Qualification and Clinical Validation of an Immunodiagnostic Assay for Detecting 11 Additional Streptococcus pneumoniae Serotype-specific Polysaccharides in Human Urine.

BACKGROUND: Identifying Streptococcus pneumoniae serotypes by urinary antigen detection (UAD) assay is the most sensitive way to evaluate the epidemiology of nonbacteremic community-acquired pneumonia (CAP). We first described a UAD assay to detect the S. pneumoniae serotypes 1, 3, 4, 5, 6A, 6B, 7F, 9V, 14, 18C, 19A, 19F, and 23F, covered by the licensed 13-valent S. pneumoniae conjugate vaccine. To assess the substantial remaining pneumococcal disease burden after introduction of several pneumococcal vaccines, a UAD-2 assay was developed to detect 11 additional serotypes (2, 8, 9N, 10A, 11A, 12F, 15B, 17F, 20, 22F, and 33F) in individuals with radiographically confirmed CAP. METHODS: The specificity of the UAD-2 assay was achieved by capturing pneumococcal polysaccharides with serotype-specific monoclonal antibodies, using Luminex technology. Assay qualification was used to assess accuracy, precision, and sample linearity. Serotype positivity was based on cutoffs determined by nonparametric statistical evaluation of urine samples from individuals without pneumococcal disease. The sensitivity and specificity of the positivity cutoffs were assessed in a clinical validation, using urine samples obtained from a large study that measured the proportion of radiographically confirmed CAP caused by S. pneumoniae serotypes in hospitalized US adults. RESULTS: The UAD-2 assay was shown to be specific and reproducible. Clinical validation demonstrated assay sensitivity and specificity of 92.2% and 95.9% against a reference standard of bacteremic pneumonia. In addition, the UAD-2 assay identified a S. pneumoniae serotype in 3.72% of nonbacteremic CAP cases obtained from hospitalized US adults. When combined with bacteremic CAP cases, the proportion of pneumonias with a UAD-2 serotype was 4.33%. CONCLUSIONS: The qualified/clinically validated UAD-2 method has applicability in understanding the epidemiology of nonbacteremic S. pneumoniae CAP and for assessing the efficacy of future pneumococcal conjugate vaccines that are under development.

The effect of preexisting anti-carrier immunity on subsequent responses to CRM197 or Qb-VLP conjugate vaccines.

CONTEXT: Certain antigens, such as haptens (small molecules), short peptides, and carbohydrates (e.g. bacterial polysaccharides) are non- or poorly immunogenic unless conjugated to a carrier molecule that provides a structural scaffold for antigen presentation as well as T cell help required for B-cell activation and maturation. However, the carriers themselves are immunogenic and resulting carrier-specific immune responses may impact the immunogenicity of other conjugate vaccines using the same carrier that are administered subsequently. OBJECTIVE: Herein, using two different carriers (cross-reactive material 197, CRM and Qb-VLP), we examined in mice the impact that preexisting anti-carrier antibodies (Ab) had on subsequent immune responses to conjugates with either the same or a different carrier. METHOD: For this purpose, we used two nicotine hapten conjugates (NIC7-CRM or NIC-Qb), two IgE peptide conjugates (Y-CRM or Y-Qb), and a pneumococcal polysaccharide conjugate (Prevnar 13(®)). RESULTS: Prior exposure to CRM or Qb-VLP significantly reduced subsequent responses to the conjugated antigen having the homologous carrier, with the exception of Prevnar 13® where anti-polysaccharide responses were similar to those in animals without preexisting anti-carrier Ab. CONCLUSION: Collectively, the data suggest that the relative sizes of the antigen and carrier, as well as the conjugation density for a given conjugate impact the extent of anti-carrier suppression. All animals developed anti-carrier responses with repeat vaccination and the differences in Ab titer between groups with and without preexisting anti-carrier responses became less apparent; however, anti-carrier effects were more durable for Ab function.