KRAS and leukemia: We therefore introduced oncogenic Kras into p16p19−/− bone marrow cells by ex vivo gene transduction, and then transplanted these genetically altered cells to induce systemic leukemias (by retro-orbital injection), as well as to produce the first transplantable model of murine histiocytic sarcoma (by injection into the gastrocnemius muscles of NOD.SCID mice).