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Streptococcus pneumoniae colonizes the upper respiratory tract of healthy individuals, from where it can be transmitted to the community. Occasionally, bacteria invade sterile niches, causing diseases. The pneumococcal surface protein C (PspC) is a virulence factor that is important during colonization and the systemic phases of the diseases. Here, we have evaluated the effect of nasal or sublingual immunization of mice with Lactobacillus casei expressing PspC, as well as prime-boosting protocols using recombinant PspC, on nasopharyngeal pneumococcal colonization. None of the protocols tested was able to elicit significant levels of anti-PspC antibodies before challenge. However, a significant decrease in pneumococcal recovery from the nasopharynx was observed in animals immunized through the nasal route with L. casei-PspC. Immune responses evaluated after colonization challenge in this group of mice were characterized by an increase in mucosal anti-PspC immunoglobulin A (IgA) 5 days later, a time point in which the pneumococcal loads were already low. A negative correlation between the concentrations of anti-PspC IgA and pneumococcal recovery from the nasopharynx was observed, with animals with the lowest colonization levels having higher IgA concentrations. These results show that nasal immunization with L. casei-PspC primes the immune system of mice, prompting faster immune responses that result in a decrease in pneumococcal colonization., (© 2011 Federation of European Microbiological Societies. Published by Blackwell Publishing Ltd. All rights reserved.)

A mycobacterial codon-optimized gene encoding the Sm14 antigen of Schistosoma mansoni was generated using oligonucleotide assembly. This synthetic gene enhanced approximately fourfold the protein expression level in recombinant Mycobacterium bovis Bacille Calmette-Guérin (rBCG) when compared to that obtained using the native gene in the same expression vector. Immunization of mice with rBCG expressing Sm14 via the synthetic gene induced specific cellular Th1-predominant immune responses, as determined by interferon-gamma production of Sm14-stimulated splenocytes, which were comparable to those recorded in animals immunized with an rBCG strain expressing the native gene. Administration of a single dose of the rBCG-Sm14 construct carrying the synthetic gene conferred protection against cercarial challenge in outbred Swiss mice, at a level equivalent to those provided by either a single dose of rBCG expressing the native gene or three doses of Escherichia coli-derived recombinant Sm14. Our data demonstrated that despite improving the level of antigen expression, the codon optimization strategy did not result in enhanced immunity or protection against cercarial S. mansoni challenge.

The 7-valent polysaccharide conjugate vaccine currently administered against Streptococcus pneumoniae has been shown to be highly effective in high risk-groups, but its use in developing countries will probably not be possible due to high costs. The use of conserved protein antigens using the genetic vaccination strategy is an interesting alternative for the development of a cost-effective vaccine. We have analyzed the potential of DNA vaccines expressing genetically detoxified derivatives of pneumolysin (pneumolysoids) against pneumococcal infections, and compared this with immunization using recombinant protein. The purified recombinant pneumolysoid with the highest residual cytolytic activity was able to confer partial protection against a lethal intraperitoneal challenge, with the induction of high antibody levels. Immunization with DNA vaccines expressing pneumolysoids, on the other hand, induced a significantly lower antibody response and no protection was observed.

Streptococcus pneumoniae is a major public health problem and new strategies for the development of cost-effective alternative vaccines are important. The use of protein antigens such as PspA (pneumococcal surface protein A) is a promising approach to increase coverage at reduced costs. We have previously described the induction of a strong antibody response by a DNA vaccine expressing a C-terminal fragment of PspA. Fusion of this fragment with the cytoplasmic variant of SV40 large T-antigen (CT-Ag) caused reduction in specific interferon-gamma produced by stimulated spleen cells. In this work we show that the DNA vaccine expressing the C-terminal region of PspA elicits significant protection in mice against intraperitoneal challenge with a virulent strain of S. pneumoniae. Furthermore, fusion with CT-Ag completely abrogated the protection elicited by DNA immunization with this fragment. In this case, protection did not correlate with total anti-PspA antibody production nor with total IgG2a levels. The anti-PspA sera obtained from both constructs showed equivalent opsonic activity of pneumococci, indicating that the antibodies produced were functional. We could, though, observe a correlation between a lower IgG1:IgG2a ratio, which is indicative of a stronger bias towards Th1 responses, and protection. We also show that a vector expressing the most variable N-terminal alpha-helical region induces higher antibody formation, with increased protection of mice against intraperitoneal challenge with a more virulent strain of S. pneumoniae. As a whole, these results indicate that antibodies elicited against PspA would not be solely responsible for the protection induced by DNA vaccination and that cell-mediated immune responses could also be involved in protection against pneumococcal sepsis.