The NIBSC have been involved in the development of cell-based assays to test biological medicines for the presence of pyrogens for many years. The work began in the 1980s’s following reports that intravenously administered products could cause adverse pyrogenic reactions despite being found clear of contamination in the bacterial endotoxin test (BET) and the rabbit pyrogen test (RPT). Investigations by our scientists revealed that this contamination could be detected using human peripheral monocytes, which produced pro-inflammatory cytokines in response to pyrogens. Development of this test continued across specialist laboratories worldwide and the monocyte activation test (MAT) was included in the European Pharmacopoeia in 2010. Whilst its use for screening intravenously administered substances grew, its use for testing vaccines was limited.
In 2014, a novel meningococcal vaccine designed to control group B disease was licensed. This vaccine (called Bexsero) contained four antigens, one of which was an outer membrane vesicle (OMV) derived from meningococcal cultures. Bexsero was granted a licence and included the RPT as a safety test, however a number of elements made the test unsuitable. In order to pass this test the vaccine had to be highly diluted; the vaccine was administered intravenously to rabbits whereas the vaccine is given to humans intramuscularly; using animal models is limited due to species differences. Therefore we proposed the development of the in-house MAT to replace the test as it is able measure pyrogenic content quantitatively, uses human cells providing a better link to the patient and negates the use of large numbers of animals in line with the National Centre for the Replacement, Refinement and Reduction of Animals in Research (3Rs). After successful development the test is now used by the European regulatory laboratories and the manufacturer.
Building on the success of using the assay to release batches of the meningococcal vaccine, the NIBSC have been collaborating with scientists at GSK Vaccines for Global Health (GVGH) to develop similar methods for novel vaccines which are being produced using their Generalized Modules for Membrane Antigens (GMMA) platform. GMMA’s are in essence OMVs derived from genetically modified bacteria, namely Shigella and non-typhoidal salmonella. As such these vaccines have the same complicating factors making the use of the RPT as a safety test unsuitable. Post-doctoral scientist Dr Danielle Carson has been leading this piece of work which is funded by the Future Vaccine Manufacturing Research-hub. To date Dr Carson and colleagues have successfully developed a method for the Shigella vaccine and are now working on development of the method for the invasive non-typhoidal salmonella (iNTS) vaccine.
The EDQM have a goal to remove RPT from all European Pharmacopeial texts within 5 years quoting the MAT as the best alternative. This work supports the EDQM goal and we hope to continue to play an active part in developing the MAT as a quality control test to ensure vaccine safety.
Dr Danielle Carson said: “There are high levels of morbidity associated with enteric bacterial infection including Shigella and iNTS. The development of the MAT supports the advancement of novel vaccines to tackle such infections and improve public health, especially in lower and middle income countries. In addition, the assay utilises human cells to provide meaningful output, stepping away from traditional animal based methods”