Broad protective immune responses elicited by bacterium-like particle-based intranasal pneumococcal particle vaccine displaying PspA2 and PspA4 fragments.

Streptococcus pneumoniae is an infectious pathogen mainly infecting host bodies through the respiratory system. An effective pneumococcal vaccine would be targeted to the mucosa and provide not only protection against invasive infection but also against colonization in the respiratory system. In the present work, we applied bacterium-like particles (BLPs) as an adjuvant for the development of a PspA mucosal vaccine, in which the PspA protein was displayed on the surface of BLPs. Intranasal immunization with the PspA-BLP pneumococcal vaccine, comprised of PspA2 from pneumococcal family 1 and PspA4 from pneumococcal family 2, not only induced a high level of serum IgG antibodies but also a high level of mucosal SIgA antibodies. Analysis of binding of serum antibodies to intact bacteria showed a broad coverage of binding to pneumococcal strains expressing PspA from clade 1 to 5. Immunization with the PspA-BLP vaccine conferred protection against fatal intranasal challenge with both PspA family 1 and family 2 pneumococcal strains regardless of serotype. Therefore, the PspA-BLP pneumococcal vaccine was demonstrated to be a promising strategy for mucosal immunization to enhance both systemic and mucosal immune responses.

Protection elicited by nasal immunization with pneumococcal surface protein A (PspA) adjuvanted with bacterium-like particles against Streptococcus pneumoniae infection in mice.

Streptococcus pneumoniae is a major respiratory tract pathogen causing high levels of mortality and morbidity in infants and the elderly. In spite of the multitude of capsular polysaccharide vaccines used to guard against pneumococcal disease, fatal pneumococcal disease remains epidemic. Immunization with pneumococcal surface protein A (PspA), a highly immunogenic surface protein present in all strains of S. pneumoniae, can elicit protection against deadly pneumococcal infection. We have previously evaluated PspA in systemic vaccination. However, the mucosal immune system, as a first line of defense against respiratory infection, plays the most important role against the invasion of S. pneumoniae. In this study, we employed bacterium-like particles (BLPs) as an adjuvant for a PspA mucosal vaccine. The BLPs served as a carrier for PspA proteins bound to their surface. Mice were immunized intranasally with the PspA-BLP pneumococcal vaccine consisting of PspA3 from pneumococcal family 2. Not only did the immunized mice show a high level of serum IgG antibodies but also a high level of SIgA antibodies in the respiratory tract. After immunization with the PspA3-BLP vaccine, the mice were broadly protected against fatal intranasal challenge with homologous and heterogenous pneumococcal strains of different PspA families regardless of serotype, and the colony count was notably decreased in the lungs. Therefore, the PspA3-BLP pneumococcal vaccine has the potential to serve as a novel mucosal vaccine to enhance both systemic and mucosal immune responses to this disease.

Systemic and mucosal immune responses elicited by intranasal immunization with a pneumococcal bacterium-like particle-based vaccine displaying pneumolysin mutant Plym2.

Pneumolysin (Ply) is an important virulence factor in pneumococcal infection and a conserved cholesterol-binding cytotoxin expressed by all serotypes of Streptococcus pneumoniae. We previously developed a highly detoxified Ply mutant designated Plym2 by replacement of two amino acids (C428G and W433F), which lost cytotoxicity but retained the ability to induce neutralizing antibodies. In the present work, we applied bacterium-like particles (BLPs) as a carrier and immunostimulant for the development of a Plym2 intranasal vaccine, in which the Plym2 protein was displayed on the surface of BLPs. Intranasal immunization of mice with BLP-Plym2 not only induced a high level of serum IgG antibodies but also a high level of mucosal SIgA antibodies in lung lavages. Antiserum induced by the BLP-Plym2 vaccine elicited high-titer neutralization activity which could inhibit the hemolysis of wild-type Ply. In conclusion, the BLP-Plym2 vaccine was demonstrated to be a promising strategy for intranasal immunization to enhance both systemic and mucosal immune responses.

Inactivated influenza vaccine adjuvanted with bacterium-like particles induce systemic and mucosal influenza A virus specific T-cell and B-cell responses after nasal administration in a TLR2 dependent fashion.

BACKGROUND: Nasal vaccination is considered to be a promising alternative for parenteral vaccination against influenza virus as it is non-invasive and offers the opportunity to elicit strong antigen-specific responses both systemic and locally at the port of entry of the pathogen. Previous studies showed that non-living bacterium-like particles (BLPs) from the food-grade bacterium Lactococcus lactis are effective stimulators of local and systemic immune responses when administered intranasally. Moreover, in vitro, BLPs specifically interact with human Toll-like receptor 2 (TLR2), suggestive of a role for TLR2 dependent immune activation by BLPs. METHODS: In the present study, we examined the role of TLR2 in vivo in immune activation after nasal administration of BLP mixed with split influenza vaccine (BLP-SV) of influenza A virus (IAV) using TLR2 knockout mice. RESULTS: The systemic Th1 cell and subsequent B-cell responses induced after intranasal BLP-SV vaccination depended on the interaction of BLPs with TLR2. Notably, the BLP-SV-induced class switch to IgG2c depended on the interaction of BLP with TLR2. Local induced IAV-specific Th1 cell responses and the mucosal B-cell responses also depended on interaction of BLP with TLR2. Strongly reduced SIgA levels were observed in TLR2 knockout mice both in the nasal and vaginal lavages. In addition, detailed analysis of the T-cell response revealed that nasal BLP-SV vaccination promoted Th1/Th17 immune responses that coincided with increased IAV-specific IgG2c antibody production. DISCUSSION: Altogether these results indicate that nasal BLP-SV vaccination induces IAV-specific T-cell and B-cell responses, both systemically and at the site of virus entry in a TLR2-dependent manner.