Why did we fund this project?
This award aims to refine tuberculosis (TB) vaccine studies by avoiding the challenge tests in monkeys that are used to assess the protective efficacy of vaccine candidates.
TB vaccine candidates are tested in macaques after initial preclinical evaluation. The studies involve the challenge of naïve and vaccinated animals with Mycobacterium tuberculosis (M.tb), the infectious agent. Although relatively small numbers of animals are used, they can experience clinical signs such as a raised temperature, respiratory distress and weight loss, necessitating humane end-points. Dr Rachel Tanner has developed a functional in vitro assay that could be used to refine the tests by avoiding the need for the in vivo M.tb challenge. The assay – the direct mycobacterial growth inhibition assay (MGIA) – uses peripheral blood mononuclear cells (PBMCs) from naïve and vaccinated animals. Cells are co-cultured with mycobacteria and the control of mycobacterial growth is used as a measure of protective immunity.
Rachel had previously worked to optimise the MGIA for a range of species include the macaque. With NC3Rs funding, Rachel will work with researchers at Public Health England (PHE) and the Biomedical Primate Research Centre (BPRC) in the Netherlands to facilitate the adoption of the MGIA into their TB vaccine programmes.
What was achieved?
Rachel and her collaborators at PHE and BPRC have shown that the assay is reproducible between tests, laboratories and operators. The primary paper from this project is currently under review and will be followed by an associated methods paper on the NC3Rs gateway. Further validation work is being undertaken at the institutions to allow the MGIA to be fully adopted. Ultimately this could lead to a reduction in the use of around 45 macaques (30% of the total used in TB vaccine studies) annually across the two institutions as the PBMCs from a single group of animals can be used to screen multiple clinical isolates, as well as investigate immune mechanisms mediating mycobacterial control.
The grant has stimulated further interested in the MGIA by the TB research community and as a result Rachel has worked with collaborators at 13 institutions in Europe, North America and Asia to help set up the assay for various species. Rachel has received various accolades for her research including the 2019 Woman of the Future award for Science. She is the lead author of a paper published in Frontiers in Immunology in January 2020 that describes the validation of the human direct MGIA for measuring vaccine efficacy and exploring immune mechanisms with the assay, also providing an opportunity to replace animal studies in some settings. Rachel has previously published a paper on the 3Rs in Frontiers for Young Minds, a science journal for children and teenagers.
This award was featured as a case study in the 2019 Research review.
Tuberculosis (TB) remains a major global health threat, and the current vaccine (BCG) is inadequate. An improved vaccine is urgently needed, but in the absence of a validated alternative, candidate vaccines are currently tested in animal models such as mice, guinea pigs and non-human primates (NHPs). Animals are infected with pathogenic Mycobacterium tuberculosis (M.tb) following vaccination to determine efficacy; a procedure of Moderate Severity. As disease progresses, animals may experience loss of body weight, fever and respiratory distress and if left untreated will eventually die of pulmonary insufficiency; necessitating humane euthanasia. Dr Tanner has worked extensively on the development of an in vitro assay (the MGIT assay) as a correlate of protection, which may offer an alternative to in vivo M.tb infection and ultimately replace the use of animals in vaccine testing. NHPs are the most appropriate model to biologically validate the assay by comparing outcomes with measures of in vivo protection, allowing vaccine developers using this, and other preclinical models, to refine vaccine testing by replacing the infection stage. Rather, blood samples are taken from vaccinated animals and cells infected in vitro to measure vaccine efficacy. This project aims to transfer the NHP MGIT assay to two major end-user laboratories (Public Health England and the Biomedical Primate Research Centre) for use in their ongoing and future vaccine studies. Although preclinical testing may remain a regulatory requirement for progression to clinical trials, the early down-selection or gating of promising candidates using this assay will considerably reduce the numbers of animals challenged. In the longer-term, this work will offer the biological validation necessary to bridge to the use of human samples (as comparison with in vivo efficacy in humans is not logistically or ethically possible), which could largely replace the use of animals in TB vaccine efficacy testing.
Tanner R et al. (2021). A non-human primate in vitro functional assay for the early evaluation of TB vaccine candidates. npj Vaccines 6: 3. doi: 10.1038/s41541-020-00263-7
Tanner R et al. (2020). Tools for Assessing the Protective Efficacy of TB Vaccines in Humans: in vitro Mycobacterial Growth Inhibition Predicts Outcome of in vivo Mycobacterial Infection. Frontiers in Immunology 10:2983. doi: 10.3389/fimmu.2019.02983
Tanner R and McShane H (2017). Replacing, reducing and refining the use of animals in tuberculosis vaccine research. ALTEX 34(1): 157-166. doi: 10.14573/altex.1607281