Patent Publication Number: US-2023139700-A1

Title: Development and application of immune cell activator

Description:
TECHNICAL FIELD 
     The present invention relates to the technical field of bio-immunology, and particularly relates to a novel antibody or a fragment thereof that specifically bind to OX40. 
     BACKGROUND 
     There are two types of checkpoints in the immune system. One is inhibitory, such as PD-1, and the other is activating, such as OX40. The complete activation of T cells in the immune system requires two-step signals. The first signal is generated by the recognition of an antigen through a T cell antigen receptor, and the activation signal is transduced into a cell via a CD3 molecule. The second signal, known as a co-stimulatory signal, is generated by the interaction of co-stimulatory molecules on the surface of an antigen-presenting cell or a target cell and co-stimulatory molecule receptors on the surface of an activated T cell. The co-stimulatory signals promote proliferation of antigen-specific T cells and differentiation thereof into effector T cells. (Lindsay K et al.,  Immunity,  2016, 44(5): 1005-1019). 
     OX40, also known as TNFRSF4, ACT35, CD134, etc., belongs to the tumor necrosis factor receptor superfamily (TNFRSF), and is also a type I transmembrane glycoprotein. OX40 is not expressed on resting T cells but on activated CD4+ T cells, CD8+ T cells, NK cells and NKT cells (Paterson D J et al.,  Mol. Immunol.,  1987; 24: 1281-1290). T cells, after being activated by antigens, highly express OX40 molecules within 1-3 days, and the activation of OX40 signals further enhances T cell activation signals to enhance immune system responses (Gramaglia I et al.,  J. Immunol.  2000; 165: 3043-3050). 
     OX40L, also known as TNFSF4, TXGP1, gp34 and CD252, is a type II transmembrane glycoprotein and a natural ligand for OX40. It is present on activated antigen-presenting cells (APCs) such as DC cells and B cells in a trimer form, and its expression is mediated by CD40, toil-like receptors (TLRs) and inflammatory factors. OX40L is also widely present in non-hematopoietic cells such as smooth muscle cells and vascular endothelial cells (Murata K et al.,  J Immunol.  2002; 169: 4628-4636). 
     Intracellular signaling pathways of OX40 activated by OX40L are associated with multiple intracellular signaling pathways of T cells, and the intracellular signaling pathways of OX40 can be initially activated by the binding of OX40L trimer formed by intramolecular disulfide bonds to OX40 on the cell membranes of T cells (Compaan D M et al.,  Structure.  2006; 14: 1321-30). For the further or complete activation of OX40 intracellular signals, further oligomerization of the receptors is required to form hexamers or above (H Wajant.  Cell Death and Differentiation,  (2015) 22, 1727-1741). When activated, OX40 recruits TNF receptor-associated factor (TRAF) 2 and 5 through its intracellular domain, so that signaling pathways of NFκB are activated to exert the effect of anti-apoptosis, thus suppressing the apoptosis of cells (Song J et al.,  J. Immunol.  2008; 180: 7240-8). 
     In addition, the intracellular signaling pathways of OX40 also specifically assist TCR intracellular signaling pathways of T cells, mainly PKB/PI3K and calcium-associated NFAT signaling pathways, wherein the PKB/PI3K signaling pathways promote the survival of activated T cells and the cell cycle progression (Song J et al.,  Nat Immunol.  2004; 5: 150-8), and the calcium-associated NFAT signaling pathways promote the proliferation of activated T cells and the secretion of corresponding cytokines (So T et al.,  Proc Natl Acad Sci USA.  2006; 103: 3740-5). 
     Researchers have found that OX40 is also highly expressed on tumor-infiltrating CD4+ Treg cells (regulatory T cells). Treg cells can suppress effector T cells (Teff). At present, there is no consensual and determined view on the regulatory role of the OX40 signaling pathways on the function of Treg cells. Some studies have shown that the OX40 signaling pathways can inhibit the immunosuppressive function of Treg cells (Piconese S et al.,  J. Exp. Med.  2008; 205: 825-39; Voo K S et al.,  J. Immunol.  2013; 191: 3641-50), while others have shown that OX40 is necessary for Treg cells to completely exert the immunosuppressive function thereof (Piconese S et al.,  Eur. J. Immunol.  2010; 40: 2902-13; Griseri T et al.,  J. Exp. Med.  2010; 207: 699-709). The effect of the OX40 intracellular signaling pathways on the proliferation and apoptosis of Treg cells varies with the microenvironment in which the cells are placed. It has also been found that the activation of OX40 strongly promotes the proliferation of Treg cells in the absence of IFN-γ and IL-4 or in the presence of FoxP3 expression (Ruby C E et al.,  J. Immunol.  2009; 183: 4853-7), while the activation of OX40 does not affect the proliferation of Treg cells in other microenvironments (Vu M D et al.,  Blood.  2007; 110: 2501-10). 
     At present, it is widely believed that anti-OX40 antibodies activate T cells in the immune system and inhibit tumors mainly through the following three cell physiological mechanisms: the first one is directly activating CD4+ and CD8+ effector T cells to promote their proliferation and survival and the secretion of related inflammatory factors; the second one is inhibiting the signals and activities of Treg cells to weaken their inhibitory effect on the immune system; the third one is depleting Treg cells by ADCC, ADCP or the like to reduce their suppression on Teff cells (J. Willoughby et al.,  Molecular Immunology  83, 2017, 13-22). 
     The concept of using anti-OX40 antibodies or signaling pathways of OX40 to treat tumors has been strongly verified on a large number of mouse tumor models. According to the existing researches, it is strongly indicated that OX40 is a very promising activating target in tumor immunotherapy and it can provide a new means for tumor immunotherapy. 
     SUMMARY 
     The present invention provides a novel antibody or a fragment thereof that can specifically recognize and bind to OX40 (particularly human OX40 (hOX40)), wherein the antibody or the fragment thereof can bind to hOX40 with a higher affinity without competing with OX40 ligand (OX40L), can more effectively activate T cells, generate stronger immune responses, and improve anti-tumor activity. 
     The present invention discloses an antibody or an antigen-binding fragment thereof that specifically binds to OX40, which comprises one or more amino acid sequences in (a)-(f): 
     (a) a VH CDR1 set forth in SEQ ID NO: 1, 4, 10, 16, 104 or 22; 
     (b) a VH CDR2 set forth in SEQ ID NO: 2, 5, 7, 8, 11, 13, 14, 17, 20, 23 or 26; 
     (c) a VH CDR3 set forth in SEQ ID NO: 3, 6, 9, 12, 15, 18, 21, 24 or 27; 
     (d) a VL CDR1 set forth in SEQ ID NO: 28, 31, 37, 40, 43, 46, 49, 52, 55, 58 or 61; 
     (e) a VL CDR2 set forth in SEQ ID NO: 19, 25, 29, 32, 35, 38, 44, 47, 50, 56, 59 or 62; and 
     (f) a VL CDR3 set forth in SEQ ID NO: 30, 33, 34, 36, 39, 41, 42, 45, 48, 51, 53, 54, 57, 60 or 63. 
     In some embodiments, the antibody or the fragment thereof comprises a VH CDR1 set forth in SEQ ID NO: 1, 4, 10, 16, 104 or 22. In some embodiments, the antibody or the fragment thereof comprises a VH CDR2 set forth in SEQ ID NO: 2, 5, 7, 8, 11, 13, 14, 17, 20, 23 or 26. In some embodiments, the antibody or the fragment thereof comprises a VH CDR3 set forth in SEQ ID NO: 3, 6, 9, 12, 15, 18, 21, 24 or 27. In some embodiments, the antibody or the fragment thereof comprises a VL CDR1 set forth in SEQ ID NO: 28, 31, 37, 40, 43, 46, 49, 52, 55, 58 or 61. In some embodiments, the antibody or the fragment thereof comprises a VL CDR2 set forth in SEQ ID NO: 19, 25, 29, 32, 35, 38, 44, 47, 50, 56, 59 or 62. In some embodiments, the antibody or the fragment thereof comprises a VL CDR3 set forth in SEQ ID NO: 30, 33, 34, 36, 39, 41, 42, 45, 48, 51, 53, 54, 57, 60 or 63. 
     In some embodiments, the antibody or the fragment thereof comprises a VH CDR1 set forth in SEQ ID NO: 10. In some embodiments, the antibody or the fragment thereof comprises a VH CDR2 set forth in SEQ ID NO: 7, 11, 13 or 26. In some embodiments, the antibody or the fragment thereof comprises a VH CDR3 set forth in SEQ ID NO: 12 or 27. In some embodiments, the antibody or the fragment thereof comprises a VL CDR1 set forth in SEQ ID NO: 37, 43 or 61. In some embodiments, the antibody or the fragment thereof comprises a VL CDR2 set forth in SEQ ID NO: 19, 25, 38, 44 or 62. In some embodiments, the antibody or the fragment thereof comprises a VL CDR3 set forth in SEQ ID NO: 34, 39, 41, 45, 53 or 63. 
     In some embodiments, the antibody or the fragment thereof comprises: a VH CDR1 set forth in SEQ ID NO: 1, 4, 10, 16, 104 or 22; a VH CDR2 set forth in SEQ ID NO: 2, 5, 7, 8, 11, 13, 14, 17, 20, 23 or 26; and a VH CDR3 set forth in SEQ ID NO: 3, 6, 9, 12, 15, 18, 21, 24 or 27. In some embodiments, the antibody or the fragment thereof comprises: a VL CDR1 set forth in SEQ ID NO: 28, 31, 37, 40, 43, 46, 49, 52, 55, 58 or 61; a VL CDR2 set forth in SEQ ID NO: 19, 25, 29, 32, 35, 38, 44, 47, 50, 56, 59 or 62; and a VL CDR3 set forth in SEQ ID NO: 30, 33, 34, 36, 39, 41, 42, 45, 48, 51, 53, 54, 57, 60 or 63. 
     In some embodiments, the antibody or the fragment thereof comprises: a VH CDR1 set forth in SEQ ID NO: 1, 4, 10, 16, 104 or 22; a VH CDR2 set forth in SEQ ID NO: 2, 5, 7, 8, 11, 13, 14, 17, 20, 23 or 26; a VH CDR3 set forth in SEQ ID NO: 3, 6, 9, 12, 15, 18, 21, 24 or 27; a VL CDR1 set forth in SEQ ID NO: 28, 31, 37, 40, 43, 46, 49, 52, 55, 58 or 61; a VL CDR2 set forth in SEQ ID NO: 19, 25, 29, 32, 35, 38, 44, 47, 50, 56, 59 or 62; and a VL CDR3 set forth in SEQ ID NO: 30, 33, 34, 36, 39, 41, 42, 45, 48, 51, 53, 54, 57, 60 or 63. 
     In some embodiments, the antibody or the fragment thereof comprises: a VH CDR1 set forth in SEQ ID NO: 10; a VH CDR2 set forth in SEQ ID NO: 7, 11, 13 or 26; a VH CDR3 set forth in SEQ ID NO: 12 or 27; a VL CDR1 set forth in SEQ ID NO: 37, 43 or 61; a VL CDR2 set forth in SEQ ID NO: 19, 25, 38, 44 or 62; and a VL CDR3 set forth in SEQ ID NO: 34, 39, 41, 45, 53 or 63. 
     In some embodiments, the antibody or the fragment thereof comprises: a VH CDR1 set forth in SEQ ID NO: 1; a VH CDR2 set forth in SEQ ID NO: 2; a VH CDR3 set forth in SEQ ID NO: 3; a VL CDR1 set forth in SEQ ID NO: 28; a VL CDR2 set forth in SEQ ID NO: 29; and a VL CDR3 set forth in SEQ ID NO: 30. 
     In some embodiments, the antibody or the fragment thereof comprises: a VH CDR1 set forth in SEQ ID NO: 4; a VH CDR2 set forth in SEQ ID NO: 5; a VH CDR3 set forth in SEQ ID NO: 6; a VL CDR1 set forth in SEQ ID NO: 31; a VL CDR2 set forth in SEQ ID NO: 32; and a VL CDR3 set forth in SEQ ID NO: 33. 
     In some embodiments, the antibody or the fragment thereof comprises: a VH CDR1 set forth in SEQ ID NO: 1; a VH CDR2 set forth in SEQ ID NO: 8; a VH CDR3 set forth in SEQ ID NO: 9; a VL CDR1 set forth in SEQ ID NO: 31; a VL CDR2 set forth in SEQ ID NO: 35; and a VL CDR3 set forth in SEQ ID NO: 36. 
     In some embodiments, the antibody or the fragment thereof comprises: a VH CDR1 set forth in SEQ ID NO: 10; a VH CDR2 set forth in SEQ ID NO: 11; a VH CDR3 set forth in SEQ ID NO: 12; a VL CDR1 set forth in SEQ ID NO: 37; a VL CDR2 set forth in SEQ ID NO: 38; and a VL CDR3 set forth in SEQ ID NO: 39. 
     In some embodiments, the antibody or the fragment thereof comprises: a VH CDR1 set forth in SEQ ID NO: 10; a VH CDR2 set forth in SEQ ID NO: 11; a VH CDR3 set forth in SEQ ID NO: 12; a VL CDR1 set forth in SEQ ID NO: 40; a VL CDR2 set forth in SEQ ID NO: 29; and a VL CDR3 set forth in SEQ ID NO: 42. 
     In some embodiments, the antibody or the fragment thereof comprises: a VH CDR1 set forth in SEQ ID NO: 10; a VH CDR2 set forth in SEQ ID NO: 11; a VH CDR3 set forth in SEQ ID NO: 12; a VL CDR1 set forth in SEQ ID NO: 43; a VL CDR2 set forth in SEQ ID NO: 44; and a VL CDR3 set forth in SEQ ID NO: 39. 
     In some embodiments, the antibody or the fragment thereof comprises: a VH CDR1 set forth in SEQ ID NO: 10; a VH CDR2 set forth in SEQ ID NO: 26; a VH CDR3 set forth in SEQ ID NO: 27; a VL CDR1 set forth in SEQ ID NO: 61; a VL CDR2 set forth in SEQ ID NO: 25; and a VL CDR3 set forth in SEQ ID NO: 34. 
     In some embodiments, the antibody or the fragment thereof comprises: a VH CDR1 set forth in SEQ ID NO: 10; a VH CDR2 set forth in SEQ ID NO: 14; a VH CDR3 set forth in SEQ ID NO: 15; a VL CDR1 set forth in SEQ ID NO: 46; a VL CDR2 set forth in SEQ ID NO: 47; and a VL CDR3 set forth in SEQ ID NO: 48. 
     In some embodiments, the antibody or the fragment thereof comprises: a VH CDR1 set forth in SEQ ID NO: 16; a VH CDR2 set forth in SEQ ID NO: 17; a VH CDR3 set forth in SEQ ID NO: 18; a VL CDR1 set forth in SEQ ID NO: 49; a VL CDR2 set forth in SEQ ID NO: 50; and a VL CDR3 set forth in SEQ ID NO: 51. 
     In some embodiments, the antibody or the fragment thereof comprises: a VH CDR1 set forth in SEQ ID NO: 16; a VH CDR2 set forth in SEQ ID NO: 17; a VH CDR3 set forth in SEQ ID NO: 18; a VL CDR1 set forth in SEQ ID NO: 52; a VL CDR2 set forth in SEQ ID NO: 29; and a VL CDR3 set forth in SEQ ID NO: 54. 
     In some embodiments, the antibody or the fragment thereof comprises: a VH CDR1 set forth in SEQ ID NO: 1; a VH CDR2 set forth in SEQ ID NO: 20; a VH CDR3 set forth in SEQ ID NO: 21; a VL CDR1 set forth in SEQ ID NO: 55; a VL CDR2 set forth in SEQ ID NO: 56; and a VL CDR3 set forth in SEQ ID NO: 57. 
     In some embodiments, the antibody or the fragment thereof comprises: a VH CDR1 set forth in SEQ ID NO: 22; a VH CDR2 set forth in SEQ ID NO: 23; a VH CDR3 set forth in SEQ ID NO: 24; a VL CDR1 set forth in SEQ ID NO: 58; a VL CDR2 set forth in SEQ ID NO: 59; and a VL CDR3 set forth in SEQ ID NO: 60. 
     In some embodiments, the antibody or the fragment thereof comprises: a VH CDR1 set forth in SEQ ID NO: 10; a VH CDR2 set forth in SEQ ID NO: 26; a VH CDR3 set forth in SEQ ID NO: 27; a VL CDR1 set forth in SEQ ID NO: 61; a VL CDR2 set forth in SEQ ID NO: 62; and a VL CDR3 set forth in SEQ ID NO: 63. 
     In some embodiments, the antibody or the fragment thereof comprises: a VH CDR1 set forth in SEQ ID NO: 10; a VH CDR2 set forth in SEQ ID NO: 11; a VH CDR3 set forth in SEQ ID NO: 27; a VL CDR1 set forth in SEQ ID NO: 61; a VL CDR2 set forth in SEQ ID NO: 62; and a VL CDR3 set forth in SEQ ID NO: 34. 
     In some embodiments, the antibody or the fragment thereof comprises: a VH CDR1 set forth in SEQ ID NO: 10; a VH CDR2 set forth in SEQ ID NO: 26; a VH CDR3 set forth in SEQ ID NO: 27; a VL CDR1 set forth in SEQ ID NO: 61; a VL CDR2 set forth in SEQ ID NO: 44; and a VL CDR3 set forth in SEQ ID NO: 39. 
     In some embodiments, the antibody or the fragment thereof comprises: a VH CDR1 set forth in SEQ ID NO: 10; a VH CDR2 set forth in SEQ ID NO: 11; a VH CDR3 set forth in SEQ ID NO: 12; a VL CDR1 set forth in SEQ ID NO: 61; a VL CDR2 set forth in SEQ ID NO: 25; and a VL CDR3 set forth in SEQ ID NO: 34. 
     In some embodiments, the antibody or the fragment thereof comprises: a VH CDR1 set forth in SEQ ID NO: 10; a VH CDR2 set forth in SEQ ID NO: 26; a VH CDR3 set forth in SEQ ID NO: 27; a VL CDR1 set forth in SEQ ID NO: 61; a VL CDR2 set forth in SEQ ID NO: 25; and a VL CDR3 set forth in SEQ ID NO: 39. 
     In some embodiments, the antibody or the fragment thereof comprises: a VH CDR1 set forth in SEQ ID NO: 10; a VH CDR2 set forth in SEQ ID NO: 26; a VH CDR3 set forth in SEQ ID NO: 27; a VL CDR1 set forth in SEQ ID NO: 61; a VL CDR2 set forth in SEQ ID NO: 44; and a VL CDR3 set forth in SEQ ID NO: 34. 
     In some embodiments, the antibody or the fragment thereof comprises: a VH CDR1 set forth in SEQ ID NO: 10; a VH CDR2 set forth in SEQ ID NO: 11; a VH CDR3 set forth in SEQ ID NO: 27; a VL CDR1 set forth in SEQ ID NO: 61; a VL CDR2 set forth in SEQ ID NO: 25; and a VL CDR3 set forth in SEQ ID NO: 39. 
