From the comments yesterday: "there's not any nasty side effects apart from the bummer immune system?"
Well, actually, because of the bummer immune system, there are tons of nasty side effects. Serious infections, including tuberculosis, sepsis and pneumonia can happen. There have been rare reports of lymphoma (a blood cancer) occurring in some people. COPD can develop. If you're a carrier of Hepatitis B, that can redevelop. Rare cases of liver damage have been reported, including fatal damage. Blood and nerve disorders have been reported. Any and all of these reports have the potential to be fatal.
There are also allergic reactions that can happen while you're being infused or within a week or two after. These include: respiratory problems, hives, chest pain, high or low blood pressure, swelling of the face and hands, and fever or chills.
Most common side effects? Headache, stomach pain, respiratory infections, rash and coughing. Luckily, I just get these last things.