PDCD1 and central nervous system cancer: To assess the effect of combined TGF-β inhibition and immune checkpoint modulation on immune cell activation, we performed co-culture assays using mouse glioma cells and syngeneic splenocytes, with or without the TGF-β inhibitor SD208, antibodies targeting GITR, CD137, OX40, LAG3, or PD-1, or their respective combinations.