     In some embodiments, the antibody or the fragment thereof comprises: a VH CDR1 set forth in SEQ ID NO: 10; a VH CDR2 set forth in SEQ ID NO: 11; a VH CDR3 set forth in SEQ ID NO: 27; a VL CDR1 set forth in SEQ ID NO: 61; a VL CDR2 set forth in SEQ ID NO: 44; and a VL CDR3 set forth in SEQ ID NO: 34. 
     In some embodiments, the antibody or the fragment thereof comprises a heavy chain variable region comprising an amino acid sequence set forth in SEQ ID NO: 64, 65, 66, 67, 68, 69, 70, 71 or 72, or an amino acid sequence having at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98% or at least 99% sequence homology to the amino acid sequence set forth in SEQ ID NO: 64, 65, 66, 67, 68, 69, 70, 71 or 72. 
     In some embodiments, the antibody or the fragment thereof comprises a heavy chain variable region comprising an amino acid sequence set forth in SEQ ID NO: 67 or 72, or an amino acid sequence having at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98% or at least 99% sequence homology to the amino acid sequence set forth in SEQ ID NO: 67 or 72. 
     In some embodiments, the antibody or the fragment thereof comprises a light chain variable region comprising an amino acid sequence set forth in SEQ ID NO: 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83 or 84, or an amino acid sequence having at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98% or at least 99% sequence homology to the amino acid sequence set forth in SEQ ID NO: 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83 or 84. 
     In some embodiments, the antibody or the fragment thereof comprises a light chain variable region comprising an amino acid sequence set forth in SEQ ID NO: 76, 78 or 84, or an amino acid sequence having at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98% or at least 99% sequence homology to the amino acid sequence set forth in SEQ ID NO: 76, 78 or 84. 
     In some embodiments, the antibody or the fragment thereof comprises a heavy chain variable region set forth in SEQ ID NO: 72 and a light chain variable region set forth in SEQ ID NO: 84. 
     In some embodiments, the antibody or the fragment thereof is of one of the isotypes IgG, IgM, IgA, IgE and IgD. 
     In some embodiments, the antibody or the fragment thereof is of the IgG isotype; in some embodiments, the antibody or the fragment thereof is of the IgG1 isotype, IgG2 isotype, IgG3 isotype or IgG4 isotype. Without limitation, the antibody or the fragment thereof is a chimeric antibody, a humanized antibody or a fully human antibody. In a certain aspect, the antibody or the fragment thereof is a humanized antibody. 
     In some embodiments, the antibody or the fragment thereof further comprises a heavy chain constant region, a light chain constant region, an Fc region, or a combination thereof. 
     In some embodiments, the antibody described herein is of the IgG isotype. In some embodiments, the constant region of the antibody is of the human IgG1 isotype, and includes a heavy chain constant region comprising an amino acid sequence set forth in SEQ ID NO: 90 and a light chain constant region comprising an amino acid sequence set forth in SEQ ID NO: 91. 
     In some embodiments, the constant region of the antibody is of the human IgG2 isotype, and includes a heavy chain constant region comprising an amino acid sequence set forth in SEQ ID NO: 92 and a light chain constant region comprising an amino acid sequence set forth in SEQ ID NO: 93. 
     In some embodiments, the constant region of the antibody is of the human IgG4 isotype, and includes a heavy chain constant region comprising an amino acid sequence set forth in SEQ ID NO: 94 and a light chain constant region comprising an amino acid sequence set forth in SEQ ID NO: 95. 
     In some embodiments, the Fc region is an Fc region of a human antibody. In some embodiments, a heavy chain of the human Fc region comprises an amino acid R at position 345 (E345R) (Eu numbering). In some embodiments, a heavy chain of the human Fc region comprises an amino acid Y at position 440 (S440Y) (Eu numbering). In some embodiments, the human Fc region comprises an amino acid sequence set forth in SEQ ID NO: 88 or SEQ ID NO: 89. 
     In some embodiments, the heavy chain constant region comprises an amino acid sequence set forth in SEQ ID NO: 88, 89 or 90, and/or the light chain constant region comprises an amino acid sequence set forth in SEQ ID NO: 91. In some embodiments, the heavy chain constant region comprises an amino acid sequence set forth in SEQ ID NO: 90, and/or the light chain constant region comprises an amino acid sequence set forth in SEQ ID NO: 91. 
     In some embodiments, the antibody or the fragment thereof is a chimeric antibody or a fragment thereof, a humanized antibody or a fragment thereof, or a fully human antibody or a fragment thereof. 
     In some embodiments, the antibody comprises a heavy chain and a light chain, wherein the heavy chain comprises an amino acid sequence set forth in SEQ ID NO: 86 or an amino acid sequence having at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98% or at least 99% sequence homology to the amino acid sequence set forth in SEQ ID NO: 86; and the light chain comprises an amino acid sequence set forth in SEQ ID NO: 87 or an amino acid sequence having at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98% or at least 99% sequence homology to the amino acid sequence set forth in SEQ ID NO: 87. 
     In some embodiments, the antibody comprises a heavy chain set forth in SEQ ID NO: 86 and a light chain set forth in SEQ ID NO: 87. 
     In some embodiments, the antibody or the fragment thereof can specifically recognize and bind to human OX40 or rhesus monkey OX40. 
     In some embodiments, the antibody or the fragment thereof activates, enhances or induces activity of OX40. 
     In some embodiments, the antibody or the fragment thereof can activate T cells. 
     In some embodiments, the antibody or the antigen-binding fragment thereof promotes further activation of activated T cells, resulting in secretion of more inflammatory factors. 
     In some embodiments, the antibody or the antigen-binding fragment thereof can activate an intracellular signaling pathway of OX40. 
     In some embodiments, the antibody or the fragment thereof has an affinity value K D  of ≤5 nM for OX40. In some embodiments, the antibody or the fragment thereof has an affinity value K D  of ≤3.5 nM for OX40. In some embodiments, the antibody or the fragment thereof has an affinity value K D  of ≤2 nM for OX40. In some embodiments, the antibody or the fragment thereof has an affinity value K D  of ≤1 nM for OX40. In some embodiments, the antibody or the fragment thereof has an affinity value K D  of ≤0.2 nM for OX40. 
     In some embodiments, the antibody or the fragment thereof is a monoclonal antibody or a fragment thereof. 
     In some embodiments, the antibody or the fragment thereof is expressed in CHO cells. 
     In some embodiments, the antibody or the fragment thereof is expressed in a CHO cell with an edited genome, wherein an antibody or a fragment thereof with a low content of fucose or without fucose is expressed in the CHO cell. In some embodiments, the CHO cell with an edited genome is a CHO cell in which one or more of the following genes are reduced or knocked out: the α-1,6-fucosyltransferase 8 gene (fut8 gene), the GDP-mannose 4,6-dehydratase (GMD) gene, the GDP-4-keto-6-deoxymannose-3,5-epimerase-4-reductase (GMER) gene and the GDP-fucose transporter (GFT) gene (e.g., Slc35c1 gene). In some embodiments, the antibody or the fragment thereof is expressed in a CHO cell in which the fut8 gene is knocked out. 
     In some embodiments, the antibody or the fragment thereof has one, two or three amino acid residues modified by fucose. 
     In some embodiments, in the antibody or the fragment thereof, the content of fucose is no more than 10%. In some embodiments, in the antibody or the fragment thereof, the content of fucose is no more than 5%. In some embodiments, in the antibody or the fragment thereof, the content of fucose is no more than 1%. In some embodiments, in the antibody or the fragment thereof, the content of fucose is no more than 0.5%. In some embodiments, the antibody or the fragment thereof does not bind to fucose. 
     In some embodiments, the antibody or the fragment thereof is an isolated antibody or an antigen-binding fragment thereof. 
     In some embodiments, the present invention also provides a polynucleotide encoding the antibody or the fragment thereof. In some embodiments, the polynucleotide is an isolated polynucleotide. 
     In some embodiments, the polynucleotide comprises one or more nucleotide sequences set forth in SEQ ID NOs: 96-101. In some embodiments, the polynucleotide comprises nucleotide sequences set forth in SEQ ID NOs: 96, 97 and 98. In some embodiments, the polynucleotide comprises nucleotide sequences set forth in SEQ ID NOs: 99, 100 and 101. In some embodiments, the polynucleotide comprises a nucleotide sequence set forth in SEQ ID NO: 102. 
     In some embodiments, the polynucleotide comprises a nucleotide sequence set forth in SEQ ID NO: 103. In some embodiments, the polynucleotide comprises a nucleotide sequence set forth in SEQ ID NO: 102 and/or a nucleotide sequence set forth in SEQ ID NO: 103. 
     In some embodiments, the present invention further provides a vector comprising one or more polynucleotides encoding the antibody or the fragment thereof. In some embodiments, the vector is an isolated vector. In some embodiments, the vector is an expression vector, including a plasmid or a virus. 
     In some embodiments, the present invention further provides a cell comprising one or more polynucleotides encoding the antibody or the fragment thereof. In some embodiments, the cell is an isolated cell. In some embodiments, the cell is a CHO cell. In some embodiments, the cell comprises the vector. In some embodiments, one or more genes of the cell are edited, so that an antibody or a fragment thereof with a low content of fucose or without fucose is expressed in the CHO cell. In some embodiments, the CHO cell with an edited genome is a CHO cell in which one or more of the following genes are reduced or knocked out: the Slc35c1 gene, the fut8 gene, the GDP-mannose 4,6-dehydratase (GMD) gene, the GDP-4-keto-6-deoxymannose-3,5-epimerase-4-reductase (GMER) gene and the GDP-fucose transporter (GFT) gene. 
     In some embodiments, the present invention further provides a composition comprising the antibody or the fragment thereof, the polynucleotide or the cell, and a pharmaceutically acceptable carrier. 
     In some embodiments, the present invention further provides a method for treating a cancer or an infection in a patient in need, which comprises administering to the patient an effective dose of the antibody or the fragment thereof. In some embodiments, the present invention further provides use of the antibody or the fragment thereof described herein in treating a cancer or an infection. In some embodiments, the present invention further provides use of the antibody or the fragment thereof described herein in preparing a medicament for treating a cancer or an infection. 
     In some embodiments, the cancer is a solid tumor. 
     In some embodiments, the cancer is selected from non-Hodgkin&#39;s lymphoma (NHL), acute lymphocytic leukemia (ALL), acute myelogenous leukemia (AML), chronic lymphocytic leukemia (CLL), chronic myelogenous leukemia (CML), multiple myeloma (MM), breast cancer, ovarian cancer, head and neck cancer, bladder cancer, melanoma, colorectal cancer, pancreatic cancer, lung cancer, leiomyoma, leiomyosarcoma, glioma, glioblastoma, etc. Solid tumors include, for example, breast cancer, ovarian cancer, lung cancer, prostate cancer, melanoma, colorectal cancer, head and neck cancer, bladder cancer, esophageal cancer, liver cancer and renal cancer. 
     In some embodiments, the method further comprises administering to the patient a second cancer therapeutic agent. 
     In some embodiments, the infection is a viral infection, a bacterial infection, a fungal infection or a parasitic infection. 
     In some embodiments, the present invention further provides a method for treating a cancer or an infection in a patient in need, which comprises: (a) treating a cell with the antibody or the fragment thereof described herein in vitro; and (b) administering to the patient the treated cell. In some embodiments, the method further comprises isolating the cell from an individual prior to step (a). In some embodiments, the cell is isolated from the patient. In some embodiments, the cell is isolated from a donor individual different from the patient. 
     In some embodiments, the cell is a T cell. In some embodiments, the T cell is a tumor infiltrating T lymphocyte, a CD4+ T cell, a CD8+ T cell, or a combination thereof. 
     In some embodiments, the present invention further provides a method for detecting OX40 expression in a sample, which comprises contacting the sample with the antibody or the fragment thereof described herein to allow the antibody or the fragment thereof to bind to OX40, and detecting the binding that reflects the OX40 expression in the sample. In some embodiments, the sample comprises a tumor cell, a tumor tissue, an infected tissue or a blood sample. 
     In some embodiments, the present invention further provides a method for treating a disease requiring an enhanced immune function in a patient in need, which comprises administering to the patient an effective dose of the antibody or the fragment thereof. 
     The present invention provides an antibody or a fragment thereof that binds to human OX40 or rhesus monkey OX40, wherein an anti-OX40 antibody or a fragment thereof of the present invention retains strong binding to human OX40 or rhesus monkey OX40. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    shows flow cytometric patterns demonstrating the binding of candidate antibodies to Jurkatx cells highly expressing OX40, where the X-axis represents the fluorescence intensity of 50 nM hOX40-FC binding. 
         FIG.  2    shows that antibody-F23-32k does not bind to Jurkat-TIM3, Jurkat-CTLA4, Jurkat-TIGIT, CHO and Raji cells. 
         FIG.  3    shows the in vitro activation activities of candidate antibodies detected by the NFκB reporter gene system. 
         FIG.  4    shows the in vitro activation activities detected by the NFκB reporter gene system, when the candidate antibodies are aggregated by protein A; and the unit of EC50 values in  FIG.  4    is μh/mL. 
         FIG.  5    shows the detected secretion level of inflammatory factor IL-2 from PBMCs activated with SEB under stimulation of the antibodies described herein. 
         FIG.  6    shows the in vitro activation activities of Fc mutants 32k-RY and 32k-R of experimental antibodies, as well as the change in activation activity in the presence of protein A or raji, as measured by the NFκB reporter gene system. 
         FIG.  7    shows the inhibitory effect of candidate antibodies on tumor (MC38) growth in vivo. 
         FIG.  8    shows the binding capacity of affinity-matured antibodies for OX40 on the cell surface, and the unit of EC50 values in  FIG.  8    is nM. 
         FIG.  9    shows the detection of candidate antibodies for ADCC effects, and the unit of EC50 values in  FIG.  9    is μg/mL. 
         FIG.  10    shows the in vitro activation activities of affinity-matured antibodies in the presence of Raji cells detected by the NFκB reporter gene system. 
         FIG.  11    shows the inhibitory effect of affinity-matured antibodies on tumor (MC38) growth in vivo. 
         FIG.  12    shows the inhibitory effect of affinity-matured antibodies on tumor (MC38) growth in vivo at day 21. 
         FIG.  13    shows the detection of antibodies for ADCC effects, wherein the abscissa represents concentration and the ordinate represents cytotoxicity. 
         FIG.  14    shows the detection of the effect of antibodies on the secretion of IL-2 from activated PBMCs. 
         FIG.  15    shows the detection of the effect of antibodies on the release of PBMC cytokines under a non-activating condition. 
     
