The present invention relates to cell-penetrating effector proteins of type III secretion system (T3SS)-containing bacteria of the genus Salmonella or Shigella and variants, fragments and immunomodulatory domains thereof, for use in immunotherapy. The present invention further relates to cell-penetrating effector proteins of type III secretion system (T3SS)-containing bacteria of the genus Salmonella or Shigella and variants, fragments and immunomodulatory domains thereof, for delivering cargo molecules into eukaryotic cells.