Regulatory T cells (Tregs) are required to control immune responses and maintain homeostasis, but are a significant barrier to anti-tumor immunity 1 . Conversely, Treg instability, characterized by loss of the master transcription factor Foxp3 and acquisition of pro-inflammatory properties 2 , can promote autoimmunity and/or facilitate more effective tumor immunity 3 , 4 . A comprehensive understanding of the pathways that regulate Foxp3 could lead to more effective Treg therapies for autoimmune disease and cancer. Despite improved functional genetic tools that now allow for systematic interrogation, dissection of the gene regulatory programs that modulate Foxp3 expression has not yet been reported. In this study, we developed a CRISPR-based pooled screening platform for phenotypes in primary mouse Tregs and applied this technology to perform a targeted loss-of-function screen of ~490 nuclear factors to identify gene regulatory programs that promote or disrupt Foxp3 expression. We discovered several novel modulators including ubiquitin-specific peptidase 22 (Usp22) and ring finger protein 20 (Rnf20). Usp22, a member of the deubiquitination module of the SAGA chromatin modifying complex, was discovered to be a positive regulator that stabilized Foxp3 expression; whereas the screen suggested Rnf20, an E3 ubiquitin ligase, can serve as a negative regulator of Foxp3. Treg-specific ablation of Usp22 in mice reduced Foxp3 protein and created defects in their suppressive function that led to spontaneous autoimmunity but protected against tumor growth in multiple cancer models. Foxp3 destabilization in Usp22-deficient Tregs could be rescued by ablation of Rnf20, revealing a reciprocal ubiquitin switch in Tregs. These results reveal novel modulators of Foxp3 and demonstrate a screening method that can be broadly applied to discover new targets for Treg immunotherapies for cancer and autoimmune disease.

One hundred fifty-seven patients in the study had ACLF and 175 patients had no ACLF (non-ACLF) pretransplant. Thirty-four patients in the entire cohort received dual organs, 10 of them (29.4%) had ACLF. Seventy-six percent of the patients with ACLF had acute kidney injury as their reason for decompensation and 23.6% had an infection. Mean Model for End-Stage Liver Disease score at transplant was significantly different between the groups (ACLF 28.77 vs. non-ACLF 21.23, P<0.0001). A total of 16.6% of the patients achieved an estimated glomerular filtration rate (eGFR) less than 30 mL/min, 21% of patients died, 12.3% developed cirrhosis, and 7.5% received a second transplant. There was no difference in mean eGFR between the ACLF and non-ACLF cohorts at 3 years posttransplant (56.35 mL/min vs. 59.93 mL/min, respectively, P=0.27). On multivariate analysis, ACLF was not significantly associated with eGFR less than 30 mL/min, death, recurrent cirrhosis, or retransplantation when adjusted for potential confounders.