Step 1: Understanding the Problem:
Tumor cells can often evade detection and destruction by the immune system. In certain cancer therapies, patients are given substances called biological response modifiers to stimulate their immune response.
Step 2: Approach and Formula:
Identify the specific cytokine used clinically in immunotherapy to activate the immune system against cancer cells.
Step 3: Detailed Explanation:
- Histamine and Serotonin are chemicals involved in inflammation and allergic reactions, not primarily in destroying tumors.
- $\alpha$-Lactalbumin is a protein found in milk, notably produced in transgenic animals (like the Rosie cow), and is unrelated to cancer therapy.
- $\alpha$-Interferon is a potent cytokine that acts as a biological response modifier. When administered to cancer patients, it rapidly activates the immune system (such as Natural Killer cells and macrophages) to identify and effectively destroy tumor cells.
Step 4: Final Answer:
The correct substance is $\alpha$-Interferon.