TNFRSF18 and neoplasm: Further studies by Ronchetti et al. also suggest that mouse GITR may be a co-stimulatory signal in the activation of CD8 T effector cells (30), which is in line with our results demonstrating a negative effect of CD8+ T cell depletion, although the depletion did not fully abrogate the decreased tumor growth seen in mice treated with anti-GITR, anti-PD1, and radiation therapy.