You can fight fire with fire – it’s a thing. The problem is having anything left to salvage after the fire is out, and thus the conundrum of IL-2: the cytokine’s ability to supercharge T cells against cancer has been known for years, but the problem has always been its profound toxicity. Fahar Merchant, CEO of Medicenna explains how directed evolution has allowed him to turn the agent of wildfires into a tool for a controlled therapeutic burn.