Suppression and Modulation of Cellular and Humoral Immune Responses toHaemophilus influenzaeType B (Hib) Conjugate Vaccine in Hib–Diphtheria‐Tetanus Toxoids–Acellular Pertussis Combination Vaccines: A Study in a Rat Model

We assessed a rat model to evaluate the immunogenicity of Haemophilus influenzae type b (Hib) conjugate vaccines and the effect on Hib immunogenicity of combining 2 Hib vaccines (Hib-tetanus toxoid [TT]-A and Hib-TT-B) with diphtheria-TT-acellular pertussis (DTaP)(3) or DTaP(5)/inactivated poliovirus (IPV) vaccines. Rats were immunized subcutaneously with Hib alone or with Hib and DTaP-based vaccines; anti-Hib capsular polysaccharide IgG, poly-ribosyl-ribitol-phosphate (PRP), IgG subclass, and cellular immune responses were evaluated. Results showed a significant reduction in the antibody response to PRP when Hib-TT-A was administered in combination with DTaP(3) and showed changes in the anti-PRP IgG subclass distribution between the separate and combination groups. However, combining Hib-TT-B with DTaP(5)/IPV did not reduce the anti-PRP antibody response. These results suggest that the model can predict the effect of combined administration of Hib and DTaP vaccines on Hib immunogenicity and would be suitable for preclinical studies of mechanisms of interference in Hib/DTaP vaccines.