Mucosal adjuvanticity and mucosal booster effect of colibactin-depleted probiotic Escherichia coli membrane vesicles

ABSTRACT

There is a growing interest in development of novel vaccines against respiratory tract infections, due to COVID-19 pandemic. Here, we examined mucosal adjuvanticity and the mucosal booster effect of membrane vesicles (MVs) of a novel probiotic E. coli derivative lacking both flagella and potentially carcinogenic colibactin (ΔflhDΔclbP). ΔflhDΔclbP-derived MVs showed rather strong mucosal adjuvanticity as compared to those of a single flagellar mutant strain (ΔflhD-MVs). In addition, glycoengineered ΔflhDΔclbP-MVs displaying serotype-14 pneumococcal capsular polysaccharide (CPS14⁺MVs) were well-characterized based on biological and physicochemical parameters. Subcutaneous (SC) and intranasal (IN) booster effects of CPS14⁺MVs on systemic and mucosal immunity were evaluated in mice that have already been subcutaneously prime-immunized with the same MVs. With a two-dose regimen, an IN boost (SC-IN) elicited stronger IgA responses than homologous prime-boost immunization (SC-SC). With a three-dose regimen, serum IgG levels were comparable among all tested regimens. Homologous immunization (SC-SC-SC) elicited the highest IgM responses among all regimens tested, whereas SC-SC-SC failed to elicit IgA responses in blood and saliva. Furthermore, serum IgA and salivary SIgA levels were increased with an increased number of IN doses administrated. Notably, SC-IN-IN induced not only robust IgG response, but also the highest IgA response in both serum and saliva among the groups. The present findings suggest the potential of a heterologous three-dose administration for building both systemic and mucosal immunity, e.g. an SC-IN-IN vaccine regimen could be beneficial. Another important observation was abundant packaging of colibactin in MVs, suggesting increased applicability of ΔflhDΔclbP-MVs in the context of vaccine safety.

KEYWORDS:

• Administration route
• mucosal adjuvanticity
• immunogenicity
• heterologous prime-boost immunization
• respiratory tract infection
• Streptococcus pneumoniae
• capsular polysaccharide
• probiotic Escherichia coli
• membrane vesicles

Acknowledgments

The authors thank Fumiko Takashima, Junko Sugita, Toru Kikuchi, Hirotaka Kobayashi (National Institute of Infectious Diseases, Japan), Hirayama Satoru (Niigata University, Japan) for their valuable assistance. We are also grateful for Bernt Eric Uhlin and Sun Nyunt Wai (Umeå University, Sweden) and Mario F. Feldman and M. Florencia Haurat (Washington University, United States) for providing the precious materials.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Author contributions

R.N. designed the study, wrote the first draft of the manuscript, and did the final edits. H.U., T.Y., N.O., K.W., K.A., H.M., and R.N. conducted experiments. H.U., T.K., T.Y., N.O., K.W., K.A., H.M., M.T., N.N., Y.A., and R.N. reviewed manuscript. All authors contributed to the article and approved the submitted version.

Supplementary material

Supplemental data for this article can be accessed on the publisher’s website at https://doi.org/10.1080/21645515.2024.2337987.

Additional information

Funding

This work was supported by grants from KAKENHI of the Japan Society for the Promotion of Science (JSPS) [nos. 19K22644, 20K09943, 21KK0164, and 21K18284] and Ministry of Education, Culture, Sports, Science and Technology (MEXT) [no. 20H03861].