Abstract
Synthetic oligodeoxynucleotides (ODN) containing unmethylated CpG motifs, CpG ODN, are Toll-like receptor 9 agonists (TLR9a), which have been used as adjuvants in pneumococcal vaccines to improve antibody responses in immunodeficient patients. Here, we examined whether the coadministration of TLR9a with pneumococcal CRM(197)-conjugate vaccine enhances protection against pneumococcal colonization, the levels of antipolysaccharide antibodies, and the CD4(+) T-cell responses. Wild-type BALB/c mice and B-cell-deficient BALB/c Igh-J(tm1Dhu) mice were immunized twice with the following: (i) PCV alone; (ii) simultaneous PCV and TLR9a; (iii) PCV and then TLR9a, after a 48-h delay; (iv) TLR9a alone; and (v) phosphate-buffered saline. Nasopharyngeal protection, serum antibodies, CD4(+) T-cell responses, and clearance of bacteremia after intraperitoneal challenge with Streptococcus pneumoniae 6B were evaluated. We found decreased nasopharyngeal protection against S. pneumoniae 6B colonization after simultaneous immunization with PCV and TLR9a compared to immunization with PCV alone in wild-type BALB/c mice (P = 0.037). A similar trend was observed in B-cell-deficient BALB/c Igh-J(tm1Dhu) mice. Simultaneous administration did not enhance antibody levels and lowered the CRM(197)-specific cytokine release of gamma interferon, interleukin-2 (IL-2), IL-5 and IL-13. Immunization with PCV and then TLR9a, after a 48-h delay, significantly improved nasopharyngeal protection compared to simultaneous administration (P = 0.011). Furthermore, delaying TLR9a delivery increased antibody titers compared to both simultaneous administration (P = 0.001) and PCV immunization alone (P = 0.026). In conclusion, the immunological and clinical impact of adjuvanting a pneumococcal conjugate vaccine (Prevnar; Pfizer) with a TLR9a is highly depended on timing of the adjuvant administration. Thus, careful timing of adjuvant administration may improve novel vaccine formulations.