Antithymocyte Globulin | Encyclopeptide

Chemical Identity

Property	Value
Molecular Weight	~150 kDa (IgG)
Structure	Polyclonal IgG (rabbit or equine)
Target	Multiple T-cell antigens
Sources	Rabbit (Thymoglobulin), Equine (ATGAM)
Route	IV infusion

Structure

Antithymocyte globulin (ATG) is a polyclonal antibody preparation containing antibodies against multiple human T-cell surface antigens. Rabbit ATG (Thymoglobulin) is produced by immunizing rabbits with human thymocytes. Equine ATG (ATGAM) uses horse immunization. The polyclonal nature provides broad T-cell targeting.

Mechanism of Action

ATG contains antibodies against multiple T-cell antigens (CD2, CD3, CD4, CD8, CD11a, CD18, CD25, CD44, CD45, HLA-DR), causing T-cell depletion through complement-mediated lysis, opsonization, and apoptosis. It also modulates adhesion molecules and may promote regulatory T-cell generation.

Clinical Applications

Kidney transplant induction: High immunological risk patients
Acute rejection: Steroid-resistant rejection treatment
Aplastic anemia: First-line immunosuppressive therapy
Bone marrow transplant: Conditioning regimen
GvHD prevention: T-cell depletion protocols

Pharmacokinetics

Halflife: 2-3 days (rabbit), 5-7 days (equine)
T-cell depletion: Occurs within hours
Duration: 2-4 weeks (T-cell recovery)
Dosing: 1.5 mg/kg/day for 7-14 days (rabbit)
Route: IV infusion (central line preferred)

Safety and Side Effects

Cytokine release syndrome (first dose), fever, chills, thrombocytopenia, leukopenia, serum sickness (7-10 days), infections (CMV, EBV, PTLD), and malignancy risk. Premedication required.

References

Brennan, D.C., et al. (1999). Rabbit ATG for kidney transplant. New England Journal of Medicine, 340, 1075-1080.
Scheinberg, P., et al. (2011). Horse versus rabbit ATG for aplastic anemia. New England Journal of Medicine, 365, 430-438.