Muromonab-CD3

Chemical Identity

Property	Value
Molecular Weight	~150 kDa
Structure	Murine IgG2a monoclonal antibody
Target	CD3 (T-cell receptor complex)
CAS Number	140608-64-0
Route	IV bolus

Structure

Muromonab-CD3 (OKT3) was the first monoclonal antibody approved for clinical use (1986). It is a murine IgG2a antibody targeting the epsilon chain of the CD3 complex on all mature T cells. Being fully murine, it is highly immunogenic in humans.

Mechanism of Action

Muromonab-CD3 binds CD3 on all mature T cells, initially causing T-cell activation (cytokine release syndrome) followed by T-cell depletion through opsonization and complement-mediated lysis. It also modulates the TCR complex, rendering remaining T cells non-functional.

Clinical Applications

• Acute transplant rejection: First-line treatment for steroid-resistant rejection
• Induction therapy: Transplant induction (largely replaced)
• Historical significance: First therapeutic monoclonal antibody
• Largely obsolete: Replaced by less immunogenic antibodies

Pharmacokinetics

• Half-life: 18 hours (first dose), shorter with subsequent doses (HAMA)
• T-cell clearance: Within minutes of first dose
• CD3 saturation: 7-14 days
• Dosing: 5 mg IV daily for 10-14 days
• Route: IV bolus

Safety and Side Effects

Cytokine release syndrome (first-dose: fever, chills, dyspnea, hypotension - severe), pulmonary edema, aseptic meningitis, and HAMA formation (human anti-mouse antibodies). Premedication with methylprednisolone, acetaminophen, and diphenhydramine required.

References

• Cosimi, A.B., et al. (1981). OKT3 monoclonal antibody for renal allograft rejection. New England Journal of Medicine, 305, 308-314.
• Ortho Multicenter Transplant Study Group (1985). OKT3 for renal transplant rejection. New England Journal of Medicine, 313, 337-342.