Mycobacterium tuberculosis (Mtb) is a leading worldwide infectious killer, in part, due to a large reservoir of latent infection that contributes to ongoing transmission. Yet some individuals resist Mtb infection despite heavy and repeated exposure as indicated by persistently negative tuberculin skin tests (TSTs) and interferon gamma (IFNg) release assays (IGRAs). Elucidation of the mechanisms employed by these human resisters (RSTRs) may yield novel targets for host-directed therapies or identify immune signatures that correlate with host protection. Dr. Simmons?s collaborators longitudinally followed a group of highly-exposed household contacts (HHCs) of index pulmonary tuberculosis (TB) patients in Uganda and define RSTRs as the ~7% that remain TST/IGRA-negative over 8-10 years of follow-up. Using whole transcriptome analysis (RNAseq), Dr. Simmons found that monocyte-derived macrophages (MDMs) from RSTRs versus HHCs with latent Mtb infection (LTBI) have distinct transcriptional responses after ex vivo Mtb infection. He further identifies a network of genes differentially expressed in RSTR versus LTBI macrophages. Gene products of this RAB11 network play roles in intracellular phagosome or vesicle trafficking. Common polymorphisms in one of these genes, YTHDC2, were found to associate with protection from TB disease in Uganda but the immunologic mechanisms are unknown. The long-term objectives of this proposal are to define macrophage pathways or genes that characterize the protective RSTR response. Dr. Simmons will determine whether RAB11 network candidate resistant genes are required for microbicidal activities of phagosome pathways in Aim 1, and confirm these phagosome processes are distinct in primary RSTR and LTBI macrophages.
In Aim 2, he proposes genetic approaches to identify natural variants in the RAB11 network gene YTHDC2, fine map the functional polymorphism(s), and measure the impact that relative YTHDC2-deficiency has on phagosome maturation and other macrophage responses to Mtb. Once the immune signatures and cellular effectors are identified in this unique cohort of human RSTRs, host-directed therapies that augment these protective functions can be developed to improve the efficacy of currently available antimicrobials. Dr. Simmons is currently a Senior Fellow in the Division of Allergy and Infectious Diseases at the University of Washington. He additionally proposes a comprehensive career development program that includes: 1) Mentored training and formal didactics in large data set analyses (e.g. statistical genetics, systems biology); 2) mentorship in design of case-control studies and human subjects research; 3) structured opportunities to present his work to local and international scientific audiences; and 4) Scientific Advisory Committee meetings that ensure scientific and career development progress. By the conclusion of this award, Dr. Simmons will transition to an independently-funded expert in the Mtb host response who will direct his own laboratory.
We have identified unique macrophage responses in humans who resist infection with Mycobacterium tuberculosis (Mtb) despite heavy exposure. The aims of this proposal are to uncover genetic determinants of this macrophage resistance and define the underlying cellular mechanisms. Once cellular factors are known, these protective macrophage pathways can be augmented with host-directed therapies that improve killing of drug-sensitive and drug-resistant Mtb.