A de-immunised polypeptide derived from a parental Shiga toxin A Subunit effector polypeptide, wherein the parental Shiga toxin A Subunit effector polypeptide comprises or consists of: (i) amino acids 75 to 251 of SEQ ID NO:1, SEQ ID NO:2, or SEQ ID NO:3; (ii) amino acids 1 to 241 of SEQ ID NO:1, SEQ ID NO:2, or SEQ ID NO:3; (iii) amino acids 1 to 251 of SEQ ID NO:1, SEQ ID NO:2, or SEQ ID NO:3; or (iv) amino acids 1 to 261 of SEQ ID NO:1, SEQ ID NO:2, or SEQ ID NO:3; wherein the parental Shiga toxin A Subunit effector polypeptide is capable of routing to a cytosol compartment of a cell in which it is present; wherein the de-immunised polypeptide comprises an amino acid sequence having at least 70% sequence identity to: (i) amino acids 75 to 251 of SEQ ID NO: 1, SEQ ID NO: 2, or SEQ ID NO: 3; (ii) amino acids 1 to 241 of SEQ ID NO: 1, SEQ ID NO: 2, or SEQ ID NO: 3; (iii) amino acids 1 to 251 of SEQ ID NO: 1, SEQ ID NO: 2, or SEQ ID NO: 3; or (iv) amino acids 1 to 261 of SEQ ID NO: 1, SEQ ID NO: 2, or SEQ ID NO: 3; wherein the de-immunised polypeptide comprises a heterologous, CD8+ T-cell epitope embedded in said parental Shiga toxin A Subunit effector polypeptide; wherein the embedded, heterologous, CD8+ T-cell epitope replaces an equivalent number of amino acid residues in the parental Shiga toxin A Subunit effector polypeptide, such that the de-immunised polypeptide comprising the embedded, heterologous, CD8+ epitope has the same total number of amino acids as the parental Shiga toxin A Subunit effector polypeptide absent the embedded, heterologous, CD8+ T-cell epitope; wherein the embedded, heterologous, CD8+ T-cell epitope disrupts an endogenous B-cell epitope and/or CD4+ T-cell epitope of the parental Shiga toxin A Subunit effector polypeptide, as evidenced by reduced B-cell antigenicity or immunogenicity and/or reduced CD4+ T-cell antigenicity or immunogenicity of the Shiga toxin A Subunit effector polypeptide comprising the embedded, heterologous, CD8+ T-cell epitope, as compared to the parental Shiga toxin A Subunit effector polypeptide absent the embedded, heterologous, CD8+ T-cell epitope; and wherein said endogenous B-cell epitope is positioned at an amino acid sequence selected from the group of natively positioned amino acids consisting of: the B-cell epitope regions: 1-15 of SEQ ID NO:1 or SEQ ID NO:2; 3-14 of SEQ ID NO:3; 26-37 of SEQ ID NO:3; 27-37 of SEQ ID NO:1 or SEQ ID NO:2; 39-48 of SEQ ID NO:1 or SEQ ID NO:2; 42-48 of SEQ ID NO:3; 53-66 of SEQ ID NO:1, SEQ ID NO:2, or SEQ ID NO:3; 94-115 of SEQ ID NO:1, SEQ ID NO:2, or SEQ ID NO:3; 141-153 of SEQ ID NO:1 or SEQ ID NO:2; 140-156 of SEQ ID NO:3; 179-190 of SEQ ID NO:1 or SEQ ID NO:2; 179-191 of SEQ ID NO:3; 204 of SEQ ID NO:3; 205 of SEQ ID NO:1 or SEQ ID NO:2; 