Programmed death-ligand 1 expression in human cancer three-dimensional cell culture models

Programmed death-ligand 1 (PD-L1) expression is a survival mechanism employed by tumours to mediate immune evasion and tumour progression. PD-1/PD-L1-targeted therapies have revolutionised the cancer therapy landscape due to their ability to promote durable anti-tumour immune responses in select patients with advanced cancers. However, some patients are unresponsive, hyper-progressive or develop resistance. Better characterisation of the 3D architecture of solid tumours by utilising 3D cell culture could provide an environment that more closely recapitulates in vivo human tumours for investigating tumour-intrinsic PD-L1 signalling and immunotherapy responses. Here we investigated whether PD-L1 expression by human breast, prostate and colorectal cancer cell lines altered in 3D cell culture models compared to their 2D monolayer counterparts. We found that PD-L1 expression changed in 3D-cultured cancer cells when compared to 2D-cultured cells. Additionally, the expression of immunological markers, PD-1, PD-L2, CD44, DR4, DR5, Fas, and HLA-ABC were assessed in 3D cell culture and compared to their expression in 2D. These markers were also altered in 3D compared to 2D-cultured cells, highlighting the importance of utilising 3D models which may better able the investigation of tumour-intrinsic PD-L1 signalling, responses to PD-1/PD-L1-targeted therapy, and combination therapies.