    
    
     DETAILED DESCRIPTION 
     Definitions 
     Unless otherwise defined, scientific and technical terms used in the present invention have the meanings that are commonly understood by those skilled in the art. Generally, the nomenclature and techniques used in cell culture, molecular biology and protein purification described herein are well known and commonly used in the art. Standard techniques are used for recombinant DNA, oligonucleotide synthesis and cell culture and transformation (e.g., electroporation and lipofection). Enzymatic reactions and purification techniques are performed according to the manufacturer&#39;s instructions, or methods commonly used in the art or described herein. The aforementioned techniques and methods are generally used as described in various comprehensive and specific documents that are well known in the art and that are cited and discussed in this specification. See, e.g., Sambrook et al., Molecular Cloning: A Laboratory Manual (2 nd  edition, Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y. (1989)). 
     As used herein, the term “polypeptide” is intended to encompass both the singular form “polypeptide” and the plural form “polypeptides”, and refers to a molecule consisting of monomers (amino acids) linearly linked by amide bonds (also known as peptide bonds). The term “polypeptide” refers to any single chain or multiple chains of two or more amino acids and does not refer to a particular length of the product. Thus, included within the definition of “polypeptide” are peptides, dipeptides, tripeptides, oligopeptides, “proteins”, “amino acid chains” or any other term used to refer to chains of two or more amino acids, and the term “polypeptide” may be used in place of, or interchangeably with, any of the above terms. The wan “polypeptide” is also intended to refer to a product of post-expression polypeptide modification, including but not limited to glycosylation, acetylation, phosphorylation, amidation, derivatization by known protecting/blocking groups, proteolytic cleavage or non-naturally occurring amino acid modification. The polypeptide may be derived from a natural biological source or produced by recombinant techniques, but it is not necessarily translated from a specified nucleic acid sequence. It may be produced in any manner, including chemical synthesis, etc. 
     The “amino acid” refers to a compound containing both amino and carboxyl functional groups, such as α-amino acids. Two or more amino acids may form a polypeptide through amide bonds (also known as peptide bonds). A single amino acid is encoded by a nucleic acid consisting of three nucleotides (so-called codon or base triplet). Each amino acid is encoded by at least one codon. An amino acid may be encoded by different codons, which is known as “codon degeneracy”. Amino acids include natural amino acids and non-natural amino acids. Natural amino acids include alanine (three-letter symbol: Ala, one-letter symbol: A), arginine (Arg, R), asparagine (Asn, N), aspartic acid (Asp, D), cysteine (Cys, C), glutamine (Gln, Q), glutamic acid (Glu, E), glycine (Gly, G), histidine (His, H), isoleucine (Ile, I), leucine (Leu, L), lysine (Lys, K), methionine (Met, M), phenylalanine (Phe, F), proline (Pro, P), serine (Ser, S), threonine (Thr, T), tryptophan (Trp, W), tyrosine (Tyr, Y) and valine (Val, V). 
     The term “isolated” as used herein with respect to cells, nucleic acids, polypeptides, antibodies and the like, e.g., “isolated” DNA or RNA, refers to molecules that are separated from other components, such as natural DNA or RNA, respectively. The term “isolated” as used herein also refers to nucleic acids or polypeptides that are substantially free of cellular materials, viral materials or cell culture media when produced by recombinant DNA techniques, or of chemical precursors or other chemicals when chemically synthesized. In addition, “isolated nucleic acid” is intended to include nucleic acid fragments that do not occur in nature. The term “isolated” is also used herein to refer to cells or polypeptides that are separated from other cellular proteins or tissues. Isolated polypeptides are intended to include both purified and recombinant polypeptides. Isolated polypeptides, antibodies and the like are usually prepared by at least one purification step. In some embodiments, isolated nucleic acids, polypeptides, antibodies and the like are at least 50%, 60%, 70%, 80%, 90% or 95% pure. 
     In the present invention, the term “recombinant”, with regard to a polypeptide or polynucleotide, is intended to refer to a polypeptide or polynucleotide that does not occur in nature, and it means that a polynucleotide or polypeptide that does not normally occur can be produced by combination. 
     “Homology” or “identity” or “similarity” refers to sequence similarity between two polypeptides or between two nucleic acid molecules. Homology is determined by comparing the positions that can be aligned in the sequences. When a position of the compared sequences is occupied by the same base or amino acid, then the molecules are homologous at that position. The degree of homology between the sequences is a function of the number of matching or homologous positions shared by the sequences. 
     A polynucleotide or polynucleotide region (or a polypeptide or polypeptide region) having a certain percentage (e.g., 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 98% or 99%) “sequence identity” or “sequence homology” to another sequence means that the percentage of bases (or amino acids) are identical between the two sequences compared when the sequences are aligned. The alignment and the percentage homology or sequence identity can be determined using software programs known in the art, such as the software programs described in Ausubel et al. eds., (2007)  Current Protocols in Molecular Biology . In some embodiments, the alignment is performed using default parameters. One alignment program is BLAST using default parameters. Biologically equivalent polynucleotides are polynucleotides having the above specified percentage homology and encoding polypeptides having identical or similar biological activity. 
     The terms “polynucleotide” and “oligonucleotide” are used interchangeably and refer to a polymeric form of nucleotides of any length, whether deoxyribonucleotides or ribonucleotides or analogs thereof. The polynucleotide may have any three-dimensional structure and may perform any function, known or unknown. Examples of polynucleotides include: genes or gene fragments (such as probes, primers, EST or SAGE tags), exons, introns, messenger RNA (mRNA), transfer RNA, ribosomal RNA, ribozymes, cDNA, dsRNA, siRNA, miRNA, recombinant polynucleotides, branched polynucleotides, plasmids, vectors, isolated DNA of any sequence and isolated RNA of any sequence. Polynucleotides can include modified nucleotides, such as methylated nucleotides and nucleotide analogs. Structural modifications to the nucleotides can be made before or after assembly of the polynucleotide. The sequence of nucleotides can be interrupted by non-nucleotide components. The polynucleotide may be further modified after polymerization. This term also refers to double-stranded and single-stranded molecules. Unless otherwise stated or required, any polynucleotide disclosed herein includes a double-stranded form and each of the two complementary single-stranded forms known or predicted to constitute the double-stranded form. 
     The term “encoding” as applied to a polynucleotide refers to a polynucleotide that can “encode” a polypeptide. If in its natural state or manipulated by methods well known to those skilled in the art, the polynucleotide can be transcribed and/or translated to produce the mRNA for a polypeptide and/or a fragment thereof. An antisense strand is a complement sequence of such a nucleic acid. The encoding sequence of the antisense strand can be deduced from the nucleic acid. 
     In the present invention, “antibody” or “antigen-binding fragment” refers to a polypeptide or polypeptide complex that specifically recognizes and binds to an antigen. The antibody may be an intact antibody or any antigen-binding fragment thereof or a single chain thereof. The term “antibody” thus includes proteins or peptides comprising a portion or the whole of an immunoglobulin molecule that has biological activity for binding to an antigen. The antibody includes, but is not limited to, complementarity determining regions (CDRs), heavy chain variable regions (VHs), light chain variable regions (VLs), heavy chain constant regions (CHs), light chain constant regions (CLs), framework regions (FRs) or any portion thereof of a heavy chain or a light chain or a ligand binding portion thereof. The CDRs include CDRs of the light chain (VL CDRs) and CDRs of the heavy chain (VH CDRs). Classes of the heavy chain of the antibody include γ, μ, α, δ, ε and some subclasses (e.g., γ1-γ4). The nature of this chain determines the “type” of the antibody as IgG, IgM, IgA, IgD or IgE. Some of these can be further divided into immunoglobulin subclasses (isotypes), such as IgG1, IgG2, IgG3, IgG4 and the like. Classes of the light chain include κ and λ. Each heavy chain may be connected with a κ or λ light chain. In general, when an immunoglobulin is produced by a hybridoma, a B cell or a genetically engineered host cell, the light and heavy chains are bound by covalent bonds, and the “tail” portions of the two heavy chains are bound by covalent disulfide bonds or non-covalent bonds. In the heavy chains, the amino acid sequence extends from the N terminus at the forked end of the Y configuration to the C terminus at the bottom of each chain. The immunoglobulin κ light chain variable region is Vκ; the immunoglobulin λ light chain variable region is Vλ. The VL commonly used in the present invention is Vκ. Although some discussions are directed to the IgG class of immunoglobulin molecules, all classes of immunoglobulins are within the protection scope disclosed herein. With respect to IgG, a standard immunoglobulin molecule comprises two identical light chain polypeptides having a molecular weight of about 23,000 Daltons and two identical heavy chain polypeptides having a molecular weight of about 53,000-70,000 Daltons. Both the light and heavy chains can be divided into structurally and functionally homologous regions. The terms “constant” and “variable” are used in accordance with function. In this regard, it should be understood that the VL and VH determine the antigen recognition and specificity. Antigen-binding sites on the VL and VH can recognize antigenic determinants and specifically bind to antigens. The antigen-binding sites are defined by three CDRs in each of the VH and VL (i.e., VH CDR1, VH CDR2, VH CDR3, VL CDR1, VL CDR2 and VL CDR3). The CL and CH (CH1, CH2 or CH3) impart important biological properties such as secretion, transplacental movement, Fc receptor binding, complement binding and the like. By convention, the numbering of amino acids in the constant regions increases as they become further away from the antigen-binding site of the antibody or amino terminus. The N-terminal portion is the variable region, and the C-terminal portion is the constant region; the CH3 and CL domains actually comprise the carboxyl termini of the heavy chain and light chain, respectively. 
     In the present invention, the heavy chain constant region of the antibody may be derived from different immunoglobulin molecules. For example, the heavy chain constant region of the antibody may include a CH1 domain derived from an IgG1 molecule and a hinge region derived from an IgG3 molecule. In another embodiment, the heavy chain constant region may include a hinge region derived partially from an IgG1 molecule and partially from an IgG3 molecule. In another embodiment, a portion of the heavy chain may include a chimeric hinge region derived partially from an IgG1 molecule and partially from an IgG4 molecule. 
     In the present invention, the term “hinge region” includes a portion of the heavy chain structure connecting the CH1 domain and CH2 domain. The hinge region comprises about 25 residues and is flexible, thereby enabling independent movement of the two N-terminal antigen-binding regions. 
     As used herein, the term “disulfide bond” includes a covalent bond formed between two sulfur atoms. Cysteine comprises a thiol group which can form a disulfide bond or bridge with a second thiol group. In most naturally occurring IgG molecules, the CH1 and CL regions are linked by a disulfide bond, and the two heavy chains are linked by two disulfide bonds. 
     In the present invention, the term “fragment”, “antibody fragment” or “antigen-binding fragment” is a portion of an antibody, such as F(ab′)2, F(ab)2, Fab′, Fab, Fv, scFv, etc. Regardless of its structure, the antibody fragment binds to the same antigen recognized by an intact antibody. The term “antigen-binding fragment” includes aptamers, mirror image isomers and bivalent antibodies, and also includes any synthetic or genetically engineered protein that functions as an antibody by binding to a particular antigen to form a complex. 
     The “scFv” refers to a fusion protein of a VH and a VL of an immunoglobulin. In some aspects, these regions are linked to a short linker peptide having about 10 to about 25 amino acids. The linker may be enriched with glycine to improve flexibility, and enriched with serine or threonine to improve solubility, and may link the N terminus of VH and the C terminus of VL, or vice versa. Although the protein has the constant region removed and the linker introduced, it retains the specificity of the original immunoglobulin. 
     Antibodies, antigen-binding fragments, variants or derivatives disclosed herein include, but are not limited to, polyclonal, monoclonal, multispecific, fully human, humanized, primatized or chimeric antibodies, single-chain antibodies and epitope-binding fragments. 
     The term “epitope” as used herein includes any protein determining region that can specifically bind to an immunoglobulin or a fragment thereof or a T cell receptor. The epitope determinant generally consists of chemically active surface groups of molecules (such as amino acids or sugar side chains), and usually has specific three-dimensional structural properties and specific charge properties. When the dissociation constant is less than or equal to 1 μM (e.g., less than or equal to 100 nM, less than or equal to 10 nM, or less than or equal to 1 nM), it can be said that an antibody specifically binds to an antigen. 
