Maternal Vaccination With a Monocomponent Pertussis Toxoid Vaccine Is Sufficient to Protect Infants in a Baboon Model of Whooping Cough.

Background: Bordetella pertussis is a human pathogen responsible for serious respiratory illness. The disease is most severe in infants too young to be vaccinated with most hospitalizations and deaths occurring within this age group. The Advisory Committee on Immunization Practices recommended immunization of pregnant women to protect infants from birth until their first vaccination at 6-8 weeks of age. We previously demonstrated that maternal vaccination with licensed acellular pertussis vaccines protected newborn baboons from disease. We hypothesized that protection was due to toxin-neutralizing, maternal anti-pertussis toxin antibodies and predicted that maternal vaccination with a pertussis toxoid (PTx)-only vaccine would protect newborns from disease. Methods: Infant baboons born to unvaccinated mothers or mothers vaccinated with a PTx-only vaccine were challenged with B. pertussis at 5 weeks of age and followed for infection and signs of disease. Results: Although all challenged infants were heavily colonized, the infant baboons born to mothers vaccinated with PTx-only vaccine were free from clinical disease following exposure to B. pertussis. In contrast, disease was observed in infants born to unvaccinated mothers. Conclusions: Our results demonstrated that maternal vaccination with a PTx-only vaccine is sufficient to protect newborn baboons from disease following exposure to pertussis.

Towards replacement of the acellular pertussis vaccine safety test: Comparison of in vitro cytotoxic activity and in vivo activity in mice.

Because of the exquisite sensitivity of the murine histamine sensitization test (HIST) in detecting minute amounts of active pertussis toxin (PTx), this animal-based test has been used to assure the safety of acellular pertussis vaccines in the United States and other countries around the world. Prompted by humane considerations, efforts are underway to find a suitable in vitro replacement assay that has critical attributes comparable to that of the HIST. In this study, we compared the sensitivity of the in vivo HIST with an in vitro Chinese Hamster Ovary (CHO) cell-based assay. Using vaccine samples that had been spiked with PTx, we found that both assays were capable of detecting as little as 4-10 ng of active pertussis toxin per dose of vaccine; thus, the sensitivities of the two assays are comparable. Because the strength of adsorption of PTx to the vaccine adjuvant could change over time, we also used both assays to examine the bioavailability of PTx in spiked vaccine samples that had been stored at 25 °C for 9 weeks, mimicking long term vaccine storage conditions. We found that both assays detected similar amounts of active PTx in these samples, indicating that bioavailability of the toxin in stored samples was similar. Taken together, our results indicate that critical attributes of the HIST are met by the CHO cell assay used in this study and provide proof of concept that the CHO cell assay may be further considered as a replacement for the in vivo HIST.