Because in vitro coculture assays and xenograft mouse models likely do not reveal the full potential for off-tumor toxicities given the cross-species differences in IL13-ligand binding, we developed a fully murine IL13(E12Y)-CAR to further study the safety and specific tumor targeting of IL13-BBζ CAR T cells in a syngeneic, immunocompetent mouse brain tumor model (Fig. 7A; ref. 13). Here, IL13 is linked to neoplasm.