Abstract
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.
Highlights
Influenza virus remains one of the main threats to humanity, in spite of a long battle to eliminate infection
As NF-κB and AP-1 serves as key transcriptional proinflammatory regulators of immune response activity, we used a readout assay based on NF-κB/AP-1-dependent secreted embryonic alkaline phosphatase (SEAP) reporter RAW-Blue cells expressing both TLR4 and NOD2 to select the ratio of monophosphoryl lipid A (MPLA) (1 μg) and MDP (20 μg) that needs to be encapsulated into one dose of PLGA NPs to achieve the potentiation effect on the activity of these transcriptional factors (Figure S3)
In spite of numerous approaches aimed at improvement, the effectiveness of most subunit vaccines is still behind those types commonly regarded as the “gold standard”: inactivated or live attenuated [29,30]
Summary
Influenza virus remains one of the main threats to humanity, in spite of a long battle to eliminate infection. Vaccination is considered to be the Vaccines 2020, 8, 519; doi:10.3390/vaccines8030519 www.mdpi.com/journal/vaccines. Vaccines 2020, 8, 519 most effective strategy to preventing infectious diseases [2]. Choosing the highest safety characteristics as a primary requirement for modern vaccines, it is rational to use single highly purified antigenic molecules for subunit vaccine preparation. Subunit vaccines containing precisely defined antigenic molecules generally cause fewer side effects than vaccines based on either inactivated or live attenuated whole pathogens. A significant reduction in pathogen-specific molecules presents an immune portrait in which subunit vaccines are scarce and, rather distant from the original pathogen, which, in turn, is reflected by their decreased immunogenicity. Some “danger” signals associated with pathogens should be brought back into vaccine composition in an attempt to restore immunogenicity without affecting safety characteristics
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
