Anti-Human CD38 (Isatuximab) [Clone SAR-650984]

Research-grade Isatuximab biosimilars are used as calibration standards or reference controls in PK bridging ELISAs to provide a known quantity and structure of the antibody for quantifying Isatuximab concentrations in serum samples during biosimilar development and bridging studies.

Context and Supporting Details:

• Role as Calibration Standards: In PK (pharmacokinetic) bridging ELISAs, the research-grade Isatuximab biosimilar—produced to match the sequence and structure of the clinical antibody—serves as the analytical standard to create the assay's calibration curve. Known concentrations of the biosimilar are serially diluted, generating a standard curve that spans the expected sample concentration range. Test (serum) samples' signals are then interpolated onto this curve to determine unknown drug concentrations.

• Reference Controls for Analytical Comparability: During validation, both the biosimilar and reference product (e.g., originator Isatuximab) are spiked into quality control (QC) serum samples. Their recovery and measured concentrations are compared, assessing whether the assay quantifies both products equivalently. This bioanalytical equivalence is established by showing the assay's accuracy and precision for both products fall within predefined criteria (e.g., 90% confidence intervals for measured ratios fall within [0.8, 1.25]).

• Single Standard Use: Regulatory and industry best practice encourages use of a single analytical standard (typically the biosimilar) rather than separate standards for biosimilar and innovator, to minimize inter-assay variability and simplify blinded analysis. Method validation includes demonstrating that the biosimilar standard accurately quantifies both itself and the reference product in all relevant matrices.

• Characteristics of Research-Grade Biosimilars: Research-use-only (RUO) Isatuximab biosimilars are purified to high homogeneity, free of stabilizers, and typically supplied in buffers suitable for ELISA. They are structurally and immunologically matched to the originator drug, ensuring their effectiveness as standards or controls in ligand-binding assays.

• Typical ELISA Implementation:

  • Prepare a series of at least 5-7 standards from the biosimilar in serum/plasma matrix.
  • Run test samples alongside standards to enable interpolation from the standard curve.
  • Use additional QC samples at various concentrations (low, mid, high) using either biosimilar or reference product to monitor assay performance.

• Biosimilar Applications: These standards are suitable for PK and ADA (antidrug antibody) ELISAs, neutralization studies, and any assay requiring detection or quantification of Isatuximab in biological matrices.

In summary, research-grade Isatuximab biosimilars act as the key quantitative standard and reference control in PK ELISAs, enabling precise and comparable measurement of drug levels in biosimilar development, following industry and regulatory expectations for standardization and accuracy.

The primary models used for in vivo administration of research-grade anti-CD38 antibodies to study tumor growth inhibition and analyze tumor-infiltrating lymphocytes (TILs) are syngeneic mouse tumor models, where the tumors and host share the same genetic background, allowing for a fully immunocompetent environment.

Key details and supporting context:

• Syngeneic models, especially in mice such as C57BL/6 or 129/Sv backgrounds, are most commonly used for these studies. Examples include:

  • LLC (Lewis Lung Carcinoma) in C57BL/6 mice
  • KP-derived lung cancer lines in 129/Sv mice
  • MC38 (colon adenocarcinoma), Hepa1-6 (hepatoma), CT-26 (colon carcinoma), and EMT-6 (breast carcinoma) in corresponding syngeneic hosts

• In these setups, anti-CD38 antibodies (such as clone NIMR-5) are administered systemically to tumor-bearing mice. This approach allows researchers to monitor both tumor growth inhibition and the effects on the immune microenvironment, with detailed phenotyping of TILs (especially CD8^+^ T cells, regulatory T cells, and exhausted T cell populations by FACS).

• The cited research specifically reports that anti-CD38 antibody treatment in these syngeneic mouse models leads to significant inhibition of primary tumor growth and metastasis, especially when combined with immune checkpoint inhibitors (e.g., anti-PD-L1). These effects were shown to be CD8^+^ T cell-dependent, as the inhibition was reversed when CD8^+^ T cells were depleted.

• Tumor-infiltrating lymphocytes are comprehensively profiled in these models, with key findings including:

  • Increased infiltration and activity of CD8^+^ T cells upon CD38 blockade.
  • Reduced levels of exhausted (PD-1^+^ TIM3^+^ CD8^+^) T cells in the tumor microenvironment.
  • Detailed depletion and modulation experiments showing the relative roles of different TIL subsets in tumor growth and therapy response.

• Humanized models (where human immune cells are engrafted into immunodeficient mice) are not directly referenced in the available search results for administered anti-CD38 antibody in this specific context, likely due to the species-specificity and pharmacology of research anti-CD38 antibodies (most used clones do not cross-react with human antigens, or vice versa, limiting their use in humanized settings for murine tumor models).

Summary Table of Primary Syngeneic Models:

• The most widely-used and mechanistically-revealing approaches involve C57BL/6 and 129/Sv syngeneic models, with detailed immune profiling in response to anti-CD38 antibody treatment.

• Functional outcomes (tumor inhibition, TIL phenotype alterations) are most readily observed and experimentally manipulable in these syngeneic murine systems.

