Investigation of an aerosol challenge model as alternative to the intracerebral mouse protection test for potency assay of whole cell pertussis vaccines

Protocol for aerosolization challenge of mice with Bordetella pertussis

Bordetella pertussis causes whooping cough and is transmitted via respiratory droplets. Here, we present a protocol to challenge mice with Bordetella pertussis. We describe bacteria preparation and long-term storage, followed by manufacturing a challenge dose for use in a commercial exposure chamber with controlled nebulization of B. pertussis into aerosols. We then detail the aerosol challenge of mice through a more natural administration than intranasal instillation and post-challenge data collection. This protocol allows for better comparisons between preclinical pertussis studies.

Whole-cell pertussis vaccine potency assays: the Kendrick test and alternative assays

Whole-cell pertussis vaccines are still widely used across the globe and have been shown to produce longer lasting immunity against pertussis infection than acellular pertussis vaccines. Therefore, whole-cell vaccines are likely to continue to be used for the foreseeable future. The intracerebral mouse protection test (Kendrick test) is effective for determining the potency of whole-cell pertussis vaccines and is the only test that has shown a correlation with protection in children. Here we review the Kendrick test in terms of international requirements for vaccine potency and critical technical points to be considered for a successful test including test validity, in-house references and statistical analysis. There are objections to the Kendrick test on animal welfare and technical grounds. Respiratory challenge assays, nitric oxide induction assay and serological assays have been developed and have been proposed as possible methods which might provide alternatives to the Kendrick test. These methods and their limitations are also briefly discussed. Establishment of validated in vitro correlates of protection has yet to be achieved. New technical developments, such as genome sequence and the use of gene microarrays to screen responses triggered by vaccine components may also provide leads to alternative assays to the Kendrick test by identifying biomarkers of protection.

The mouse intranasal challenge model for potency testing of whole-cell pertussis vaccines

INTRODUCTION

A mouse intracerebral challenge model is used for potency testing of whole-cell pertussis (wP) vaccines. We investigated the use of a mouse nasopharyngeal challenge model, which better reflects the clinical features of pertussis disease, to differentiate between efficacy of wP vaccines.

METHODS

Efficacy of three wP vaccines (Quinvaxem(®), Easyfive(®) and Pentavac(®)) was tested in the nasopharyngeal challenge model. Mice were vaccinated at 4 and 7 weeks and challenged with Bordetella pertussis at 9 weeks. Vaccine efficacy was determined based on CFU in the lungs 5 days after challenge.

RESULTS

The mouse nasopharyngeal challenge model has the capacity to differentiate between the efficacy of whole cell pertussis vaccines.

CONCLUSION

The mouse nasopharyngeal challenge model could be considered as a potency and release assay for wP vaccines. Whether this model directly correlates with clinical vaccine efficacy requires further investigations. Whether this model directly correlates with clinical vaccine efficacy requires further investigations. The mouse nasopharyngeal challenge model could be considered as a potency and release assay for wP vaccines.

Toxicity and potency evaluation of pertussis vaccines

Current methods for determining the potency and toxicity of pertussis vaccines are outdated and require improvement. The intracerebral challenge test is effective for determining the potency of whole-cell vaccines but is objectionable on animal welfare and technical grounds. The same applies to its modification for assaying acellular pertussis vaccines. Respiratory challenge methods offer an interim solution pending establishment of validated in vitro correlates of protection, for example nitric oxide induction. Their evaluation is being promoted by the World Health Organization through the Pertussis Vaccines Working Group. Current toxicity assays based on weight gain and histamine sensitization of mice are imprecise and need replacement. Limits need to be established for specific toxin content of both acellular and whole-cell vaccines and should be supported by specific assays. More precise methods based on determination of ribosyltransferase activity in tandem with receptor-binding assays are under evaluation. Genome sequence data and the use of gene microarrays to screen responses triggered by vaccine components may also provide leads to improved methods for assessing both toxicity and immunogenicity.

Evaluation of respiratory model employing conventional NIH mice to access the immunity induced by cellular and acellular pertussis vaccines

The increasing number of pertussis cases reported on the last twenty years and the existence of new acellular vaccines reinforce the need of research for experimental models to assure the quality of available pertussis vaccines. In this study, allotments of whole-cell and acellular pertussis vaccines were tested through the Intranasal Challenge Model (INM) using conventional NIH mice. The results have been compared to those achieved by the "Gold standard" Intracerebral Challenge Model (ICM). In contrast to ICM, INM results did not show intralaboratorial variations. Statistical analysis by Anova and Ancova tests revealed that the INM presented reproducibility and allowed identification and separation of different products, including three-component and four-component accellular pertussis vaccines. INM revealed differences between pertussis vaccines. INM provides lower distress to the mice allowing the reduction of mice number including the possibility of using conventional mice (less expensive) under non-aseptic environment. Thus, INM may be used as an alternative method of verifying the consistence of allotment production, including acellular pertussis vaccines.

Value of an inhalational model of invasive aspergillosis

Animal models of invasive aspergillosis have been used for virulence studies and antifungal efficacy evaluations but results have been inconsistent. In an attempt to reproduce human infection, many Aspergillus animal models have utilized a 'pulmonary route' for delivery of conidia, largely through intranasal instillation. However, several radiolabeled particle studies have shown that aerosol delivery is preferable to intranasal instillation to create a more homogenous delivery to the lungs. We hypothesized that an inhalational model would be more robust for studies of invasive aspergillosis pathogenesis and antifungal therapy. We developed an inhalational model of Aspergillus fumigatus infection using a Hinners inhalation chamber and demonstrated by quantitative polymerase chain reaction that this new inhalational model creates a more homogenous murine pneumonia, facilitating analysis of mutant strains and treatment regimens.

Molecular epidemiology of Bordetella pertussis isolated in Taiwan, 1992-1997

In Taiwan, the number of pertussis cases including various types of infection has been increasing in recent years, especially in 1997. Since 71% of the reported cases concentrated in the densely populated Taipei metropolitan area, concerns have been raised that a highly contagious strain of Bordetella pertussis might have appeared in Taipei. In this study, 114 strains of B. pertussis including those isolated in 1992-1996 (n = 53) and 1997 (n = 61) were subjected to pulsed-field gel electrophoresis (PFGE) of the Xba I digests from their chromosomes. Based on the band patterns, they were divided into 21 subtypes, P1 to P21. The strains isolated in 1997 consist of 17 subtypes including 9 new subtypes which did not appear in the previous years, indicating that the outbreaks in 1997 were not caused by a sole specific virulent strain. Dendrogram analysis indicated that the 21 subtypes can be grouped into five clusters, with the first four subtypes possessing 60 to 95% relatedness to one another, whereas relatedness between cluster 5 (containing P21 only) and the other clusters is less than 50%. Notably, all the subtypes except P12 and P21 appeared at least once in Taipei and the majority of the strains (54%) belong to two clusters, 3 and 4. These results suggest that highly dense population may facilitate spread and accelerate genetic divergence of this pathogen. This is the first report on pertussis molecular epidemiology in Taiwan.