     Where the terms used and/or accepted in the art have two or more definitions, the definitions of the terms used herein include all of these meanings unless explicitly indicated as opposite. 
     Unless otherwise stated, the numbering of residues in various domains of antibodies is based on the EU numbering scheme, which is also known as EU index as described in Kabat et al.,  Sequences of Proteins of Immunological Interest,  5 th  Ed., Public Health Service, National Institutes of Health, Bethesda, Md., 1991. 
     The antibodies disclosed herein may be derived from any animal, including birds and mammals Preferably, the antibodies are human, murine, donkey, rabbit, goat, guinea pig, camel, llama, horse or chicken antibodies. In another embodiment, the variable region may be derived from a chondrichthyes source (e.g., from a shark). 
     In the present invention, the term “chimeric antibody” is considered to be any antibody in which the variable region of the antibody is obtained or derived from a first species, and the constant region thereof (which may be intact, partial or modified in the present invention) is derived from a second species. In some embodiments, the variable region is derived from a non-human source (e.g., mouse or primate) and the constant region is derived from a human source. 
     “Specifically bind to” or “specific for” generally refers to that an antibody binds to an epitope through its antigen-binding domain, and that the binding requires complementarity between the antigen-binding domain and the epitope. By this definition, an antibody is said to “specifically bind to” an epitope when it binds to the epitope more readily through its antigen-binding domain than it binds to a random, irrelevant epitope. The term “specificity” is used herein to define the relative affinity of a specific antibody for binding to a specific epitope. The strength or affinity of an immunological binding interaction can be expressed as an equilibrium dissociation constant (K D ) of the interaction, where a smaller K D  indicates a stronger affinity. The immunological binding properties of the selected polypeptides may be quantified using methods well known in the art. One such method requires the measurement of the rates of antigen-binding site/antigen complex formation and dissociation, where those rates depend on the concentration of the complex partners, the affinity of the interaction and geometric parameters that affect the rates equally in both directions. Thus, both “association rate constant” (K on ) and “dissociation rate constant” (K off ) can be determined by calculating the concentration and the actual association and dissociation rates (see  Nature  361: 186-87 (1993)). The ratio K off /K on  can eliminate parameters that are independent of the affinity and is equal to the equilibrium dissociation constant K D , i.e., the affinity value (generally see Davies et al. (1990)  Annual Rev Biochem  59: 439-473). Antibodies disclosed herein can be considered to specifically bind to OX40 when the equilibrium binding constant (K D ) to OX40 is ≤1 μM. 
     In the present invention, the “content” of fucose in an antibody refers to a molar ratio of glycoform moieties comprising fucose to all glycoform moieties in the antibody. In some embodiments, the content of fucose in an antibody is not less than about 90%, about 91%, about 92%, about 93%, about 94%, about 95%, about 96%, about 97%, about 98% or about 99%. In some embodiments, the content of fucose in an antibody is about 96%. In some embodiments, the content of fucose in an antibody is no more than about 10%, about 9%, about 8%, about 7%, about 6%, about 5%, about 4%, about 3%, about 2%, about 1% or about 0.5%. In some embodiments, the content of fucose in an antibody is about 0. 
     In the present invention, the term “treatment” refers to prophylactic measures and/or therapeutic treatments, the purpose of which is to prevent, slow down and/or eliminate the progression of an undesirable physiological change or disorder (such as a cancer). Beneficial or desired clinical results include, but are not limited to, for example, the alleviation of symptoms, the reduction in the severity of a disease, the stabilization (i.e., no worsening) of a disease state, the delay or slowing of disease progression, the amelioration or alleviation of a disease state and the like. 
     “Treatment” also means an extended survival (compared to the expected survival for those without treatment). Those in need of the treatment include those with the condition or disorder, as well as those susceptible to the condition or disorder, or those in whom the condition or disorder is to be prevented. 
     “Patient” generally refers to any patient, particularly a mammalian patient, in need of diagnosis, prognosis or treatment. Mammalian patients include humans, dogs, cats, guinea pigs, rabbits, rats, mice, horses, bovines, cows, etc., particularly humans. 
     In the present invention, for example, “a patient in need of treatment” includes patients, e.g., mammalian patients, that benefit from administration of the antibodies or compositions disclosed herein for detection, diagnostic procedures, prevention and/or treatment. 
     Unless otherwise stated, the term “OX40” refers to any natural OX40 derived from any vertebrate (including mammals, such as primates (e.g., humans and rhesus monkeys), and rodents (e.g., mice and rats)). The term encompasses “full-length”, unprocessed OX40, and OX40 in any form resulting from intracellular processing. 
     “OX40 activation” refers to the activation of OX40 receptors. Generally, OX40 activation results in signal transduction. 
     “Activating T cells” means inducing, causing or stimulating effector or memory T cells to have renewed, sustained or amplified biological function. Examples of enhancing T cell functions include: increased secretion of γ-interferon (e.g., IFNg) or interleukin (e.g., IL-2) from a CD8+ effector T cell, increased secretion of γ-interferon (e.g., IFNg) or interleukin (e.g., IL-2) from a CD4+ memory and/or effector T cell, enhanced proliferation of a CD4+ effector and/or memory T cell, enhanced proliferation of a CD8+ effector T cell and enhanced antigen responsiveness (e.g., clearance) relative to such levels before the intervention. The relevant measurement methods are known to those skilled in the art. 
     The term “cytokine” is a generic term for proteins that are released by a cell population and act as intercellular mediators on another cell. Examples of such cytokines are lymphokines, monokines, interleukins (ILs) (such as IL-1, IL-1α, IL-2, IL-3, IL-4, IL-5, IL-6, IL-7, IL-8, IL-9, IL-11, IL-12, IL-15), tumor necrosis factors (such as TNF-α or TNF-β) and other polypeptide factors (including LIF and kit ligand (KL) and γ-interferon). As used herein, the term “cytokine” includes proteins from natural sources or from recombinant cell cultures and biologically active equivalents of natural sequence cytokines. The biologically active equivalents include small molecule entities produced by artificial synthesis, and pharmaceutically acceptable derivatives and salts thereof. 
     As used herein, the term “label” or “labeled” refers to incorporation of a detectable marker, e.g., by incorporation of a radiolabeled amino acid or attachment to a polypeptide of biotinyl moieties that can be detected by marked avidin (e.g., streptavidin containing a fluorescent marker or enzymatic activity that can be detected by optical or calorimetric methods). In certain instances, the label or labels may also be therapeutic. Various methods for labeling polypeptides and glycoproteins are known in the art and can be used. Examples of labels for polypeptides include, but are not limited to: radioisotopes or radionuclides (e.g.,  3 H,  14 C,  15 N,  35 S,  90 Y,  99 Tc,  111 In,  125 I, and  131 I), fluorescent labels (e.g., FITC, rhodamine and lanthanide phosphor), enzymatic labels (e.g., horseradish peroxidase, β-galactosidase, luciferase and alkaline phosphatase), chemiluminescent labels, biotinyl groups and predetermined polypeptide epitopes recognized by secondary reporter genes (e.g., leucine zipper pair sequences, secondary antibody-binding sites, metal binding domains and epitope tags). In some embodiments, the labels are connected by spacer arms of various lengths to reduce potential steric hindrance. 
     Anti-OX40 Antibody 
     Antibodies of the present invention have the ability to bind to OX40 and can activate intracellular signaling pathways of OX40, particularly in the presence of Fc receptors or cells expressing Fc receptors, thereby promoting the activation of T cells and inhibiting tumor growth or metastasis. For example, the function in activating T cells may be detected by using the NFκB reporter gene system described in the examples herein. 
     In some embodiments, the present invention provides an antibody or an antigen-binding fragment thereof that binds to human OX40 or rhesus monkey OX40. In some embodiments, the anti-OX40 antibody or the antigen-binding fragment thereof of the present invention retains strong binding to human OX40 or rhesus monkey OX40 (e.g., comparable to or stronger than known anti-OX40 antibodies, such as OX40mAb24 and 11D4). 
     In some embodiments, the antibody or the antigen-binding fragment thereof of the present invention binds to human OX40 or rhesus monkey OX40. The antibody or the antigen-binding fragment thereof of the present invention does not bind to or has lower (compared to human OX40 or rhesus monkey OX40) binding to murine OX40, such as mouse OX40. 
     In some embodiments, the anti-OX40 antibody or the antigen-binding fragment thereof of the present invention binds to human OX40 with a K D  of less than or equal to about 20 nM, about 19 nM, about 12 nM, about 6 nM, about 5 nM, about 4 nM or about 2 nM. In some embodiments, the K D  is less than or equal to about 1 nM, about 0.8 nM, about 0.6 nM, about 0.4 nM or about 0.2 nM. In some embodiments, the K D  is about 0.16 nM. In some embodiments, the antibody binding affinity is determined using biological optical interferometry (e.g., Fortebio affinity assay). 
     In some embodiments, the binding of the antibody or the antigen-binding fragment thereof of the present invention to human OX40 is determined using a flow cytometry assay. In some embodiments, the EC50 for binding to human OX40 is less than or equal to about 1.5 nM. In some embodiments, the EC50 for binding to human OX40 is less than or equal to about 1.33 nM or about 1.0 nM. 
     In some embodiments, the agonist activity of the anti-OX40 antibody is assessed by OX40 signaling, and determined mainly by Jurkat cells transfected with OX40 and NFκB reporter genes. The present invention provides an anti-OX40 antibody or an antigen-binding fragment thereof that increases the level of NFκB-mediated transcriptional activity compared to an IgG control antibody. In some embodiments, the anti-OX40 antibody or the antigen-binding fragment thereof can increase the level of NFκB-mediated transcriptional activity by about 9-fold or more in the presence of Raji cells, compared to a corresponding control IgG. In some embodiments, the anti-OX40 antibody or the fragment thereof can increase the level of NFκB-mediated transcriptional activity by about 5-fold or more compared to a corresponding control IgG. 
     In some embodiments, an Fc of the anti-OX40 antibody is mutated with RY (E345R and S440Y) and R (E345R), and its activity is determined using Jurkat cells transfected with OX40 and NFκB reporter genes. The activity of the antibody with RY mutation is 12-fold higher than that of the antibody without mutation, and the activity of the antibody with R mutation is 10-fold higher than that of the antibody without mutation. 
     In some embodiments, the agonist activity of the anti-OX40 antibody is assessed by the level of cytokines (IL-2) released from PBMC cells after activation. The anti-OX40 antibody or the fragment thereof of the present invention can increase the level of IL-2 secreted by PBMC cells by up to about 1-fold, about 2-fold, about 3-fold or more compared to a corresponding control IgG. 
     In some embodiments, the affinity of the anti-OX40 antibody or the antigen-binding fragment thereof is increased by about 5-fold, about 10-fold, about 20-fold or about 70-fold after affinity maturation. 
     In some embodiments, the anti-OX40 antibody or the antigen-binding fragment thereof of the present invention comprises a heavy chain variable region (VH), wherein the VH comprises complementarity determining regions VH CDR1, VH CDR2 and VH CDR3, wherein the VH CDR1 comprises or consists of an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% identity or 100% identity to an amino acid sequence selected from SEQ ID NOs: 1, 4, 10, 16, 104 and 22; the VH CDR2 comprises or consists of an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% identity or 100% identity to an amino acid sequence selected from SEQ ID NOs: 2, 5, 7, 8, 11, 13, 14, 17, 20, 23 and 26; and the VH CDR3 comprises or consists of an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% identity or 100% identity to an amino acid sequence selected from SEQ ID NOs: 3, 6, 9, 12, 15, 18, 21, 24 and 27. 
     In some embodiments, the anti-OX40 antibody or the antigen-binding fragment thereof of the present invention comprises a light chain variable region (VL), wherein the VL comprises complementarity determining regions (CDRs) VL CDR1, VL CDR2 and VL CDR3, wherein the VL CDR1 comprises or consists of an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% identity or 100% identity to an amino acid sequence selected from SEQ ID NOs: 28, 31, 37, 40, 43, 46, 49, 52, 55, 58 and 61; the VL CDR2 comprises or consists of an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% identity or 100% identity to an amino acid sequence selected from SEQ ID NOs: 19, 25, 29, 32, 35, 38, 44, 47, 50, 56, 59 and 62; and the VL CDR3 comprises or consists of an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% identity or 100% identity to an amino acid sequence selected from SEQ ID NOs: 30, 33, 34, 36, 39, 41, 42, 45, 48, 51, 53, 54, 57, 60 and 63. The VH CDR1, VH CDR2, VH CDR3, VL CDR1, VL CDR2 and VL CDR3 in the antibody or the antigen-binding fragment thereof of the present invention can be any exemplary combination of amino acid sequences corresponding to the CDRs in Table 1. 
     
