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. 2021 Jul 22;11:693321. doi: 10.3389/fonc.2021.693321

Table 1.

Immune checkpoints structure and expression.

Immune checkpoints Structure and expression
PD-1

  • ① 288 amino acid and a single IgV extracellular domain

  • ② on the surface of activated T cells, B cells, NKT cells, NK cells, and macrophages
CTLA-4

  • ① a 36-amino acid cytoplasmic tail

  • ② on the surface of activated T cells and Treg cells as a receptor
LAG-3

  • ① D1–D4 four immunoglobulin-like domains

  • ② on the surface of activated CD4+ T cells, CD8+ T cells, NK cells, and Treg cells
TIGIT

  • ① the IgV domain, transmembrane domain and an immune receptor tyrosine-based domain

  • ② on the surface of CD4+ T cells, CD8+ T cells, NK cells, and Treg cells
TIM-3

  • ① 5 tyrosines in the cytoplasmic domain

  • ② on the surface of CD4+ T cells, CD8+ T cells, NK cells, DCs, and monocytes
SIGLEC-15

  • ① the sialic acid-binding immunoglobulin-type lectin structure

  • ② on the surface of myeloid cells, and in various types of cancers
IDO-1 on the surface of APC and epithelial-derived tumor cells
VISTA (B7-H5)

  • ① 309 amino acids include

  • 136 amino acid single IgV extracellular domain

  • 23 amino acid stalk domain

  • 21 amino acid domain

  • 97 amino acid cytoplasmic domain

  • ② on the surface of T cells, activated Treg cells, myeloid cells, and mature APC cells
VTCN1 (B7-H4)

  • ① 282 amino acids include

  • a transmembrane domain

  • a 2 amino acids intracellular domain

  • 7 N-glycosylation sites extracellular domain

  • ② on the surface of tumor cells
CD276 (B7-H3)

  • ① two IgC and variable (IgV) domains

  • ② on the surface of tumor cells
CD70

  • ① 193 amino acids, with over 20 membrane bound and secreted protein ligands

  • ② on the surface of activated T, B cells, thymic medulla epithelial cells, DC cells, and APC cells
CD47

  • ① 5-time transmembrane spanning domain, single extracellular V-set immunoglobulin,short cytoplasmic region

  • ② on all the normal cells and overexpressed on tumor cells
TNFSF14 (LIGHT)

  • ① homologous to lymphotoxins and engages the herpes virus entry mediator (HVEM) and the Lymphotoxin-β receptor

  • ② on the surface of activated T cells, NK cells and immature DCs
TNFRSF4

  • ① 4 cysteine-rich domains

  • ② on CD4+ and CD8+ T cells, NK, NKT cells and neutrophils
TNFRSF9

  • ① 255 amino acid include

  • 2 N-linked glycosylation

  • 169 amino acid extracellular domain

  • 27 amino acid transmembrane domain

  • ② on the surface of T cells, NK cells, DCs, Treg, NKT cells, neutrophils, monocytes, and eosinophils
TNFRSF18 (GITR)

  • ① 241 amino acids

  • ② on epithelial cells, T cells, DCs, and the Treg cells in tumors
CD28

  • ① extracellular immunoglobulin-like domain

  • ② on CD4+, CD8+ T cells, bone marrow stroma cells, neutrophils and eosinophils