Insights into protection against Mycobacterium tuberculosis infection: time to officially confirm another phenotype?

Immune correlates of protection against infection with Mycobacterium tuberculosis (Mtb) remain elusive. In this issue of the JCI, Dallmann-Sauer and authors demonstrate that lack of tuberculin skin test (TST) and interferon γ release assay (IGRA) conversion among people with HIV despite years-long Mtb exposure is associated with alveolar lymphocytosis, including specific poly-cytotoxic T cells, and M1-type alveolar macrophages with a stronger ex vivo response to the pathogen. Studies in these rare individuals, termed "TB resisters" and in tuberculosis household contacts who are repeatedly IGRA negative in the months after a specific exposure event (known as "early clearers") help elucidate manipulatable mechanisms to boost protection against Mtb infection.