Development of an ex vivo mycobacterial growth inhibition assay using murine lung cells for tuberculosis vaccine testing
In the absence of a robust correlate(s) of protection against human tuberculosis (TB) and a validated animal model of the disease, tools to facilitate vaccine development and testing must be identified. We present an optimised ex vivo mycobacterial growth inhibition assay (MGIA) for use with murine lung cells, to assess the ability of host immune cells to inhibit mycobacterial growth, using both Bacille Calmette–Guérin (BCG) and Mycobacterium tuberculosis (MTB). A 0.39, 0.96 and 0.73 log10 reduction in BCG CFU was observed following co-culture with lung cells from mice vaccinated with subcutaneous (s.c.) or intranasal (i.n.) BCG, or BCG s.c. + spore-FP1 (s.c. + mucosal boost), respectively, versus naïve mice. Comparatively, a 0.49 (s.c.), 0.60 (i.n) and 0.81 (s.c. + mucosal boost) log10 reduction in MTB Erdman CFU was found. Residual BCG in lung samples from i.n. vaccinated mice was 2.87 log10 CFU per MGIA input. A BCG growth inhibitor, 2-thiophenecarboxylic acid hydrazide (TCH), was used to prevent quantification of residual BCG from immunisation and allow accurate MTB quantification. In the presence of TCH, a further 0.58 log10 reduction in MTB Erdman CFU was revealed in the i.n. group that had been previously masked. In addition, preliminary studies indicate variation in the ability of lung cells isolated from mice receiving BCG s.c. to control growth of clinical isolates representative of lineages 1–6 of the MTB complex. With further development, the ex vivo lung MGIA could be used in the future as a tool for analysis of vaccine efficacy and the underlying immune mechanisms associated with vaccination in combination with current methods of preclinical TB vaccine assessment.
I am currently undertaking a MRC-funded PhD studentship at LSHTM (2016-2020), jointly supervised by Helen Fletcher, Rajko Reljic and Andrea Zelmer. My PhD project focuses on immune correlates and the host immune response to TB vaccination, using the mycobacterial growth inhibition assay (MGIA) and RNAseq. We are particularly interested in using the MGIA to determine whether different TB vaccines demonstrate variation in protection against different lineages of the Mycobacterium tuberculosis complex. In 2018, I look part in a three-month bioinformatics placement at the South African Tuberculosis Vaccine initiative (SATVI) under the supervision of Elisa Nemes and Stanley Kimbung Mbandi. The project focused on host correlates of risk of BCG IRIS in HIV+ infants starting ART.