Anti-Human CD4 (Clone OKT-4) – Purified in vivo GOLD™ Functional Grade

Clone OKT-4 is a mouse monoclonal antibody that specifically recognizes human CD4, not mouse CD4. Its in vivo applications in mice are limited to situations where human CD4 is expressed, such as in mouse models reconstituted with human immune systems (humanized mice).

Common in vivo applications of clone OKT-4 in mice:

• Depleting or blocking human CD4+ T cells in humanized mouse models (mice transplanted with human immune cells or tissues that express human CD4).
• Studying human-specific immune responses in the context of infection, autoimmunity, or transplantation where human CD4+ cells play a role.

Important context and limitations:

• OKT-4 does not react with endogenous mouse CD4. For depleting or studying mouse CD4+ T cells, other clones (such as GK1.5 or YTS 177) are required.
• The antibody is often used in vivo for functional blockade, depletion, or tracking of human CD4+ cells in immunodeficient mice reconstituted with human peripheral blood mononuclear cells (PBMCs) or hematopoietic stem cells.
• Examples of in vivo studies: Modulating HIV infection, graft-versus-host disease, transplantation tolerance, or CD4+ T cell function in the human immune system environment within a mouse.

Summary table:

Conclusion:
OKT-4 is widely used in vivo in mice only when those mice bear a human immune system; it does not work for native murine CD4+ cells. For targeting mouse CD4+ cells, mouse-specific clones should be used.

The most commonly used antibodies or proteins studied alongside OKT-4 (an anti-human CD4 monoclonal antibody) in the literature typically target other immune cell markers or CD4 epitopes, depending on the research context.

Key antibodies or proteins frequently used with OKT-4 include:

• Ibalizumab: Another anti-CD4 monoclonal antibody, but it binds a different domain (domain 2) of CD4 than OKT-4 (which binds domain 3). Studies often compare or combine OKT-4 and ibalizumab to differentiate epitope-specific effects or in competitive binding experiments.

• Other anti-CD4 antibodies: For example, custom antibodies or recombinant single-chain antibodies are used for cross-validation, competitive assays, or to map different CD4 domains. These antibodies may recognize overlapping or distinct epitopes on the CD4 molecule.

• CD4 protein fragments or domains: Studies often use CD4 structural fragments such as D1D2 (domains 1+2), D3D4 (domains 3+4), or full-length CD4 (D1D4) for epitope mapping or functional analysis with OKT-4.

• HIV gp120: In HIV research, OKT-4 is used alongside HIV envelope protein gp120 to study binding to CD4 and to analyze how various antibodies affect this interaction.

• Protein A/G or other capture proteins: For surface immobilization and detection of antibody-antigen interactions (e.g., in Biacore/SPR experiments).

• Other leukocyte subset markers: In multi-color flow cytometry, OKT-4 is frequently combined with antibodies to:

  • CD3 (pan-T cell marker)
  • CD8 (cytotoxic T cells)
  • CD45 (leukocyte common antigen)
  • CD25, CD69 (activation markers)
  • These combinations allow for the identification and quantification of CD4+ T cells among broader immune populations.

Summary Table: Commonly Used Antibodies/Proteins with OKT-4

When cited in immunology and HIV research, OKT-4 is specifically associated with human CD4+ T cell detection and functional assays, and often combined with these markers to give a comprehensive view of immune cell populations and their responses.

Key Findings for Clone OKT-4 in Scientific Literature

Clone OKT-4 refers to a well-characterized monoclonal antibody against the human CD4 molecule, which marks helper T cells and some cytotoxic T cells (CTLs). The scientific citations reveal two primary research contexts for OKT-4: immunology (particularly T cell function and specificity) and clinical/diagnostic applications. Below are the key findings from relevant literature.

Immunological Role and Specificity

• OKT-4+ Cells as HLA-DR-Specific Cytotoxic T Lymphocytes: OKT-4+ CTL clones (such as clone B8 and C6) were shown to specifically recognize HLA-DR antigens by functional assays. Clone B8 specifically lysed target cells expressing DR6, while clone C6 recognized a supratypic determinant common to some DR molecules or possibly another human Ia-like antigen. This demonstrates that some OKT-4+ (CD4+) T cells can function as cytotoxic effectors against MHC class II-expressing targets, a finding that expanded the understanding of CD4+ T cell diversity beyond just helper function.
• Blocking Studies and Phenotype: The cytolytic activity of these OKT-4+ CTL clones could be blocked by both OKT3 and OKT4 antibodies (but not OKT8), confirming their CD4+ phenotype and dependence on the TCR-CD3 complex for activation. Monoclonal antibodies against DR molecules also blocked target recognition, highlighting the importance of MHC class II interaction.
• Relevance to T Cell Subsets: OKT4 reacts with approximately 55% of human peripheral T cells and 80% of thymocytes, selectively marking the helper/inducer subset. This antibody has been instrumental in defining and isolating CD4+ T cell populations for functional studies.

Clinical and Molecular Applications

• Binding Specificity: The OKT4 antibody binds to the D3 domain of CD4 and does not interfere with HIV binding to CD4, which is relevant for research on HIV entry and pathogenesis.
• Functional Grade Antibody: OKT-4 antibodies are available in purified, in vivo functional grade for experimental use, indicating their utility in both research and potentially therapeutic contexts.
• Colony-Stimulating Activity: OKT4+ T cells from human T cell colonies can produce potent colony-stimulating activity, suggesting a role in hematopoiesis and immune regulation beyond classic helper functions.

Summary Table: Properties of OKT-4+ (CD4+) T Cell Clones

Conclusion

Clone OKT-4 and the OKT4 antibody have been pivotal in demonstrating that CD4+ T cells are not exclusively helper cells but can also exhibit cytotoxic activity against MHC class II-expressing targets. The antibody is widely used for phenotyping, isolating CD4+ T cells, and studying their functional diversity. Its specific binding characteristics (e.g., D3 domain, non-interference with HIV binding) make it valuable for both basic and translational immunology research.

Dosing regimens for OKT-4 (anti-CD4, clone OKT4) vary considerably based on the specific mouse model, disease context, and study objectives, though comprehensive standardized protocols remain limited in the literature. The available evidence indicates that researchers must often adapt dosing strategies based on their particular experimental requirements.

General Dosing Considerations

The variability in OKT-4 dosing reflects the broader challenges in antibody administration across different mouse models. Factors influencing dosing decisions include the administration route, the specific disease model being studied, and whether the goal is depletion, modulation, or blockade of CD4+ cells. Because OKT-4 targets human CD4, its use is typically restricted to humanized mouse models rather than conventional mice.

Documented Dosing Examples

In humanized mouse models, specific dosing regimens have been documented with considerable range. For instance, in studies using HuCD4/Tg mice, researchers have employed three daily doses at either 1 mg/kg or 100 mg/kg to achieve cumulative doses of 3 mg/kg and 300 mg/kg respectively. This represents a 100-fold difference in dosing, highlighting the substantial variation in experimental approaches.

Broader Context of Antibody Dosing in Mouse Models

The challenge of establishing optimal dosing regimens for therapeutic antibodies in mice is well-recognized across immunology research. Dosing frequencies in preclinical mouse studies typically differ from human protocols, with mice often receiving more frequent administrations. Researchers commonly aggregate doses over standardized time windows to facilitate comparison—for example, converting multiple doses given every few days into an equivalent single dose or weekly dose for analysis purposes.

The lack of standardized protocols for OKT-4 dosing necessitates that researchers carefully consider their experimental endpoints and conduct pilot studies to determine appropriate doses for their specific applications.