Pneumococcal Surface Protein A-Hybrid Nanoparticles Protect Mice from Lethal Challenge after Mucosal Immunization Targeting the Lungs

Abstract

Pneumococcal disease remains a global burden, with current conjugated vaccines offering protection against the common serotype strains. However, there are over 100 serotype strains, and serotype replacement is now being observed, which reduces the effectiveness of the current vaccines. Pneumococcal surface protein A (PspA) has been investigated as a candidate for new serotype-independent pneumococcal vaccines, but requires adjuvants and/or delivery systems to improve protection. Polymeric nanoparticles (NPs) are biocompatible and, besides the antigen, can incorporate mucoadhesive and adjuvant substances such as chitosans, which improve antigen presentation at mucosal surfaces. This work aimed to define the optimal NP formulation to deliver PspA into the lungs and protect mice against lethal challenge. We prepared poly(glycerol-adipate-co-ω-pentadecalactone) (PGA-co-PDL) and poly(lactic-co-glycolic acid) (PLGA) NPs using an emulsion/solvent evaporation method, incorporating chitosan hydrochloride (HCl-CS) or carboxymethyl chitosan (CM-CS) as hybrid NPs with encapsulated or adsorbed PspA. We investigated the physicochemical properties of NPs, together with the PspA integrity and biological activity. Furthermore, their ability to activate dendritic cells in vitro was evaluated, followed by mucosal immunization targeting mouse lungs. PGA-co-PDL/HCl-CS (291 nm) or CM-CS (281 nm) NPs produced smaller sizes compared to PLGA/HCl-CS (310 nm) or CM-CS (299 nm) NPs. Moreover, NPs formulated with HCl-CS possessed a positive charge (PGA-co-PDL +17 mV, PLGA + 13 mV) compared to those formulated with CM-CS (PGA-co-PDL −20 mV, PLGA −40 mV). PspA released from NPs formulated with HCl-CS preserved the integrity and biological activity, but CM-CS affected PspA binding to lactoferrin and antibody recognition. PspA adsorbed in PGA-co-PDL/HCl-CS NPs stimulated CD80+ and CD86+ cells, but this was lower compared to when PspA was encapsulated in PLGA/HCl-CS NPs, which also stimulated CD40+ and MHC II (I-A/I-E)+ cells. Despite no differences in IgG being observed between immunized animals, PGA-co-PDL/HCl-CS/adsorbed-PspA protected 83% of mice after lethal pneumococcal challenge, while 100% of mice immunized with PLGA/HCl-CS/encapsulated-PspA were protected. Therefore, this formulation is a promising vaccine strategy, which has beneficial properties for mucosal immunization and could potentially provide serotype-independent protection.

A bacterial vesicle-based pneumococcal vaccine against influenza-mediated secondary Streptococcus pneumoniae pulmonary infection

“…A recent study showed that PspA immunization was more protective than the PCV13 against influenza-mediated secondary Spn infection but was not good against a high-dose (10 4 colony forming unit [CFU]) secondary Spn challenge 23 . To enhance the efficacy of protein vaccines and promote mucosal immune responses, there is emergent interest in the application of bacterial vesicles or other nanoparticles delivering candidate pneumococcal proteins as vaccines 24 – 26 . Recently, we have established a self-adjuvanting Yersinia pseudotuberculosis (Yptb) outer membrane vesicle (OMV) platform to deliver heterologous antigens to achieve protection against corresponding respiratory bacterial infections 27 , 28 .…”

Recent progress in pneumococcal protein vaccines

“…Subcutaneous immunization with PspA has proven effective in protecting mice from fatal infections ( 63 ), while intranasal immunization with PspA has shown efficacy in protection against nasopharyngeal carriage in an adult mouse carriage model ( 64 , 65 ). Furthermore, mucosal vaccination with PspA has successfully elicited both mucosal and systemic immune responses ( 66 , 67 ). Initially, there were concerns that a vaccine targeting PspA might not provide adequate coverage due to its high variability ( 68 ).…”

Evolution of Vaccines Formulation to Tackle the Challenge of Anti-Microbial Resistant Pathogens

“…These results suggest the potential adjuvant activity of PLGA/chitosan NPs in stimulating systemic immune responses. The supposed mechanism of action is related to the maturation of DCs upregulating CD40, CD80, and CD86, triggered by the production of MHC II molecules [124]. Another report detailed an improved CD8 T-cell immune response after the prolonged release of M. tuberculosis antigen Mtb8.4 after a single administration.…”