Drivers and barriers in the consistency approach for vaccine batch release testing: Report of an international workshop

Safety and potency assessment for batch release testing of established vaccines still relies partly on animal tests. An important avenue to move to batch release without animal testing is the consistency approach. This approach is based on thorough characterization of the vaccine, and the principle that the quality of subsequent batches is the consequence of the application of consistent production of batches monitored by a GMP quality system. Efforts to implement the consistency approach are supported by several drivers from industry, government, and research, but there are also several barriers that must be overcome. A workshop entitled "Consistency Approach, Drivers and Barriers" was organized, which aimed to discuss and identify drivers and barriers for the implementation of the 3Rs in the consistency approach from three different perspectives/domains (industry, regulatory and science frameworks). The workshop contributed to a better understanding of these drivers and barriers and resulted in recommendations to improve the overall regulatory processes for the consistency approach. With this report, we summarise the outcome of this workshop and intend to offer a constructive contribution to the international discussion on regulatory acceptance of the consistency approach.

Toward a mechanism-based in vitro safety test for pertussis toxin

Pertussis vaccines are routinely administered to infants to protect them from whooping cough. Still, an adequate safety test for pertussis toxin (PT), one of the main antigens in these vaccines, is not available. The histamine sensitization test is currently the only assay accepted by regulatory authorities to test for the absence of active PT in vaccines. This is however, a lethal animal test with poor reproducibility. In addition, it is not clear whether the assumed underlying mechanism, i.e., ADP-ribosylation of G proteins, is the only effect that should be considered in safety evaluation of PT. The in vitro safety test for PT that we developed is based on the clinical effects of PT in humans. For this, human cell lines were chosen based on the cell types involved in the clinical effects of PT. These cell lines were exposed to PT and analyzed by microarray. In this review, we discuss the clinical effects of PT and the mechanisms that underlie them. The approach taken may provide as an example for other situations in which an in vitro assay based on clinical effects in humans is required.

Identification of biomarkers to detect residual pertussis toxin using microarray analysis of dendritic cells

In this study we aimed to identify genes that are responsive to pertussis toxin (PTx) and might eventually be used as biological markers in a testing strategy to detect residual PTx in vaccines. By microarray analysis we screened six human cell types (bronchial epithelial cell line BEAS-2B, fetal lung fibroblast cell line MRC-5, primary cardiac microvascular endothelial cells, primary pulmonary artery smooth muscle cells, hybrid cell line EA.Hy926 of umbilical vein endothelial cells and epithelial cell line A549 and immature monocyte-derived dendritic cells) for differential gene expression induced by PTx. Immature monocyte-derived dendritic cells (iMoDCs) were the only cells in which PTx induced significant differential expression of genes. Results were confirmed using different donors and further extended by showing specificity for PTx in comparison to Escherichia coli lipopolysaccharide (LPS) and Bordetella pertussis lipo-oligosaccharide (LOS). Statistical analysis indicated 6 genes, namely IFNG, IL2, XCL1, CD69, CSF2 and CXCL10, as significantly upregulated by PTx which was also demonstrated at the protein level for genes encoding secreted proteins. IL-2 and IFN-γ gave the strongest response. The minimal PTx concentrations that induced production of IL-2 and IFN-γ in iMoDCs were 12.5 and 25IU/ml, respectively. High concentrations of LPS slightly induced IFN-γ but not IL-2, while LOS and detoxified pertussis toxin did not induce production of either cytokine. In conclusion, using microarray analysis we evaluated six human cell lines/types for their responsiveness to PTx and found 6 PTx-responsive genes in iMoDCs of which IL2 is the most promising candidate to be used as a biomarker for the detection of residual PTx.