Okay, let's tackle this question. The question is about an immunosuppressant drug that inhibits IL-2 action without affecting its transcription. First, I need to recall which drugs target IL-2. IL-2 is a cytokine important for T-cell proliferation.

Immunosuppressants like cyclosporine and tacrolimus are calcineurin inhibitors. They work by inhibiting the dephosphorylation of NFAT, which is needed for IL-2 transcription. But the question says transcription isn't inhibited, so those drugs might not be the answer here.

Then there's another class of drugs that target IL-2 directly. For example, basiliximab and daclizumab are monoclonal antibodies against IL-2 or its receptor. Basiliximab is an anti-IL-2 monoclonal antibody, while daclizumab targets the IL-2 receptor. These would block IL-2 action by binding to it or its receptor, preventing signaling. Since they don't inhibit transcription, they fit the question's requirement.

So the correct answer should be either basiliximab or daclizumab. Let me check the options again. If the options include these, then that's the answer. The other options like cyclosporine, tacrolimus, or mycophenolate mofetil would inhibit transcription. Mycophenolate inhibits inosine monophosphate dehydrogenase, affecting purine synthesis, not IL-2 directly. So those are out.

Therefore, the drug in question is likely a monoclonal antibody against IL-2 or its receptor. The key is that it blocks IL-2's action post-transcriptionally.

**Core Concept**
This question tests knowledge of immunosuppressant drugs targeting interleukin-2 (IL-2), a cytokine critical for T-cell activation and proliferation. The key distinction is between drugs inhibiting IL-2 **transcription** (e.g., calcineurin inhibitors) versus those blocking IL-2 **action post-transcription** (e.g., monoclonal antibodies).

**Why the Correct Answer is Right**
**Daclizumab** is a monoclonal antibody targeting the **IL-2 receptor (CD25)** on T-cells. It prevents IL-2 from binding to its receptor, thereby inhibiting T-cell activation and proliferation **without affecting IL-2 transcription**. This mechanism differs from calcineurin inhibitors (e.g., cyclosporine), which block IL-2 transcription by inhibiting nuclear factor of activated T-cells (NFAT) dephosphorylation.

**Why Each Wrong Option is Incorrect**
**Option A (Cyclosporine):** Inhibits calcineurin, preventing NFAT dephosphorylation required for IL-2 transcription.
**Option B (Mycophenolate mofetil):** Inhibits inosine monophosphate dehydrogenase, blocking purine synthesis and T-cell proliferation, unrelated to IL-2.
**Option C (Basiliximab):** A monoclonal antibody against IL-2 receptor (like daclizumab), but often paired with cyclosporine in options. If absent, daclizumab

✓ Correct Answer: D. Sirolimus