The disclosure features vaccine adjuvants comprising prokaryotic mRNA, and methods of vaccination using the adjuvants. More specifically, the disclosure provides a vaccine composition comprising a nonviable immunogen (e.g., heat-killed bacterium), a tumor antigen, or an immunogenic peptide of microbial or mammalian origin, and an adjuvant, wherein adjuvant comprises prokaryotic mRNA (e.g., bacterial mRNA), as well as the methods of using the vaccine compositions. Further disclosed are the structural features of the prokaryotic mRNA used as the adjuvants.
