Abstract 3533: Claudin 6 vaccines effectively inhibit tumor growth in a syngeneic mouse colon cancer model

Abstract Human Claudin 6 (CLDN6) is a member of the Claudin family of proteins, which play a crucial role in the structure and function of tight junctions. The expression of CLDN6 is restricted to stem cells and embryonic tissues. In human adults, CLDN6 mRNA is only detected at very low levels in testis, pancreas, and placenta. However, several types of cancers have been found to express CLDN6 at high levels, suggesting that CLDN6 is an ideal tumor-associated antigen and target for immunotherapy, albeit its precise role in cancer remains to be defined. Here, we designed and produced vaccine proteins consisting of multiple human B- and/or T-cell epitopes of CLDN6, which were selected from computer-predicted sequences, fused with an immune enhancer/carrier, and investigated their immunogenicity and anti-cancer activities in mice. First, C57BL/6 mice were vaccinated subcutaneously once a week for 5 times with the different vaccine proteins. CpG oligodeoxynucleotides were used as the vaccine adjuvant. Using the IFNγ ELISpot assay, we found that splenocytes collected from mice vaccinated with vaccine proteins containing T-cell epitopes displayed potent IFNγ release activity after stimulation with T-cell epitope peptides, suggesting that these CLDN6 vaccine proteins may inhibit the growth of CLDN6-expressing cancer by activating specific cytotoxic T-cells to destroy cancer cells. To explore this potential, we investigated the anti-cancer activity of the vaccine proteins by monitoring the tumor growth of CLDN6-humanized MC38 mouse colon cancer cells inoculated subcutaneously in vaccinated C57BL/6 mice for 4 weeks. We found that the growth of tumors was inhibited 98-100% (compared to the adjuvant-only control group) in two groups of mice (N=8 in each group) vaccinated with proteins containing multiple T-cell epitopes. In the first group, all 8 tumors disappeared within 4 weeks. In the second group, 7 of 8 tumors disappeared within 3 weeks and the last tumor stopped growing after the second week. In mice treated with adjuvant only, all tumors (N=8) displayed the same growth rate and reached an average of ∼1, 000 mm3 in volume, similar to mice treated with PBS. Collectively, our results demonstrate that CLDN6 vaccines effectively inhibited the growth of CLDN6-expressing cancer cells in mice. These findings suggest that CLDN6 protein vaccines hold promise for treating CLDN6-expressing cancers in humans, and this potential will be further explored in future studies. Citation Format: Na Wang, Melvin Toh, Hong Wang. Claudin 6 vaccines effectively inhibit tumor growth in a syngeneic mouse colon cancer model [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 3533.