       
         
           
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 CDR sequence corresponding to 
               
               
                 each sequence number 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 SEQ 
                   
                 SEQ 
                   
                 SEQ 
                   
               
               
                 ID 
                   
                 ID 
                   
                 ID 
                   
               
               
                 NO 
                 VH CDR1 
                 NO 
                 VH CDR2 
                 NO 
                 VH CDR3 
               
               
                   
               
               
                 1 
                 GETESSYA 
                 2 
                 ISYDG 
                 3 
                 ARELGVYS 
               
               
                   
                   
                   
                 SNK 
                   
                 GYDTPFDY 
               
               
                   
               
               
                 4 
                 GFTFDDYA 
                 3 
                 IGGSGGST 
                 6 
                 AKDRGYGD 
               
               
                   
                   
                   
                   
                   
                 YYWYFDL 
               
               
                   
               
               
                 10 
                 SYGMH 
                 7 
                 VISEDG 
                 9 
                 AKDPLGS 
               
               
                   
                   
                   
                 SNQYYAD 
                   
                 SWFEYFQH 
               
               
                   
                   
                   
                 SVKG 
                   
                   
               
               
                   
               
               
                 16 
                 GFTFSTYA 
                 8 
                 ISGSG 
                 12 
                 DNQDSSPD 
               
               
                   
                   
                   
                 GNT 
                   
                 VGIDY 
               
               
                   
               
               
                 22 
                 GFTVSSNY 
                 11 
                 VISYDG 
                 15 
                 AKDGPYFDY 
               
               
                   
                   
                   
                 SNQYYA 
                   
                   
               
               
                   
                   
                   
                 DSVKG 
                   
                   
               
               
                   
               
               
                 104 
                 GFTFSSYG 
                 13 
                 VIAEVG 
                 18 
                 AKSSSTVAT 
               
               
                   
                   
                   
                 SNQYYA 
                   
                 DFDYGMDV 
               
               
                   
                   
                   
                 DSVKG 
                   
                   
               
               
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 14 
                 ISNSGGST 
                 21 
                 ARGDSSSW 
               
               
                   
                   
                   
                   
                 FIFQD 
               
               
                   
               
               
                   
                 17 
                 ISGTGDWA 
                 24 
                 ARVVVPGYFDL 
               
               
                   
               
               
                   
                 20 
                 ISGSGGST 
                 27 
                 DNQDTSPDV 
               
               
                   
                   
                   
                   
                 GIDY 
               
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                 23 
                 IYYGGST 
                   
               
               
                   
               
               
                   
                 26 
                 VIWEDG 
                   
               
               
                   
                   
                 SNQYYA 
                   
               
               
                   
                   
                 DSVKG 
               
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 SEQ 
                   
                 SEQ 
                   
                 SEQ 
                   
               
               
                 ID 
                   
                 ID 
                   
                 ID 
                   
               
               
                 NO 
                 VL CDR1 
                 NO 
                 VL CDR2 
                 NO 
                 VL CDR3 
               
               
                   
               
               
                 28 
                 RDIRDD 
                 19 
                 AAVALQS 
                 30 
                 LQDSDYPLT 
               
               
                   
               
               
                 31 
                 SSDVGGYNY 
                 25 
                 AAVGLQS 
                 33 
                 SSYTTSSTLV 
               
               
                   
               
               
                 37 
                 QDILGY 
                 29 
                 AAS 
                 34 
                 QQYTDYPLT 
               
               
                   
               
               
                 40 
                 QSISSYLN 
                 32 
                 DVS 
                 36 
                 SSYSSSSTLVV 
               
               
                   
               
               
                 43 
                 RASQNISP 
                 35 
                 EVS 
                 39 
                 QQYNSYPLT 
               
            
           
           
               
            
               
                 ILN 
               
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 46 
                 QGIGDD 
                 38 
                 ATS 
                 41 
                 QQYDDYPLT 
               
               
                   
               
               
                 49 
                 EEIGSWLAW 
                 44 
                 AASSLQS 
                 42 
                 LQIDSYPLT 
               
               
                   
               
               
                 52 
                 EDIGRW 
                 47 
                 KAS 
                 45 
                 QQYNDYPLT 
               
               
                   
               
               
                 55 
                 SSNMGSNP 
                 50 
                 EAS 
                 48 
                 QQAHSFPPT 
               
               
                   
               
               
                 58 
                 DSLRSYYAS 
                 56 
                 NNN 
                 51 
                 QQYGSYPPT 
               
               
                   
               
               
                 61 
                 RASQNISP 
                 59 
                 NNR 
                 53 
                 QQYSDYPLT 
               
               
                   
                 FLN 
                   
                   
                   
                   
               
               
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 62 
                 AAVGSQS 
                 54 
                 QQYYNYPPT 
               
               
                   
               
               
                   
                 60 
                 HSRDSS 
                 57 
                 AAWDDGLNG 
               
               
                   
                   
                 GKYV 
                   
                 WV 
               
               
                   
               
               
                   
                 63 
                 QQYTDYPL 
               
               
                   
               
            
           
         
       
     
     In some embodiments, the anti-OX40 antibody or the fragment thereof of the present invention comprises a heavy chain variable region VH comprising or consisting of an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% identity or 100% identity to an amino acid sequence selected from SEQ ID NOs: 64-72. 
     In some embodiments, the anti-OX40 antibody or the antigen-binding fragment thereof of the present invention comprises a light chain variable region VL comprising or consisting of an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% identity or 100% identity to an amino acid sequence selected from SEQ ID NOs: 73-84. 
     In some embodiments, the heavy chain variable region VH and the light chain variable region VL in the antibody or the antigen-binding fragment thereof of the present invention are exemplary combinations in Table 3. 
     In some embodiments, the antibody or the fragment thereof further comprises a heavy chain constant region, a light chain constant region, an Fc region, or a combination thereof. 
     In some embodiments, the antibody comprises a heavy chain set forth in SEQ ID NO: 86 and a light chain set forth in SEQ ID NO: 87. 
     An antibody, an antigen-binding fragment, a variant or a derivative is disclosed herein. The variant refers to an antibody or an antigen-binding fragment thereof obtained by deletion and/or substitution of one or more amino acid residues or insertion of one or more amino acid residues in an antibody or an antigen-binding fragment thereof. The derivative includes modified derivatives, i.e., modified by covalent binding of any type of molecules to antibodies, wherein the covalent binding does not prevent antibodies from binding to epitopes. For example, but not by way of limitation, an antibody may be modified by glycosylation, acetylation, pegylation, phosphorylation, amidation, derivatization by known protecting/blocking groups, proteolytic cleavage, attachment to cellular ligands or other proteins, or the like. Any of a number of chemical modifications may be made by techniques in the prior art, including but not limited to specific chemical cleavage, acetylation, formylation, metabolic synthesis of tunicamycin, and the like. In addition, the antibody may comprise one or more unnatural amino acids. 
     In some embodiments, the antibody may be conjugated to a therapeutic agent, a prodrug, a peptide, a protein, an enzyme, a virus, a lipid, a biological response modifier, an agent, or PEG. 
     The antibody may be conjugated or fused to a therapeutic agent, which may include a detectable label (such as a radiolabel), an immunomodulator, a hormone, an enzyme, an oligonucleotide, a photoactive therapeutic or diagnostic agent, a cytotoxic agent which may be a drug or a toxin, an ultrasound enhancing agent, a nonradioactive label, a composition thereof, and other such agents known in the art. 
     The antibody may be detectably labeled by coupling to a chemiluminescent compound. The presence of the chemiluminescent-labeled antigen-binding fragment is then determined by detecting the luminescence that occurs during the chemical reaction. Examples of particularly useful chemiluminescent-labeled compounds include lumina isoluminol, aromatic acridinium esters, imidazole, acridinium salts and oxalate esters. 
     In some embodiments, the heavy chain and/or light chain of the anti-OX40 antibody or the fragment thereof of the present invention further comprise a signal peptide sequence, such as MEFGLSWVFLVAILKGVQC (SEQ ID NO: 85). 
     In some embodiments, the antibody of the present invention further encompasses a variant of the amino acid sequence of the anti-OX40 antibody, and an antibody that binds to the same epitope as any of the antibodies described above. 
     In some embodiments, the anti-OX40 antibody of the present invention further encompasses an antibody fragment thereof; in some embodiments, the antibody fragment is selected from the following fragments: Fab, Fab′-SH, Fv, scFv and (Fab′)2. 
     The anti-OX40 antibody of the present invention can be prepared by conventional recombinant DNA techniques, e.g., by using recombinant DNA techniques well known to those skilled in the art to select, construct and culture DNA encoding the antibody, and vectors and cell lines producing the antibody. These techniques are described in various laboratory manuals and main publications. In this aspect, for the techniques suitable for use in the present invention described below, reference is made to current  Protocols in Immunology , Coligan et al., Eds., Green Publishing Associates and Wiley-Interscience, John Wiley and Sons, New York (1991), which is incorporated herein by reference in its entirety, including the supplements. 
     In some embodiments, the DNA encoding the antibody can be designed and synthesized according to the antibody amino acid sequence described herein by conventional methods, inserted into an expression vector, and transfected into a host cell. The transfected host cell is then cultured in a medium to produce the monoclonal antibody. In some embodiments, the vector expressing the antibody comprises at least one promoter element, an antibody coding sequence, a transcription termination signal and a poly-A tail. Other elements include enhancers, Kozak sequences, and donor and acceptor sites inserted into two ends of the sequence for RNA splicing. Efficient transcription can be obtained by early and late promoters of SV40, long terminal repeats from retroviruses such as RSV, HTLV1 and HIVI, and early promoters of cytomegalovirus, and promoters from other cells such as actin promoter can also be used. Suitable expression vectors may include pIRES1neo, pRetro-Off, pRetro-On, PLXSN, or Plncx, pcDNA3.1 (+/−), pcDNA/Zeo (+/−), pcDNA3.1/Hygro(+/−), PSVL, PMSG, pRSVcat, pSV2dhfr, pBC12MI, pCS2, etc. Commonly used mammalian cells include 293 cells, Cos1 cells, Cos7 cells, CV1 cells, murine L cells, CHO cells and the like. 
     In some embodiments, the inserted gene fragment should comprise a screening label, common ones of which include screening genes such as dihydrofolate reductase, glutamine synthetase, neomycin resistance and hygromycin resistance, to facilitate the screening and separation of cells that have been successfully transfected. The constructed plasmid is transfected into a host cell, and the successfully transfected cells are cultured in a large quantity in a selective culture medium to produce the desired target protein. 
     In some embodiments, the present invention provides a nucleic acid encoding any of the above anti-OX40 antibodies or fragments thereof. In one embodiment, a vector comprising the nucleic acid is provided. In one embodiment, the vector is an expression vector, including plasmids, retroviruses, YAC, EBV-derived episomes and the like. In one embodiment, a host cell comprising the vector is provided. In one embodiment, the host cell is eukaryotic. In another embodiment, the host cell is selected from a yeast cell, a mammalian cell (e.g., CHO cell or 293F cell), and other cells suitable for preparing an antibody or an antigen-binding fragment thereof. 
     In some embodiments, the polynucleotide comprises one or more nucleotide sequences set forth in SEQ ID NOs: 96-101. In some embodiments, the polynucleotide comprises nucleotide sequences set forth in SEQ ID NOs: 96, 97 and 98. In some embodiments, the polynucleotide comprises nucleotide sequences set forth in SEQ ID NOs: 99, 100 and 101. In some embodiments, the polynucleotide comprises a nucleotide sequence set forth in SEQ ID NO: 102. 
     In some embodiments, the polynucleotide comprises a nucleotide sequence set forth in SEQ ID NO: 103. In some embodiments, the polynucleotide comprises a nucleotide sequence set forth in SEQ ID NO: 102 and/or a nucleotide sequence set forth in SEQ ID NO: 103. In some embodiments, a polynucleotide comprising a nucleotide sequence set forth in SEQ ID NO: 96, 97, 98, 99, 100 or 101 can encode a polypeptide comprising an amino acid sequence set forth in SEQ ID NO: 10, 26, 27, 61, 62 or 63, respectively. In some embodiments, a polynucleotide comprising a nucleotide sequence set forth in SEQ ID NO: 102 can encode a polypeptide comprising an amino acid sequence set forth in SEQ ID NO: 72; in some embodiments, a polynucleotide comprising a nucleotide sequence set forth in SEQ ID NO: 103 can encode a polypeptide comprising an amino acid sequence set forth in SEQ ID NO: 84. In some embodiments, a polynucleotide comprising a nucleotide sequence set forth in SEQ ID NO: 105 can encode a polypeptide comprising an amino acid sequence set forth in SEQ ID NO: 90; in some embodiments, a polynucleotide comprising a nucleotide sequence set forth in SEQ ID NO: 106 can encode a polypeptide comprising an amino acid sequence set forth in SEQ ID NO: 91. Nucleotide sequences are shown in Table 2 below. 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Sequence listing of each numbered nucleotide 
               
            
           
           
               
               
            
               
                 SED 
                   
               
               
                 ID 
                   
               
               
                 NO: 
                 Sequence 
               
               
                   
               
               
                 96 
                 tcctacggcatgcac 
               
               
                   
               
               
                 97 
                 gtgatctgggaggatggctccaaccagtactatgc 
               
               
                   
                 cgacagcgtgaaggga 
               
               
                   
               
               
                 98 
                 gacaaccaagacaccagccccgacgtgggcatcga 
               
               
                   
                 ttat 
               
               
                   
               
               
                 99 
                 agagccagccagaacatctccccctttctgaat 
               
               
                   
               
               
                 100 
                 gccgctgtgggactgcagagc 
               
               
                   
               
               
                 101 
                 cagcagtataccgactaccctctgacc 
               
               
                   
               
               
                 102 
                 caagtgcagctggtggagagcggaggaggagtggt 
               
               
                   
                 gcaacccggcgagtccctcagactgagctgtgccg 
               
               
                   
                 ccagcggcttcaccttcagctcctacggcatgcac 
               
               
                   
                 tgggtgagacaagcccccggcaaaggactggagtg 
               
               
                   
                 ggtggccgtgatctgggaggatggctccaaccagt 
               
               
                   
                 actatgccgacagcgtgaagggaagattcaccatc 
               
               
                   
                 tctagagacaactccaagaacacactgtatctgca 
               
               
                   
                 gatgaactctctgagggccgaggacaccgccgtgt 
               
               
                   
                 actactgcgccaaggacaaccaagacaccagcccc 
               
               
                   
                 gacgtgggcatcgattattggggccagggtaccct 
               
               
                   
                 ggttaccgttagcagc 
               
               
                   
               
               
