B7-H3 (CD276): A broadly transcribed but protein-restricted immune checkpoint molecule and tumor therapeutic target

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This article focuses on the molecular structure, expression regulation, and immune functions of B7-H3 (CD276), systematically elaborating on the separation phenomenon between its gene encoding and widespread transcript distribution as a type I transmembrane protein of the immunoglobulin superfamily and its highly restricted protein expression, analyzing its expression characteristics on immune cells and its bidirectional regulatory effects on NK cells, cytotoxic T cells, and conventional T cells, and exploring its association with overexpression and poor prognosis in solid tumors such as bladder cancer, prostate cancer, and melanoma, as well as diverse therapeutic strategies including monoclonal antibodies, bispecific antibodies, ADCs, and CAR-T.

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B7-H3 (CD276): An Immune Checkpoint Molecule with Broad Transcripts but Restricted Protein Expression, and a Tumor Therapeutic Target

Brief introduction: This article focuses on the molecular structure, expression regulation, and immune functions of B7-H3 (CD276), systematically elaborating on its gene encoding as a type I transmembrane protein of the immunoglobulin superfamily and the separation phenomenon of broad transcript distribution but highly restricted protein expression, analyzing its expression characteristics on immune cells and its bidirectional regulatory effects on NK cells, cytotoxic T cells, and conventional T cells, and discussing its association with overexpression and poor prognosis in solid tumors such as bladder cancer, prostate cancer, and melanoma, as well as diverse therapeutic strategies including monoclonal antibodies, bispecific antibodies, ADCs, and CAR-T.

I. Molecular Identity and Structural Classification of B7-H3.

CD276 is a type I transmembrane protein encoded by the human CD276 gene, belonging to the immunoglobulin superfamily, also known as B7-H3. As a member of the immunoglobulin superfamily, its molecular structure is characterized by extracellular immunoglobulin-like domains as the core feature, anchored to the cell membrane surface via a transmembrane region. B7-H3 belongs to the members of the B7 family whose ligand has not been clearly identified; this "orphan receptor" attribute determines that its functional research cannot simply apply the classical ligand-receptor blocking paradigm, but rather requires analysis from multiple dimensions including expression distribution, cellular sources, and functional phenotypes. From the perspective of molecular nomenclature, CD276 and B7-H3 refer to the same molecule and are often used interchangeably in the literature; understanding this nomenclature correspondence is a prerequisite for organizing related research.

II. The Separation Phenomenon of Transcripts and Protein in B7-H3 Expression Regulation.

B7-H3 transcripts are widely present in normal tissues and solid tumors, but its protein is highly expressed only in tumor tissues, with extremely low expression in normal tissues. This separation phenomenon of "broad transcripts, restricted protein" is one of the most characteristic expression regulation features of B7-H3. From a molecular mechanism perspective, this separation may originate from multi-level precise control such as post-transcriptional regulation, differences in translation efficiency, or protein stability regulation. Its biological significance lies in: B7-H3 protein expression does not simply follow changes in transcription levels, but is subject to strict constraints independent of the transcriptional level; when this constraint is lifted during tumorigenesis, B7-H3 protein exhibits high expression in tumor tissues. This feature also suggests that detecting only the mRNA level of B7-H3 in research may not accurately reflect its functional status, and protein-level detection is more critical for evaluating its clinical significance.

III. Expression of B7-H3 on Immune Cells and Its Bidirectional Immune Functions.

B7-H3 is mainly expressed on immune cells such as antigen-presenting cells, myeloid cells, monocytes, and T cells, with its ligand unknown. At the functional level, B7-H3 exhibits noteworthy bidirectionality: it can inhibit NK cell-mediated cytolysis while enhancing the induction of cytotoxic T cells, selectively producing IFN-γ; on the other hand, it can also exert inhibitory effects on T cells, contributing to immune evasion of tumor cells. This characteristic of "differential effects on different immune cell subsets" makes it difficult to summarize the functional positioning of B7-H3 with a single "co-stimulatory" or "co-inhibitory" label. A more accurate understanding is that the net immune effect of B7-H3 depends on the cell type, microenvironmental context, and composition of interacting immune cell populations, which also explains why reports on the functional direction of B7-H3 differ among different studies.

