TB challenge in vitro
Dr Rachel Tanner was awarded funding to transfer the mycobacterial growth inhibition assay (MGIA) to two end-user laboratories to refine the use of monkeys in tuberculosis (TB) vaccine studies by avoiding challenge infection studies.
Principal Investigator: Dr Rachel Tanner
Organisation: University of Oxford
Award type: Skills and Knowledge Transfer grant
Start date: 2017
Duration: 1 year
There are ten million new cases of TB and 1.6 million deaths worldwide each year. The disease can be cured by targeting the causative agent Mycobacterium tuberculosis (Mtb) with appropriate antibiotics. However, limited access to drugs in developing countries and the recent emergence of multi-drug resistant Mtb strains makes TB an increasing global health threat. The only established vaccine, the BCG vaccine, is not always protective, particularly against pulmonary disease and in areas where TB is prevalent. Consequently, there is considerable international effort from governmental and philanthropic organisations to develop new vaccines to halt the TB epidemic. Vaccine candidates are typically evaluated using mice, guinea pigs and nonhuman primates (NHPs), which are immunised with a test vaccine prior to challenge with Mtb.
As in humans, animals that become infected experience clinical signs that may include raised temperature, respiratory distress and weight loss, and humane endpoints are used to avoid unnecessary suffering.
3Rs benefits (actual and potential)
The MGIA is an in vitro functional assay that can be used to refine the use of animals in Mtb vaccine research by avoiding the need to undertake infection challenge studies. In the MGIA, peripheral blood mononuclear cells (PBMCs) from naïve and vaccinated animals are cultured over four days with Mtb (or other mycobacteria) and the inhibition of bacterial growth is used as an estimate of protective immunity.
Rachel had previously undertaken optimisation of the MGIA in a number of species, including the NHP. This involved demonstrating a correlation between the in vitro response using PBMCs taken from macaques and in vivo protection in BCG and Mtb challenge studies in the same animals, as well as clinical concordance based on comparison with epidemiological data. Despite this, the MGIA has been under-utilised by the TB research community because of concerns about the reproducibility and reliability of mycobacteriabased functional assays. With NC3Rs funding, Rachel is working with scientists at Public Health England (PHE) and the Biomedical Primate Research Centre (BPRC) in the Netherlands to build confidence and facilitate the adoption of the NHP MGIA in their TB vaccine programmes.
By using PBMCs from previous in vivo challenge studies in the NHP MGIA, Rachel and her collaborators Dr Sally Sharpe at PHE and Dr Frank Verreck at BPRC have shown that the assay is highly reproducible between tests, operators, labs and institutions. The MGIA is currently being used alongside the in vivo challenge study to provide additional validation data. As well as the animal welfare benefits of avoiding challenge studies, in the future the MGIA could lead to a combined 30% (= 45 animals) reduction in macaque use at the two institutions annually. This is because the PBMCs can be used to screen multiple clinical isolates and vaccine candidates. More broadly the work has underpinned a general shift in the acceptance of the MGIA by the TB research community and through the NC3Rs grant Rachel has helped to set up the assays for various species at 13 institutions in Europe, North America and Asia, providing protocols and technical support.
Scientific and technological benefits
The MGIA may be used for early vaccine evaluation as part of the ‘gating’ strategy that has been established by the global TB community to accelerate the development of the most promising vaccine candidates. Since the MGIA measures most aspects of the complex host immune response to Mtb and it is easy to manipulate individual components of the assay, it can be used to determine the immune mechanisms controlling mycobacterial growth and identify correlates of protection – studies which are difficult and costly to do in vivo.
Rachel has presented the MGIA data at various international vaccine and TB conferences. This includes organising a workshop, with 25 participants from 14 different institutions, alongside the TBVAC2020 meeting in Switzerland. She was awarded the TB Vaccine Initiative Young Scientist Award in 2017 which allowed Rachel to present work arising from the NC3Rs grant at the Global Forum for TB Vaccines in Delhi; and the Collaboration for TB Vaccine Discovery Junior Investigator Award in 2018 which allowed her to present at its annual meeting in Seattle.
Rachel, who was only awarded her PhD in 2015, has recently secured a two-year Fellowship from VALIDATE (an MRC/BBSRC funded network) to continue her research on TB vaccine development and antigen discovery. Working with Professor Helen McShane at the University of Oxford and collaborators, Rachel has contributed to a publication describing a refined non-virulent NHP model of mycobacterial infection and the development of a MGIA for studying TB infection in cattle, as well as three publications on the human MGIA. She has also published a paper in Frontiers for Young Minds, a science journal for children and teenagers. The paper titled ‘The 3Rs: What are medical scientists doing about animal testing?’ has been viewed more than 3,500 times.
This case study was published in our 2019 Research Review.