Along with their excellent safety profiles, subunit vaccines are typically characterized by much weaker immunogenicity and protection efficacy compared to whole-pathogen vaccines. Here, we present an approach aimed at bridging this disadvantage that is based on synergistic collaboration between pattern-recognition receptors (PRRs) belonging to different families. We prepared a model subunit vaccine formulation using an influenza hemagglutinin antigen incorporated into poly-(D,L-lactic-co-glycolic acid) (PLGA) nanoparticles adjuvanted with monophosphoryl lipid A (TLR4 agonist) and muramyl dipeptide (NOD2 agonist). The efficacy studies were conducted in comparison to control vaccine formulations containing individual PRR agonists. We show that the complex adjuvant based on TLR4 and NOD2 agonists potentiates proinflammatory cell responses (measured by activity of transcription factors and cytokine production both in vitro and in vivo) and enhances the phagocytosis of vaccine particles up to comparable levels of influenza virus uptake. Finally, mice immunized with vaccine nanoparticles containing both PRR agonists exhibited enhanced humoral (IgG, hemagglutination-inhibition antibody titers) and cellular (percentage of proliferating CD4+ T-cells, production of IFNɣ) immunity, leading to increased resistance to lethal influenza challenge. These results support the idea that complex adjuvants stimulating different PRRs may present a better alternative to individual PAMP-based adjuvants and could further narrow the gap between the efficacy of subunit versus whole-pathogen vaccines.

Background: The SARS-CoV-2 virus continuously acquires mutations, leading to the emergence of new variants. Notably, the effectiveness of global vaccination efforts has significantly declined with the rise and spread of the B.1.1.529 (Omicron) variant. Methods: The study used virological, immunological and histological research methods, as well as methods of working with laboratory animals. In this study, we evaluated the Gam-COVID-Vac (Sputnik V), an adenoviral vaccine developed by the N.F. Gamaleya National Research Center for Epidemiology and Microbiology, and conducted experiments on hemizygous K18-ACE2-transgenic F1 mice. The variants studied included B.1.1.1, B.1.1.7, B.1.351, B.1.1.28/P.1, B.1.617.2, and B.1.1.529 BA.5. Results: Our findings demonstrate that the Sputnik V vaccine elicits a robust humoral and cellular immune response, effectively protecting vaccinated animals from challenges posed by various SARS-CoV-2 variants. However, we observed a notable reduction in vaccine efficacy against the B.1.1.529 (Omicron BA.5) variant. Conclusions: Our results indicate that ongoing monitoring of emerging mutations is crucial to assess vaccine efficacy against new SARS-CoV-2 variants to identify those with pandemic potential. If protective efficacy declines, it will be imperative to develop new vaccines tailored to current variants of the virus.