Immuno-therapy was a type of medical procedure involving immunity.
Dr. Julian Bashir had been working on an immuno-therapy project on Bajor, and had written a paper on it as of 2371. Dr. Elizabeth Lense was impressed by his writing and found it brilliant, saying she envied him the opportunity to do a long-term project, whereas her posting, the USS Lexington, didn't allow for such involved study. (DS9: "Explorers")