Report on the international workshop on alternatives to the murine histamine sensitization test (HIST) for acellular pertussis vaccines: state of the science and the path forward.

Regulatory authorities require safety and potency testing prior to the release of each production lot of acellular pertussis (aP)-containing vaccines. Currently, the murine histamine sensitization test (HIST) is used to evaluate the presence of residual pertussis toxin in aP containing vaccines. However, the testing requires the use of a significant number of mice and results in unrelieved pain and distress. NICEATM, ICCVAM, their partners in the International Cooperation on Alternative Test Methods, and the International Working Group for Alternatives to HIST organized a workshop to discuss recent developments in alternative assays to the HIST, review data from an international collaborative study on non-animal alternative tests that might replace the HIST, and address the path toward global acceptance of this type of method. Currently, there are three potential alternative methods to HIST. Participants agreed that no single in vitro method was sufficiently developed for harmonized validation studies at this time. It is unlikely that any single in vitro method would be applicable to all aP vaccines without modification, due to differences between vaccines. Workshop participants recommended further optimization of cell-based assays under development. Participants agreed that the next international collaborative studies should commence in 2013 based on discussions during this workshop.

Workshop on Animal free Detection of Pertussis Toxin in Vaccines--Alternatives to the Histamine Sensitisation Test.

The Paul-Ehrlich-Institut (PEI), the Nederlands Vaccin Instituut (NVI) and the European Directorate for the Quality of Medicines & HealthCare (EDQM) organised the international scientific workshop "Animal free Detection of Pertussis Toxin in Vaccines--Alternatives to the Histamine Sensitisation Test" at the PEI in Langen (Germany) on 09-10 June 2011. Twenty-seven experts (regulators, representatives from national control laboratories, vaccine manufacturers and academia) from 7 countries participated in this workshop. The meeting was triggered by the lack of satisfaction with the current safety testing for acellular pertussis vaccines, the "Histamine Sensitisation Test" (HIST) in mice, and the growing attention for the alternatives under development. The workshop objectives were: a) to review the current status of available alternative methods, b) to discuss the sensitivity that an alternative test needs, c) to plan experiments that allow for comparison of the alternative tests. The results of the workshop are summarised in this meeting report.

Bordetella Pertussis Toxin does not induce the release of pro-inflammatory cytokines in human whole blood.

Pertussis Toxin (PTx) is one of the most important virulence factors of Bordetella pertussis, the cause of whooping cough. Therefore, the inactivated toxin is an obligatory constituent of acellular pertussis vaccines. It is described in the literature that both native PTx and recombinant Pertussis Toxin (PTg) activate human monocytes whereas others report an inhibition of mammalian monocytes during pertussis infection. B. pertussis, as a Gram-negative bacterium, harbours naturally lipopolysaccharide (LPS, also known as endotoxin), one of the strongest stimulators of monocytes. The latter is triggered via the interaction of endotoxin with inter alia the surface receptor CD14. Consequently, it is necessary to consider a potential contamination of Pertussis Toxin preparations with LPS. First, we determined the LPS content in different preparations of PTx and PTg. All preparations examined were contaminated with LPS; therefore, possible PTx- and PTg-driven monocyte activation independently of LPS was investigated. To meet these aims, we examined monocyte response to PTx and PTg while blocking the LPS receptor CD14 with a specific monoclonal antibody (anti-CD14 mAb). In addition, all toxin preparations examined underwent an LPS depletion. Our results show that it is contaminating LPS, not Pertussis Toxin, which activates human monocytes. Blocking the CD14 receptor prevents Pertussis Toxin-mediated induction of pro-inflammatory cytokines in human monocytes. The depletion of LPS from Pertussis Toxin leads to the same effect. Additionally, the PTx toxicity after LPS depletion procedure was confirmed by animal tests. In contrast, the original Pertussis Toxin preparations not treated as mentioned above generate strong monocyte activation. The results in this publication allow the conclusion that purified Pertussis Toxin preparations do not induce the release of pro-inflammatory cytokines in human whole blood.