**Core Concept**
Cell-mediated immunity is a type of immune response that involves the activation of T lymphocytes (T cells) to defend against infections and diseases. This process is crucial for controlling and eliminating intracellular pathogens, such as viruses and certain bacteria. The development of cell-mediated immunity is mediated by various cytokines, which play a pivotal role in regulating the immune response.

**Why the Correct Answer is Right**
Interleukin-2 (IL-2) is a cytokine that plays a central role in the development of cell-mediated immunity. It is produced by activated T cells, particularly CD4+ T helper cells, and promotes the proliferation and differentiation of T cells into effector cells, such as cytotoxic T cells and T helper cells. IL-2 also stimulates the production of other cytokines that are essential for the activation and function of T cells. The mechanism of IL-2 involves binding to its receptor on the surface of T cells, which triggers a signaling cascade that leads to cell proliferation and differentiation.

**Why Each Wrong Option is Incorrect**
**Option A:** Interferon-gamma (IFN-γ) is a cytokine that is involved in the activation of macrophages and the induction of antiviral and antimicrobial responses, but it is not primarily associated with the development of cell-mediated immunity.
**Option B:** Tumor necrosis factor-alpha (TNF-α) is a cytokine that plays a role in systemic inflammation and is involved in the regulation of immune responses, but it is not directly involved in the development of cell-mediated immunity.
**Option C:** Interleukin-4 (IL-4) is a cytokine that promotes the differentiation of naive T cells into Th2 cells, which are involved in humoral immunity and the production of antibodies, rather than cell-mediated immunity.

**Clinical Pearl / High-Yield Fact**
IL-2 is a key cytokine in the development of cell-mediated immunity, and its administration has been used as an immunotherapy to enhance the immune response in patients with cancer and HIV infection.

**Correct Answer: C. Interleukin-2 (IL-2)**