To do this job, you need to have a Ph.D. or M.D. Most colleges are also very selective about who gets in. Getting into medical school means taking and passing the MCAT, which is no walk in the park.
Once you've earned that magical piece of graduation paper, you'll also need to spend a couple of years getting certified by an accredited immunology program. You know what that means...yep—another exam to pass.
Then it's time to get to work. It's important to publish your work and stay current on the latest advancements in your field. Would you go to a dentist who's never heard of Novocain?