Solid tumours are characterised by a three-dimensional (3D) architecture that provides specific survival advantages such as resistance to anti-cancer drugs. The expression of programmed death-ligand 1 (PD-L1) is one such survival mechanism employed by tumours to mediate immune evasion, drug resistance and tumour progression. Here we investigated whether the expression of PD-L1 by human cancer cell lines altered in a 3D cell culture setting as opposed to their two-dimensional (2D) monolayer counterparts. We utilised well-established 3D cell culturing systems that facilitate the formation of spheroids and display heterogeneous populations of cells resembling that found in the tumour microenvironment, to assess PD-L1 expression. We found that PD-L1 expression changed in human breast, prostate and colorectal cancer cell lines in 3D cell culture systems when compared to their 2D counterparts. The level of expression of PD-L1 by tumour cells in 3D cell culture is more likely to mimic that of an in vivo tumour microenvironment than 2D cell culture, and may better able the investigation of the tumour-intrinsic role of PD-L1
