Anti-Human CD4 [Clone OKT-4] — Purified in vivo PLATINUM™ Functional Grade

Clone OKT-4 is a mouse monoclonal antibody that specifically recognizes human CD4, not mouse CD4, and is commonly used in vivo primarily in humanized mouse models.

The main in vivo applications of OKT-4 in mice include:

• Depletion of human CD4+ T cells in humanized mice (mice engrafted with human immune cells) to study the role of CD4+ T cells in immune responses, infection, or immunotherapy.
• Functional blockade of human CD4 to inhibit or modulate human T helper cell responses in vivo in these humanized systems.
• Tracking, targeting, or imaging of human CD4+ cells—for example, to investigate trafficking, localization, or depletion outcomes using in vivo imaging or tissue analysis after antibody administration.

Key context:

• OKT-4 is not cross-reactive with mouse CD4, so it does not deplete or block mouse T cells in wild-type mice; its in vivo utility is restricted to experimental systems containing human CD4+ cells.
• Standard mouse models require a different antibody (like clone GK1.5 or YTS 177) for targeting murine CD4.
• Functional grade or low-endotoxin preparations of OKT-4 are formulated specifically for these in vivo depletion/blockade studies to minimize off-target effects and systemic toxicity in mice.

Summary Table: Common In Vivo Applications of OKT-4 in Mice

There are no standard in vivo applications of OKT-4 in normal (wild-type) mice due to lack of cross-reactivity with mouse CD4; its use is limited to systems where human CD4+ T cells are present.

In the literature, the OKT-4 antibody, which targets the CD4 molecule, is often used in conjunction with other antibodies or proteins to study immune responses, particularly in the context of T cell activation and function. Some commonly used antibodies or proteins in these studies include:

• Ibalizumab: This is an anti-CD4 antibody that binds to a different domain of CD4 than OKT-4. While OKT-4 targets domain 3, ibalizumab targets domain 2. It is used to modulate immune responses, particularly in HIV infection.

• Adnectins: Such as 4945_G06, these are engineered proteins that can bind to specific targets, like CD4, and are used for studying immune interactions and mechanisms.

• Keyhole limpet hemocyanin (KLH): This carrier protein is often used in conjunction with other antigens to enhance immune responses, such as in the development of vaccines against cancer stem cell markers like OCT4.

• OCT4 Antibodies: Although not directly used with OKT-4 for the same applications, OCT4 antibodies are used in stem cell research and cancer immunology, focusing on differentiating stem cells and targeting cancer stem cells.

• Toll-like receptor (TLR) agonists: These are used to enhance immune responses in vaccine development, such as with OCT4-based vaccines, though not typically in direct combination with OKT-4.

These proteins and antibodies are selected based on their roles in either modulating or studying immune responses, particularly in the context of T cells and cancer stem cells.

Key Findings from Clone OKT-4 Citations in Scientific Literature

Clone OKT-4 is primarily referenced in the immunological literature, particularly in studies of human T-cell surface molecules and their roles in immune recognition.

HLA-DR Recognition by Cytotoxic T Lymphocytes

• OKT4+ cytotoxic T lymphocyte (CTL) clones have been isolated and studied for their specificity toward major histocompatibility complex (MHC) class II HLA-DR antigens.
• Specificity and Diversity: One clone, B8, specifically recognized HLA-DR6 antigens, while another, C6, recognized a determinant shared by some HLA-DR3, -DR5, and -DR6 target cells—possibly a supratypic (shared) determinant or another human Ia-like antigen.
• Phenotype and Blocking: Both clones were characterized as OKT3+, OKT4+, and OKT8−. Their cytolytic activity could be blocked by anti-OKT3 and anti-OKT4 monoclonal antibodies but not by anti-OKT8, confirming the surface phenotype and functional role of the OKT4 molecule in antigen recognition.
• Inhibition Studies: Monoclonal antibodies directed at DR molecules efficiently blocked target cell recognition by these CTL clones, highlighting the role of the OKT4 antigen in mediating HLA-DR-specific cytotoxicity.

Marker for T-Cell Subsets

• OKT4 Antibody: The OKT4 monoclonal antibody identifies a subset of human T cells, staining about 55% of peripheral T cells and 80% of thymocytes, and is selective for T cells.
• Helper Function: Helper (OKT4) T cells are noted for their role in supporting immune responses, including the production of colony-stimulating activity, which is relevant in hematopoietic cell growth.
• CD4 Binding: The OKT4 antibody binds to the D3 domain of the CD4 molecule on T cells and does not block HIV binding, which is important for studies of HIV pathogenesis and CD4 function.

Summary Table: Key Attributes of OKT4-Related Findings

Conclusion

The OKT-4 clone and associated antibody have been instrumental in characterizing HLA-DR-specific cytotoxic T cells, defining CD4+ T-cell subsets, and advancing understanding of T-cell function and surface marker specificity in human immunology. Its use has clarified the molecular basis of antigen recognition by helper T cells and provided tools for dissecting immune responses at the cellular level.

Dosing regimens of clone OKT-4 (anti-human CD4) in mouse models vary substantially depending on the mouse strain (typically human CD4 transgenic or humanized mice), the study objective (depletion vs. blockade), and the disease model context.

Key details and variations include:

• In most commonly reported regimens: The typical dose of clone OKT-4 is 200–250 micrograms per mouse, delivered by intraperitoneal injection every 2–3 days. This mirrors standard immune cell–depleting antibody protocols for similar targets (such as GK1.5 for mouse CD4), but is specifically adapted for human CD4-expressing models.

• In published studies using human CD4 transgenic (HuCD4/Tg) mice: Regimens range much broader, from 5 to 250 mg/kg body weight, with selection based on the intensity and duration of CD4+ T cell modulation required by the disease or experimental endpoint. Lower doses may be used for checkpoint modulation; higher doses are used when complete and sustained CD4+ T cell depletion is necessary.

• Route and frequency: The preferred route is intraperitoneal injection, repeated at intervals of 2–3 days for acute depletion, or as a single dose for transient blockade. Frequency and number of doses are typically guided by pilot studies that measure in vivo depletion or functional effect.

• Variation by model and application:

  • Humanized mice (engrafted with a human immune system): Doses and frequency often mirror those above but are sometimes adjusted for differences in engraftment efficiency, mouse weight, or functional requirements.
  • Disease models (autoimmunity, infection, cancer): Dosing may be optimized empirically to achieve partial versus complete CD4+ T cell depletion, or to block function without causing severe immune deficiency.

Table: Reported Dosing Strategies for Clone OKT-4 in Mouse Models

Additional Details:

• Adjustments are often made for mouse weight (particularly with very high or very low engraftment).
• Study goals (e.g. partial vs. full depletion, or functional blockade) are the main reason for variation.
• Empirical titration based on flow cytometric analysis of CD4+ cell depletion is recommended for each new disease or mouse model.
• If using a different route (e.g., intravenous) or formulation, dosing may require further adjustment.

Summary:
For most studies in humanized or human CD4 transgenic mouse models, a dose of 200–250 μg per mouse, intraperitoneally, every 2–3 days is a standard starting point, but experimental goals and model specifics may warrant significant adjustment, with some studies reporting up to 250 mg/kg in certain contexts. All protocols should be empirically validated in the intended experimental context.