The tumor microenvironment
The PD-L1 immunologic checkpoint
Plays a key role in tumor progression
What is the tumor microenvironment (TME)?
The tumor microenvironment (TME) consists of different cellular, including immune cells, and non-cellular components in and around the tumor. The TME has been recognized to play a significant role in tumor progression.1,2
Why is the TME important?
The TME shapes tumor evolution (whether the tumor regresses, develops resistance, evades the immune system and/or metastasizes) and consequently impacts patient outcomes.3 An association has been observed between the levels of tumor infiltrating immune cells, key components of the TME, and patient prognosis: a colorectal cancer study showed that higher levels of tumor infiltrating CD3+ immune cells were associated with better disease free survival. 4
What is the role of PD-L1 in the TME?
Aberrant expression of PD-L1 on tumor cells has been reported to impede anti-tumor immunity, resulting in immune evasion.5 Therefore, interruption of the PD-L1/PD-1 pathway represents an attractive strategy to reinvigorate tumor-specific T cell immunity suppressed by the expression of PD-L1 in the TME. This approach has proven effective: PD-L1 expression on immune cells in the TME has been shown to identify urothelial cancer patients who are most likely to benefit from atezolizumab an anti-PD-L1 drug.6