The Tumor Microenvironment Enhances Treg Fitness through Upregulation of a Foxp3-specific Deubiquitinase Module

Abstract Through abnormal vascularization, cytokine production, and nutrient depletion, tumors can create a highly immunosuppressive microenvironment that favors the functionality of immune regulatory programs over anti-tumor effector responses. Particularly, the highly immunosuppressive tumor microenvironment (TME) favors T regulatory (Treg) cell stability and function, while diminishing the anti-tumor activity of effector T cells. Here, we characterized previously unknown TME-specific cellular and molecular mechanisms that promote intratumoral Treg adaptation through Foxp3. We uncovered the critical role of FOXP3-targeting deubiquitinases, ubiquitin specific peptidase 22 (Usp22) and 21 (Usp21) as environmentally sensitive factors of multiple TME-specific environmental stressors including TGF-β, hypoxia, and nutrient deprivation. Specifically, Usp22 and Usp21 maintain optimal Foxp3 expression through HIF, AMPK, and mTOR activity. The simultaneous loss of both USPs synergizes to alter Treg metabolic signatures and impair suppressive mechanisms, resulting in enhanced anti-tumor activity. Our findings unveil new mechanisms underlying the functional uniqueness of intratumoral Treg cells, and identify Usp22 and Usp21 as a antitumor therapeutic targets that inhibit Treg adaptability in the TME.