To rule out the possibility that during the blood passage the non-covalently bound mAbs on the surface of the coated Lm-spa+ bacteria might be displaced by the IgG antibodies of the blood serum fresh murine serum was added to Trastuzumab-coated Lm-spa+ bacteria prior to in vitro infection of 4T1-HER2 cells. Here, ERBB2 is linked to infection.