• Vaccine Name: Nontypeable H. influenzae rTbpB vaccine
• Target Pathogen: Haemophilus influenzae
• Target Disease: Meningitis
• Vaccine Ontology ID: VO_0000510
• Type: Subunit vaccine
• Antigen: Nontypeable H. influenzae vaccine recombinant transferrin binding protein B
• Adjuvant:
  • Adjuvant name:
  • VO adjuvant ID: VO_0000142
• Preparation: The NTHI strain UC19 (289-I) was originally derived from the sputum of a patient with chronic bronchitis and has been routinely used in this laboratory as the challenge strain when assessing the efficacy of immunization with NTHI antigens. The gene encoding the mature form of UC19 TbpB was then amplified and cloned into the BamHI restriction sites in plasmid pGEX2T (Pharmacia Biotech, Uppsala, Sweden) to produce plasmid pCU17. This plasmid is engineered to express recombinant TbpB as a glutathione S-transferase (GST) fusion protein with a thrombin cleavage recognition site between the two proteins (Webb et al., 1999).
• Description: The transferrin receptor is composed of two subunits. The interaction of the receptor with transferrin is probably initiated by transferrin binding protein B (TbpB), a peripheral lipoprotein that forms a complex with TbpA, a TonB-dependent integral outer membrane protein that is thought to form a gated pore to facilitate the transport of transferrin-derived iron across the outer membrane (Webb et al., 1999).

Rat Response

• Host Strain: Wistar rat
• Vaccination Protocol: Lyophilized rTbpB was resuspended in PBS and emulsified in an equal volume of incomplete Freund’s adjuvant (IFA) to give a final protein concentration of either 400 or 800 μg/ml. Peyer’s patches in male, 8-week-old Wistar rats were each injected with 2 to 5 μl of antigen, with each rat receiving a total of either 20 or 40 μg of rTbpB. A control group of animals was either sham immunized with PBS-IFA or left unimmunized. The animals were boosted intratracheally 14 days later with the same antigen dose as in the primary immunization in 50 μl of PBS (Webb et al., 1999).
• Challenge Protocol: 7 days after the booster dose, the rats were lightly sedated with halothane and 5 × 108 CFU of UC19 in 50 μl was instilled into the lungs via an intratracheal cannula. After 4 h, the animals were killed and bronchoaveolar lavage (BAL) fluid, serum, and homogenized lung samples were obtained. The numbers of viable bacteria in BAL fluid and lung homogenates were estimated by plating serial dilutions onto chocolate blood agar (Webb et al., 1999).
• Efficacy: The efficacy of immunization with a recombinant form of TbpB (rTbpB) was determined by assessing the pulmonary clearance of viable bacteria 4 h after a live challenge with NTHI. There was a significant reduction in the number of viable bacteria in both the bronchoalveolar lavage fluid (34% for the 20-μg dose and 58% for the 40-μg dose) and lung homogenates (26% for the 20-μg dose and 60% for the 40-μg dose) of rats immunized with rTbpB compared to the control animals. While rTbpB-specific antibodies from immunized rats were nonspecific in the recognition of TbpB from six heterologous NTHI strains on Western blots, these antibodies differed in their ability to block transferrin binding to heterologous strains and to cross-react in bactericidal assays (Webb et al., 1999).