Pneumococcal Surface Protein A: A Promising Candidate for the Next Generation of Pneumococcal Vaccines

Streptococcus pneumoniae is the bacterium that causes pneumococcal disease which often results in pneumonia, meningitis, otitis media, septicemia and sinusitis. Pneumonia, particularly, is a significant cause of worldwide morbidity and a global health burden as well. Treatment often relies on antimicrobials, to which the pathogen is frequently mutating and rendering infective. Consequently, vaccination is the most effective approach in dealing with pneumococcal antimicrobial resistance (AMR). Unfortunately, the current pneumococcal polysaccharide and conjugate vaccines have a narrow serotype coverage. Therefore, the current need for vaccines with a broader serotype coverage cannot be overstated. Pneumococcal Surface Protein A and C are potential vaccine candidate antigens present in over 90% of the strains from clinical isolates as well as laboratory non-encapsulated strains. Pneumococcal Surface Protein A is an active virulent factor that pneumococci use to evade complement-mediated host immune responses and has been shown to elicit immune responses against pneumococcal infections. This review explores the potential utilization of Pneumococcal Surface Protein A to immunize against S. pneumoniae.

Distribution and Variation of Serotypes and Pneumococcal Surface Protein A Clades of Streptococcus pneumoniae Strains Isolated From Adult Patients With Invasive Pneumococcal Disease in Japan

Pneumococcal surface protein A (PspA) is a surface protein of Streptococcus pneumoniae that may be a candidate antigen for new pneumococcal vaccines. This study investigates the distribution of PspA clades of the causative strains of adult invasive pneumococcal disease (IPD) in Japan. Of the 1,939 strains isolated from cases of adult IPD during 2014–2019, the PspA clades of 1,932 (99.6%) strains were determined, and no pspA was detected in the remaining 7 strains (0.4%). PspA clades 1–6 were detected in 786 (40.5%), 291 (15.0%), 443 (22.8%), 369 (19.0%), 33 (1.7%), and 6 (0.3%) strains, respectively. New PspA clades (0.2%) were identified in two non-typeable and two serotype 35B pneumococci. The proportions of clade 1 and clade 2 showed significantly decreased and increased trends, respectively. Furthermore, the PspA clade of pneumococcal strains was partially serotype- and sequence type-dependent. The majority of strains belonging to serotypes contained in both the 13-valent pneumococcal conjugate vaccine (PCV13) and the 23-valent pneumococcal polysaccharide vaccine (PPSV23) belonged to PspA clades 1 or 3. In contrast, the distribution of clades in non-vaccine serotypes was wider than that of vaccine serotype pneumococci. Our findings demonstrate that almost all pneumococcal strains from adult IPD express PspA clades 1–4, especially for non-vaccine serotypes. These results may be useful for the development of a new pneumococcal vaccine with PspA.

Evaluation of Pneumococcal Surface Protein A as a Vaccine Antigen against Secondary Streptococcus pneumoniae Challenge during Influenza A Infection

Secondary bacterial pneumonia is responsible for significant morbidity and mortality during seasonal and pandemic influenza. Due to the unpredictability of influenza A virus evolution and the time-consuming process of manufacturing strain-specific influenza vaccines, recent efforts have been focused on developing anti-Streptococcus pneumoniae immunity to prevent influenza-related illness and death. Bacterial vaccination to prevent viral-bacterial synergistic interaction during co-infection is a promising concept that needs further investigation. Here, we show that immunization with pneumococcal surface protein A (PspA) fully protects mice against low-dose, but not high-dose, secondary bacterial challenge using a murine model of influenza A virus-S. pneumoniae co-infection. We further show that immunization with PspA is more broadly protective than the pneumococcal conjugate vaccine (Prevnar). These results demonstrate that PspA is a promising vaccine target that can provide protection against a physiologically relevant dose of S. pneumoniae following influenza infection.