**Core Concept**
Basiliximab is a chimeric monoclonal antibody that targets the interleukin-2 receptor (IL-2R) alpha subunit, used primarily for preventing acute rejection in organ transplantation. Its pharmacokinetics, particularly its half-life, are crucial for determining dosing intervals and efficacy.

**Why the Correct Answer is Right**
The correct half-life of basiliximab is approximately 7 days. This duration allows for sustained immunosuppression, which is essential for preventing acute rejection in transplant patients. The mechanism of action involves binding to the IL-2R alpha subunit, thereby inhibiting IL-2-mediated T-cell activation and proliferation. The half-life of basiliximab is influenced by the binding affinity to the IL-2R alpha subunit and the subsequent receptor-mediated clearance.

**Why Each Wrong Option is Incorrect**
**Option B:** 7 hours is an implausibly short half-life for a monoclonal antibody like basiliximab, which would not provide sufficient immunosuppressive effects.
**Option C:** 15 days is longer than the actual half-life of basiliximab, which might suggest a longer dosing interval but could also lead to increased side effects due to prolonged exposure.
**Option D:** 24 hours is shorter than the actual half-life, which would necessitate more frequent dosing to maintain therapeutic levels.

**Clinical Pearl / High-Yield Fact**
When using basiliximab in transplant patients, it is essential to consider its half-life and dosing interval to avoid suboptimal immunosuppression or increased side effects. Regular monitoring of IL-2R alpha subunit expression and T-cell activation markers can help optimize basiliximab therapy.

**✓ Correct Answer: A. 7 days**