The first in class immunomodulatory mAb ipilimumab, currently in clinical use for advanced melanoma and undergoing a large number of clinical trials for the therapy of lung and prostate cancers, has been used in this work for the following two purposes: the first one was to confirm the expression and the role of CTLA-4 in tumor cells and NK cells as, recently, some authors have reported the unexpected expression of this receptor on these cell populations [12,14,17,38], even though its role in this context has not yet been accurately investigated and only little attention has been paid. This evidence concerns the gene CTLA4 and prostate carcinoma.