A new tool for tuberculosis vaccine screening: Ex vivo Mycobacterial Growth Inhibition Assay indicates BCG-mediated protection in a murine model of tuberculosis

Andrea Zelmer*, Rachel Tanner, Elena Stylianou, Timon Damelang, Sheldon Morris, Angelo Izzo, Ann Williams, Sally Sharpe, Ilaria Pepponi, Barry Walker, David A. Hokey, Helen McShane, Michael Brennan, Helen Fletcher

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

19 Citations (Scopus)

Abstract

Background: In the absence of a validated animal model and/or an immune correlate which predict vaccine-mediated protection, large-scale clinical trials are currently the only option to prove efficacy of new tuberculosis candidate vaccines. Tools to facilitate testing of new tuberculosis (TB) vaccines are therefore urgently needed. Methods: We present here an optimized ex vivo mycobacterial growth inhibition assay (MGIA) using a murine Mycobacterium tuberculosis infection model. This assay assesses the combined ability of host immune cells to inhibit mycobacterial growth in response to vaccination. C57BL/6 mice were immunized with Bacillus Calmette-Guérin (BCG) and growth inhibition of mycobacteria by splenocytes was assessed. Mice were also challenged with Mycobacterium tuberculosis Erdman, and bacterial burden was assessed in lungs and spleen. Results: Using the growth inhibition assay, we find a reduction in BCG CFU of 0.3-0.8 log10 after co-culture with murine splenocytes from BCG vaccinated versus naïve C57BL/6 mice. BCG vaccination in our hands led to a reduction in bacterial burden after challenge with Mycobacterium tuberculosis of approx. 0.7 log10 CFU in lung and approx. 1 log10 CFU in spleen. This effect was also seen when using Mycobacterium smegmatis as the target of growth inhibition. An increase in mycobacterial numbers was found when splenocytes from interferon gamma-deficient mice were used, compared to wild type controls, indicating that immune mechanisms may also be investigated using this assay. Conclusions: We believe that the ex vivo mycobacterial growth inhibition assay could be a useful tool to help assess vaccine efficacy in future, alongside other established methods. It could also be a valuable tool for determination of underlying immune mechanisms.

Original languageEnglish
Article number412
JournalBMC Infectious Diseases
Volume16
Issue number1
DOIs
Publication statusPublished - 12 Aug 2016

Bibliographical note

Funding Information:
Funding for this work was provided by Aeras and the European Union Horizon2020 program (TBVAC2020).

Publisher Copyright:
© 2016 The Author(s).

Keywords

  • Growth inhibition assay
  • Mycobacteria
  • Tuberculosis
  • Vaccines

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