IV. Overexpression of B7-H3 in Solid Tumors and Its Prognostic Association.

Importantly, B7-H3 is highly overexpressed in various human solid tumors, such as bladder cancer, prostate cancer, and melanoma, and is generally associated with poor prognosis and inferior clinical treatment outcomes. Recent studies have shown that B7-H3 plays an important role in tumor growth, invasion, migration, as well as angiogenesis and metastasis. From a clinical relevance perspective, the stable association of B7-H3 overexpression with poor prognosis, together with its functional involvement in tumor growth, invasion, and metastasis, jointly constitute the dual basis for its role as a therapeutic target——both as a prognostic marker and as a functional driver molecule. Due to its role in immune evasion, B7-H3 has become a new immunotherapeutic target.

V. Immunotherapeutic Approaches and Combination Strategies Targeting B7-H3.

The main immunotherapeutic approaches include: monoclonal antibodies, bispecific antibodies, small molecules, ADC drugs, CAR-T therapy, etc. This diversified modality layout reflects two characteristics of the B7-H3 target: first, due to the unknown ligand, the development of traditional neutralizing blocking antibodies is limited, and more strategies have shifted toward utilizing its high tumor expression as a delivery anchor or a target for immune cell recognition; second, the broad expression of B7-H3 in tumor cells and the tumor microenvironment makes it suitable as a target for killing modalities such as ADCs and CAR-T. In terms of combination therapy, B7-H3 and PD-L1 exert inhibitory effects on T cells, altering the T cell microenvironment to evade anti-tumor immune responses; and B7-H3 and CTLA-4 may also have synergistic effects, similar to B7-H3 in the PD-1 pathway. The core of this combination logic lies in: B7-H3 and the PD-L1/PD-1 or CTLA-4 pathways have complementarity in immunosuppressive mechanisms, and simultaneously blocking multiple checkpoint nodes may produce synergistic effects, overcoming the efficacy limitations of single-pathway blockade.

VI. Conclusion.

B7-H3 (CD276), as a type I transmembrane protein of the immunoglobulin superfamily, with its expression regulation separation phenomenon of broad transcript presence but high protein expression only in tumor tissues, its bidirectional immune functions exhibiting differential effects on NK cells and T cells on immune cells, its clinical association of overexpression in solid tumors such as bladder cancer, prostate cancer, and melanoma and correlation with poor prognosis, as well as its functional involvement in tumor growth, invasion, migration, and angiogenesis, has become a highly promising target in the field of tumor immunotherapy.

VIII. Frequently Asked Questions on B7-H3 Binding Activity Detection and Product Information

To facilitate researchers and drug development teams in retrieving evaluation schemes and product information for B7-H3 interactions, this section addresses common questions about B7-H3 binding activity detection in a Q&A format and provides the product positioning and applicable scenarios of B7-H3/CD276 His Tag Protein, Human.

Q1: What methods are used to detect the binding activity of B7-H3?
As an "orphan receptor" with an unidentified ligand, B7-H3-targeted drug evaluation relies more on the direct binding of antibodies to the extracellular immunoglobulin-like domains of B7-H3. Currently, in vitro methods for evaluating this interaction mainly include enzyme-linked immunosorbent assay (ELISA), surface plasmon resonance (SPR) and biolayer interferometry (BLI), and time-resolved fluorescence resonance energy transfer (TR-FRET). Among them, ELISA and SPR/BLI can directly quantify the binding affinity and kinetic parameters of antibodies to B7-H3, and are commonly used methods for early antibody drug screening and batch release.

Q2: How does ELISA evaluate the binding activity of B7-H3-targeted antibodies?
In a typical ELISA system, recombinant B7-H3 protein is coated in the wells of a microplate, gradient-diluted candidate antibodies are added and incubated, and absorbance signals are read through enzyme-labeled secondary antibody color development. By plotting antibody concentration against signal values, the half-maximal effective concentration (EC50) can be fitted to compare the binding capacity of different antibodies to B7-H3. Since the B7-H3 protein carries a His tag, an anti-His antibody can also be used to capture B7-H3 followed by detection of candidate antibody binding, flexibly adapting to different experimental needs.

