PROJECT SUMMARY / ABSTRACT Cryptococcus neoformans is an opportunistic fungal pathogen that causes localized and disseminated disease, cryptococcosis, in immunocompromised individuals, such as in people living with HIV. A life- threatening manifestation of cryptococcosis is cryptococcal meningitis (CM); a central nervous system infection with acute inflammation of the meninges and the most common cause of meningitis in those with HIV. Sub- Saharan Africa carries the majority of the global CM disease burden and mortality. Because the host immune response is crucial to clearance of the infection and resolution of symptoms, a solid understanding of the host immune response in the state of cryptococcal infection is essential in order to reduce morbidity and mortality. Natural killer (NK) cells are an innate lymphoid immune cell that has been understudied in CM. NK cells have antigen independent cytotoxic ability that render them ideal for targeting both intracellular and extracellular pathogens. This key feature of NK cells could make them an important aspect in the immune response to C. neoformans, which is both an intracellular and extracellular pathogen. Standard antifungal therapy targets the pathogen, yet mortality still occurs, including among persons with sterile CSF cultures. My preliminary data has shown that low CSF concentrations of NK cell cytotoxicity associated soluble molecules are associated with increased risk of acute 14-day mortality in persons with CM. Therefore, improving NK cytotoxic activity may be an innovative therapeutic pathway toward reducing cryptococcal mortality. Additionally, the identification of genes and pathways implicated in impaired NK cell function that could be modulated to improve cytotoxicity could be targets for future therapeutics. My central hypothesis is that NK cells contribute to fungal clearance of C. neoformans, but that a combination of NK cell exhaustion, impaired cytokine production, increased inhibitory receptors, and decreased activating receptor expression due to the underlying HIV infection disrupts their cytotoxic abilities. To test the central hypothesis, I am proposing the following Aims: Aim 1 seeks to compare NK cell natural cytotoxicity and antibody-dependent cell mediated cytotoxicity between HIV-infected persons with CM who die within 14-days of diagnosis and those who survive >14 day. Aim 2 seeks to determine if persons with CM who die within 14-days have high levels of differentially expressed genes involved in exhaustion and inhibition of cytotoxicity pathways when compared to persons who survive CM. Collectively, these findings will provide the first quantification of NK cell cytotoxicity against clinical isolates of C. neoformans and the identification of differentially expressed genes associated with acute CM mortality. This information will provide us with specific genes that are involved in exhaustion, cytokine production, and cytotoxicity that could be modulated in the futur...