Anti-Human CD38 (Clone OKT10) – Purified in vivo PLATINUM™ Functional Grade

In Vivo Applications of Clone OKT10 in Mice

Clone OKT10 is a mouse-derived monoclonal antibody that specifically targets human CD38, a surface glycoprotein expressed highly on plasma cells and certain malignant cells, such as those found in multiple myeloma. Its in vivo use in mice is primarily experimental and focused on cancer research, particularly as a tool for targeted therapies.

Pretargeted Radioimmunotherapy (PRIT) in Multiple Myeloma Models

The most prominent in vivo application of clone OKT10 in mice is as a targeting agent in pretargeted radioimmunotherapy (PRIT) studies for human multiple myeloma xenografts implanted in immunodeficient mice. In these studies, OKT10 is used to deliver highly potent radionuclides specifically to CD38-positive tumor cells, minimizing exposure to healthy tissues.

• Procedure: Mice bearing subcutaneous human myeloma (e.g., NCI-H929 or L363) tumors are first injected with OKT10 (or a bispecific OKT10 construct such as OKT10-CC or OKT10-FP), allowing the antibody to localize to the tumor. Subsequently, a radiolabeled small molecule (e.g., (^{111})In-DOTA-biotin or (^{90})Y-DOTA-biotin) is administered, which binds to the prelocalized OKT10 at the tumor site, delivering a focused dose of radiation directly to the cancer cells.
• Efficacy: Studies have demonstrated that OKT10 PRIT leads to significant tumor shrinkage and high rates of complete remission compared to controls. For example, all mice treated with OKT10-CC followed by a therapeutic radionuclide showed tumor shrinkage within 6 days, and a majority remained tumor-free and alive at 20 days post-treatment.
• Biodistribution: Biodistribution studies show that OKT10 PRIT achieves high tumor-to-normal organ ratios of radioactivity (e.g., 10:1 for lung, 8:1 for liver, 6:1 for kidney at 24 hours), indicating precise tumor targeting and reduced off-target effects.
• Survival: Long-term survival data indicate dose-dependent efficacy, with higher administered radioactivity correlating to increased percentages of tumor-free animals at later time points.

Other Potential Applications

While PRIT for multiple myeloma is the most thoroughly documented in vivo use in mice, OKT10’s specificity for human CD38 also suggests potential utility in other xenograft models or immunodeficient mouse systems where human CD38-expressing cells are studied. However, detailed published evidence for applications beyond multiple myeloma PRIT is limited in the available literature.

Summary Table: Key In Vivo Applications of OKT10 in Mice

Conclusion

The primary in vivo application of clone OKT10 in mice is as a tumor-targeting vehicle in pretargeted radioimmunotherapy studies for human multiple myeloma xenografts, enabling highly specific delivery of therapeutic radionuclides and resulting in potent anti-tumor effects with minimal toxicity to normal tissues. Other uses remain largely unexplored or undocumented in the current literature.

In the literature, HB2 (anti-CD7 antibody) is most commonly used in combination with OKT10 (anti-CD38 antibody), especially in studies involving immunotoxins targeting T-cell acute lymphoblastic leukemia (T-ALL). Other antibodies and proteins frequently partnered or compared with OKT10 include:

• OKT3 (anti-CD3 antibody): Used in double-staining experiments and functional studies with OKT10 and OKT20 to analyze activation states of T cells.
• OKT20 (another monoclonal antibody): Used for dual-cell surface antigen recognition alongside OKT10 in studies of thymocytes and plasma cells.
• Ia-like antigens (human MHC class II): Often assessed in parallel with OKT10 to study maturation and activation of B cells, as their expression is inversely related to OKT10 antigen presence.
• Bispecific antibodies (BsAb): In certain contexts, OKT10 is referenced in combination or comparison with bispecific antibodies for enhanced cytotoxicity, particularly using the HSB-2 cell line.

Common combinatorial strategies include:

• OKT10-Saporin and HB2-Saporin immunotoxins: Used together to target heterogeneity in antigen expression and increase cytotoxic efficacy against T-ALL, both in vitro and in vivo.
• Native HB2 antibody with OKT10-Saporin: Explored for additive therapeutic effects through antibody-dependent cellular cytotoxicity (ADCC) and increased toxin delivery.

In some modern clinical investigations, OKT10 is conjugated with radioisotopes (e.g., ²¹¹At-OKT10-B10) and combined with chemotherapeutic agents such as fludarabine for novel combination therapies in hematologic malignancies.

