The deubiquitinase USP17LA negatively regulates T-cell activation and attenuates anti-tumor immunity.

T-cell activation is essential for effective immune responses, yet its precise regulatory mechanisms remain incompletely understood. In this study, we show that the deubiquitinases of the Ubiquitin-Specific Peptidase 17-like (USP17L) family are significantly upregulated following T-cell stimulation. Using CRISPR-mediated gene knockout mice, we demonstrate that USP17LA, but not USP17LB, acts as a negative regulator of T-cell activation. Loss of Usp17la leads to increased production of pro-inflammatory cytokines, enhanced T-cell proliferation and effector functions, without affecting T-cell development or homeostasis. Furthermore, Usp17la deletion augments TCR signaling and anti-tumor immunity, improving T-cell-mediated tumor surveillance in murine tumor models. Mechanistically, proteomic analysis revealed that USP17LA strongly associates with cadherin-binding and calmodulin-binding pathways. Notably, USP17LA interacts with RACK1 and prevents its ubiquitin-dependent degradation, thereby promoting RACK1-mediated suppression of NFAT activity and the subsequent inhibition of T-cell function. These findings establish USP17LA as a pivotal modulator of T-cell activation and suggest that targeting USP17LA could enhance anti-tumor immunity, offering a potential strategy for cancer immunotherapy.