Development of a monoclonal antibody sandwich ELISA for the determination of antigen content and quality in diphtheria vaccines

At present, quality control of diphtheria vaccines by both manufacturers and national control laboratories relies heavily on in vivo assays to confirm potency. As part of the VAC2VAC project we have developed a monoclonal antibody (mAb) enzyme-linked immunosorbent assay (ELISA) to measure the relative amount and quality of diphtheria toxoid (DTxd) in diphtheria-tetanus based vaccines and believe this test has the potential to play a key role in a control strategy no longer including an in vivo potency test. The mAb ELISA is highly specific, has good dilutional linearity, and is suitable for detecting DTxd in a range of different human vaccine products. We demonstrate the ability of the assay to discriminate between batches of different content and quality using vaccine batches that were prepared to contain differing amounts of DTxd or were altered by exposure to heat or oxidative stress. We also demonstrate successful transfer of the method to other laboratories and show that different diphtheria antigen materials may be able to serve as a reference antigen for local standardization of the method. The assay is ideally suited for incorporation into a consistency approach for routine diphtheria vaccine quality control testing and may be suitable to serve as the stability indicating test in replacement of the current in vivo potency test.

Rational arguments for regulatory acceptance of consistency testing: benefits of non-animal testing over in vivo release testing of vaccines

INTRODUCTION

There are rational arguments to replace existing in vivo potency and safety assays for batch release testing of vaccines with more advanced non-animal techniques to measure critical quality attributes. However, introduction of in vitro alternatives to replace in vivo release assays of authorized vaccines is challenging.

AREAS COVERED

This report describes the hurdles encountered in substituting in vivo assays and ways to overcome these and provides arguments why more advanced in vitro alternatives are superior, not only as tool to monitor the quality of vaccines but also from a practical, economical and ethical point of view. The rational arguments provided for regulatory acceptance can support a strategy to replace/substitute any in vivo batch release test if an appropriate non-animal testing strategy is available.

EXPERT OPINION

For several vaccines, in vivo release assays have been replaced leading to an optimized control strategy. For other vaccines, new assays are being developed, that can expected to be introduced within 5-10 years. From a scientific, logistical and animal welfare perspective, it would be beneficial to substitute all existing in vivo batch release assays for vaccines. Given the challenges relating to development, validation and acceptance of new methods, and considering the relatively low prices of some legacy vaccines, this cannot be done without government incentives and supportive regulatory authorities from all regions.

Regulation of Clostridium tetani Neurotoxin Expression by Culture Conditions

BACKGROUND

Ensuring consistency of tetanus neurotoxin (TeNT) production by Clostridium tetani could help to ensure consistent product quality in tetanus vaccine manufacturing, ultimately contributing to reduced animal testing. The aim of this study was to identify RNA signatures related to consistent TeNT production using standard and non-standard culture conditions.

METHODS

We applied RNA sequencing (RNA-Seq) to study C. tetani gene expression in small-scale batches under several culture conditions.

RESULTS

We identified 1381 time-dependent differentially expressed genes (DEGs) reflecting, among others, changes in growth rate and metabolism. Comparing non-standard versus standard culture conditions identified 82 condition-dependent DEGs, most of which were specific for one condition. The tetanus neurotoxin gene (tetX) was highly expressed but showed expression changes over time and between culture conditions. The tetX gene showed significant down-regulation at higher pH levels (pH 7.8), which was confirmed by the quantification data obtained with the recently validated targeted LC-MS/MS approach.

CONCLUSIONS

Non-standard culture conditions lead to different gene expression responses. The tetX gene appears to be the best transcriptional biomarker for monitoring TeNT production as part of batch-to-batch consistency testing during tetanus vaccine manufacturing.