PROJECT SUMMARY/ABSTRACT Although tuberculosis (TB) has been curable and preventable for decades, TB remains a major public health threat globally, with one-quarter of the world's population currently infected. Although efforts to control TB have primarily focused on treating active TB cases, greater emphasis on preventing new infections will be needed to achieve the EndTB goal of fewer than 10 TB cases per 100,000 population by 2035. However, the development of biomedical interventions to prevent TB infection, such as a TB vaccine, has been hampered by a lack of understanding of host factors that mediate susceptibility and resistance to Mycobacterium tuberculosis (Mtb) infection following exposure. A genetic basis for resistance to Mtb infection has long been postulated. Gene expression can also be influenced by epigenetic modifications, such as DNA methylation, which can mediate inherited, behavioral and co-morbid effects (e.g., smoking, aging, diabetes), and influence immunological function. Thus, epigenetics may play a pivotal role in a variety of diseases, particularly infectious diseases. However, no study has been conducted to understand the impact of epigenetic modifications on resistance to Mtb infection at a population level. In the proposed R21, we will conduct a hypothesis-generating, epigenome-wide study of >850,000 DNA methylation sites to identify epigenetic predictors of resistance among household contacts who remain uninfected, despite well-characterized exposure to active TB. We will leverage our recently funded NIH R01 study of 4,000 household contacts (R01AI139406, MPI Gandhi/Sun). In this parent R01 study, we are identifying individuals with resistance to Mtb infection and conducting GWAS and metabolomic analysis to characterize factors associated with resistance. The proposed R21 will utilize clinical and exposure data and DNA specimens from participants enrolled in the parent R01 study, making this epigenetic study highly feasible. In Aim 1, we will conduct agnostic searches for epigenomic associations, in addition to targeted analyses of candidate genes. In Aim 2, we will combine GWAS data from the parent R01 and DNA methylation sites identified in Aim 1 to elucidate the causal relationships between epigenetic and resistance using Mendelian Randomization. The findings of this R21 would provide preliminary data to facilitate a future, definitive investigation of epigenetics and resistance to Mtb infection. A greater understanding of epigenetics in Mtb infection will provide insights for vaccine development and other novel biomedical interventions to prevent Mtb infection.