Experimental dissection of tuberculosis protective immunity: a human perspective

Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB), has plagued humankind for millennia. Claiming 1.25 million lives in 2023, TB remains the worldwide leading cause of death from a single-infectious agent. Improved vaccines, diagnostics and treatment regimens for drug-susceptible and drug-resistant cases are paramount to attain the goals of the WHO's End TB Strategy. Our knowledge gap in protective immunity in TB impedes the development of such new vaccines and host-directed interventions. Mtb is a pathogen highly adapted to humans and primarily infects the lungs. Access to relevant specimens is invasive, preventing ample human TB studies, which therefore mostly rely on peripheral blood specimens and biopsies. Thus, there is a need for relevant surrogates. In recent years, in vivo, in vitro, and in silico systems have arisen to approach and model different aspects of TB pathogenesis. Moving away from cell-line infections and classical animal models, TB research has advanced to genetically diverse mice, 3D organoid cultures and computational modelling. We will review current TB models and discuss their applicability to decipher protective human immunity, understand disease progression, transmission, as well as evaluate vaccine candidates and unravel host-directed therapeutic approaches.