Table 2.

Markers of T cell exhaustion and their ligands on different cell types [145,150,151,152].

Exhaustion Marker Expressed on T Cell	Ligand	Cells Expressing the Ligand	Influence on Antitumor Functions of T Cells
PD-1	PD-L1	Tumor cells, DCs, TAMs, Bregs	Inhibitory
CTLA-4	CD80/CD86	DCs, B cells, TAMs, Treg	Inhibitory
TIM3	Galectin 9	APC	Both inhibitory and activating, but mostly inhibitory
LAG3	MHC-I or MHC-II–Peptide complex	APC, tumor cells	Both inhibitory and activating, but mostly inhibitory
TIGIT	CD155	APC	Inhibitory
Vista	?	APC	Largely remains to be elucidated
CD96	CD112	APC, tumor cells	Largely remains to be elucidated
BTLA-4	HVEM	T cells, Tregs, APCs, tumor cells	Largely remains to be elucidated
CD160	HVEM	T cells, Tregs, APCs, tumor cells	Largely remains to be elucidated