CD40 and neoplasm: Figure 2D shows that, in all cases, tumor cells constitutively expressed the mbIL-15 whose expression was not modified after IFN-α/anti-CD40 monoclonal antibodies (mAb) treatment. Interestingly, the MeWo cell line which lacked both WT IL-15Rα and IC3 IL-15Rα transcripts expressed mbIL-15. This isoform could likely represent the so-called trans-membrane IL-15 isoform that is not retained at the cell surface by any IL-15Rα isoform (15).