Patent ID: 8048421

Claim:
An agonist antibody to a human thrombopoietin receptor (c-Mpl), wherein the agonist antibody comprises: (A) antibody constant regions comprising amino acid sequences selected from the following: (1) amino acid sequences of heavy chain and light chain constant regions of a human antibody, or (2) an amino acid sequence of a heavy chain constant region with a heavy chain constant region domain substituted between human antibody subclasses, and an amino acid sequence of a light chain constant region of a human antibody, wherein, the heavy chain constant region of (A)(1) or (A)(2) comprises: i) an upper hinge portion having the amino acid sequence of SEQ ID NO: 10; ii) a middle hinge portion having the amino acid sequence selected from the group consisting of: (a) amino acids 18 to 67 of SEQ ID NO: 101; (b) amino acids 18 to 37 of SEQ ID NO: 102; and (c) amino acids 18 to 22 of SEQ ID NO: 103; and iii) a CH1 Region having the amino acid sequence of amino acids 1 to 5 of SEQ ID NO: 99; and iv) a CH2 region having the amino acid sequence of (a) amino acids 18 to 25 of SEQ ID NO: 100, or (b) amino acids 18 to 25 of SEQ ID NO: 99, or the heavy chain constant region of (A)(1) or (A)(2) comprises: i) an upper hinge portion having the amino acid sequence of SEQ ID NO: 11; ii) a middle hinge portion having the amino acid sequence of amino acids 18 to 22 of SEQ ID NO: 104; and iii) a CH1 Region having the amino acid sequence of amino acids 1 to 5 of SEQ ID NO: 99; and iv) a CH2 region having the amino acid sequence of (a) amino acids 18 to 25 of SEQ ID NO: 100, or (b) amino acids 18 to 25 of SEQ ID NO: 99; and (B) antibody variable regions capable of binding to and activating a human thrombopoietin receptor; wherein the agonist antibody has the following properties: (a) that the antibody induces colony formation at a concentration of 10,000 ng/ml or lower as determined by the CFU-MK colony formation assay using human umbilical cord blood derived CD34+ cells; and (b) that the antibody has a maximal activity at least 50% higher than that of PEG-rHuMGDF, which comprises the amino acid sequence as shown in SEQ ID NO: 1 having the following structure and has been pegylated at the N terminus, and a 50% effective concentration (EC50) of 100 nM or less in the cell proliferation assay using UT7/TPO cells: (SEQ ID NO: 1) PEG-NH-SPAPPACDLRVLSKLLRDSHVLHSRLSQCPEVHPLPTPVLLPA VDFSLGEWKTQMEETKAQDILGAVTLLLEGVMAARGQLGPTCLSSLLGQL SGQVRLLLGALQSLLGTQLPPQGRTTAHKDPNAIFLSFQHLLRGKVRFLM LVGGSTLCVRRAPPTTAVPS-COOH.