It was anticipated that the strong CD3-mediated T-cell activation induced by tumor-directed trAbs not only ignites T-cell effector functions, but also entails CTLA-4 upregulation on the surface of activated T cells. For combining anti-CTLA-4 treatment with trAb therapy, it is necessary to establish the upregulation of CTLA-4 following trAb-dependent activation. Therefore, we determined CD69 and CTLA-4 levels at different time points after in vitro incubation of T cells isolated from mouse spleens together with DCs and tumor cells (B78-D14 or B16-EpCAM) in the presence of Surek or BiLu. While the T-cell activation marker CD69 already increased by day 1, CTLA-4 expression only peaked after 48 to 72 hours (Figure 1).