UC Berkeley

Mycobacterium tuberculosis, the causative agent of tuberculosis disease (TB), is one of the top infectious killers in the world. The sole licensed vaccine, M. bovis BCG, does not reliably confer protective immunity in adults. Although anti-mycobacterial antibiotics are available and routinely prescribed, the rise of antibiotic resistance and the shortcomings of the BCG vaccine highlight the importance of new host-directed therapies and vaccine strategies against TB. A more complete understanding of the immune response to M. tuberculosis is necessary to combat and prevent TB. Two components of innate immunity have been shown to both promote and hinder host control of M. tuberculosis: neutrophils and STING-dependent immune activation.

Neutrophil influx and infection occurs during the innate phase of infection. A lack of relevant in vitro models has historically hampered neutrophil studies, given the short half-life of ex vivo neutrophils. We overcame this problem by utilizing a model for neutrophil differentiation and responses to M. tuberculosis infection based on ER-Hoxb8 conditional immortalization of Cas9-expressing neutrophil progenitors. CRISPR/Cas9- mediated gene editing facilitated unbiased genome-wide pooled screens for genes that mediate survival during differentiation and infection. Innate immune activation is also necessary for improved TB protein subunit vaccine design. We aimed to better characterize STING activation in the context of a mucosally administered cyclic-di- nucleotide adjuvanted protein subunit TB vaccine. A previous study had correlated IL-17 producing CD4 T cells (Th17s) with mucosal vaccine protection, instead of the IFN-γ- producing CD4 T cell (Th1) response seen with subcutaneous BCG or protein subunit vaccination. We discovered that both IL-17 and IFN-γ contributed to immunity. The transcription factors STAT6 and IRF3 were not essential for mucosal vaccine-induced immunity downstream of STING, although type I IFN signaling contributed to vaccine efficacy. Dependent on vaccine antigen, our mucosal vaccine could promote durable Th17 responses and antibacterial resistance after the efficacy of BCG had waned. These results provide a clearer picture of several aspects of innate and adaptive immunity.