Anti-Mouse CD276 (Clone MJ18) – Purified in vivo GOLD™ Functional Grade

Clone MJ18 is commonly used in vivo in mice for applications aimed at blocking the function of CD276 (B7-H3), an immune checkpoint molecule thought to dampen T cell activity and promote tumor immune evasion. The intended uses have included:

• Blocking B7-H3 signaling to study its role in immune suppression and tumor immunity.
• Investigating tumor growth, tumor regression, and immune cell infiltration in syngeneic and xenograft mouse tumor models, especially to assess the impact of B7-H3 blockade on antitumor immune responses.
• Exploring T cell function and activation in vivo by interfering with negative immune regulatory pathways mediated by B7-H3.

Critical context:
Recent, rigorous studies have questioned the specificity of clone MJ18 for B7-H3 in mice. While many published studies used MJ18 under the assumption it blocks murine B7-H3, newer evidence demonstrates MJ18 does not bind B7-H3 on murine tumor cell lines, but instead appears to interact with Fc receptors on the surface of murine immune cells—especially B cells and some T cells.
Thus:

• Reported in vivo applications include tumor immunotherapy experiments and immune modulation studies, but the true molecular target of MJ18 in mice is likely not B7-H3, making earlier interpretations potentially invalid.
• Validation with alternative, confirmed anti-B7-H3 clones (such as EPNCIR122) is recommended when studying murine B7-H3 biology.

Summary of reported in vivo uses:

• Blocking (putative) B7-H3 signaling on immune/tumor cells.
• Modulation of immune cell activity in cancer and immunology models.
• Assessment of tumor growth/regression and immune infiltration after antibody administration in murine cancer models.
• Flow cytometry or functional blockade experiments to probe immune checkpoint pathways.

Important limitation:
Given the lack of validated B7-H3 specificity for MJ18 in mouse in vivo systems, results from studies using MJ18 should be interpreted with caution, and researchers are encouraged to seek independent validation.

In the scientific literature, several antibodies and proteins are commonly used alongside MJ18. These include:

• EPNCIR122 (EPN): This is another antibody specific for B7-H3, often used for comparative studies. It is noted for its specificity in targeting murine and human B7-H3, which contrasts with the non-specific binding observed for MJ18.

• NoAb (no antibody control): This is used as a control in experiments to ensure that any observed effects are due to the antibody of interest (e.g., MJ18) rather than non-specific interactions.

• Fc receptor proteins: MJ18 has been found to bind to Fc receptors on the surface of murine splenocytes, which complicates its use as a specific B7-H3 targeting agent.

These proteins and antibodies are utilized in various research contexts, including immunological studies and cancer research, to better understand immune responses and potential therapeutic targets.

The key findings from scientific literature regarding clone MJ18 are that MJ18, although widely cited as a blocking antibody for murine B7-H3 (CD276), actually does not bind B7-H3, but instead recognizes the Fc receptor FcγRIIB on murine splenocytes, predominantly on B cells.

Essential context and supporting details:

• MJ18 does not recognize B7-H3: Multiple studies have demonstrated through flow cytometry and immunoprecipitation-mass spectrometry (IP-MS) that MJ18 does not bind to B7-H3 on mouse tumor cells or splenocytes, contradicting prior assumptions and product descriptions.
• Recognizes FcγRIIB: MJ18 binds to the FcγRIIB receptor on murine B cells and T cells, rather than B7-H3, as validated by reduced fluorescence when Fc receptors are blocked.
• Implications for antibody use: The literature highlights an erroneous use of MJ18 as a B7-H3-blocking antibody, advising that its targeting mechanism should be re-evaluated in studies where MJ18 was assumed to inhibit B7-H3. Validation using FcγRIIB knockout mice is suggested to conclusively confirm this target.
• Prior product claims: Despite some commercial sources stating that MJ18 “reacts with mouse CD276 (B7-H3)” and has been used to inhibit CD4+ T-cell proliferation, recent peer-reviewed research has shown that these applications may be based on incorrect assumptions about epitope recognition.

Additional relevant information:

• Historical use: Previous studies used MJ18 in tumor immunology models and cited its function as a B7-H3 inhibitor, with experimental protocols based on this understanding.
• Validated B7-H3 antibody: The clone EPNCIR122 (distinct from MJ18) has been validated as a specific antibody for murine and human B7-H3 detection and blockade.
• Recommendation: Researchers are advised to reassess the results and interpretations of experiments involving MJ18 as a surrogate for B7-H3 blockade, given its actual binding specificity.

In summary, MJ18 does not bind B7-H3 and instead targets FcγRIIB, underscoring a significant correction to past scientific practice and literature regarding its use.

Based on available evidence, dosing regimens of clone MJ18 show minimal variation across different mouse models, with researchers typically applying a standardized protocol regardless of the specific experimental context.

Standard Dosing Protocol

The most commonly reported dosing regimen for MJ18 is remarkably consistent: 300 μg per injection administered every other day via intraperitoneal injection. This protocol has been adopted as the standard approach across various experimental settings, including genetically modified mouse models and syngeneic tumor systems.

For example, in studies using Tgfbr1/Pten 2cKO mice (a genetically engineered model with mixed FVBN/CD1/129/C57 background), researchers administered 0.3 mg of MJ18 intraperitoneally every other day starting from day 14 after tamoxifen induction. Similarly, in orthotopic rhabdomyosarcoma models (M3-9-M), investigators used the identical 300 μg per injection every other day regimen.

Lack of Model-Specific Variations

No significant published evidence suggests major variations of the MJ18 dosing regimen based on different mouse strains or tumor models. This uniformity persists despite differences in:

• Genetic backgrounds (pure strains versus mixed backgrounds)
• Tumor types and growth kinetics
• Immunogenicity of the tumor models
• Treatment initiation timing

The standardized approach contrasts with the model-specific optimization often seen with other checkpoint blockade antibodies, where doses may range significantly (for example, anti-PD-1 antibodies typically use 100-500 μg per mouse depending on the clone and application).

Important Caveat

Recent research has revealed that MJ18 does not actually recognize B7-H3 on the surface of mouse cells, despite being widely used as an anti-B7-H3 blocking antibody. Instead, MJ18 appears to bind Fc receptors on immune cells, particularly B cells. This finding raises questions about the mechanistic basis for any observed effects and suggests that the uniform dosing regimen may reflect convention rather than optimized targeting of a specific antigen.