Induction of systemic and mucosal immune response and decrease in Streptococcus pneumoniae colonization by nasal inoculation of mice with recombinant lactic acid bacteria expressing pneumococcal surface antigen A

Mucosal epithelia constitute the first barriers to be overcome by pathogens during infection. The induction of protective IgA in this location is important for the prevention of infection and can be achieved through different mucosal immunization strategies. Lactic acid bacteria have been tested in the last few years as live vectors for the delivery of antigens at mucosal sites, with promising results. In this work, Streptococcus pneumoniae PsaA antigen was expressed in different species of lactic acid bacteria, such as Lactococcus lactis, Lactobacillus casei, Lactobacillus plantarum, and Lactobacillus helveticus. After nasal inoculation of C57Bl/6 mice, their ability to induce both systemic (IgG in serum) and mucosal (IgA in saliva, nasal and bronchial washes) anti-PsaA antibodies was determined. Immunization with L. lactis MG1363 induced very low levels of IgA and IgG, possibly by the low amount of PsaA expressed in this strain and its short persistence in the nasal mucosa. All three lactobacilli persisted in the nasal mucosa for 3 days and produced a similar amount of PsaA protein (150–250 ng per 10⁹ CFU). However, L. plantarum NCDO1193 and L. helveticus ATCC15009 elicited the highest antibody response (IgA and IgG). Vaccination with recombinant lactobacilli but not with recombinant L. lactis led to a decrease in S. pneumoniae recovery from nasal mucosa upon a colonization challenge. Our results confirm that certain Lactobacillus strains have intrinsic properties that make them suitable candidates for mucosal vaccination experiments.

Expression and characterization of cholera toxin B—pneumococcal surface adhesin A fusion protein in Escherichia coli: ability of CTB-PsaA to induce humoral immune response in mice

Cholera toxin B subunit (CTB) is responsible for CT holotoxin binding to the cell and has been described as a mucosal adjuvant for vaccines. In this work, the ctxB gene was genetically fused to the psaA gene from Streptococcus pneumoniae, a surface protein involved in its colonization in the host that is also considered a vaccine antigen candidate against this pathogen. The CTB-PsaA fusion protein was expressed in Escherichia coli, and the purified protein was used for intranasal immunization experiments in Balb/C mice. CTB-PsaA was able to induce both systemic and mucosal antibodies evaluated in serum, saliva, and in nasal and bronchial wash samples, showing that CTB-PsaA is a promising molecule to be investigated as S. pneumoniae vaccine antigen candidate.

Expression and characterization of HPV-16 L1 capsid protein in Pichia pastoris

Human papillomaviruses (HPVs) are responsible for the most common human sexually transmitted viral infections. Infection with high-risk HPVs, particularly HPV16, is associated with the development of cervical cancer. The papillomavirus L1 major capsid protein, the basis of the currently marketed vaccines, self-assembles into virus-like particles (VLPs). Here, we describe the expression, purification and characterization of recombinant HPV16 L1 produced by a methylotrophic yeast. A codon-optimized HPV16 L1 gene was cloned into a non-integrative expression vector under the regulation of a methanol-inducible promoter and used to transform competent Pichia pastoris cells. Purification of L1 protein from yeast extracts was performed using heparin-sepharose chromatography, followed by a disassembly/reassembly step. VLPs could be assembled from the purified L1 protein, as demonstrated by electron microscopy. The display of conformational epitopes on the VLPs surface was confirmed by hemagglutination and hemagglutination inhibition assays and by immuno-electron microscopy. This study has implications for the development of an alternative platform for the production of a papillomavirus vaccine that could be provided by public health programs, especially in resource-poor areas, where there is a great demand for low-cost vaccines.