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Background Human trophoblast cell surface antigen 2 (hTROP2), a transmembrane glycoprotein encoded by the Tumor Associated Calcium Signal Transducer 2 (TACSTD2) gene, is primarily expressed in trophoblasts and minimally in a few adult tissues.In various cancers, hTROP2 is overexpressed, making it a promising target for cancer immunotherapy.Here, we developed hTROP2 protein and circular mRNA-lipid nanoparticle (circRNA-LNP) vaccines and evaluated their efficacy in activating cellular immunity and suppressing hTROP2+ tumors in mice.Methods Recombinant protein antigens, consisting of hTROP2 fragments with or without immune enhancers, were produced in E. coli and 293T cells.The circRNA-LNP vaccine was prepared using standard in vitro transcription, circularization, and LNP-packaging methods.Mice were vaccinated with either protein antigen adjuvanted with a mixture of Poly(I:C) and Complete/Incomplete Freund's Adjuvant by subcutaneous injection once a week for seven weeks or circRNA-LNP by one or two intramuscular injections.Cellular immunity was assessed by the INFg ELISpot assay using splenocytes.Anti-cancer efficacy was evaluated by monitoring tumor growth of TROP2humanized mouse cancer cells, MC38-hTROP2 or 4T1-hTROP2, inoculated subcutaneously in mice that received vaccine or control.Results hTROP2 vaccines demonstrated robust activity in activating cellular immunity in both wildtype and several HLA-I allele-humanized transgenic mice.Two highly immunogenic fragments, T1 and T2, were identified in these mice.hTROP2 protein vaccine inhibited the growth of MC38-hTROP2 tumors in C57BL6 mice by 80% and completely suppressed the growth of 4T1-hTROP2 tumors in BABL/c mice.In MC38-hTROP2 tumors collected from the vaccinated mice, the percentage of CD8a+/IFNg+ T-cells was increased significantly albeit the cell number of CD8a+ T-cells remained unchanged, indicating that anti-tumor cytotoxicity was activated.hTROP2 circRNA-LNP vaccine achieved complete tumor inhibition in both MC38-hTROP2 and 4T1-hTROP2 tumor models.Conclusions hTROP2 vaccines effectively produce and present mouse and human MHC-I peptides, to activate cellular immunity in mouse models, leading to complete or near-complete hTROP2+ tumor suppression.hTROP2 vaccines, consisting of multiple epitopes for broad applicability across HLA variants, are promising for further development to treat TROP2+ cancers in humans.Ethics Approval All animal studies mentioned in this abstract were approved by Institutional Animal Care and Use Committee of CK Life Sciences Limited.The protocols of immunization and anti-cancer study were approved with the protocol number of 2023-01 and 2023-02, respectively.The period of these two protocols is from 5th Jan, 2024 to 4th Jan, 2027.