PDCD1 and neoplasm: Because the 29F.1A12 PD-1 blocking ab4,8 inhibits B16-F10 melanoma growth in three-dimensional (3D) tumor spheroid, but not standard two-dimensional (2D) cultures5, we next assessed if anti-PD-1 ab binding to WT B16-F10 cells was enhanced in 3D versus 2D conditions.