Table 1.

Selected potential biomarkers for immunotherapy

	Basis	Challenges
PD-L1	IHC approach to measuring PD-L1 expression on tumour and immune cells	Variability in assays, antibodies and tumour microenvironment
CD8+ T cells	PD-1/PD-L1 expression on CD8+ T cells predicts response to PD-1 agents	Optimal cut-off points, scoring metrics and agreement on magnitude of change needed for meaningful prediction of response
Tumour mutation load	High mutation load resulting from various factors correlated with response to checkpoint inhibitors in exceptional responders	Availability of adequate tissue for sequencing; whole exome sequencing expensive and slow turnaround time vs. other clinical assays
Neoantigen burden	Predict clinical benefit to ipilimumab and PD-1 blockade in melanoma and lung cancer	As above
Gene expression profiling	IFN-induced signatures may predict response to checkpoint inhibitors	Sizable tissue collection needed to validate testing and training sets