Neutralizing Antibodies Elicited by a Novel Detoxified Pneumolysin Derivative, PlyD1, Provide Protection against Both Pneumococcal Infection and Lung Injury

Abstract

<jats:title>ABSTRACT</jats:title><jats:p><jats:named-content xmlns:xlink="http://www.w3.org/1999/xlink" content-type="genus-species" xlink:type="simple">Streptococcus pneumoniae</jats:named-content>pneumolysin (PLY) is a virulence factor that causes toxic effects contributing to pneumococcal pneumonia. To date, deriving a PLY candidate vaccine with the appropriate detoxification and immune profile has been challenging. A pneumolysin protein that is appropriately detoxified and that retains its immunogenicity is a desirable vaccine candidate. In this study, we assessed the protective efficacy of our novel PlyD1 detoxified PLY variant and investigated its underlying mechanism of protection. Results have shown that PlyD1 immunization protected mice against lethal intranasal (i.n.) challenge with pneumococci and lung injury mediated by PLY challenge. Protection was associated with PlyD1-specific IgG titers and<jats:italic>in vitro</jats:italic>neutralization titers. Pretreatment of PLY with PlyD1-specific rat polyclonal antiserum prior to i.n. delivery of toxin reduced PLY-mediated lung lesions, interleukin-6 (IL-6) production, and neutrophil infiltration into lungs, indicating that protection from lung lesions induced by PLY is antibody mediated. Preincubation of PLY with a neutralizing monoclonal PLY antibody also specifically reduced the cytotoxic effects of PLY after i.n. inoculation in comparison to nonneutralizing monoclonal antibodies. These results indicate that the induction of neutralizing antibodies against PLY can contribute to protection against bacterial pneumonia by preventing the development of PLY-induced lung lesions and inflammation. Our detoxified PlyD1 antigen elicits such PLY neutralizing antibodies, thus serving as a candidate vaccine antigen for the prevention of pneumococcal pneumonia.</jats:p>

A Combination of Recombinant Mycobacterium bovis BCG Strains Expressing Pneumococcal Proteins Induces Cellular and Humoral Immune Responses and Protects against Pneumococcal Colonization and Sepsis

“…Interestingly, when we evaluated the functionality of these antibodies, we observed that only sera generated against rBCG Mix/rMix or rMix were able to inhibit the hemolytic activity of Ply on sheep red blood cells. Indeed, the in vivo neutralization of Ply can be correlated with protection against tissue damage during a pneumococcal infection (38). The result obtained using sera from mice immunized with WT-BCG/rMix is in accordance with our previous study in which sera from mice receiving a priming dose of WT-BCG and boosted with rPspA-PdT showed poor ability to inhibit the cytolytic activity of Ply (31).…”

Human Antibodies to PhtD, PcpA, and Ply Reduce Adherence to Human Lung Epithelial Cells and Murine Nasopharyngeal Colonization by Streptococcus pneumoniae

“…Several studies have explored the use of different S. pneumoniae surface proteins as vaccine candidates in mouse immunization challenge models (35,48). While this was informative, a question remained as to whether the protection observed was due to mouse-specific antibodies and therefore inherent in an artificial immunization model.…”

“…The mutations in PlyD1 are T65C, G293C, and C428A (34). PlyD1 lacks hemolytic activity and induces neutralizing antibodies against the wild-type toxin (35).…”

Multivalent Pneumococcal Protein Vaccines Comprising Pneumolysoid with Epitopes/Fragments of CbpA and/or PspA Elicit Strong and Broad Protection

“…It protects mice from diverse S. pneumoniae strains when used as either a single immunogen or in combination with other proteins, particularly PspA and CbpA (24)(25)(26)(27)(28). More recently, a triple mutant toxoid, PlyD1 (comprising T65C, G293C, and C428A mutations), with only 0.001% residual hemolytic activity, was also shown to elicit protection against pneumococcal infection and lung injury (29). A novel Ply toxoid devoid of detectable cytotoxicity contains an L460D substitution, which disrupts a threonine-leucine pair that comprises the cholesterol recognition motif (CRM) and is critical for cholesterol binding on target cells by several cholesterol-dependent cytolysins (CDCs) (30).…”