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Immune Checkpoint Protein Targets

B7-1 binds to CD28 or CTLA-4 to deliver a co-stimulatory or co-inhibitory signal that regulates T cell activitation.

B7-CD28 Families

Members of the B7 family of immune checkpoint proteins bind to receptors belonging to the CD28 family and promote or inhibit T cell activation following antigenic peptide/MHC recognition by the TCR. The B7 and CD28 families include the immune checkpoint proteins, PD-L1, PD-1, and CTLA-4, which are some of the most highly investigated targets for cancer immunotherapy.

Butyrophilin family proteins can function as co-stimulatory and co-inhibitory molecules to regulate T cell activation.


Butyrophilins are T cell co-inhibitory/co-stimulatory molecules that are structurally related to the B7 family of immune checkpoint proteins and appear to have similar immunomodulatory functions. For these reasons, they are currently being investigated as potential next generation immune checkpoint targets.

The CD47-SIRP pathway is an innate immune checkpoint pathway that suppresses the phagocytic activity of myeloid cells.

CD47-SIRP Pathway

The SIRP/CD47 pathway is an innate immune checkpoint that suppresses the phagocytic activity of myeloid cells. CD47 is overexpressed in a variety of hematologic and solid tumor cancers, indicating that tumor cells may exploit this pathway to evade phagocytic destruction.

Overexpression of IDO or TDO by tumor cells leads to the production of kynurenine, an immunosuppressive metabolite.

Kynurenine Pathway

Depletion of tryptophan and kynurenine production by the kynurenine pathway can inhibit the functions of T cells and natural killer cells and promote the generation of regulatory T cells. As tumor cells or cells in the tumor microenvironment can express high levels of IDO and TDO2, two key enzymes that catalyze the initial and rate-limiting step in this pathway, inhibitors of these molecules are being investigated as potential immunotherapeutic drugs.

LAG-3 is an immune checkpoint receptor that inhibits T cell activity and enhances the functions of regulatory T cells.


LAG-3 is an inhibitory immune checkpoint receptor that negatively regulates T cell activity and promotes the suppressive activity of regulatory T cells. This receptor is up-regulated on exhausted T cells and natural killer cells in cancer and is thought to contribute to their dysfunction, making it a target for immuno-oncology researchers.

Binding of LILRB1 to HLA-G expressed on tumor cells inhibits the functions of T cells and natural killer cells.

LILRB Receptor Family

Members of the LILRB subfamily are immune checkpoint receptors that can inhibit the functions of multiple immune cell types following activation. These receptors and their ligands are being investigated by immuno-oncology researchers as they can be up-regulated on tumor cells or immune cells present in the tumor microenvironment, allowing tumors to evade immune detection.

TIGIT and DNAM-1 both bind to CD155 and CD112, but have opposing effects on the functions of T cells and NK cells.


TIGIT, DNAM-1, CD96, and PVRIG are immune checkpoint receptors that share CD155/PVR and/or CD112/Nectin-2 as ligands, but mediate opposing effects on lymphocyte functions. While DNAM-1/CD226 acts as a co-stimulatory receptor, TIGIT, PVRIG, and CD96 function as co-inhibitory receptors on T cells and natural killer cells. As a result, these proteins are being explored as targets for cancer immunotherapy.

TIM-3 binds to CEACAM-1 and Galectin-9 and suppresses immune cell functions through a variety of different mechanisms.


High level expression of TIM-3 on CD8+ T cells and natural killer cells is associated with an exhausted phenotype, and its expression on tumor-associated FoxP3+ regulatory T cells (Tregs) marks a subset of Tregs with enhanced suppressor functions and increased resiliency. Due to these characteristics, immuno-oncology researchers are investigating TIM-3 blockade to determine if they can improve anti-tumor immune responses.

Agonists of co-stimulatory TNF receptor family members are being investigated for as potential immuno-oncology targets.

TNF Receptor Superfamily Co-Stimulatory Molecules

As an alternative to immune checkpoint blockade to restore anti-tumor immune responses, agonists of co-stimulatory immune checkpoint receptors are also being explored. Many of these receptors belong to the TNF receptor superfamily and have been shown to be involved in enhancing the proliferation and effector functions of T cells and/or natural killer cells.

R&D Systems Immune Checkpoint Proteins Are Rigorously Tested to Ensure Lot-to-Lot Consistency

Lot-to-lot consistency analysis of Recombinant Human PD-1 using a binding assay with Recombinant Human PD-L1/B7-H1

R&D Systems Recombinant Human PD-1 Displays High Lot-to-Lot Consistency. Two independent lots of Recombinant Human PD-1 (R&D Systems, Catalog # 8986-PD) immobilized at 1 ug/mL were tested for their ability to bind to increasing concentrations of Recombinant Human PD-L1/B7-H1 Fc Chimera (R&D Systems, Catalog # 156-B7) in a functional ELISA. The concentration of Recombinant Human PD-L1/B7-H1 Fc Chimera that produces 50% of the optimal binding response is approximately 0.3-1.8 ug/mL. Each trace on the graph represents data obtained from Recombinant Human PD-1 from a different manufacturing run, demonstrating the lot-to-lot consistency of the protein.

