Characterization of Protective Immune Responses Induced by Pneumococcal Surface Protein A in Fusion with Pneumolysin Derivatives

Abstract

Pneumococcal surface protein A (PspA) and Pneumolysin derivatives (Pds) are important vaccine candidates, which can confer protection in different models of pneumococcal infection. Furthermore, the combination of these two proteins was able to increase protection against pneumococcal sepsis in mice. The present study investigated the potential of hybrid proteins generated by genetic fusion of PspA fragments to Pds to increase cross-protection against fatal pneumococcal infection. Pneumolisoids were fused to the N-terminus of clade 1 or clade 2 pspA gene fragments. Mouse immunization with the fusion proteins induced high levels of antibodies against PspA and Pds, able to bind to intact pneumococci expressing a homologous PspA with the same intensity as antibodies to rPspA alone or the co-administered proteins. However, when antibody binding to pneumococci with heterologous PspAs was examined, antisera to the PspA-Pds fusion molecules showed stronger antibody binding and C3 deposition than antisera to co-administered proteins. In agreement with these results, antisera against the hybrid proteins were more effective in promoting the phagocytosis of bacteria bearing heterologous PspAs in vitro, leading to a significant reduction in the number of bacteria when compared to co-administered proteins. The respective antisera were also capable of neutralizing the lytic activity of Pneumolysin on sheep red blood cells. Finally, mice immunized with fusion proteins were protected against fatal challenge with pneumococcal strains expressing heterologous PspAs. Taken together, the results suggest that PspA-Pd fusion proteins comprise a promising vaccine strategy, able to increase the immune response mediated by cross-reactive antibodies and complement deposition to heterologous strains, and to confer protection against fatal challenge.

Toll-Like Receptor 2-Dependent Protection against Pneumococcal Carriage by Immunization with Lipidated Pneumococcal Proteins

“…Another approach is to create fusion proteins, including a lipid motif, as shown here with the fusion of SP_2108 and SP_1912. Such enhancement of immunogenicity and protection against pneumococcal colonization by fusion of proteins had been previously demonstrated with pneumolysin, a TLR4 agonist (39)(40)(41). Here we show this with a TLR2 agonist fused to the antigenic cargo, which likely enhances MHC class II (MHC-II) presentation (42).…”

Protective Immune Responses Elicited by Fusion Protein Containing PsaA and PspA Fragments

“…More than one pneumococcal protein can be prepared as a mixture or as fusion proteins. Some studies have demonstrated that fused antigens may be more effective than mixed formulations (Goulart et al, 2013;Lu et al, 2009;Nguyen et al, 2011). In our study, we found that sometimes mixing two or more antigens as the vaccine did not yield the predicted enhanced effect and may even result in a worse outcome than that obtained with just each of the proteins alone (data not shown).…”

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

“…To evaluate the neutralizing capacity of antisera containing anti-Ply antibodies, a hemolysis inhibition assay was performed as described previously (30). Briefly, pooled antisera (1:80) were incubated with Ply, and 2% sheep red blood cells were added.…”

“…Previously, we selected a PspA molecule able to induce antibodies with broad cross-reactivity (29) and demonstrated the potential use of this PspA molecule in fusion with PdT (30). Recently, in order to improve the immunogenicity of this fusion protein, we constructed a recombinant BCG (rBCG) strain expressing the PspA-PdT fusion protein (rBCG PspA-PdT) (31).…”