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.
Streptococcus pneumoniae, or pneumococcus, is part of the human microbiota, but in some cases it can cause diseases, such as pneumonia, bacteremia and meningitis. One of the main forms of controlling pneumococcal infections was the development of vaccines based on the induction of antibodies against capsular polysaccharide (PS). Since a limited number of serotypes are included in pneumococcal conjugate vaccines (PCVs) and their effectiveness against non-invasive diseases is still controversial, the development of a new generation of serotype-independent vaccines is still a priority. Pneumococcal surface protein A (PspA) is an antigen with great potential for vaccine use. PspA shows some variability between strains and is divided in family 1 (clades 1 and 2), family 2 (clades 3, 4 and 5) and family 3 (clade 6). The aim of this work is to evaluate the immunogenicity and efficacy of poly (glycerol-adipate-coω-pentadecalactone) (PGA-co-PDL) nanoparticles (NPs) containing PspA (PspA4Pro) and formulated in micrometric particles (NP/NCMP PspA4Pro) in a murine model of pulmonary immunization. Initially, three inoculation techniques were tested for lung immunization of mice. Both the inoculation of the NP/NCMPs as dry powder using a pulmonary insufflator and inoculation of the resuspension of the NP/NCMPs in saline using a microsprayer did not induce IgG serum antibodies reproducibly. For the third immunization strategy, a micropipette was used for immunization through nasal instillation of two doses of the resuspension of the NP/NCMPs. Immunization with NP/NCMP PspA4Pro using this technique showed reproducible results, with the induction of anti-PspA4Pro IgG in serum and bronchoalveolar lavage (BALF). IgG antibodies induced by immunization with NP/NCMP PspA4Pro showed binding to the surface of intact bacteria expressing PspA from clades 3, 4 and 5 (family 2), but no binding was observed for bacteria expressing PspA from clades 1 and 2 (family 1). Immunized mice were then challenged with strains ATCC6303 (serotype 3, PspA clade 5) or EF3030 (serotype 19F, PspA1) and BALF was collected after 12 and 24 hours, respectively. A reduction in bacterial load in BALF was observed in mice challenged with ATCC6303. A reduction in IL-6, TNF- KC/CXCL1 and MIP-2 CXCL2 levels in BALF of mice immunized with NP/NCMP PspA4Pro was also observed. Reduction in bacterial load was not observed for mice challenged with strain EF3030 though. A challenge with strain ATCC6303 strain was also performed to evaluate overall survival and partial protection was observed for the group immunized with NP/NCMP PspA4Pro. In conclusion, lung immunization with NP/NCMP PspA4Pro is able to induce antibodies in serum and lungs, conferring protection against a pneumococcal strain expressing PspA from the same family. Future studies are thus necessary to guarantee broader vaccine protection.
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