Chronic Spontaneous Uriticaria

The goal of this clinical trial is to learn if human interleukin-2 (IL-2) works to treat moderate to severe chronic spontaneous urticaria in adults who remain symptomatic despite oral antihistamine treatment (refractory CSU). It will also learn about the safety of IL-2. The main questions it aims to answer are: Does IL-2 alleviate the symptoms of urticaria in patients? What medical problems do participants have when given IL-2? Researchers will compare IL-2 to a placebo (a look-alike and smell-like substance that contains no IL-2) to see if IL-2 works to treat refractory, moderate to severe CSU. Participants will: Receive IL-2 or a placebo intramuscular injections for 3 rounds at Week 0, 4 and 8, in which each round includes one injection daily for seven consecutive days. Visit the clinic for checkups and tests at Week 2, 4, 8, 12 and 24. Keep a diary of their symptoms and the number of tablets of oral antihistamines.