                 103 
                 gacatccagatgacccagagccctagctctctgtc 
               
               
                   
                 cgctagcgtgggagatagagtgaccatcacatgca 
               
               
                   
                 gagccagccagaacatctccccctttctgaattgg 
               
               
                   
                 tatcagcagaagcccggcaaggcccctaagctgct 
               
               
                   
                 gatctatgccgctgtgggactgcagagcggagtgc 
               
               
                   
                 cttccagattctccggcagcggcagcggaaccgac 
               
               
                   
                 ttcacactgaccatcagctctctgcagcccgagga 
               
               
                   
                 cttcgccacctactactgccagcagtataccgact 
               
               
                   
                 accctctgaccttcggaggcggcaccaaggtggag 
               
               
                   
                 atcaag 
               
               
                   
               
               
                 105 
                 gcgagcaccaaaggcccgagcgtgtttccgctggc 
               
               
                   
                 cccgagcagcaaaagcaccagcggtggcaccgcag 
               
               
                   
                 cgctgggttgcctggtgaaagattatttcccggaa 
               
               
                   
                 ccggtgacggtgtcgtggaactcaggcgccctgac 
               
               
                   
                 cagcggcgtgcacaccttcccggctgtcctacagt 
               
               
                   
                 cctcaggactctactccctcagcagcgtggtgacc 
               
               
                   
                 gtgccctccagcagcttgggcacccagacctacat 
               
               
                   
                 ctgcaacgtgaatcacaagcccagcaacaccaagg 
               
               
                   
                 tggacaagaaagttgagcccaaatcttgtgacaaa 
               
               
                   
                 actcacacatgcccacegtgeceageacctgaact 
               
               
                   
                 cetggggggaccgtcagtcttcctcttccccccaa 
               
               
                   
                 aacccaaggacaccctcatgatctcccggacccct 
               
               
                   
                 gaggtcacatgcgtggtggtggacgtgagccacga 
               
               
                   
                 agaccctgaggtcaagttcaactggtacgtggacg 
               
               
                   
                 gcgtggaggtgcataatgccaagacaaagccgcgg 
               
               
                   
                 gaggagcagtacaacagcacgtaccgtgtggtcag 
               
               
                   
                 cgtcctcaccgtcctgcaccaggactggctgaatg 
               
               
                   
                 gcaaggagtacaagtgcaaggtctccaacaaagcc 
               
               
                   
                 ctcccagcccccatcgagaaaaccatctccaaagc 
               
               
                   
                 caaagggcagccccgagaaccacaggtgtacaccc 
               
               
                   
                 tgcccccatcecgggatgagctgaccaagaaccag 
               
               
                   
                 gtcagcetgacctgcctggtcaaaggettetatcc 
               
               
                   
                 cagcgacatcgccgtggagtgggagagcaatgggc 
               
               
                   
                 agccggagaacaactacaagaccacgcctcccgtg 
               
               
                   
                 ctggactccgacggctccttcttcctctacagcaa 
               
               
                   
                 gctcaccgtggacaagagcaggtggcagcagggga 
               
               
                   
                 acgtcttctcatgctccgtgatgcatgaggctctg 
               
               
                   
                 cacaaccactacacgcagaagagcctctccctgtc 
               
               
                   
                 tccgggtaaa 
               
               
                   
               
               
                 106 
                 cgtacggtggctgeaccatctgtcttcatcttccc 
               
               
                   
                 gccatctgatgageagttgaaatctggaactgcct 
               
               
                   
                 ctgttgtgtgcctgctgaataacttctatcccaga 
               
               
                   
                 gaggccaaagtacagtggaaggtggataacgccct 
               
               
                   
                 ccaatcgggtaactcccaggagagtgtcacagagc 
               
               
                   
                 aggacagcaaggacagcacctacagcctcagcagc 
               
               
                   
                 accctgacgctgagcaaagcagactacgagaaaca 
               
               
                   
                 caaagtctacgcctgcgaagtcacccatcagggcc 
               
               
                   
                 tgagctcgcccgtcacaaagagcttcaacagggga 
               
               
                   
                 gagtgt 
               
               
                   
               
            
           
         
       
     
     Pharmaceutical compositions of the present invention may comprise the antibody or the antigen-binding fragment thereof of the present invention. These pharmaceutical compositions may be contained in a kit, such as a diagnostic kit. 
     The present invention further provides a method for alleviating symptoms of cancer or other neoplastic diseases or infection by administering to a patient in need one or more antibodies or fragments described herein. The antibody should be administered at a dose sufficient to alleviate the symptoms of cancer or other neoplastic diseases or infection in the patient. In some embodiments, the patient is a human. In some embodiments, the antibody is chimeric, humanized or fully human. In some embodiments, the antibody or the fragment thereof can activate T cells and promote their proliferation or secretion of inflammatory factors. In some embodiments, the antibody or the fragment thereof is of an IgG isotype selected from the group consisting of IgG1 isotype, IgG2 isotype. IgG3 isotype and/or IgG4 isotype. In some embodiments, the antibody or the antigen-binding fragment thereof is of an IgG isotype selected from IgG4P and IgG4PE. In some embodiments, the antibody or the antigen-binding fragment thereof is of an IgG isotype selected from one comprising RY (E345R and S440Y) and R (E345R). 
     In some embodiments, the anti-OX40 antibody and other therapeutic agents are prepared as a single therapeutic composition, and the anti-OX40 antibody and the other therapeutic agents are administered simultaneously. Alternatively, the anti-OX40 antibody and the other therapeutic agents are independent of each other, for example, are each prepared as an independent therapeutic composition, and the anti-OX40 antibody and the other therapeutic agents are administered simultaneously, or the anti-OX40 antibody and the other therapeutic agents are administered at different time points during implementation of a therapeutic regimen. For example, the anti-OX40 antibody is administered before the other therapeutic agents, the anti-OX40 antibody is administered after the other therapeutic agents, or the anti-OX40 antibody and the other therapeutic agents are administered in an alternating scheme. In the present invention, the anti-OX40 antibody and the other therapeutic agents are administered at a single dose or at multiple doses. 
     It will be understood by those skilled in the art that the antibodies of the present invention can be widely used. For example, the antibodies of the present invention can be used as therapeutic agents, reagents in diagnostic kits or diagnostic tools, or reagents in competitive experiments to produce therapeutic agents. 
     The present invention provides antibodies and sequences thereof in Table 3. In the present invention, these antibodies are collectively referred to as anti-OX40 antibodies. 
     Some properties of the antibodies described herein include: specific binding to human OX40 and rhesus monkey OX40; ability in activating intracellular signaling pathways of OX40; ability in promoting T cell activation; and strong tumor suppressing activity. 
     The equilibrium dissociation constant (K D ) for the binding of the antibody and the fragment thereof of the present invention to the human OX40 epitope is determined using biological optical interferometry and BIACORE, and it is less than or equal to about 20 nM, about 19 nM, about 12 nM, about 6 nM, about 5 nM, about 4 nM or about 2 nM. In some embodiments, the K D  is less than or equal to about 1 nM or 0.16 nM. 
     The equilibrium binding constant (K D ) for the binding of the antibody or the fragment thereof of the present invention to the human OX40 epitope is determined using a flow cytometry assay. In some embodiments, the EC50 for binding to human OX40 is less than or equal to about 1.5 nM. In some embodiments, the EC50 for binding to human OX40 is less than or equal to about 1.33 nM or 1.0 nM. The determined K D  thereof is equal to or less than that of the known control antibody. 
     The activity of the anti-OX40 antibody of the present invention in activating OX40 is identified using the NFκB reporter gene system, and the EC50 is about 0.14 μg/mL in the presence of protein A and the EC50 is about 0.0602 μg/mL and 0.0722 μg/mL in the presence of Raji cells. Exemplary antibodies of the present invention include antibody-F10, antibody-F15-1L, antibody-A2, antibody-X35-6L, antibody-A6-1k, antibody-M5-5k, antibody-M5-7k, antibody-F23-4k, antibody-F23-7k, antibody-F23-32k, antibody-FE-16H and antibody M. Exemplary antibodies of the present invention include an antibody comprising a variable heavy chain having a sequence selected from SEQ ID NOs: 64-72 and a variable light chain (VL) having a sequence selected from SEQ ID NOs: 73-84. In particular, exemplary antibodies include those provided in Table 3. 
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Sequence listing of each numbered anti-OX40 antibody 
               
            
           
           
               
               
               
               
            
               
                 No. 
                 Name 
                 Heavy chain variable region 
                 Light chain variable region 
               
               
                   
               
            
           
           
               
               
               
               
            
               
                 1 
                 Antibody- 
                 QVQLQESGGGLEKPGRSLRLSCAAS GFT   
                 DIQMTQSPSSLSASVGDRITITCRAS RDIR   
               
               
                   
                 F10 
                   FSSYA MHWVRQAPGKGLEWVAV ISYDG   
                   DD LAWYQQKPGGAPKLLIY AAS TLQSG 
               
               
                   
                   
                   SNK YYADSVKGRFTISRDNSKNTLYLQM 
                 VPSRFSGSGSGTDFTLTISSLQPEDFATYY 
               
               
                   
                   
                 NSLRAEDTAVYYC ARELGVYSGYDTPF   
                 C LQDSDYPLT FGGGTKLEIK 
               
               
                   
                   
                   DY WGQGTLVTVSS 
                 (SEQ ID NO: 73) 
               
               
                   
                   
                 (SEQ ID NO: 64) 
                   
               
               
                   
               
               
                 2 
                 Antibody- 
                 EVQLVESGGGLVQPGRSLRLSCAAS GFT   
                 SSELTQPASVSGSPGQSITISCTGT SSDVG   
               
               
                   
                 X35-6L 
                   FDDYA MHWVRQAPGRGLEWVSG IGGS   
                   GYNY VSWYQQHPGKAPKLMIY DVS NR 
               
               
                   
                   
                   GGST YYADSVKGRFTISRDNSKNTLYLQ 
                 PSGVSNRFSGSKSGNTASLTISGLQAEDE 
               
               
                   
                   
                 MNGLGAEDTAVYYC AKDRGYGDYYW   
                 ADYY CSSYTTSSTLV FGGGTKVTVL 
               
               
                   
                   
                   YFDL WGRGTLVTVSS 
                 (SEQ ID NO: 74) 
               
               
                   
                   
                 (SEQ ID NO: 65) 
                   
               
               
                   
               
               
                 3 
                 Antibody- 
                 QVQLRESGGGLVQPGGSLRLSCAAS GFT   
                 QSALTQPASVSGSPGQSITISCTGT SSDV   
               
               
                   
                 F15-IL 
                   FSSYA MNWVRQAPGKGLEWVSA ISGSG   
                   GGYNY VSWYQKHPGKAPKLMIY EVS N 
               
               
                   
                   
                   GNT YYADSVKGRLTISRDNSKNTLYLQM 
                 RPSGVSNRFSGSKSANTASLTISGLQAED 
               
               
                   
                   
                 NSLRAEDTAVYYC AKDPLGSSWFEYFQ   
                 EADYFC SSYSSSSTLV VFGGGTKLTVL 
               
               
                   
                   
                 HWGQGTLVTVSS 
                 (SEQ ID NO: 75) 
               
               
                   
                   
                 (SEQ ID NO: 66) 
                   
               
               
                   
               
               
                 4 
                 Antibody- 
                 QVQLEESGGGVVQPGESLRLSCAASGFT 
                 DIWTQSPSSLSASVGDRVTITCRAS QDI   
               
               
                   
                 F23-4k 
                 FS SYGMH WVRQAPGKGLEWVA VISYDG   
                   LGY VNWYQQKPGKAPILLIY ATS GLQGG 
               
               
                   
                   
                   SNQYYADSVKG RFTISRDNSKNTLYLQM 
                 VPSRFSGSGSGTDFTLTISSLQPEDFATYY 
               
               
                   
                   
                 NSLRAEDTAVYYCAK DNQDSSPDVGID   
                 C QQYNSYPLT FGGGTKVDIK 
               
               
                   
                   
                   Y WGQGTLVTVSS 
                 (SEQ ID NO: 76) 
               
               
                   
                   
                 (SEQ ID NO: 67) 
                   
               
               
                   
               
               
                 5 
                 Antibody- 
                 QVQLEESGGGVVQPGESLRLSCAASGFT 
                 DIQMTQSPSSLSASVGDRVTITCRAS QSI   
               
               
                   
                 F23-7k 
                 FS SYGMH WVRQAPGKGLEWVA VISYDG   
                   SSYLN WYQQKPGKAPKLLMY AAS SLQSGV 
               
               
                   
                   
                   SNQYYADSVKG RFTISRDNSKNTLYLQM 
                 PSRFSGSGSGTDFTLTISSLQPEDFATY 
               
               
                   
                   
                 NSLRAEDTAVYYCAK DNQDSSPDVGID   
                 Y CLQIDSYPLT FGGGTKVEIK 
               
               
                   
                   
                   Y WGQGTLVTVSS 
                 (SEQ ID NO: 77) 
               
               
                   
                   
                 (SEQ ID NO: 67) 
                   
               
               
                   
               
               
                 6 
                 Antibody- 
                 QVQLEESGGGVVQPGESLRLSCAASGFT 
                 DIQMTQSPSSLSASVGDTVTI T C RASQNI   
               
               
                   
                 F23-32k 
                 FS SYGMH WVRQAPGKGLEWVA VISYDG   
                   SPFLN WYQ Q KPGKAPKLLIY AAS SLQSGV 
               
               
                   
                   
                   SNQYYADSVKG RFTISRDNSKNTLYLQM 
                 PSRFSGSGSGTDFTLTISSLQPEDFATYY 
               
               
                   
                   
                 NSLRAEDTAVYYCAK DNQDSSPDVGID   
                 C QQYNSYPLT FGGGTKVEIK 
               
               
                   
                   
                   Y WGQGTLVTVSS 
                 (SEQ ID NO: 78) 
               
               
                   
                   
                 (SEQ ID NO: 67) 
                   
               
               
                   
               
               
                 7 
                 Antibody- 
                 QVQLQRSGGGLVQPGGSLRLSCAAS GFT   
                 DIQMTQSPSTLSASVGDRVTITCRVS QGI   
               
               
                   
                 A6-lk 
                   FSSYG MTWWRQAPGKGLEWVSA ISNSG   
                   GDD LGWYQQKPGKAPKLLIY KAS NLESGV 
               
               
                   
                   
                   GST YYADSVKGRFTISRDNSKNTLYLQM 
                 PSRFSGSGSGTDFSLTISSLQPEDFATY 
               
               
                   
                   
                 NSLRAEDTAVYYC AKDGPYFDY WGQG 
                 FC QQAHSFPPT FGGGTKLEIK 
               
               
                   
                   
                 TLVTVSS 
                 (SEQ ID NO: 79) 
               
               
                   
                   
                 (SEQ ID NO: 68) 
                   
               
               
                   
               
               
                 8 
                 Antibody- 
                 QVQLVESGGGLIQPGGSLRLSCTAS GFTF   
                 ETTLTQSPSTLSASVGDRVTITCRAS EEIG   
               