Q3: What is the B7-H3/CD276 His Tag Protein, Human product?
B7-H3/CD276 His Tag Protein, Human (Catalog No. UA010010) is a human-derived B7-H3 recombinant protein provided by UniOne (UA-Bio), expressed in the HEK293 expression system, with the expressed sequence being Leu29-Pro245 and a C-terminal His tag, facilitating efficient purification through immobilized metal affinity chromatography and enabling detection and capture through anti-His tag antibodies. The product has a purity greater than 95% (SDS-PAGE under reducing conditions) and an endotoxin content of less than 0.1 EU/μg, making it suitable for binding activity analysis of B7-H3 with targeted antibodies, research on interactions mediated by extracellular immunoglobulin domains, and in vitro screening of antibody-drug conjugates and bispecific antibodies targeting B7-H3.

Q4: What experimental scenarios is this product suitable for?
The main application scenarios of this product include: binding activity analysis and EC50 determination of B7-H3 with targeted antibodies; research on protein-protein interactions mediated by extracellular immunoglobulin domains of B7-H3; in vitro screening and activity evaluation of monoclonal antibodies, bispecific antibodies, and antibody-drug conjugates (ADCs) targeting B7-H3; exploration of the functional mechanisms of B7-H3 in immune cell regulation; and parallel comparison of binding activity between different antibody or protein batches.

Q5: What are the characteristics of His-tagged proteins in B7-H3 research?
The His tag facilitates efficient purification through immobilized metal affinity chromatography, improving protein yield and purity; meanwhile, the His tag can serve as a capture or detection tag, directionally immobilizing B7-H3 on ELISA plates or SPR chip surfaces through anti-His antibodies, flexibly adapting to various experimental modes such as "protein coating—antibody detection" or "antibody capture—protein detection." For immune checkpoint molecules with unknown ligands such as B7-H3, His-tagged proteins provide a universal and easy-to-operate reagent basis for antibody binding activity evaluation.

Product Information at a Glance

Product Name	B7-H3/CD276 His Tag Protein, Human (Catalog No.: UA010010)
Brand	UniOne (UA-Bio)
Molecular Aliases	B7-H3, CD276, B7H3, CD276 antigen, CD276 molecule, B7-H34Ig-B7-H3, B7-H3B7 homolog 3, Costimulatory molecule
Accession	Q5ZPR3-2
Expressed Sequence	Leu29-Pro245, with C-terminal His Tag
Expression System	HEK293
Molecular Weight	38-48 kDa (Reducing)
Purity	>95% by SDS-PAGE under reducing conditions
Endotoxin Content	<0.1 EU/μg
Tag	His Tag
Form	Lyophilized Powder
Buffer System	PBS pH7.2, 5% trehalose
Reconstitution Method	After rapid centrifugation, reconstitute with ultrapure water to a concentration of less than 1 mg/mL according to the specification
Storage Conditions	Lyophilized powder stored at -20 to -80°C, stable for 12 months from the date of receipt; after reconstitution, stable for 3 months at -20 to -80°C and 1 week at 2 to 8°C under sterile conditions; avoid repeated freeze-thaw cycles
Core Applications	Quantitative binding activity analysis, targeted antibody screening and activity evaluation, EC50 determination, mechanism of action validation
Common Search Terms	B7-H3 binding activity detection, B7-H3/CD276 His Tag Protein, B7-H3 antibody screening, B7-H3 ELISA, B7-H3 recombinant protein, UA010010, UniOne

If you need to conduct B7-H3 binding activity detection or activity evaluation of antibody drugs targeting B7-H3, you can search for the full product name "B7-H3/CD276 His Tag Protein, Human" or the catalog number "UA010010" in the UniOne (UA-Bio) Product Center to obtain the product manual, experimental protocols, and supporting reagent information.

This article is reviewed and published by the technical expert team of UA

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