What is the best cleanse to boost immunity?

Scams. Forgive me. I think almost all healthtap physicians will agree that "cleanses" are non-evidence-based medicine, promoted by (often-sincere) practitioners not held to the same standards as we are. They may make you feel better because they were unpleasant, you paid money & the proponents said nice things, but I've never seen any scientific evidence beyond anecdote that they ever improved immunity.