Bioengineered ClearColi™-derived outer membrane vesicles displaying CT26 neoepitopes as potent vaccine adjuvants...

The mutation frequency of colorectal cancer, the third most diagnosed tumor worldwide, is usually very high. To simultaneously target several mutations, we previously designed a CT26 polytope containing neoepitopes and epitopes of the murine CT26 colon cancer cell line. Additionally, to overcome the low immunogenicity of the CT26 polytope vaccine, we isolated recombinant outer membrane vesicles (rOMVs) displaying CT26 polytope from ClearColi™ and found that they induce antitumor immunity. In light of our previous studies, in this study, the recombinant CT26 polytope was chosen as the antigen to investigate the role of ClearColi™-derived OMVs and rOMVs displaying the CT26 polytope as adjuvants against colorectal carcinoma. CT26 polytope vaccine alone and in combination with OMV, rOMV displaying CT26 polytope, and alum as adjuvants were administered to BALB/c mice. Then, the humoral immunity specific to CT26-M90 and CT26 polytope and the stimulated IFN-γ, TNF-α, IL-10, and granzyme B were evaluated. Furthermore, the preventive effect of different immunization strategies against CT26 cells was assessed. Herein, immunization with OMVs and, particularly, rOMVs as adjuvants in combination with CT26 polytope resulted in higher production of CT26 polytope- and CT26-M90 peptide-specific IgG2a antibodies, an indicator of potential Th1 response, and enhanced levels of IFN-γ and TNF-α compared to alum. Furthermore, rOMVs as adjuvants induced higher levels of granzyme B and protection against CT26 characterized by significant reduction of tumor size compared to alum as adjuvants. This study indicates the efficacy of rOMVs and OMVs as adjuvants in combination with the CT26 polytope in a preventive CT26 mouse model. rOMVs delivering polytopic antigens, including different neoepitopes and epitopes as adjuvants, can provide promising platforms for the development of personalized cancer vaccines and vaccines against diseases containing highly variable antigens.