Inhalable vaccine of bacterial culture supernatant extract mediates protection against fatal pulmonary anthrax

ABSTRACT

Pulmonary anthrax is the most fatal clinical form of anthrax and currently available injectable vaccines do not provide adequate protection against it. Hence, next-generation vaccines that effectively induce immunity against pulmonary anthrax are urgently needed. In the present study, we prepared an attenuated and low protease activity Bacillus anthracis strain A16R-5.1 by deleting five of its extracellular protease activity-associated genes and its lef gene through the CRISPR-Cas9 genome editing system. This mutant strain was then used to formulate a lethal toxin (LeTx)-free culture supernatant extract (CSE) anthrax vaccine, of which half was protective antigen (PA). We generated liquid, powder, and powder reconstituted formulations that could be delivered by aerosolized intratracheal inoculation. All of them induced strong humoral, cellular, and mucosal immune responses. The vaccines also produced LeTx neutralizing antibodies and conferred full protection against the lethal aerosol challenges of B. anthracis Pasteur II spores in mice. Compared to the recombinant PA vaccine, the CSE anthrax vaccine with equal PA content provided superior immunoprotection against pulmonary anthrax. The preceding results suggest that the CSE anthrax vaccine developed herein is suitable and scalable for use in inhalational immunization against pulmonary anthrax.

KEYWORDS:

• Inhalable vaccine
• pulmonary anthrax
• culture supernatant extract
• protective antigen
• mucosal immune response

Acknowledgments

The authors thank Wei Zhang for technical assistance in this study.

Author contributions

D.S.Z., T.Y.F., W.H.Y. and Y.C.W. conceived and designed the study. L.N.Z., Y.Z, X.L.S., and L.L.Z. performed animal experiments. T.T.Q., Z.J.Z., J.Z.W., C.Y.S., M.L. and L.F.H. performed other experiments. L.N.Z., Y.Z contributed to data analysis and interpretation, and writing the first draft of the manuscript. D.S.Z., T.Y.F., W.H.Y. and Y.C.W. revised the manuscript.

Disclosure statement

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