Cell-surface proteins play an essential role in regulating cell communication by mediating immune activation, cell adhesion, receptor signaling, and tissue homeostasis.1
Image Credit: Corona Borealis Studio/Shutterstock.com
Numerous cell surface proteins, such as immune checkpoints, co-stimulatory receptors, tumor-associated antigens, and lineage markers, have emerged as key therapeutic targets and biomarkers in cancer, autoimmune diseases, and other immune disorders.2,3
Their pivotal roles in physiology and disease have accelerated the development of precision therapeutics and increased the demand for robust instruments in target characterization and translational studies.
Characterizing these cell-surface targets frequently relies on sensitive detection, binding, and cell-based assays, in which labeled recombinant proteins are commonly used to enable reliable and reproducible evaluation.
Site-specific labeling enables conjugation at defined amino acid sites with precise control over labeling position and stoichiometry, helping maintain native protein conformation and biological activity.
To facilitate studies of cell-surface targets, Sino Biological provides high-quality, site-specifically labeled recombinant proteins. Designed to maintain native conformation and biological activity, these proteins deliver exceptional stability and batch-to-batch consistency for applications in target validation, cell sorting, flow cytometry, and therapeutic antibody discovery.
Physiological and pathological roles of cell-surface proteins
Cell-surface proteins function through specific interactions with ligands, receptors, and antibodies to regulate immune responses, cell adhesion, signal transduction, and tissue homeostasis.
These interactions dictate various physiological processes while ensuring accurate communication between cells. Dysregulated expression, aberrant signaling, or disrupted molecular interactions can lead to the development of cancer, autoimmune conditions, inflammatory disorders, and infectious diseases.
Since these biological activities rely on native protein conformation and precise molecular recognition, preserving native protein structure and function is crucial for the accurate study of cell-surface proteins and their interactions.1,2
Cell-surface proteins in therapeutic development
Cell-surface proteins have evolved from fundamental biological regulators into a major class of therapeutic targets, fueled by the rapid growth of therapies targeting these molecules.
Immune checkpoint proteins such as PD-1 and B7-H3, co-stimulatory receptors including CD28 and 4-1BB, and tumor-associated antigens such as CD19, BCMA, CD38, and GUCY2C are now commonly employed for the development of monoclonal antibodies, bispecific antibodies, antibody–drug conjugates (ADCs), and CAR-T cell therapies.4,5,6,7,8
At the same time, adhesion molecules such as NCAM1 and Cadherin-17 are proving to be promising biomarkers and therapeutic targets in cancer and other conditions. As these therapeutic modalities continue to diversify, accurately characterizing target expression, receptor occupancy, ligand binding, and antibody specificity has become increasingly valuable throughout therapeutic discovery and development.
To meet these rising demands, high-quality recombinant proteins that accurately retain native structure and biological function are essential, offering dependable tools for translational studies and therapeutic development.8
Table 1. Representative cell surface protein targets and approved or clinical-stage therapeutics. Source: Sino Biological Inc.
| Cell-surface protein |
Representative therapeutics |
Therapeutic modality |
Major indications |
Development status |
| PD-1 |
Keytruda®, Opdivo® |
Monoclonal antibody |
Multiple cancers |
Approved |
| PD-L1 |
Tecentriq®, Imfinzi®, Bavencio® |
Monoclonal antibody |
Multiple cancers |
Approved |
| HER2 |
Herceptin®, Enhertu® |
Monoclonal antibody/ADC |
Breast and gastric cancers |
Approved |
| CD19 |
Kymriah®, Yescarta®, Breyanzi® |
CAR-T cell therapy |
B-cell malignancies |
Approved |
| BCMA |
Abecma®, Carvykti® |
CAR-T cell therapy |
Multiple myeloma |
Approved |
| CD20 |
Rituxan®,
Gazyva® |
Monoclonal antibody |
B-cell lymphoma, CLL |
Approved |
| CD38 |
Darzalex®, Sarclisa® |
Monoclonal antibody |
Multiple myeloma |
Approved |
| B7-H3 |
DS-7300,
IBI334 |
ADC/Bispecific antibody |
Solid tumors |
Clinical development |
| GUCY2C |
TAK-164 |
ADC |
Gastrointestinal cancers |
Clinical development |
Site-specific labeling for cell-surface protein research
Cell-surface proteins mediate highly specific molecular interactions, including receptor–ligand binding, antigen–antibody recognition, and protein–protein interactions. Since these functions rely on intact binding sites and native conformation, recombinant proteins employed in cell-based assays must preserve their biological activity following labeling.
Fluorescent dyes, biotin, and other labels are often used to enable applications such as target validation, receptor–ligand binding analysis, CAR-expressing cell detection, flow cytometry, and therapeutic antibody characterization. However, traditional labeling can cause heterogeneity or disrupt functional regions, which may affect binding activity and assay performance.10
These challenges are addressed through site-specific labeling, which enables controlled conjugation at defined amino acid sites alongside exact labeling stoichiometry. For example, recombinant proteins are designed with a specific labeling tag placed away from functional binding sites. Site-specific conjugation enables attachment of a detection label at one predetermined site without altering native protein conformation and biological activity.
In contrast to standard random chemical labeling, this approach reduces interference with ligand- or antibody-binding epitopes, enhances batch-to-batch consistency, and facilitates dependable applications across flow cytometry, cell sorting, target validation, and therapeutic antibody discovery.
Figure 1. Site-specific labeling strategy for recombinant proteins. Image Credit: Sino Biological Inc.
Site-specifically labeled recombinant proteins from Sino Biological
To support studies of cell-surface targets, Sino Biological offers a broad suite of site-specifically labeled recombinant proteins that maintain native protein conformation and biological activity while delivering strong, reliable fluorescence signals.
