Utilization of Cholera Toxin B as an Adjuvant for the Subunit PspA Vaccine, Provides Effective Protection against Streptococcus pneumoniae Challenge

Streptococcus pneumoniae is a prevalent human pathogen associated with pneumonia. It is estimated that approximately 1 million people around the world die each year, specifically with young children and the elderly comprising a significant portion. Currently, antibiotics can treat the infection but individuals such as the young or elderly are more susceptible to bodily damage from symptoms, such as pneumonia, meningitis, and sepsis, thus require more preventive measures. As a result, vaccinations are a key solution to providing effective protection against infectious pathogens. Presently, two vaccinations exist in the market: PPSV23 and PCV13, which only protect against select 23 or 13 serotypes respectively of Streptococcus pneumoniae out of the possible 90. Researchers are searching for alternative antigenic markers conserved throughout the multitude of serotypes to formulate cross-protective vaccinations. One such proponent is known as Pneumococcal Surface Protein A (PspA) which is a surface protein conserved throughout most serotypes and a potential candidate as a subunit vaccine against Streptococcus pneumoniae. To increase the immunogenicity of PspA for long term and effective protection, this study utilizes Cholera Toxin B (CTB) as an adjuvant to effectively increase vaccine efficacy. We assessed the efficacy of the subunit vaccine, PspA, administered intranasally (i.n.) in conjunction with CTB as an adjuvant. Our results indicated increased survival in mice immunized with both PspA and CTB accompanied with reduced lung bacterial burden, increased levels of S. pneumoniae-specific IgG subclass antibodies, increased cytokine production, and a reduced acute inflammatory response