Adjuvant combination and antigen multimerization shape neutralizing antibody and T cell responses to a SARS-CoV-2 RBD...

Area of Science:

• Immunology
• Vaccinology
• Virology

Background:

• COVID-19 vaccine development faced challenges with inequity and emerging SARS-CoV-2 variants of concern (VOCs).
• The Spike protein's receptor binding domain (RBD) is a key target for neutralizing antibodies and a promising antigen for subunit vaccines.
• Enhancing RBD immunogenicity requires strategies like antigen multimerization and adjuvant addition.

Purpose of the Study:

• To compare the immunogenic properties of Wuhan RBD monomer, homodimer, and a heterotrimer (Delta, Beta, Gamma variants).
• To screen adjuvants for optimizing humoral and cellular immunity against SARS-CoV-2.
• To identify specific RBD epitopes that induce T cell responses.

Main Methods:

• Immunization of mice with RBD monomer, dimer, and trimer formulations.
• Screening of adjuvants, including AddaS03 and Poly I:C, alone and in combination.
• Assessment of humoral immunity (antibody response, neutralization) and cellular immunity (T cell responses, cytokine production).
• Analysis of viral replication in mouse lungs post-challenge.

Main Results:

• RBD dimer and trimer formulations with AddaS03 adjuvant induced higher humoral responses and broader neutralization.
• RBD-trimer immunization showed more effective inhibition of viral replication in mice.
• A combination of AddaS03 and Poly I:C adjuvants demonstrated synergistic effects, enhancing antibody affinity and generating long-lived plasma cells.
• Specific RBD peptides were identified as immunodominant CD4 (Peptide 12) and CD8 (Peptides 28, 29) T cell epitopes.

Conclusions:

• Antigen multimerization, particularly using trimers, significantly improves vaccine immunogenicity.
• Strategic combinations of adjuvants, like AddaS03 and Poly I:C, can synergistically enhance both humoral and cellular immunity.
• The identified T cell epitopes provide targets for developing next-generation SARS-CoV-2 vaccines.