ABSTRACT
Intradermal delivery of self-replicating RNA (srRNA) is a promising vaccine platform. Considering that human skin temperature is around 33{degrees}C, lower than core body temperature of 37{degrees}C, we have developed an srRNA that functions optimally at skin temperature and is inactivated at or above 37{degrees}C as a safety switch. This temperature-controllable srRNA (c-srRNA), when tested as an intradermal vaccine against SARS-CoV-2, functions when injected naked without lipid nanoparticles. Unlike most currently available vaccines, c-srRNA vaccines predominantly elicit cellular immunity with little or no antibody production. Interestingly, c-srRNA-vaccinated mice produced antigen-specific antibodies upon subsequent stimulation with antigen protein. Antigen-specific antibodies were also produced when B-cell stimulation using antigen protein was followed by c-srRNA booster vaccination. Using c-srRNA, we have designed a pan-coronavirus booster vaccine that incorporates both spike receptor binding domains as viral surface proteins and evolutionarily conserved nucleoproteins as viral non-surface proteins, from both SARS-CoV-2 and MERS-CoV. It can thereby potentially immunize against SARS-CoV-2, SARS-CoV, MERS-CoV, and their variants. c-srRNA may provide a route to activate cellular immunity against a wide variety of pathogens.