No no no, don't worry about
that! They are using your own blood and only tagging it with a radioactive marker that will quickly deteriorate and won't cause you any problems. It's like having a bone scan done, have you ever had one of those? They pump radioactive material into you and it congregates around areas of bone that are diseased. It's the exact same thing only they are using your white blood cells as the carriers. No risk of disease transmission or "tainting!"