Drugs can influence and support your immune system, or by pass steps needed to activate an immune response. Sometimes we need to be careful about how fast and strong an immune response we generate or else it can have consequences for the patient. We’re very much still learning how to do this properly.
There was an incident in a clinical trial for an immune therapy that went wrong in London in 2006. A drug called TGN1412 was given to patients that invoked a powerful immune response really quickly. This got out of control and lead to severe health risks and loss of limbs due to severe inflammation. If you’re interested you can learn more about it here on this documentary.