Compared with equivalent commercial reagents, the representative products have been verified for sensitive detection of CAR-expressing cells, minimal nonspecific binding, and outstanding fluorescence performance (Figures 2 and 3). These verified reagents deliver dependable support for flow cytometry, engineered cell characterization, and therapeutic antibody studies.
(A) Recombinant human CD19 protein (Site-specific APC-conjugated)
Cat#: 11880-H08W1-SA
(B) Recombinant human CD19 protein (Site-specific PE-conjugated)
Cat#: 11880-H08W1-SP
Figure 2. Superior fluorescence performance of Sino Biological site-specifically labeled human CD19 protein. (A) APC-conjugated human CD19 protein (Cat# 11880-H08W1-SA) specifically detects CD19 CAR-expressing cells by flow cytometry with minimal background staining in non-transduced cells and negative control protein. (B) PE-conjugated human CD19 protein (Cat# 11880-H08W1-SP) exhibits higher fluorescence intensity than a comparable commercial reagent during flow cytometric detection of CD19 CAR-expressing cells. Image Credit: Sino Biological Inc.
(A) Recombinant human B7-H3 protein (Site-specific PE-conjugated)
Cat#: 11188-H86H-SP
(B) Recombinant human B7-H3 protein (Site-specific AF 647-conjugated)
Cat#: 11188-H86H-SG
Figure 3. Superior fluorescence performance of Sino Biological site-specifically labeled human B7-H3 protein. (A) Site-specifically PE-conjugated human B7-H3 protein (Cat# 11188-H86H-SP) provides stronger fluorescence signals than a comparable commercial reagent for flow cytometric detection of B7-H3 CAR-expressing cells, supporting sensitive and robust cell characterization. (B) Flow cytometric analysis using AF 647-conjugated B7-H3 protein. The protein exhibited stable performance after 14 days of storage at 37°C, as measured on Day 0, Day 7, and Day 14. Image Credit: Sino Biological Inc.
Table 2. Representative Site-Specifically Labeled Recombinant Protein. Source: Sino Biological Inc.
References and further reading
- Alberts, B., Johnson, A., Lewis, J., Morgan, D., Raff, M., Roberts, K. & Walter, P. Molecular Biology of the Cell. 6th ed. Garland Science (2015).
- Hanahan, D. (2022). Hallmarks of Cancer: New Dimensions. Cancer Discovery, 12(1), pp.31–46. DOI:10.1158/2159-8290.cd-21-1059. https://aacrjournals.org/cancerdiscovery/article/12/1/31/675608/Hallmarks-of-Cancer-New-DimensionsHallmarks-of.
- Topalian, S.L., Drake, C.G. and Pardoll, D.M. (2015). Immune Checkpoint Blockade: A Common Denominator Approach to Cancer Therapy. Cancer Cell, 27(4), pp.450–461. DOI:10.1016/j.ccell.2015.03.001. https://linkinghub.elsevier.com/retrieve/pii/S1535610815000896.
- June, C.H. and Sadelain, M. (2018). Chimeric Antigen Receptor Therapy. New England Journal of Medicine, 379(1), pp.64–73. DOI:10.1056/nejmra1706169. https://www.nejm.org/doi/10.1056/NEJMra1706169.
- Munshi, N.C., et al. (2021). Idecabtagene Vicleucel in Relapsed and Refractory Multiple Myeloma. New England Journal of Medicine, 384(8), pp.705–716. DOI:10.1056/nejmoa2024850. https://www.nejm.org/doi/10.1056/NEJMoa2024850.
- Picarda, E., Ohaegbulam, K.C. and Zang, X. (2016). Molecular Pathways: Targeting B7-H3 (CD276) for Human Cancer Immunotherapy. Clinical Cancer Research, 22(14), pp.3425–3431. DOI:10.1158/1078-0432.ccr-15-2428. https://aacrjournals.org/clincancerres/article/22/14/3425/79210/Molecular-Pathways-Targeting-B7-H3-CD276-for-Human.
- Beck, A., et al. (2017). Strategies and Challenges for the next Generation of Antibody–drug Conjugates. Nature Reviews Drug Discovery, 16(5), pp.315–337. DOI:10.1038/nrd.2016.268. https://www.nature.com/articles/nrd.2016.268.
- Kaplon, H., Chenoweth, A., Crescioli, S. et al. Antibodies to watch in 2025. mAbs 17, 2445493 (2025).
- Toseland, C.P. (2013). Fluorescent labeling and modification of proteins. Journal of Chemical Biology, 6(3), pp.85–95. DOI:10.1007/s12154-013-0094-5. doi.org/10.1007/s12154-013-0094-5.
About Sino Biological Inc.
Sino Biological is an international reagent supplier and service provider. The company specializes in recombinant protein production and antibody development. All of Sino Biological's products are independently developed and produced, including recombinant proteins, antibodies, and cDNA clones. Sino Biological is the researchers' one-stop technical services shop for the advanced technology platforms they need to make advancements. In addition, Sino Biological offers pharmaceutical companies and biotechnology firms pre-clinical production technology services for hundreds of monoclonal antibody drug candidates.
Sino Biological's core business
Sino Biological is committed to providing high-quality recombinant protein and antibody reagents and to being a one-stop technical services shop for life science researchers around the world. All of our products are independently developed and produced. In addition, we offer pharmaceutical companies and biotechnology firms pre-clinical production technology services for hundreds of monoclonal antibody drug candidates. Our product quality control indicators meet rigorous requirements for clinical use samples. It takes only a few weeks for us to produce 1 to 30 grams of purified monoclonal antibody from gene sequencing.
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