Microneedle-delivered adeno-associated virus vaccine amplified anti-viral immunity by improving antigen-presenting cells infection.

Adeno-associated viruses (AAV) have significant potential as vaccine carriers due to their excellent biosafety and efficient antigen gene delivery. However, most AAV vaccines show limited capacity to transduce antigen-presenting cells (APCs) following intramuscular injection which may cause inadequate cellular immune responses and undesired side effects due to transducing other tissues or cells. Herein, we developed a soluble microneedle patch for targeting the AAV vaccines to the epidermal and dermal APCs. To preserve the biological activity of the AAV vaccine, the microneedles were fabricated via an optimized two-step low-temperature strategy and using 20 % trehalose as a protective agent. AAV serotype 8, which expresses the trimeric receptor-binding domain (RBD) of the SARS-CoV-2 spike protein (AAV8-RBD), remained 100 % biological activity after being loaded into the microneedles (MN-A8R). Upon a single-dose vaccination on the dorsal skin of mice, MN-A8R efficiently recruited APCs to the vaccination site and improved AAV8-RBD infection in APCs. Furthermore, MN-A8R prompted an increased formation of germinal centers in the draining lymph nodes. Compared to hypodermic needle-mediated intradermal injection, MN-A8R induced significantly stronger cellular immune responses and long-lasting, high-quality neutralizing antibodies. Importantly, MN-A8R demonstrated more comprehensive and robust cross-protection against three common SARS-CoV-2 pseudoviruses for at least six months. Our findings highlight the use of optimized polymeric microneedles for preserving AAV vaccine biological activity and enhancing the AAV vaccine efficacy by up-regulating APC infection.