*2.5.2. Side effects*

The major side effect of azathioprine is bone marrow suppression, including leukopenia (common), and thrombocytopenia (less common). Other important adverse effects include increased susceptibility to infections (especially varicella and herpes simplex viruses) and hepatotoxicity [1].

### **2.6. Anti-IL-2 receptor (Anti-CD25) antibodies**

There are two anti–IL-2R preparations for use in clinical transplantation: daclizumab and basiliximab. These are used for prophylaxis of acute organ rejection in adult patients. Basilix‐ imab is considered a chimeric antibody, because it consists of approximately 70% human and 30% murine proteins. This agent has low immunogenicity potential due to the incorporation of human protein sequences. Daclizumab consists of 90% human and 10% murine components. The effectiveness of daclizumab is comparable to that of basiliximab, with an adverse-effect profile comparable to that seen with placebo [1,46].

#### *2.6.1. Mechanism of action*

Basiliximab binds with high affinity to the alpha subunit of the IL-2 receptor, also known as CD25, where it acts as a receptor antagonist. The antagonistic effect on the IL-2 receptor prevents T-cell activation and subsequent proliferation without causing lysis or cell destruc‐ tion. Daclizumab, like basiliximab, is a nondepleting monoclonal antibody that acts as an antagonist at the CD25 subunit of T cells and received marketing approval in 1997 for induction therapy in renal transplant recipients. In Phase III trials, the half-life of daclizumab was 20 days, resulting in saturation of the IL-2Rα on circulating lymphocytes for up to 120 days after transplantation. In these trials, daclizumab was used with maintenance immunosuppression regimens (CsA, azathioprine, and steroids; CsA and steroids). Subsequently, daclizumab was successfully used with a maintenance triple-therapy regimen—either with CsA or TRL, steroids, and MMF substituting for azathioprine. In the Phase III trials, the half-life of basilix‐ imab was 7 days. In one randomized trial, basiliximab was safe and effective when used in a maintenance regimen consisting of CsA, MMF, and prednisone [1,47].
