Objective:To express NY-ESO-1 epitopes using circular RNA (circRNA) and construct circRNA cancer vaccines using a novel lipid-like material C1, and to evaluate the transfection efficiency and T cell activation potential at cellular level.Methods:In vitro transcription was used to synthesize mRNA and circRNA expressing EGFP and NY-ESO-1 epitopes. Then, they were transfected into COS7 cells and the expression of target proteins were detected in vitro. Lipid-like material C1 and commercial transfection agent TransIT-mRNA were used as delivery systems for mRNA NY-ESO-1 and circRNA NY-ESO-1, and their delivery efficiency was compared. Results:The expression of EGFP was observed under fluorescence microscopy after transfection of mRNA EGFP and circRNA EGFP into COS7 cells for 24 h. The secretion of IFN-γ by T cell receptor-engineered T (TCR-T) cells targeting NY-ESO-1/HLA-A2 was stimulated by COS7-A*02: 01 cells transfected with mRNA NY-ESO-1 and circRNA NY-ESO-1. Compared with mRNA NY-ESO-1, circRNA NY-ESO-1 was able to express the target antigen and stimulate the target cells to release IFN-γ more persistently. The delivery efficiency of C1 material was better than that of commercial transfection reagents when COS7 cells were transfected in vitro. Conclusions:Compared with the linear mRNA, transfection of COS7-A*02: 01 cells with circRNA can lead to more efficient and durable activation of T cells, suggesting that it could be a more suitable candidate for clinical treatment of tumors in the future. The lipid-like material C1 can effectively deliver linear mRNA and circular RNA molecules. This study provides reference for further research on circRNA tumor vaccines.