               
                   
                 M5-5k 
                 STYAMSWVRQAPGKGLEWVSA ISGTGD   
                   SWLAW YQQTPGKAPKRLIY EAS SLQSGVP 
               
               
                   
                   
                   WA SYADSVKGRFTTSRDNSRNTLYLQM 
                 SRFSGSGSGTDFTLTISSLQPEDFATYY 
               
               
                   
                   
                 NNLRDEDTAIYYC AKSSSTVATDFDYGM   
                 C QQYGSYPPT FGQGTKVEIK 
               
               
                   
                   
                   DV WGQGTLVTVSS 
                 (SEQ ID NO: 80) 
               
               
                   
                   
                 (SEQ ID NO: 69) 
                   
               
               
                   
               
               
                 9 
                 Antibody- 
                 QVQLVESGGGLIQPGGSLRLSCTAS GFTF   
                 DIVMTQSPSTLSASVGDRVTVTCRAS EDI   
               
               
                   
                 M5-7k 
                   STYA MSWVRQAPGKGLEWVSA ISGTGD   
                   GRW LAWYQQKPGKAPKRLIY AAS SLQS 
               
               
                   
                   
                   WA SYADSVKGRFTTSRDNSRNTLYLQM 
                 GVPSRFSGSGSGTEFTLTISSLQPEDFATY 
               
               
                   
                   
                 NNLRDEDTAIYYC AKSSSTVATDFDYGM   
                 YC QQYYNYPPT FGQGTKVEIK 
               
               
                   
                   
                   DV WGQGTLVTVSS 
                 (SEQ ID NO: 81) 
               
               
                   
                   
                 (SEQ ID NO: 69) 
                   
               
               
                   
               
               
                 10 
                 Antibody- 
                 QVQLVESGGGLVQPGGSLRLSCAAS GFT   
                 QSVLTQPPSASGTPGQRVTISCSGS SSNM   
               
               
                   
                 FE-16H 
                   FSSYA MSWVRQAPGKGLEWVSA ISGSG   
                   GSNP VNWYQQLPGEAPQLLMY NNN QR 
               
               
                   
                   
                   GST YYADSVKGRFTISRDNSKNSLYLQM 
                 PSGVPDRFSGSKSGTSASLAISGLQSEDE 
               
               
                   
                   
                 NSLRAEDTAVYYC ARGDSSSWFIFQD W 
                 AEYYC AAWDDGLNGWV FGGGTKLTVL 
               
               
                   
                   
                 GQGTLVTVSS 
                 (SEQ ID NO: 82) 
               
               
                   
                   
                 (SEQ ID NO: 70) 
                   
               
               
                   
               
               
                 11 
                 Antibody- 
                 QVQLVESGGGLIQPGGSLRLSCAAS GFT   
                 SSELTQDPAVSVALGQTVSITCQ GDSLRS   
               
               
                   
                 A2 
                   VSSNY MSWVRQAPGEGLEWIAT IYYGG   
                   YYAS WYQQKPGQAPVPVIYGK NNR PSG 
               
               
                   
                   
                   ST YYNPSLKSRVTISADMSKNQFSLKLSS 
                 IPDRFSGSSSGNTASLTITGAQAEDEADY 
               
               
                   
                   
                 MTAADTAVYYC ARVVVPGYFDL WGRG 
                 YC HSRDSSGKYV FGVGTKLTVL 
               
               
                   
                   
                 TLVTVSS 
                 (SEQ ID NO: 83) 
               
               
                   
                   
                 (SEQ ID NO: 71) 
                   
               
               
                   
               
               
                 12 
                 Antibody 
                 QVQLVESGGGVVQPGESLRLSCAASGFT 
                 DIQMTQSPSSLSASVGDRVTITC RASQNI   
               
               
                   
                 M 
                 FS SYGMH WVRQAPGKGLEWVAVIWED 
                   SPFLN WYQQKPGKAPKLLIY AAVGLQS GV 
               
               
                   
                   
                   GSNQYYADSVKG RFTISRDNSKNTLYLQ 
                 PSRFSGSGSGTDFTLTISSLQPEDFATYY 
               
               
                   
                   
                 MNSLRAEDTAVYYCAK DNQDTSPDVGI   
                 C QQYTDYPLT FGGGTKVEIK 
               
               
                   
                   
                   DY WGQGTLVTVSS 
                 (SEQ ID NO: 84) 
               
               
                   
                   
                 (SEQ ID NO: 72) 
               
               
                   
               
            
           
         
       
     
     The present invention further comprises an antibody that binds to the same epitope as the anti-OX40 antibody described herein. For example, the antibody of the present invention specifically binds to an epitope comprising one or more amino acid residues on human OX40 (see, e.g., P43489 in Uniprot). 
     Those skilled in the art will recognize that it can be determined whether an antibody binds to the same epitope as the antibody described herein (e.g., the antibody listed in Table 3, or one antibody comprising a variable heavy chain having a sequence selected from SEQ ID NOs: 64-72 and a variable light chain having a sequence selected from SEQ ID NOs: 73-84) simply by ascertaining whether a test antibody prevents the known antibody from binding to OX40 without undue experiments. As shown by the reduction in the binding of the antibody described herein, if the test antibody competes with the antibody disclosed herein, both antibodies may bind to the same or similar epitope. 
     An alternative method for determining whether an antibody has the specificity of the antibody described herein is to pre-incubate the antibody described herein with soluble OX40 protein to which the antibody generally responses and then add the test antibody to determine whether the ability of the test antibody to bind to OX40 is suppressed. If the test antibody is suppressed, it has the same or functionally the same epitope specificity as the antibody disclosed herein. 
     In some embodiments, the antibodies of the present invention can be prepared using, for example, the methods described in the examples provided below. In some embodiments, the antibodies may also be prepared by using Trioma technology, human B-cell hybridoma technology (see Kozbor et al., 1983,  Immunol Today,  4: 72), EBV hybridoma technology (see Cole et al., 1985, In:  Monoclonal Antibodies and Cancer Therapy , Alan R. Liss, Inc., pp. 77-96), and the like. 
     Antibodies can be purified by known techniques, for example, affinity chromatography, immunoaffinity chromatography and the like using protein A or protein G. For example, purification of immunoglobulins is discussed by D. Wilkinson ( The Scientist , published by The Scientist, Inc., Philadelphia Pa., Vol. 14, No. 8 (2000), pp. 25-28). 
     Monoclonal anti-OX40 antibodies of the present invention have the ability to regulate, promote, activate and initiate intracellular signals of OX40 and/or otherwise enable them to be activated. In some embodiments, the anti-OX40 antibodies (such as fully human antibodies or humanized antibodies) can be produced by, for example, a yeast surface display method. See patents WO2009036379 and WO2010105256. In this method, a natural or recombinant OX40 or a fragment thereof is used to screen a combinatorial library of yeast carrying random pairs of light and heavy chains. 
     Fc Modification 
     Relevant effector functions of the antibodies described herein can be modified to improve, for example, the efficacy of the antibodies in treating diseases and disorders associated with OX40 signaling. For example, since tumor-infiltrating regulatory T cells (Tregs) are ubiquitously expressed, one or more mutations may be introduced into the Fc region of the antibody to improve the function of ADCC, thereby killing Tregs more effectively. For another example, complete activation of intracellular signals of OX40 requires aggregation of multiple OX40 receptors or even oligomerization thereof, and therefore one or more mutations can be introduced into the Fc region of the antibody to improve aggregation capacity of the antibody itself or improve binding capacity to Fc receptors to promote the aggregation of the antibody, thereby more completely activating intracellular signals of OX40. 
     In some embodiments, the antibody described herein is of the IgG isotype. In some embodiments, a constant region of the antibody is of a human IgG1 isotype and has amino acid sequences set forth in SEQ ID NO: 90 and SEQ ID NO: 91. In some embodiments, specific amino acids on the human IgG1 constant region are modified to modify the glycosylation of the antibody, e.g., afucosylation of N297. In some embodiments, the antibody or the antigen-binding fragment thereof comprises a small amount of fucose modification, or little fucose modification, or no fucose modification, and the ADCC effect is significantly improved. In some embodiments, the antibody or the fragment thereof has up to one (or up to two or three) amino acid residues modified by fucose. In some embodiments, the antibody or the fragment thereof comprises no more than 0.01%, 0.1%, 1%, 2%, 3%, 4% or 5% of protein molecules modified by fucose. In some embodiments, an antibody with reduced or eliminated fucose modification has stronger ADCC effect and is suitable for certain therapeutic use. In some embodiments, the antibody or the antigen-binding fragment thereof is expressed in an engineered CHO cell. In some embodiments, the engineered CHO cell is a CHO cell in which one or more of the following genes are reduced or knocked out: a Slc35c1 gene, a fut8 gene, a GDP-mannose 4,6-dehydratase (GMD) gene, a GDP-4-keto-6-deoxymannose-3,5-epimerase-4-reductase (GMER) gene and a GDP-fucose transporter (GFT) gene. In some embodiments, the engineered CHO cell is a CHO cell with the fut8 gene knocked out. 
     In some embodiments, specific amino acids on the antibody constant region are modified to change the interaction of Fc receptors, e.g., mutations of S267E/L328F. 
     In some embodiments, a constant region of the antibody is of a human IgG2 isotype and has amino acid sequences set forth in SEQ ID NOs: 92 and 93, wherein the amino acid sequence set forth in SEQ ID NO: 92 is: 
     
       
         
           
               
               
            
               
                   
                 ASTKGPSVFPLAPCSRSTSESTAALGCLVKDYFPE 
               
               
                   
                   
               
               
                   
                 PVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVT 
               
               
                   
                   
               
               
                   
                 VPSSNFGTQTYTCNVDHKPSNTKVDKTVERKCCVE 
               
               
                   
                   
               
               
                   
                 CPPCPAPPVAGPSVFLFPPKPKDTLMISRTPEVTC 
               
               
                   
                   
               
               
                   
                 VVVDVSHEDPEVQFNWYVDGVEVHNAKTKPREEQF 
               
               
                   
                   
               
               
                   
                 NSTFRVVSVLTVVHQDWLNGKEYKCKVSNKGLPAP 
               
               
                   
                   
               
               
                   
                 IEKTISKTKGQPREPQVYTLPPSREEMTKNQVSLT 
               
               
                   
                   
               
               
                   
                 CLVKGFYPSDIAVEWESNGQPENNYKTTPPMLDSD 
               
               
                   
                   
               
               
                   
                 GSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHY 
               
               
                   
                   
               
               
                   
                 TQKSLSLSPGK; 
               
            
           
         
       
     
     wherein the amino acid sequence set forth in SEQ ID NO: 93 is: 
     
       
         
           
               
               
            
               
                   
                 RTVAAPSVFIFPPSDEQLKSGTASVVCLLNNFYPR 
               
               
                   
                   
               
               
                   
                 EAKVQWKVDNALQSGNSQESVTEQDSKDSTYSLSS 
               
               
                   
                   
               
               
                   
                 TLTLSKADYEKHKVYACEVTHQGLSSPVTKSFNRG 
               
               
                   
                   
               
               
                   
                 EC. 
               
            
           
         
       
     
     In some embodiments, a constant region of the antibody is of a human IgG4 isotype and has amino acid sequences set forth in SEQ ID NOs: 94 and 95, wherein the amino acid sequence set forth in SEQ ID NO: 94 is: 
     
       
         
           
               
               
            
               
                   
                 ASTKGPSVFPLAPCSRSTSESTAALGCLVKDYFPE 
               
               
                   
                   
               
               
                   
                 PVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVT 
               
               
                   
                   
               
               
                   
                 VPSSSLGTKTYTCNVDHKPSNTKVDKRVESKYGPP 
               
               
                   
                   
               
               
                   
                 CPPCPAPEFLGGPSVFLFPPKPKDTLMISRTPEVT 
               
               
                   
                   
               
               
                   
                 CVVVDVSQEDPEVQFNWYVDGVEVHNAKTKPREEQ 
               
               
                   
                   
               
               
                   
                 FNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKGLPS 
               
               
                   
                   
               
               
                   
                 SIEKTISKAKGQPREPQVYTLPPSQEEMTKNQVSL 
               
               
                   
                   
               
               
                   
                 TCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDS 
               
               
                   
                   
               
               
                   
                 DGSFFLYSRLTVDKSRWQEGNVFSCSVMHEALHNH 
               
               
                   
                   
               
               
                   
                 YTQKSLSLSLGK; 
               
            
           
         
       
     
     wherein the amino acid sequence set forth in SEQ ID NO: 95 is: 
     
       
         
           
               
               
            
               
                   
                 RTVAAPSVFIFPPSDEQLKSGTASVVCLLNNFYPR 
               
               
                   
                   
               
               
                   
                 EAKVQWKVDNALQSGNSQESVTEQDSKDSTYSLSS 
               
               
                   
                   
               
               
                   
                 TLTLSKADYEKHKVYACEVTHQGLSSPVTKSFNRG 
               
               
                   
                   
               
               
                   
                 EC. 
               
