Provided are novel fusion proteins, nucleic acids encoding said proteins, vectors comprising said nucleic acids, compositions comprising said nucleic acids or vectors, host cells comprising said nucleic acids, vectors or compositions or pharmaceutical compositions. Provided are methods of reducing (down regulating) a target membrane-bound
protein (MBP) level in a
cell, methods of producing a
cell having a reduced target membrane-bound
protein level, or methods of treating a
disease, or methods of reducing or preventing GvHD in a subject associated with the administration of one or more CAR T-cells to the subject.