Summary Table: Key Partners and Contexts with OKT10

Key context: HB2 and OKT10 (both native antibodies and immunotoxins) are the most frequently combined proteins in published literature, particularly in immunotoxin strategies to overcome antigen heterogeneity in hematologic malignancies. OKT3 and OKT20 are otherwise important in cell phenotyping and activation marker studies.

The key findings from scientific literature regarding clone OKT10 are as follows:

• Epitope and Target: OKT10 is a mouse monoclonal antibody that specifically binds to human CD38, a 45 kDa type II transmembrane glycoprotein expressed on a variety of immune cells and certain malignancies.

• Cellular Reactivity: OKT10 recognizes CD38 on pre-B lymphocytes, plasma cells, thymocytes, monocytes, and activated T and B cells. It also reacts with malignant cells in diseases like acute lymphoblastic leukemia (ALL), Burkitt’s lymphoma, multiple myeloma, acute myeloid leukemia (AML), and chronic lymphocytic leukemia (CLL).

• Differential Expression: CD38 is poorly expressed on resting peripheral T cells but becomes strongly expressed upon T-cell activation. Notably, OKT10 studies revealed that certain membrane changes (such as antibody-induced perturbation) can expose “hidden” CD38 on seemingly resting cells, suggesting an unexpressed form is present in the membrane of resting T cells.

• Utility in Research and Diagnostics:

  • Used for detection and fractionation of CD38-positive and -negative cell subsets, employing technologies like MACS (magnetic-activated cell sorting).
  • The inverse or complementary relationship between OKT10 (CD38) expression and Ia-antigen expression provides a tool for studying B cell maturation and diagnosing B cell malignancies, serving as complementary markers in research and clinical diagnostics.

• Cross-species Reactivity: OKT10 binds CD38 in several non-human primate species (e.g., rhesus, baboon, cynomolgus, squirrel monkey), facilitating preclinical studies in animal models. However, cross-reactivity varies by species and even by cell type, depending on the structural conservation of the antibody’s target epitope.

• Epitope Mapping: OKT10 requires the 15 C-terminal amino acids of CD38 for binding, corresponding to the sixth disulfide loop of the protein. This defines a conformational and sequence-specific epitope, distinct from the epitopes recognized by some other anti-CD38 antibodies.

• Functional and Therapeutic Roles:

  • OKT10 can induce antibody-dependent cellular cytotoxicity (ADCC) and has shown relatively weak but measurable therapeutic effects in preclinical leukemia models.
  • Antibody-drug conjugates (e.g., OKT10-saporin immunotoxin) using OKT10 have demonstrated enhanced anti-tumor activity in animal models, especially when used in combination with other targeted therapies.

• Enzymatic Activity Relevance: OKT10 also aids in identifying and studying CD38’s enzymatic activity (NAD glycohydrolase/cyclase) across human and non-human cells, which has functional implications for immune regulation and intracellular signaling.

In summary, OKT10 is a fundamental tool for immunophenotyping, leukemia/lymphoma research, functional T and B cell studies, animal modeling, and preclinical drug development, with most findings concurring on its specificity for a critical region of human (and certain primate) CD38 and its value in both basic and translational immunology.

The dosing regimens of clone OKT10, a monoclonal antibody targeting CD38, can vary significantly across different mouse models based on the experimental design and specific application. Here are some key points regarding the dosing of OKT10 in mouse models:

Dosage and Administration

• Dose: A common dose used in mouse models is 1.4 nmol, which is equivalent to approximately 300 µg of OKT10-CC. This dosage is often administered to target CD38-positive tumor xenografts.
• Application: In studies involving pretargeted radioimmunotherapy, OKT10 is used to localize to CD38-positive cells before the administration of a radiolabeled compound like ({}^{90})Y-DOTA-biotin.

Experimental Models

• Tumor Models: In models of multiple myeloma (e.g., L363 xenografts), OKT10 is used as part of a pretargeting strategy followed by radioimmunotherapy. The effectiveness of this approach is demonstrated by significant tumor regression and improved survival in treated animals compared to controls.

Variability Across Models

• While specific dosing regimens (e.g., 300 µg) are commonly used, the effectiveness and required dosage can vary depending on the specific mouse model, tumor type, and experimental design. For example, combinations with other therapies or different radiolabeled compounds may require adjustments in dosing to achieve optimal outcomes.

General Considerations

• The choice of dosing regimen often depends on factors such as the goal of the study (e.g., tumor reduction, survival improvement), the specific characteristics of the tumor model, and whether the antibody is used alone or as part of a combination therapy.

Overall, while there is a standard dose used in some models, dosing regimens can be tailored to the specific requirements of each study to maximize therapeutic efficacy while minimizing potential side effects.