immunization-adult-zebrafish-for-preclinical-screening-dna-based

Immunization of Adult Zebrafish for the Preclinical Screening of DNA-based Vaccines

The interest in DNA-based vaccination has increased during the past two decades. DNA vaccination is based on the cloning of a sequence of a selected ...

University of Tampere

Tuberculosis (TB) is a major global health problem, and new drugs and vaccines are urgently needed. As clinical trials in humans require tremendous resources, preclinical drug and vaccine development largely relies on valid animal models that recapitulate the pathology of human disease and the immune responses of the host as closely as possible.

Animal models in tuberculosis research - where is the beef?

Tuberculosis (TB) remains a major global health challenge and the development of a better vaccine takes center stage in fighting the disease. For this purpose, animal models that are capable of replicating the course of the disease and are suitable for the early-stage screening of vaccine candidates are needed. A Mycobacterium marinum infection in adult zebrafish resembles human TB. Here, we present a pre-clinical screen for a DNA-based tuberculosis vaccine in the adult zebrafish using an M. marinum infection model. We tested 15 antigens representing different types of mycobacterial proteins, including the Resuscitation Promoting factors (Rpf), PE/PPE protein family members, other membrane proteins and metabolic enzymes. The antigens were expressed as GFP fusion proteins, facilitating the validation of their expression in vivo. The efficiency of the antigens was tested against a low-dose intraperitoneal M. marinum infection (≈ 40 colony forming units), which mimics a primary M. tuberculosis infection. While none of the antigens was able to completely prevent a mycobacterial infection, four of them, namely RpfE, PE5_1, PE31 and cdh, led to significantly reduced bacterial burdens at four weeks post infection. Immunization with RpfE also improved the survival of the fish against a high-dose intraperitoneal injection with M. marinum (≈ 10.000 colony forming units), resembling the disseminated form of the disease. This study shows that the M. marinum infection model in adult zebrafish is suitable for the pre-clinical screening of tuberculosis vaccines and presents RpfE as a potential antigen candidate for further studies.

Identification of novel antigen candidates for a tuberculosis vaccine in the adult zebrafish (Danio rerio).

Roughly one third of the human population carries a latent  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  infection are insufficiently understood. Here, we used a natural fish pathogen, , to model the reactivation of a mycobacterial infection in the adult zebrafish (). 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- 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.

Article	Year
Animal models in tuberculosis research - where is the beef? Expert opinion on drug discovery\| PubMed ID: 26073097	2015
Identification of novel antigen candidates for a tuberculosis vaccine in the adult zebrafish (Danio rerio). PloS one\| PubMed ID: 28742838	2017
Identification of protective postexposure mycobacterial vaccine antigens using an immunosuppression-based reactivation model in the zebrafish. Disease models & mechanisms\| PubMed ID: 29590635	2018

Mirja Niskanen

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