relA is Achilles’ heel for mycobacterial pathogens as demonstrated with deletion mutants in Mycobacterium avium subsp. paratuberculosis and mycobacterium bovis bacillus Calmette-Guérin (BCG)

Authors: ABDELLRAZEQ, GABER - Washington State University; MAHMOUD, ASMAA - Washington State University; PARK, KUN-TAEK - Inje University; Fry, Lindsay; ELNAGGAR, MAHMOUD - Washington State University; Schneider, David; HULUBEI, VICTORIA - Washington State University; DAVIS, WILLIAM - Washington State University

Submitted to: Tuberculosis
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/13/2020
Publication Date: 1/15/2020
Citation: Abdellrazeq, G.S., Mahmoud, A.H., Kun-Taek, P., Fry, L.M., Elnaggar, M.M., Schneider, D.A., Hulubei, V., Davis, W.C. 2020. relA is Achilles’ heel for mycobacterial pathogens as demonstrated with deletion mutants in Mycobacterium avium subsp. paratuberculosis and mycobacterium bovis bacillus Calmette-Guérin (BCG). Tuberculosis. 120. https://doi.org/10.1016/j.tube.2020.101904.
DOI: https://doi.org/10.1016/j.tube.2020.101904

Interpretive Summary: The development of a vaccine to protect cattle from Johnes Disease, caused by Mycobacterium avium subsp. paratuberculosis, is of urgent importance to reduce animal losses and improve meat and milk yields from cattle. Protective immunity to this organism requires the development of a functional CD8+ cytotoxic T lymphocyte (CTL) response. In this study, we show that bovine white blood cells mount a more efficacious CTL response when stimulated with M. avium bacteria lacking a gene known as relA compared to cells stimulated with the currently used, attenuated BCG vaccine. This finding will help in vaccine development because it paves the way for the development of an improved, attenuated live vaccine to protect against Mycobacterial infections of animals and humans.

Technical Abstract: Studies with Mycobacterium avium subsp. paratuberculosis (Map) in cattle revealed deletion of relA, a global regulator gene, abrogated ability of the mutant to establish a persistent infection, attributed to development of an immune response that cleared infection. Analysis of the recall response demonstrated presence of CD8 cytotoxic T cells that kill intracellular bacteria. Replication of the primary response demonstrated the CTL response could be elicited with the 'Map/relA mutant or the target of the immune response, a 35 kD membrane protein. Follow up comparative studies with Mycobacterium bovis bacillus Calmette-Guérin (BCG) and a BCG relA ('BCG/relA) deletion mutant revealed deletion of relA enhanced the CTL response compared to BCG. Analysis of the cytokine profile of cells proliferating in response to stimulation with BCG or BCG/relA showed increased expression of IFN-', TNF-a, and IL-17 by cells stimulated with 'BCG/relA in comparison with BCG. The proliferative and CTL responses were markedly reduced in response to stimulation with heat killed BCG or 'BCG/relA. Intracellular bacterial killing was mediated through the perforin, granzyme B (GnzB), and the granulysin pathway. The data indicate relA is the Achilles’ heel for pathogenic mycobacteria and deletion may be key to improving efficacy of attenuated vaccines for mycobacterial pathogens.