Introduction: Adjuvants play crucial roles in developing new and improved vaccines. Yet adjuvant discovery has been a slow process. We recently took a different approach to developing physical radiofrequency-based adjuvants (RFAs) to stimulate thermal tissue stress to enhance vaccine-induced immune responses. In murine models, RFA profoundly enhanced intradermal influenza-vaccine-induced humoral and cellular immune responses, with an adjuvant potency comparable to that of commonly used chemical adjuvants. RFA also showed potent dose-sparing effects for influenza vaccines, with an adjuvant potency superior to that of the MF59-like AddaVax adjuvant. Interestingly, the physical RFA only induced transient, low-level local inflammation without a significant change in the local proteome, in sharp contrast to chemical adjuvants. It is intriguing how RFA induces potent adjuvant effects without the induction of strong local inflammation or a significant change in the proteome.
Methods: This study focuses on uncovering the underlying action mechanisms of the physical RFA and its low-level local inflammation in murine models. Mice were subjected to RFA or Sham treatment, followed by intradermal injection of a fluorescence antigen. Inducible HSP70 expression and antigen uptake in diverse skin cell types were analyzed through flow cytometry. We further used HSP70 KO mice to evaluate the potential roles of HSP70 in antigen uptake and RFA-induced cytokine release.
Results: We found that RFA could induce rapid heat-shock protein 70 (HSP70) synthesis in the dendritic cells (DCs), which could release extracellularly and bind intradermally injected antigens. Furthermore, inducible HSP70 played crucial roles in mediating enhanced antigen uptake following RFA treatment. Interestingly, HSP70 suppressed the RFA-induced TLR4/NFκB signaling pathway and IL-6 release.
Conclusion: These studies indicate dual roles of in situ-induced HSP70 in antigen delivery and immunoregulation. This work supports the further development of alternative RFA to boost influenza vaccination with good local, systemic, and long-term safety.