210-218 of SEQ ID NO:3; 240-260 of SEQ ID NO:3; 243-257 of SEQ ID NO:1 or SEQ ID NO:2; and 254-268 of SEQ ID NO:1 or SEQ ID NO:2; and/or wherein said endogenous CD4+ T-cell epitope is positioned at an amino acid sequence selected from the group of natively positioned amino acids consisting of the CD4+ T-cell epitope regions: 4-33 of SEQ ID NO: 1 or SEQ ID NO: 2; 34-78 of SEQ ID NO:1 or SEQ ID NO:2; 77-103 of SEQ ID NO:1 or SEQ ID NO:2; 128-168 of SEQ ID NO:1 or SEQ ID NO:2; 160-183 of SEQ ID NO:1 or SEQ ID NO:2; and 236-258 of SEQ ID NO:1 or SEQ ID NO:2; and wherein the de-immunised polypeptide comprising the embedded, heterologous, CD8+ epitope is capable of intracellular delivery of the embedded, heterologous, CD8+ T-cell epitope from an early endosomal compartment to a MHC class I molecule of a cell in which the polypeptide is present. (i) amino acids 75 to 251 of SEQ ID NO:1, SEQ ID NO:2, or SEQ ID NO:3; (ii) amino acids 1 to 241 of SEQ ID NO:1, SEQ ID NO:2, or SEQ ID NO:3; (iii) amino acids 1 to 251 of SEQ ID NO:1, SEQ ID NO:2, or SEQ ID NO:3; or (iv) amino acids 1 to 261 of SEQ ID NO:1, SEQ ID NO:2, or SEQ ID NO:3; (i) amino acids 75 to 251 of SEQ ID NO: 1, SEQ ID NO: 2, or SEQ ID NO: 3; (ii) amino acids 1 to 241 of SEQ ID NO: 1, SEQ ID NO: 2, or SEQ ID NO: 3; (iii) amino acids 1 to 251 of SEQ ID NO: 1, SEQ ID NO: 2, or SEQ ID NO: 3; or (iv) amino acids 1 to 261 of SEQ ID NO: 1, SEQ ID NO: 2, or SEQ ID NO: 3; the B-cell epitope regions: 1-15 of SEQ ID NO:1 or SEQ ID NO:2; 3-14 of SEQ ID NO:3; 26-37 of SEQ ID NO:3; 27-37 of SEQ ID NO:1 or SEQ ID NO:2; 39-48 of SEQ ID NO:1 or SEQ ID NO:2; 42-48 of SEQ ID NO:3; 53-66 of SEQ ID NO:1, SEQ ID NO:2, or SEQ ID NO:3; 94-115 of SEQ ID NO:1, SEQ ID NO:2, or SEQ ID NO:3; 141-153 of SEQ ID NO:1 or SEQ ID NO:2; 140-156 of SEQ ID NO:3; 179-190 of SEQ ID NO:1 or SEQ ID NO:2; 179-191 of SEQ ID NO:3; 204 of SEQ ID NO:3; 205 of SEQ ID NO:1 or SEQ ID NO:2; 210-218 of SEQ ID NO:3; 240-260 of SEQ ID NO:3; 243-257 of SEQ ID NO:1 or SEQ ID NO:2; and 254-268 of SEQ ID NO:1 or SEQ ID NO:2; and/or wherein said endogenous CD4+ T-cell epitope is positioned at an amino acid sequence selected from the group of natively positioned amino acids consisting of the CD4+ T-cell epitope regions: 4-33 of SEQ ID NO: 1 or SEQ ID NO: 2; 34-78 of SEQ ID NO:1 or SEQ ID NO:2; 77-103 of SEQ ID NO:1 or SEQ ID NO:2; 128-168 of SEQ ID NO:1 or SEQ ID NO:2; 160-183 of SEQ ID NO:1 or SEQ ID NO:2; and 236-258 of SEQ ID NO:1 or SEQ ID NO:2; and wherein the de-immunised polypeptide comprising the embedded, heterologous, CD8+ epitope is capable of intracellular delivery of the embedded, heterologous, CD8+ T-cell epitope from an early endosomal compartment to a MHC class I molecule of a cell in which the polypeptide is present.