F9 and hemophilia B: Lastly, one important point to keep in mind when discussing transgene immunity is that most of the clinical experience to date derives from studies in which cross-reactive immunologic material (CRIM) positive subjects and subjects with prior exposure to the therapeutic protein [e.g., recombinant or plasma-derived factor IX (FIX) for hemophilia B patients] were enrolled (9, 48, 60, 61).