PDCD1 and neoplasm: First, in order to confirm bi-functional mechanism of action (Additional file 2: Figure S1D-F); more specifically – the ability of PD1-Fc-OX40L to physically ‘tether’ tumor cells with T cells and stimulate potent cytotoxic activity, we used the visual tool of time-lapse immunofluorescent live cell imaging (Fig. 6a).