A Novel Polymer Nanoparticle Polydimethyl Diallyl Ammonium Chloride as An Adjuvant Enhances the Immune Response of SARS-CoV-2 Subunit Vaccine.

The COVID-19 pandemic caused by SARS-CoV-2 has had a significant impact on global health and the economy. It has underscored the urgent need for a stable, easily produced and effective vaccine. In this study, we presented a novel approach using SARS-CoV-2 spike (S) protein-conjugated nanoparticles (NPs) in combination with cGAMP (S-NPs-cGAMP) as a subunit vaccine. When mice were immunized, the antiserum of S-NPs-cGAMP group exhibited a 16-fold increase in neutralizing activity against a pseudovirus, compared to S protein group. Additionally, S-NPs-cGAMP induced even higher levels of neutralizing antibodies. Remarkably, the vaccine also triggered a robust humoral immune response, as evidenced by a notable elevation in virus-specific IgG and IgM antibodies. Furthermore, after 42 days of immunization, there was an observed increase in specific immune cell populations in the spleen. CD3 + CD4 + and CD3 + CD8 + T lymphocytes, as well as B220 + CD19 + and CD3 - CD49b + NK lymphocytes, showed an upward trend, indicating a positive cellular immune response. Moreover, the S-NPs-cGAMP demonstrated promising results against the Delta strain and exhibited good cross-neutralization potential against other variants. These findings suggest that pDMDAAC NPs is potential adjuvant and could serve as a versatile platform for future vaccine development. This article is protected by copyright. All rights reserved.