A phase I clinical study of a live attenuated Bordetella pertussis vaccine--BPZE1; a single centre, double-blind, placebo-controlled, dose-escalating study of BPZE1 given intranasally to healthy adult male volunteers

Abstract

Background: Acellular pertussis vaccines do not control pertussis. A new approach to offer protection to infants is necessary. BPZE1, a genetically modified Bordetella pertussis strain, was developed as a live attenuated nasal pertussis vaccine by genetically eliminating or detoxifying 3 toxins.

Methods: We performed a double-blind, placebo-controlled, dose-escalating study of BPZE1 given intranasally for the first time to human volunteers, the first trial of a live attenuated bacterial vaccine specifically designed for the respiratory tract. 12 subjects per dose group received 10³, 10⁵ or 10⁷ colony-forming units as droplets with half of the dose in each nostril. 12 controls received the diluent. Local and systemic safety and immune responses were assessed during 6 months, and nasopharyngeal colonization with BPZE1 was determined with repeated cultures during the first 4 weeks after vaccination.

Results: Colonization was seen in one subject in the low dose, one in the medium dose and five in the high dose group. Significant increases in immune responses against pertussis antigens were seen in all colonized subjects. There was one serious adverse event not related to the vaccine. Other adverse events were trivial and occurred with similar frequency in the placebo and vaccine groups.

Conclusions: BPZE1 is safe in healthy adults and able to transiently colonize the nasopharynx. It induces immune responses in all colonized individuals. BPZE1 can thus undergo further clinical development, including dose optimization and trials in younger age groups.

Trial registration: ClinicalTrials.gov NCT01188512.

Figure 1. CONSORT Flow Diagram.

Number of subjects assessed for eligibility, enrolled and randomized to study vaccine or placebo. Subjects were included in a step-wise fashion with 16 subjects in each group. Interim safety analysis was performed before vaccination of the next, higher dose group.

Figure 2. Colonization of nasopharyngeal mucosa from day 4 to day 28 after vaccination.

Culture positive samples are shown in red.

Figure 3. Serum IgG levels over time to B. pertussis antigens in respective dose group.

A) anti-PT, B) anti-FHA, C) anti-PRN, and D) anti-Fim. Day 0 = Day of vaccination, 5–6 m = 5–6 months after vaccination. PT, pertussis toxin; FHA, filamentous hemagglutinin; PRN, pertactin; and Fim, fimbriae 2/3. Results are presented as boxplots with medians and interquartile ranges and whiskers for min-max range.

Figure 4. Serum IgG levels over time to B. pertussis antigens in the colonized compared to non-colonized subjects.

A) anti-PT, B) anti-FHA, C) anti-PRN, and D) anti-Fim. PT, pertussis toxin; FHA, filamentous hemagglutinin; PRN, pertactin; and Fim, fimbriae 2/3. Significant differences were found between the two groups for anti-PT at 28 days (p = 0.001) and 5–6 months (p = 0.001); for anti-FHA at 5–6 months (p = 0.026); and for anti-PRN at 28 days (p = 0.009) and 5–6 months (p = 0.008). Results are presented as medians (circles) and interquartile ranges (error bars).

Figure 5. Pre-vaccination serum IgG levels to B. pertussis antigens in the seven culture-negative and the five culture-positive volunteers vaccinated with high dose BPZE1.

PT, pertussis toxin; FHA, filamentous hemagglutinin; PRN, pertactin; and Fim, fimbriae 2/3. Culture positive volunteers are shown in blue filled circles and culture negative volunteers in red open circles. P-values were: PT p = 0.246; FHA p = 0.034 (*): PRN p = 0.006 (**); Fim p = 0.034 (*).