Transfer of a non-human primate (NHP) in vitro functional assay for the early evaluation of TB vaccine candidates and the associated immune response

Lead Research Organisation: University of Oxford
Department Name: The Jenner Institute

Abstract

Tuberculosis (TB) remains a serious global health threat and the only currently available vaccine, BCG, is inadequate. A more effective vaccine is urgently needed. However, as it is unclear which measures of immunity indicate protection, new vaccine candidates are currently tested in animal models such as mice, cattle and non-human primates (NHPs). NHPs are considered particularly relevant as they develop the most human-like form of TB, and the use of NHPs in the field is increasing. Animals are vaccinated and then infected with the causative agent of TB, Mycobacterium tuberculosis (M.tb), to test whether the vaccine is protective. This procedure is classified as Moderate in severity, meaning that the animals are likely to experience "short term moderate pain, suffering or distress or long-lasting mild pain, suffering or distress... or moderate impairment of the well-being or general condition". 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.

For the past 6 years, Dr Tanner has led the development of an in vitro, or "test tube", assay which measures control of M.tb (or other bacteria from the same family as a surrogate) by blood or cells from a vaccinated animal or person, rather than infecting the animal or person themselves. This downgrades the severity of vaccine testing in animals considerably, falling under the 'refinement' category of the 3Rs. It also allows the testing of multiple conditions or immune responses in a set of cells from a single group of animals, and allows early down-selection of vaccine candidates going forward to testing, thereby reducing the numbers of animals required. In the longer-term, this work aims to demonstrate that the assay is a meaningful measure of protection, allowing bridging to the use of human samples (as comparison with efficacy in humans to prove this is not logistically or ethically possible). Ability to use human cells could largely replace the use of animals in TB vaccine efficacy testing.

The primary aim of this project is to successfully transfer the NHP MGIT assay to two major laboratories in the field of NHP TB vaccine testing: Public Health England (PHE) and the Biomedical Primate Research Centre (BPRC) in the Netherlands. These laboratories use ~100-150 macaques in M.tb challenge experiments each year with capacity increasing, and implementation of the MGIT assay could drastically reduce the requirement for this procedure. The transfer will involve four phases: standardisation (ensuring that all laboratories are performing the assay in the same way), harmonisation (ensuring that results from the same samples are concordant between replicates within a laboratory and between laboratories), validation (ensuring that results are biologically meaningful compared to measures of protection following in vivo infection), and finally an exploratory phase to investigate the underlying mechanisms of immunity. Stored samples from studies previously conducted at PHE and BPRC have been allocated for this project, meaning that no further animal experiments will be necessary. By successfully transferring the assay, these groups will be able to implement it into their future vaccine studies, having considerable local impact. Furthermore, the project will yield data demonstrating proof-of-concept that the MGIT assay is reproducible and transferable, thus increasing interest from additional TB research groups worldwide. Evidence that this assay correlates strongly with protection from in vivo M.tb infection will further confirm biological validity and give confidence to scientists and vaccine developers.

Technical Summary

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.

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