Identification of protective postexposure mycobacterial vaccine antigens using an immunosuppression-based reactivation model in the zebrafish

Abstract

Roughly one third of the human population carries a latent Mycobacterium tuberculosis infection, with a 5-10% lifetime risk of reactivation to active tuberculosis and further spreading the disease. The mechanisms leading to the reactivation of a latent Mycobacterium tuberculosis infection are insufficiently understood. Here, we used a natural fish pathogen, Mycobacterium marinum, to model the reactivation of a mycobacterial infection in the adult zebrafish (Danio rerio). A low-dose intraperitoneal injection (∼40 colony-forming units) led to a latent infection, with mycobacteria found in well-organized granulomas surrounded by a thick layer of fibrous tissue. A latent infection could be reactivated by oral dexamethasone treatment, which led to disruption of the granuloma structures and dissemination of bacteria. This was associated with the depletion of lymphocytes, especially CD4+ T cells. Using this model, we verified that ethambutol is effective against an active disease but not a latent infection. In addition, we screened 15 mycobacterial antigens as postexposure DNA vaccines, of which RpfB and MMAR_4207 reduced bacterial burdens upon reactivation, as did the Ag85-ESAT-6 combination. In conclusion, the adult zebrafish-M. marinum infection model provides a feasible tool for examining the mechanisms of reactivation in mycobacterial infections, and for screening vaccine and drug candidates.This article has an associated First Person interview with the first author of the paper.

Animal Models of Tuberculosis Vaccine Research: An Important Component in the Fight against Tuberculosis

“…In addition to its use for the preclinical screening of vaccines, the zebrafish model has been used in clarifying the mechanisms underlying granuloma formation [114]. Recently, several studies have indicated that this animal model provides a feasible tool for examining the mechanisms underlying reactivation in mycobacterial infections, and confirmed its suitability for the preclinical screening of TB vaccine candidates [38,[115][116][117]. However, a recent review indicated that the zebrafish model has significant differences of TB vaccines in these models.…”

Teleost contributions to the understanding of mycobacterial diseases

“…marinum infected fish showed a collection of Th cells surrounding the granuloma, similar to that of mammalian infection models (Yoon et al, 2015). Importance of T cells for the control of mycobacterial infection was corroborated in fish, where depletion of CD4+ T cells corresponded to granuloma disruption and dissemination of M. marinum (Myllymaki et al, 2018). However, most of the research in the zebrafish has focused on the embryonic system which predates development of lymphocytes.…”

“…tuberculosis infection nor inhibits the reactivation of latent TB in humans, and so alternatives are being actively sought. The zebrafish is a useful screening tool for this search and some alternative candidate antigens have recently been identified showing promise for future novel vaccines (Myllymaki et al, 2018;Myllymaki et al, 2017). The increase in study of teleost mycobacterial models makes it seem only a matter of time before novel treatment strategies discovered in fish enter clinical trials and the clinic itself rather than being used simply to inform the clinical situation.…”

Zebrafish as an alternative animal model in human and animal vaccination research

“…Those authors proved that the M. marinum infection model in adult zebrafish was suitable for preclinical screening of tuberculosis immune's responses and vaccines. It was also a promising new model for tuberculosis vaccine research, including the pre-clinical identification of vaccine antigens [16,17,36,41,61,67];). Other species of Mycobacterium have also been studied, such as M. bovis [52,73] and M. abscessos [7].…”