PNEUMOCOCCAL DIVERSITY - CONSIDERATIONS FOR NEW VACCINE STRATEGIES WITH EMPHASIS ON PNEUMOCOCCAL SURFACE PROTEIN-A (PSPA)

Streptococcus pneumoniae is a problematic infectious agent, whose seri ousness to human health has been underscored by the recent rise in the frequency of isolation of multidrug-resistant strains. Pneumococcal p neumonia in the elderly is common and often fatal. Young children in t he developing world are at significant risk for fatal pneumococcal res piratory disease, while in the developed world otitis media in childre n results in substantial economic costs. Immunocompromised patients ar e extremely susceptible to pneumococcal infection. With 90 different c apsular types thus far described, the diversity of pneumococci contrib utes to die challenges of preventing and treating S. pneumoniae infect ions. The current capsular polysaccharide vaccine is not recommended f or use in children younger than 2 years and is not fully effective in the elderly. Therefore, innovative vaccine strategies to protect again st this agent are needed. Given the immunogenic nature of S. pneumonia e proteins, these molecules are being investigated as potential vaccin e candidates. Pneumococcal surface protein A (PspA) has been evaluated for its ability to elicit protection against S. pneumoniae infection in mouse models of systemic and local disease. This review focuses on immune system responsiveness to PspA and the ability of PspA to elicit cross-protection against heterologous strains. These parameters will be critical to the design of broadly protective pneumococcal vaccines.