Innovative Influenza Vaccines Enhance Safety and Immunity Through Proteolysis-Targeting Technology

Recent advancements in influenza vaccine technology have emerged from the Shenzhen Institutes of Advanced Technology, part of the Chinese Academy of Sciences. Researchers have developed a library of live-attenuated influenza A vaccines that utilize proteolysis-targeting, which aims to enhance both safety and cross-strain immunity in animal models.

The new strategy, termed PROTAR 2.0, represents an evolution of previous proteolysis-targeting concepts initially introduced in 2022. Traditional influenza vaccines, such as inactivated influenza vaccines (IIV) and cold-adapted live-attenuated influenza vaccines (CAIV), often face challenges due to mismatched natural antigens with circulating strains, which can lead to reduced efficacy. To address this issue, the researchers have engineered a method that converts circulating viruses into live vaccines, potentially ensuring better antigen alignment and increased effectiveness.

The team engineered PROTAR influenza viruses to be attenuated by the ubiquitin-proteasome system (UPS), allowing viral proteins to be degraded in conventional host cells while enabling efficient replication in specially engineered cell lines. By incorporating 22 distinct proteasome-targeting degrons (PTDs) into the viral protein M1, the researchers created a diverse PROTAR vaccine library. Each PTD is recognized by different E3 ligases, leading to varying levels of attenuation in vitro.

In animal studies, these PROTAR vaccine candidates demonstrated significant attenuation and induced broad-spectrum immune responses, providing robust protection against lethal infections from both homologous and heterologous viruses. These studies involved various animal models, including adult and aged mice, as well as mice with pre-existing flu immunity and ferrets.

Despite the promising results, the initial PROTAR approach had limitations, as PTDs could only be incorporated at the terminal ends of viral proteins. To enhance versatility, the researchers advanced to PROTAR 2.0, which allows for PTDs to be integrated at multiple sites within viral proteins. Their genome-wide investigation revealed that PROTAR 2.0 viruses, featuring two PTD-modified proteins, maintained effective replication in E3 ubiquitin ligase-knockout cells while being attenuated in conventional cells due to PTD-mediated proteasomal degradation.

In their evaluations with animal models, including mice and ferrets, PROTAR 2.0 viruses exhibited excellent safety profiles. A single intranasal administration of the PROTAR 2.0 vaccine sparked robust immune responses across humoral, mucosal, and T cell domains, yielding complete cross-reactive protection against various viral challenges. These findings underscore new pathways for the development of safe and effective live-attenuated vaccines.