Abstract 3652: USP7 heterozygous loss-of-function affects T-cell differentiation in pediatric T-ALL

Ubiquitin-specific-processing protease 7 (USP7), a protein deubiquitinase, is one of the most frequently mutated genes (33%) in the TAL1 subtype of pediatric T-lineage acute lymphoblastic leukemia (T-ALL). However, the functional effect of USP7 haploinsufficiency on T-ALL pathogenesis remains elusive. To understand USP7 haploinsufficiency’s impact on T-ALL, we performed gene expression analysis on 42 non-early T-cell precursor T-ALL RNAseq samples downloaded from phs000218. The gene expression analysis suggested that USP7 haploinsufficiency (USP7-mut N = 12; USP7-wt N = 30) down-regulated the expression of T-cell maturation markers (e.g. RAG1, RAG2, and CD1B), which were negatively regulated by TAL1 [1]. RNAseq on a T-ALL cell line with USP7 knocked down by shRNA also found the same TAL1 negatively regulated gene set, further supporting an increase of TAL1 activity in the USP7 mutated T-ALLs. To examine whether the T-cell maturation was affected by USP7 heterozygous knockout, we generated a conditional knockout (cKO) mouse model by cross-breeding the transgenic vav1-cre mice with the USP7fl/fl mice to obtain heterozygous USP7fl/wt-vav1-cre. Thymocytes isolated from cKO mice were co-cultured with the OP9-Δ1 cells in the medium supplied with cytokines. The cell surface differentiation markers, CD4 and CD8 were stained for flow cytometry detection, and we observed an increase of double-negative cells and a decrease of double-positive cells in USP7-het-KO mice versus control (N = 4 in each group; p-value Citation Format: Timothy I. Shaw, Li Dong, Anthony High, Yu Liu, Bensheng Ju, Kanisha Kavdia, Vishwajeeth Pagala, Bridget Shaner, John Easton, Chenxi Qian, Jiyang Yu, Janke Janke, John Kim Choi, Junmin Peng, Wei Gu, James R. Downing, Jinghui Zhang. USP7 heterozygous loss-of-function affects T-cell differentiation in pediatric T-ALL [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3652.