Abstract: The present invention relates to an isolated antigen-binding protein, which comprises a CD3-binding moiety, wherein the CD3-binding moiety comprises amino acid sequences having at least 95% identity to heavy chain variable regions HCDR1, HCDR2 and HCDR3; the amino acid sequence of the HCDR1 is set forth in any one of SEQ ID NOs: 1 and 2; the amino acid sequence of the HCDR2 is set forth in any one of SEQ ID NOs: 3, 4 and 5; the amino acid sequence of the HCDR3 is set forth in SEQ ID NO: 6; and/or, the CD3-binding moiety comprises amino acid sequences having at least 95% identity to light chain variable regions LCDR1, LCDR2 and LCDR3; the amino acid sequence of the LCDR1 is set forth in any one of SEQ ID NOs: 7, 8 and 9; the amino acid sequence of the LCDR2 is set forth in any one of SEQ ID NOs: 11 and 12; the amino acid sequence of the LCDR3 is set forth in SEQ ID NO: 13, wherein the CD3-binding moiety can induce T cell activation.