Table 1.

Summary of co-inhibitory immune checkpoint receptors.

Co-Inhibitory Checkpoint	Receptor Expression	Binding Partner	Binding Partner Expression	Clinical Development
CTLA-4	Effector T cells Regulatory T cells	B7-1 (CD80) B7-2 (CD86)	APCs Tumor MDSCs	FDA Approved (ipilimumab)
PD-1	TILs Effector T cells Regulatory T cells B cells NK cells	PD-L1 (B7-H1) PD-L2 (B7-DC)	Cancer cells APCs Tumor MDSCs	FDA Approved (pembrolizumab and nivolumab)
LAG-3	Effector T cells Regulatory T cells B cells NK cells Dendritic Cells	MHC Class II	APCs	Phase I/II Clinical Trials (IMP321 & LAG525)
BTLA	T cells B cells NK cells	HVEM	Cancer cells APCs T cells	Pre-Clinical Studies
PD-1H	T cells APCs	Unknown	N/A	Pre-Clinical Studies Phase I Clinical Trials (JNJ-61610588)
TIM-3/CEACAM1	Effector T cells	Galectin-9	Cancer cells APCs	Pre-Clinical Studies Phase I Clinical Trials (TSR-022 & MBG453)
TIGIT	Effector T cells Regulatory T cells NK cells	CD155 CD112	Cancer cells APCs	Pre-Clinical Studies Phase I Clinical Trial (OMP-313M32)
CD96	Effector T cells Regulatory T cells NK cells	CD155 CD111	Cancer cells APCs	Pre-Clinical Studies
CD112R	Effector T cells NK cells	CD112	Cancer cells APCs	Pre-Clinical Studies

LAG-3, lymphocyte activation gene-3; BTLA, B and T lymphocyte attenuator; PD-1H, programmed death-1 homolog; CTLA-4, cytotoxic T-lymphocyte-associated antigen 4; TIM-3, T-cell immunoglobulin; TIGIT, T cell immunoglobulin and immunoreceptor tyrosine-based inhibitory motif domain; PD-1, programmed death protein-1; CEACAM1, carcinoembryonic antigen cell adhesion molecule 1; MHC-II, class II major histocompatibility complex; FDA, United States Food and Drug Administration; APCs, antigen-presenting cells; MDSCs, myeloid derived suppressor celsl, HVEM, herpesvirus entry mediator.