Lung disease caused by Non-Tuberculous Mycobacteria (NTM) poses an increasing threat to individuals with preexisting lung conditions including cystic fibrosis, chronic obstructive pulmonary disease or bronchiectasis, as well as immunocompromised patients. Infections caused by the intrinsically drug resistant NTM Mycobacterium abscessus (Mab) are considered non-curable with current chemotherapy. Thus, novel therapies against Mab infection are urgently needed, and their discovery and development require predictive animal models and a detailed understanding of involved immunopathology. However, guinea pigs and wild type mouse strains typically used in antimicrobial development are resistant to Mab infection. Thus, current drug testing approaches use mice with severe immunodeficiencies, which do not develop the pathologies observed in human patients. Furthermore, the mice were infected via systemic high dose inoculation, while natural infection in humans occurs by inhalation of a low pathogen dose. Based on M. tuberculosis and NTM literature indicating that the outcome of infection depends on the genotypes of the host and the pathogen, we hypothesized that it is possible to identify a wild type (immunocompetent) mouse strain-Mab isolate pair that would recapitulate the human mode of infection, robust persistent Mab burden, and relevant pulmonary pathology. To test our hypothesis, we inoculated immunocompetent BALB/c mice intranasally with 10 different clinical Mab isolates. After 40 days, some mouse groups had cleared the infection while others had a bacterial burden of up to 3 logs in lungs, indicating a considerable variability in persistence among clinical Mab isolates. Bacilli of the most highly persistent isolate were then implanted into the lungs of 7 genetically distinct mouse strains, including collaborative cross (CC) founder strains. The kinetics of bacterial burden in lungs and spleen over 28 days and pulmonary histopathology analyses showed that Mab lung infection in wild type mice progresses through an early stage productive infection followed by a mouse genotype-dependent, broad spectrum of disease outcomes ranging from mild to severe pathology and low to high pulmonary bacterial burden. In this application we propose to build on these promising results by infecting 20 CC mouse strains covering a large array of complex genetic traits with the most virulent Mab clinical isolate identified in our preliminary experiments and study bacterial persistence and pulmonary pathology. The mouse strain most closely mimicking human Mab infection pathologically and regarding robustness of infection will be sex-specific profiled in depth including bacterial kinetics, lung pathology, cytokine analysis, specific T cell responses and the efficacy of clinically relevant antibiotics. These studies will generate a robust immunocompetent mouse model for Mab lung disease, which will provide a more predictive platform for Mab drug discovery and enable clinically relevant studies of the immunopathology of the disease.
Infections with the emerging opportunistic pathogen Mycobacterium abscessus (Mab) are incurable, therefore new therapies are urgently needed. Because standard laboratory mouse strains are mostly resistant to Mab infection, existing animal models rely on immunodeficient mice which are suboptimal for drug development and largely prevent immunology-centered studies of the disease. Overcoming these drawbacks, our proposal will identify mouse strains susceptibility to Mab infection among genetically diverse Collaborative Cross lines to develop a predictive model platform enabling therapy evaluation and immunopathology studies.
