**2.1. Thymoglobulin**

Thymoglobulin (rATG) is the most commonly used induction agent in United States. (rATG), is an antilymphocyte polyclonal antibody that is derived by injecting rabbits with human thymocytes. rATG contains polyclonal cytotoxic antibodies mainly targeted against various epitopes on human T lymphocytes and works primarily by complement mediated depletion of T lymphocytes. However, the multiple specificities of rATG against a broad range of T-cell antigens can affect multiple pathways involved in T-cell trafficking, adhesion, activation and promotion of certain T-cell subsets that may be more favorable for transplantation such as Tregulatory cells. [4-6] Although primarily a T-cell directed agent, the development of humoral responses which are dependent on T-cell help are likely compromised by rATG as well.

#### *2.1.1. Side effects*

Secondary to potential infusion reactions and other toxicities, administration of rATG requires patient monitoring and is administered in an inpatient setting or in an established infusion center. The typical dose is 1.5mg/kg/dose and involves 3-5 doses of rATG, depending on center protocols.

The antibodies in rATG can bind to proteins on the surface of granulocytes as well as platelets and hence leucopenia and thrombocytopenia are commonly encountered after rATG admin‐ istration. Cytopenias are handled either by dose reduction or holding the dose. Despite premedication, infusion reactions do occur including fevers, chills and arthralgias. Serious reactions such as anaphylaxis, acute respiratory distress syndrome (noncardiogenic pulmo‐ nary edema) occur rarely. Typically these reactions are a result of intense cytokine release from lysis of T lymphocytes. Since rATG is obtained from rabbit sera, serum sickness can occur which presents with fever, malaise, diffuse arthralgias and rash. rATG results in prolonged T cell depletion, up to 6 months post administration and recipients are at increased risk for opportunistic infections and lymphoma. Patients are typically prophylaxed for cytomegalo‐ virus infection and pneumocystis carinii infection post rATG administration.