If you require information specifically on humanized models or detailed protocols, please specify. However, based on current literature, syngeneic immunocompetent mouse models are the gold standard for this type of in vivo anti-CD38 therapeutics and TIL functional characterization.

Researchers use the Isatuximab biosimilar, an anti-CD38 monoclonal antibody, in combination with other checkpoint inhibitors (such as anti-CTLA-4 or anti-LAG-3) to investigate potential synergistic effects on tumor immune evasion and cytotoxicity in complex immune-oncology models, primarily utilizing preclinical in vitro and in vivo systems.

Isatuximab exerts anti-tumor effects predominantly via:

• Antibody-dependent cellular cytotoxicity (ADCC)
• Antibody-dependent cellular phagocytosis (ADCP)
• Complement-dependent cytotoxicity (CDC)
• Direct cytotoxicity on CD38-positive cancer cells (independent of its Fc domain).

Synergistic Rationale and Experimental Design:

• The immune microenvironment often limits the efficacy of single-agent immunotherapies due to mechanisms such as expression of inhibitory ligands (PD-L1), immunosuppressive secreted factors (e.g., TGF-β), or the recruitment of regulatory T cells.
• Combining Isatuximab with checkpoint inhibitors (e.g., anti-CTLA-4, anti-LAG-3) aims to simultaneously:
  • Enhance innate and adaptive immune responses (via Isatuximab’s effects on NK cells and myeloid cells),
  • Relieve adaptive immune suppression by blocking inhibitory signals that restrain cytotoxic T cells.

Preclinical Study Approaches:

• Researchers typically co-administer Isatuximab biosimilar with checkpoint inhibitors in mouse xenograft models bearing human tumor cells, or in vitro using co-cultures of patient-derived immune/tumor cells.
• Outcomes assessed include enhanced tumor cell killing, increased infiltration and activation of effector lymphocytes (NK and T cells), and tumor regression or improved survival rates.
• For example, Isatuximab has been shown to synergize with other agents to boost ADCC and ADCP, and researchers are investigating if checkpoint blockade further amplifies these responses by reversing immune exhaustion or overcoming tumor-induced suppression.
• There is precedent for such strategies: combinations of checkpoint inhibitors targeting different pathways (e.g., PD-1 and LAG-3, PD-1 and CTLA-4) demonstrated improved efficacy in clinical and preclinical models.

Checkpoint Inhibitors in Combination:

• Anti-CTLA-4: Boosts T cell priming and reduces regulatory T cell–mediated suppression.
• Anti-LAG-3: Releases T cells from exhaustion, often used in combination with PD-1/PD-L1 blockade to further augment anti-tumor T-cell responses.

Emerging Observations and Considerations:

• Not all combinations result in additive or synergistic efficacy—some may increase toxicity or fail to improve outcomes, highlighting the need for optimized dosing and patient selection based on tumor immune contexture.
• Preclinical work is ongoing to identify biomarkers predictive of synergy and to clarify how specific immune cell populations (e.g., NK vs T cells) contribute to therapeutic outcomes when these agents are used together.

In summary, researchers use Isatuximab biosimilars in combination with other immune checkpoint inhibitors in advanced immune-oncology models to exploit complementary mechanisms of immune activation and tumor killing, with preclinical data supporting the rationale for such combinations but also indicating that outcomes depend on the specific tumor and immune context.

A Isatuximab biosimilar can be used as either the capture or detection reagent in a bridging ADA ELISA to monitor a patient’s immune response (development of anti-drug antibodies, ADA) against Isatuximab therapy. In this assay, the biosimilar serves as a stand-in for the original drug, allowing detection of patient antibodies that bind to either molecule due to their similar antigenic structures.

How it works in a bridging ELISA:

• The Isatuximab biosimilar (sometimes labeled, e.g., with biotin or HRP) is immobilized on an ELISA plate to "capture" anti-Isatuximab antibodies (ADAs) from the patient's serum.
• Patient serum is added; any ADA present will bind to the immobilized biosimilar.
• After washing, a detection reagent—Isatuximab biosimilar labeled with either a dye, enzyme (HRP), or other tag—is added. The ADA in the patient serum forms a "bridge" between the immobilized and labeled biosimilar molecules.
• Signal generation (typically via color change with a chromogenic substrate) indicates the presence of ADA in the serum.

Key principles:

• The bridging format leverages the bivalency of the ADA: each arm of the antibody can bind one molecule of the biosimilar, "bridging" capture and detection reagents.
• Using the biosimilar as the reagent is valid as long as it is structurally and immunologically similar to the reference Isatuximab, ensuring it will capture the same ADA subtypes.
• This method does not discriminate between ADAs against the reference or biosimilar drug if they share epitopes.

Advantages/Limitations:

• High sensitivity for detecting bivalent ADA.
• The specificity relies on the biosimilar’s epitope fidelity to the originator.
• It may not detect all ADA types (e.g., monovalent), and false positives can occur due to matrix effects or interference.

References to ADA detection with other biosimilars verify this established platform broadly for therapeutic monoclonal antibodies. In summary, using an Isatuximab biosimilar as both capture and detection reagent in a bridging ADA ELISA is an accepted, effective way to monitor immunogenicity during treatment.