Across all studied mouse models, CTLA-4 expression appeared higher in the tumor and was largely restricted to CD4+FoxP3+ Treg cells (mean expression 68.3%), relative to CD4+FoxP3− effector (CD4+eff) T cells (10.2%, p < 0.0001) and CD8+ T cells (5.4%, p < 0.0001) (Figures 1A and 1B). Here, CTLA4 is linked to neoplasm.