Table 2.

The reported PD-L1 formats.

Format	Location	Structure	Source	Possible functions	Treatment response	Detection*	References
mPD-L1	Membrane	Integrity	Endogenous translation	Bind with PD-1 for immune regulation	Antibody, gene, and chemo-inhibitor	WB, IHC	(11, 12)
cPD-L1	Cytoplasm	–	Endogenous translation	Transfer to membrane, shorten disease-free survival, and cell growth and migration	Gene and chemo-inhibitor	WB, IHC	(23, 28)
nPD-L1	Nuclei	–	–	Enhance chemo-resistance	Gene and chemo-inhibitor	WB, IHC	(24, 25)
sPD-L1	Serum	Integrity or splice variant	Secretion from cancer cells/matured APCs	Bind with PD-1, associated with immune state	Antibody, gene, and chemo-inhibitor	ELISA	(29)
	Serum	Without transmembrane motifs	Enzyme cleavage	Bind with PD-1, associated with immune state	Antibody, gene, and chemo-inhibitor	ELISA	(19)
–	–	Dimeric	Crystallization	Functional units or evolution relic	–	–	(30)

^*The typical detection method: WB, Western blotting; IHC, Immunohistochemistry; ELISA, Enzyme-linked immunosorbent assay.