## Core Concept
The "Triple Therapy" immunosuppression regimen for post-renal transplant patients typically consists of a combination of three types of drugs: a **calcineurin inhibitor** (e.g., cyclosporine or tacrolimus), an **antiproliferative agent** (e.g., mycophenolate mofetil or azathioprine), and a **corticosteroid** (e.g., prednisone). This regimen aims to prevent rejection by targeting different aspects of the immune response.

## Why the Correct Answer is Right
Azathioprine and mycophenolate mofetil are both antiproliferative agents used in immunosuppressive regimens. Cyclosporine is a calcineurin inhibitor. Prednisone is a corticosteroid. Sirolimus (also known as rapamycin) is an **mTOR inhibitor**, which is a different class of immunosuppressive drug. While sirolimus can be used in renal transplant patients, it is often used in place of one of the other antiproliferative agents or calcineurin inhibitors, not typically as part of the classic "triple therapy" which usually includes a calcineurin inhibitor, an antiproliferative agent, and a corticosteroid.

## Why Each Wrong Option is Incorrect
* **Option A:** Cyclosporine is a calcineurin inhibitor, a common component of triple therapy.
* **Option B:** Azathioprine is an antiproliferative agent, another component of triple therapy.
* **Option D:** Prednisone is a corticosteroid, the third component of triple therapy.

## Clinical Pearl / High-Yield Fact
A key point to remember is that while the classic triple therapy includes a calcineurin inhibitor, an antiproliferative agent, and a corticosteroid, modern immunosuppressive regimens can be tailored to the individual patient and may include other agents like mTOR inhibitors (e.g., sirolimus) to minimize toxicity or improve efficacy.

## Correct Answer Line
**Correct Answer: C. Sirolimus.**