Protein Characterization Using SEC-MALS Analysis

A graph showing size exclusion chromatography multi-angle light scattering data for PD-1 recombinant protein

Recombinant Human PD‑1 Fc Chimera Protein SEC-MALS. Recombinant human PD-1/Fc (Catalog # 1086-PD) has a molecular weight (MW) of 125.1 kDa as analyzed by SEC-MALS, suggesting that this protein is a homodimer.  MW may differ from predicted MW due to post-translational modifications (PTMs) present (i.e. Glycosylation).


SEC-MALS Data Result
Retention Time 14.7-15.2 min
MW-Predicted (Monomer) 42.6 kDa
MW-MALS 125.1 kDa
Polydispersity 1.001
System Suitability: BSA Monomer 66.4 ± 3.32 kDa Pass

Analysis of the Binding Properties of R&D Systems Avi-tag Biotinylated Immune Checkpoint Proteins

Surface plasmon resonance data showing the affinity measurements and binding kinetics between the CD155 and TIGIT proteins.

Affinity Measurements and Binding Kinetics of the CD155/PVR:TIGIT Protein Interaction by Surface Plasmon Resonance. Sensorgram data of captured Avi-tag Biotinylated Recombinant Human CD155/PVR Fc Chimera (R&D Systems, Catalog # AVI9174) binding to Recombinant Human TIGIT His-tag (R&D Systems, Catalog # 9525-TG). The corresponding overlaid kinetic fits with the residual plot shown below. The concentration of Recombinant Human TIGIT His-tag ranged from 0.2 nM to 400 nM. The corresponding steady state affinity fit is shown at the bottom. The experiment was performed on a Biacore T200, GE Healthcare.

Related Products for Immune Checkpoint Research

Maurice: Automated cIEF and CE-SDS by ProteinSimple, a Bio-Techne brand

Maurice™ CE-SDS for Evaluating Protein Purity

Although still used in the industry for protein purity analysis, SDS-PAGE is self-limiting in terms of sensitivity, reproducibility, and its semi-quantitative nature. As an alternative, we offer the fully automated Maurice capillary electrophoresis (CE)-SDS system.This application note outlines the advantages of using Maurice over standard SDS-PAGE analysis for protein purity characterization. Read more on our Protein Simple website.


Simultaneous detection of immune cell markers and immune checkpoint targets using an RNAscope-immunofluorescence workflow.

RNAscope™ In Situ Hybridization Assays

RNAscope technology enables the rapid and efficient detection of the co-expression profiles of any target mRNAs, including immune checkpoint targets and immune cell markers, with single-molecule sensitivity and high specificity in formalin-fixed, paraffin-embedded (FFPE) tissues. This technology can be combined with immunohistochemistry or immunofluorescence on the same slide for detecting target RNAs and proteins simultaneously.

Macrophage Immune Cell

Proteins for Immune Cell Culture

Achieve robust, reproducible immune cell cultures with R&D Systems™ proteins. Our proteins are rigorously tested to ensure that they will provide superior performance and lot-to-lot consistency, so you can have confidence in their ability to promote optimal immune cell expansion and differentiation with minimal variability between cultures. To meet your needs from basic research to clinical applications, we offer research-grade, Animal-free RUO, and Animal-free GMP-grade proteins.

Avi-tag Biotinylated Recombinant Proteins banner

Avi-tag Biotinylated Proteins for Immune Checkpoint Targets

Biotinylated proteins can be powerful tools for assessing protein-protein interactions or screening antibody or small molecule libraries for potential therapeutics. We now offer a wide assortment of Avi-tag biotinylated recombinant proteins for immune checkpoint targets.

Fluorokine App Note

Fluorokines™ for Immune Checkpoint Ligands

Take advantage of our fluorescent-labeled immune checkpoint ligands to easily identify or sort cells expressing the corresponding immune checkpoint receptors. Fluorescent-labeled ligands allow cells expressing their cognate receptors to be stained in a single step and detected by flow cytometry.

Antibody Cell Surface Marker

Flow Cytometry-Validated Antibodies for Identifying Immune Cell Types

The Bio-Techne family brands, R&D Systems and Novus Biologicals, are committed to providing the highest quality antibodies to support your research. Analyze the expression of immune checkpoint proteins or their ligands using our wide selection of flow cytometry-validated antibodies.