Antigen-specific B cells responding to pneumococcal polysaccharide vaccination in newly diagnosed HIV infected individuals. (P4264)

The peripheral blood of newly diagnosed HIV infected individuals is subjected to high uncontrolled viral titers. The decimation of both T and B cells thus leaves these individuals highly susceptible to opportunistic infections, including Streptococcus pneumoniae, despite the availability of vaccines. We have previously shown using directly labeled fluorescent pneumococcal polysaccharides that the majority of pneumococcal polysaccharide-specific B cells in healthy individuals were IgM+ memory B cells. Using this method, we identified specific deficiencies in B cell populations responding to pneumococcal polysaccharide vaccination in HIV infected individuals. Namely, a significant decrease in pneumococcal polysaccharide-specific IgM+ memory B cells compared to healthy individuals. Consequently, HIV infected individuals showed reduced antibody response and opsonophagocytic titers compared to healthy individuals. Furthermore, we correlated changes in pneumococcal polysaccharide-specific B cell populations post-vaccination with individual CD4 T cell counts. We observed a decreasing trend in pneumococcal polysaccharide-specific IgM+ memory B cells with lower CD4 T cell counts. These data indicate that the loss of pneumococcal polysaccharide-specific IgM+ memory B cells in HIV infected individuals correlates with CD4 counts and results in poor responsiveness to pneumococcal vaccination.

Immune Responses to pneumococcal vaccines in children and adults: Rationale for age-specific vaccination

Streptococcus pneumoniae is a significant human pathogen and currently available pneumococcal vaccines are designed to elicit anti-capsule antibodies. The 23-valent polysaccharide vaccine has been used in older adults for many years whereas 7-, 10-, and 13-valent pneumococcal conjugate vaccines have only been used commonly for young children in the last decade. In addition to their high protective efficacy among children, the use of conjugate vaccines in young children has had a number of additional effects, including production of a serotype shift and providing new herd immunity to adults. The immunogenicity of both of these types of vaccines can be determined by using an ELISA assay to measure antibody levels or an opsonophagocytosis assay to assess opsonic function. As these assays have improved over time, awareness of the analytical limitations of older studies has grown. While the 23-valent vaccine is effective among young adults, it is less effective among elderly adults. Aging-associated ineffectiveness may be due to aging-dependent changes in the antibody repertoire and/or a reduction in IgM antibody production associated with aging-dependent changes in B cell subpopulations. The immunologic basis of aging-associated immune defects thus remains an active area of research.