Deciphering the Role of Bruton's Tyrosine Kinase in the Host Defense Against Aspergillus fumigatus

PROJECT SUMMARY Advances in medicine have revolutionized treatment strategies for end-stage organ disease, cancer, and autoimmune diseases. Most of these advances focus on manipulating the immune system. Unfortunately, these treatments portend an increased susceptibility to invasive fungal infections. A prime example of these risks is demonstrated by the development of Bruton tyrosine kinase (BTK) inhibitors to treat B cell cancers. The three FDA-approved BTK inhibitors all work by covalently attaching to the active site of this kinase, rendering it incapable of its enzymatic activity. These irreversible BTK inhibitors contribute to elevated incidences of invasive aspergillosis, particularly in the central nervous system. The molecular mechanisms of how BTK inhibition facilitates fungal infection susceptibility remain a significant knowledge gap. We and our collaborators previously demonstrated that BTK inhibition by ibrutinib, acalabrutinib, or zanubrutinib dampens neutrophil effector activity against Aspergillus fumigatus and exogenous TNFα or GM-CSF restores these functions. Furthermore, our preliminary data suggest that tissue-resident immune cells (i.e., alveolar macrophages and microglia) produce less TNFα in the presence of BTK inhibition when infected by A. fumigatus. These data argue that the diminished TNFα or GM-CSF may fail to prime neutrophils treated by BTK inhibitors, which in turn permits the establishment of invasive infection. These clinical observations, coupled with our preliminary data, reveal a previously unappreciated critical role of BTK in the innate immune response to invasive aspergillosis. Our overall testable hypothesis is that TNFα and GM-CSF prime neutrophils to respond to invading A. fumigatus and circumvent BTK inhibitors by activating downstream molecules. To address this hypothesis, we propose the following three specific aims: [1] determine the mechanism of cytokine-mediated restoration of neutrophil effector activity in BTK-inhibited neutrophils stimulated by A. fumigatus; [2] elucidate the impact of BTK inhibition on alveolar macrophages, and [3] define the impact of BTK inhibition on microglia in central nervous system aspergillosis. This work will lead to critical insights into the host mechanisms responsible for the failure to contain Af in the presence of BTK inhibition. Successful completion of the proposed studies will reveal critical insights into the host mechanisms responsible for the failure to contain A. fumigatus in the presence of BTK inhibition and provide actionable targets to improve therapeutic strategies in patients receiving BTK inhibitor therapy.