Exploring the stage-specific roles of Tcf-1 in T cell development and malignancy at single-cell resolution

Tcf-1(encoded by Tcf7)not only plays critical roles in promoting T cell development and differentiation but also has been identified as a tumor suppressor involved in preventing T cell malignancy.However,the comprehensive mechanisms of Tcf-1 involved in T cell transformation remain poorly understood.In this study,Tcf7^(fl/fl)mice were crossed with Vav-cre,Lck-cre,or Cd4-cre mice to delete Tcf-1 conditionally at the beginning of the HSC,DN2-DN3,or DP stage,respectively.The defective T cell development phenotypes became gradually less severe as the deletion stage became more advanced in distinct mouse models.Interestingly,consistent with Tcf7^(-/-)mice,Tcf^(fl/fl)Vav-cre mice developed aggressive T cell lymphoma within 45 weeks,but no tumors were generated in Tcf7^(fl/fl)Lck-cre or Tcf^(fl/fl)CdA-cre mice.Single-cell RNA-seq(ScRNA-seq)indicated that ablation of Tcf-1 at distinct phases can subdivide DN1 cells into three clusters(C1,C2,and C3)and DN2-DN3 cells into three clusters(C4,C5,and C6).Moreover,Tcf-1 deficiency redirects bifurcation among divergent cell fates,and clusters C1 and C4 exhibit high potential for leukemic transformation.Mechanistically,we found that Tcf-1 directly binds and mediates chromatin accessibility for both typical T cell regulators and proto-oncogenes#including Myb,Mycn,Runxl,and Lyl1 in the DN1 phase and Lefb ld2,Dtxb Fyn,Bclllb,and Zfp36l2 in the DN2-DN3 phase.The aberrant expression of these genes due to Tcf-1 deficiency in very early T cells contributes to subsequent tumorigenesis.Thus,we demonstrated that Tcf-1 plays stage-specific roles in regulating early thymocyte development and transformation,providing new insights and evidence for clinical trials on T-ALL leukemia.