-specific CAR structure shows good killing specificity and safety.