Objective: To examine induction and persistence of cell-mediated immunity (CMI) and antibody responses to Bordetella pertussis antigens in infants receiving antipertussis vaccines.
Design and setting: A randomized, blinded study of 142 children receiving acellular pertussis vaccines combined with diphtheria-tetanus toxoids (DTaP) (DTaP manufactured by SmithKline Beecham [DTaP-SB], Rixensart, Belgium, and DTaP manufactured by Chiron Biocin [DTaP-CB], Siena, Italy), or a whole-cell pertussis vaccine (DTwP) (Connaught Laboratories Inc, Swiftwater, Pa), or a diphtheria-tetanus (DT) (Chiron Biocine) only vaccine. Three doses of each vaccine were given at 2, 4, and 6 months of age, and CMI and antibody responses were evaluated before and at 1 and 14 months after vaccination.
Methods and main outcome measures: Cell-mediated immunity was assessed by proliferation of peripheral blood mononuclear cells stimulated in vitro by B pertussis antigens (pertussis toxin, filamentous hemagglutinin, and pertactin). Antibody titers against pertussis toxin, filamentous hemagglutinin, and pertactin were determined by a standardized enzyme-linked immunosorbent assay.
Results: A CMI-positive response to at least 1 B pertussis antigen at 1 or both postvaccination assays was detected in 46%, 55%, and 83% of DTwP, DTaP-SB, and DTaP-CB vaccine recipients, respectively. Frequency of CMI response to individual antigens ranged from less than 4.9% against pertussis toxin in DTwP recipients to 52% against pertactin in DTaP-CB recipients. The postvaccination responses measured at 14 months equalled, or had increased frequency or intensity, that of the 1-month postvaccination responses. Elevated antibody titers against the 3 antigens were present in all DTaP recipients 1 month after vaccination and were higher in CMI-positive children than in CMI-negative children. They fell, however, to low, if not negligible, levels 14 months after vaccination.
Conclusions: Acellular pertussis vaccines were better inducers of CMI response than the whole-cell vaccine, particularly against pertussis toxin. Once acquired, CMI persisted, in contrast with the rapid antibody decline. Thus, CMI responses could be a useful adjunct to serology in the evaluation of pertussis vaccine immunogenicity and a better correlate of long-term immunity to B pertussis than antibody titers.