            
           
         
       
     
     In some embodiments, the hinge region within the human IgG4 constant region is modified to avoid or reduce chain swapping. In other embodiments, amino acid 235 on the human IgG4 constant region is modified to change the interaction of Fc receptors. 
     Uses of Anti-OX40 Antibodies or Antigen-Binding Fragments Thereof 
     Diseases or disorders that can be treated by the anti-OX40 antibodies described herein include hematologic cancers and/or solid tumors. The hematologic cancers include, for example, leukemia, lymphoma and myeloma. In some embodiments, the leukemia includes acute lymphocytic leukemia (ALL), acute myelogenous leukemia (AML), chronic lymphocytic leukemia (CLL), chronic myelogenous leukemia (CML) and myeloproliferative diseases/tumors (MPDs). The lymphoma includes Hodgkin&#39;s lymphoma, indolent and aggressive non-Hodgkin&#39;s lymphoma, Burkitt&#39;s lymphoma and follicular lymphoma (both small and large cell lymphomas). The myeloma includes multiple myeloma (MM), giant cell myeloma, heavy chain myeloma and light chain or Bence-Jones myeloma. The solid tumor includes, for example, breast cancer, ovarian cancer, lung cancer, pancreatic cancer, prostate cancer, melanoma, colorectal cancer, lung cancer, head and neck cancer, bladder cancer, esophageal cancer, liver cancer and renal cancer. 
     A therapeutically effective amount of the antibody described herein relates to an amount required to achieve a therapeutic goal. The amount required for administration depends on the binding affinity of the antibody for its specific antigen, the severity of the disease, disorder or condition, the route of administration, the rate at which the antibody administered in the subject is depleted from free volume, and the like. In some embodiments, a range of the therapeutically effective dose of the antibody or the antibody fragment described herein is from about 0.01 mg/kg to about 100 mg/kg. In some embodiments, a range of the therapeutically effective dose of the antibody or the antibody fragment described herein is from about 0.1 mg/kg to about 30 mg/kg. A range of administration frequency may be, for example, once every two weeks or once every three weeks. 
     In other embodiments, antibodies for OX40 can be used in methods known in the art related to OX40 localization and/or quantification (e.g., for determining the level of OX40 and/or both OX40 and OX40L in a suitable physiological sample, for diagnostic methods, for protein imaging, etc.). 
     In some embodiments, the anti-OX40 antibody is administered to a patient diagnosed with clinical symptoms associated with one or more of the aforementioned diseases (including but not limited to cancers or other neoplastic disorders). After diagnosis, the anti-OX40 antibody is administered to reduce or reverse the effects of clinical symptoms associated with one or more of the aforementioned diseases. 
     Overexpression of OX40 is observed in certain tumor samples, and patients with cells overexpressing OX40 are likely to respond to treatment with the anti-OX40 antibody of the present invention. Thus, the antibodies of the present invention may also be used for diagnosis and prognosis. 
     In some embodiments, a sample comprising cells may be obtained from a patient, which may be a cancer patient or a patient to be diagnosed. The cells are cells of a tumor tissue or tumor mass, a blood sample, a urine sample, or any sample from the patient. After an optional pretreatment of the sample, the sample can be incubated with the antibody of the present invention under a condition allowing the antibody to interact with a OX40 protein that may be present in the sample, and the anti-OX40 antibody can be used for detecting the presence of the OX40 protein in the sample. 
     The antibody of the present invention can also be used for detecting OX40 in patient samples, and thus can be used for diagnosis. For example, the anti-OX40 antibody of the present invention is used for in vitro assays (e.g., ELISA) to detect the level of OX40 in patient samples. 
     In one embodiment, the anti-OX40 antibody of the present invention is immobilized on a solid support (e.g., wells of a microtiter plate). The immobilized antibody acts as a capture antibody to capture any OX40 that may be present in the test sample. Before the immobilized antibody is contacted with the patient sample, the solid support is washed and treated with a blocking reagent (e.g., milk protein or albumin) to avoid the nonspecific adsorption of the analyte. The wells are then treated with a test sample that may comprise antigens or a solution comprising a standard amount of antigens. Such samples are, for example, serum samples from the subject, which may have circulating antigen levels that are considered capable of diagnosing a certain lesion. After the test sample or the standard is washed away, the solid support is treated with a detectably labeled secondary antibody. The labeled secondary antibody is used as a detect antibody. The level of the detectable label is measured and the concentration of OX40 in the test sample is determined by comparing with a standard curve established for the standard sample. 
     Based on the results obtained from in vitro diagnostic assays using the anti-OX40 antibodies of the present invention, the diseases of the subjects (e.g., clinical symptoms associated with ischemia or autoimmune or inflammatory diseases) can be graded based on the expression levels of OX40 and/or OX40L. For specific diseases, blood samples are taken from subjects diagnosed to be at multiple stages of disease progression and/or at multiple points of disease treatment. A range of antigen concentrations considered to be characteristics of each stage is determined using a population of samples that provides statistically significant results for each stage of progression or therapy. 
     In some embodiments, when an anti-OX40 antibody or an antigen-binding fragment thereof described herein is used, the antibody or the fragment thereof is present in the form of a pharmaceutical composition, wherein the pharmaceutical composition can consist of the anti-OX40 antibody or the antigen-binding fragment thereof and a pharmaceutically acceptable carrier. As used herein, the term “pharmaceutically acceptable carrier” is intended to include any and all solvents, dispersion media, coatings, antibacterial and antifungal agents, isotonic and absorption delaying agents, and the like that are compatible with pharmaceutical administration. Suitable carriers are described in the latest edition of Remington&#39;s Pharmaceutical Sciences. Such carriers or diluents include, but are not limited to, water, saline, Ringer&#39;s solution, glucose solution and/or 5% human serum albumin. 
     The preparation of the pharmaceutical composition should be compatible with the intended route of administration thereof. Examples of the route of administration include parenteral administration, such as intravenous, intradermal, subcutaneous, oral (e.g., inhalational), transdermal (i.e., topical), transmucosal and rectal administration. Solutions or suspensions used for parenteral, intradermal or subcutaneous administration may include the following components: sterile diluents for injection, such as water, saline solutions, fixed oils, polyethylene glycols, glycerol, propylene glycol or other synthetic solvents; antibacterial agents, such as benzyl alcohol or methylparaben; antioxidants, such as ascorbic acid or sodium bisulfite; chelating agents, such as ethylenediamine tetraacetic acid (EDTA); buffers, such as acetates, citrates or phosphates; and agents for adjusting osmotic pressure, such as sodium chloride or dextrose. The pH can be adjusted with acids or bases, such as hydrochloric acid or sodium hydroxide. The parenteral formulation can be packaged in an ampoule, a disposable syringe or a multiple-dose vial made of glass or plastic. 
     The pharmaceutical composition suitable for injection includes a sterile aqueous solution (herein water-soluble solution) or dispersion and sterile powders for the instant preparation of a sterile injectable solution or dispersion. For intravenous administration, a suitable carrier includes normal saline, bacteriostatic water or phosphate-buffered saline (PBS). In some embodiments, the composition must be sterile and easy to be injected. The composition must be stable under the conditions of manufacture and storage and must be able to prevent the contamination of microorganisms such as bacteria and fungi. The carrier may be a solvent or dispersion medium comprising, for example, water, ethanol or polyol (e.g., glycerol, propylene glycol and liquid polyethylene glycol), and a suitable mixture thereof. In some embodiments, the pharmaceutically acceptable carrier may include an antibacterial and/or antifungal agent, e.g., p-hydroxylbenzoate, chlorobutanol, phenol, ascorbic acid and thimerosal. In some embodiments, the pharmaceutically acceptable carrier may include an isotonic agent, such as a sugar, a polyol (such as mannitol and sorbitol), and sodium chloride. 
     As desired, sterile injectable solutions can be prepared by incorporating a required amount of the antibody into a suitable solvent having combinations of one or more of the ingredients described above (as desired), and then filtered and disinfected. The aforementioned sterile solutions may also be prepared as powders by lyophilizing for the preparation of sterile injectable solutions when administration. 
     In some embodiments, the antibodies of the present invention can activate an immune response and thus be used for treating infections. 
     Infections are invasion of pathogenic factors in tissues, their reproduction, and the response of the host tissues to these factors and toxins they produce. Infections may be caused by infectious agents, such as viruses, viroids, prions, bacteria, nematodes such as parasitic ascarids and pinworms, arthropods such as ticks, mites, fleas and lice, fungi such as tinea, and other macroparasites such as cestodes and other worms. In a certain aspect, the infectious agent is a bacterium, such as a gram-negative bacterium. In a certain aspect, the infectious agent is a virus, such as a DNA virus, an RNA virus, and a retrovirus. Non-limiting examples of viruses include adenovirus, coxsackievirus, Epstein-Barr virus, hepatitis A virus, hepatitis B virus, hepatitis C virus, herpes simplex virus type 1, herpes simplex virus type 2, cytomegalovirus, human herpes virus type 8, HIV, influenza virus, measles virus, mumps virus, human papilloma virus, parainfluenza virus, poliovirus, rabies virus, respiratory syncytial virus, rubella virus and varicella-zoster virus. 
     The antibodies disclosed herein can also be used for treating infectious diseases caused by microorganisms, or for killing microorganisms by targeted binding of the microorganisms to immune cells for the purpose of eliminating the microorganisms. In a certain aspect, the microorganisms include a virus, including RNA and DNA viruses, a gram-positive bacterium, a gram-negative bacterium, a protozoan or a fungus. 
     EXAMPLES 
     Example 1: Production and Purification of OX40 Antigens and Control Antibodies 
     1.1 Preparation of human OX40 Antigens 
     The amino acid sequence of human OX40 (P43489) was obtained from the protein database Uniprot, wherein the amino acid sequence of the extracellular region of human OX40 was residues at positions 1 to 216. The amino acid sequence of human IgG1-Fc (P01857) obtained from the protein database Uniprot was residues at positions 104 to 330. Nucleotide sequences corresponding to OX40 and Fc were then obtained by artificial synthesis (General Biol) and each inserted into the pCDNA3.0 vector (purchased from Invitrogen) by digestion-ligation. Recombinant plasmids pCDNA-OX40-his and pCDNA-OX40-Fc were obtained. The above plasmids were then transiently transfected into HEK293 by PEI, the supernatant was collected after 7 days of culturing, and finally, by purification, hOX40-FC and hOX40-his protein samples were obtained for the following various examples. 
     1.2 Preparation of Positive Control Antibodies 11D4 and OX40mAb24 
     The sequences of the heavy and light chains of 11D4 were derived from U.S. Pat. No. 8,236,930. The sequences of the heavy and light chains of OX40mAb24 were derived from U.S. Pub. No. US2016/0137740. Nucleotide sequences corresponding to the above antibodies were obtained by artificial synthesis, and the nucleotides of the heavy chain and the nucleotides of the light chain were separately ligated to pCHO1.0 plasmid (purchased from Invitrogen) by digestion-ligation to obtain recombinant plasmids for expression of the full antibodies. According to the manufacturer&#39;s instructions, the recombinant plasmids above were each transfected into CHO-S cell lines using the Freedom CHO-S kit (purchased from Invitrogen), the supernatant was collected after 11 days of culturing, and finally, by purification, 11D4 and OX40mAb24 antibody protein samples were obtained for the following various examples. 
     Example 2: Preparation of Anti-OX40 Antibodies 
     According to the variable regions of each of antibodies No. 1-11 as shown in Table 3, the heavy chain constant region set forth in SEQ ID NO: 90 and the light chain constant region set forth in SEQ ID NO: 91, the corresponding nucleic acid sequences thereof were inserted into pCHO1.0 plasmid (purchased from Invitrogen) by molecular cloning technique to obtain recombinant plasmids for expressing of the full antibodies. According to the manufacturer&#39;s instructions, the recombinant plasmids above were each transfected into CHO-S cell lines using the Freedom CHO-S kit (purchased from Invitrogen), and the supernatant was collected after 11 days of culturing. Finally, the protein samples of eleven antibodies were obtained by purification, sequenced to verify the sequences and used for the following various examples. 
     The sequence of the heavy chain constant region is set forth in SEQ ID NO 90 below: 
     
       
         
           
               
               
            
               
                   
                 ASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPE 
               
               
                   
                   
               
               
                   
                 PVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVT 
               
               
                   
                   
               
               
                   
                 VPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDK 
               
               
                   
                   
               
               
                   
                 THTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTP 
               
               
                   
                   
               
               
                   
                 EVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPR 
               
               
                   
                   
               
               
                   
                 EEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKA 
               
               
                   
                   
               
               
                   
                 LPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQ 
               
               
                   
                   
               
               
                   
                 VSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPV 
               
               
                   
                   
               
               
                   
                 LDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEAL 
               
               
                   
                   
               
               
                   
                 HNHYTQKSLSLSPGK 
               
            
           
         
       
     
     The sequence of the light chain constant region is set forth in SEQ ID NO 91 below: 
     
       
         
           
               
               
            
               
                   
                 RTVAAPSVFIFPPSDEQLKSGTASVVCLLNNFYPR 
               
               
                   
                   
               
               
                   
                 EAKVQWKVDNALQSGNSQESVTEQDSKDSTYSLSS 
               
               
                   
                   
               
               
                   
                 TLTLSKADYEKHKVYACEVTHQGLSSPVTKSFNRG 
               
               
                   
                   
               
               
                   
                 EC 
               
            
           
         
       
     
     Example 3: Identification of Binding Capacity of Anti-Human OX40 Antibodies 
     3.1 Affinity of Anti-Human OX40 Antibodies as Determined by Biological Optical Interferometry 
     The ForteBio affinity assay was conducted according to the existing conventional method (Estep, P et al.,  MAbs,  2013, 5(2): 270-8). The brief process is as follows: the sensor was equilibrated offline in an assay buffer (such as PBS) for 20 min and then subjected to online test for 60 s to establish a signal baseline. The purified antibodies obtained as described above were each loaded online onto a corresponding sensor (ForteBio), and finally the ForteBio affinity assay was conducted. The biotinylated candidate antibodies were adsorbed with the SA sensor, and binding and dissociation of hOX40-FC were each detected for about 5 min. The results are shown in Table 4, and N.D indicates not detected in Table 4. Finally, kinetic analysis was performed for all by using a 1:1 binding model. The results show that the affinity of some of the antibodies described herein is superior or close to that of the control antibody. 
     
       
         
           
               
             
               
                 TABLE 4 
               
             
            
               
                   
               
               
                 Affinity (K D ) of candidate antibodies described herein for 
               
               
                 hOX40-FC as determined by biological optical interferometry 
               
            
           
           
               
               
               
            
               
                   
                   
                 Adsorption of biotinylated antibodies 
               
               
                   
                 Candidate antibodies 
                 with SA, and detection of OX40-Fc 
               
               
                   
                 Determination method 
                 (50 nM, bivalent) 
               
               
                   
                   
               
            
           
           
               
               
               
               
            
               
                   
                 OX40mAb24 
                 0.3 
                 nM 
               
            
           
           
               
               
               
            
               
                   
                 Antibody-F10 
                 N.D 
               
            
           
           
               
               
               
               
            
               
                   
                 Antibody-X35-6L 
                 &lt;0.1 
                 nM 
               
               
                   
                 Antibody-F15-1L 
                 3 
                 nM 
               
               
                   
                 Antibody-F23-4k 
                 0.6 
                 nM 
               
               
                   
                 Antibody-F23-7k 
                 2 
                 nM 
               
               
                   
                 Antibody-F23-32k 
                 0.4 
                 nM 
               
               
                   
                 Antibody-A6-1k 
                 4 
                 nM 
               
               
                   
                 Antibody-M5-5k 
                 2 
                 nM 
               
               
                   
                 Antibody-M5-7k 
                 0.4 
                 nM 
               
               
                   
                 Antibody-FE-16H 
                 3 
                 nM 
               
               
                   
                 Antibody-A2 
                 9 
                 nM 
               
               
                   
                   
               
            
           
         
       
     
     3.2 Binding Capacity of Anti-Human OX40 Antibodies for Cell Surface Antigens 
     Jurkat cells overexpressing human OX40 (Jurkat-hOX40 cells) were generated by transfecting pCMV vectors with human OX40 cDNA. Jurkat-hOX40 cells (0.5×10 6  cells) were incubated with 100 nM experimental antibody in PBS containing 0.1% BSA on ice for 40 min. The cells were then washed twice and incubated with the secondary antibody in PBS containing 0.1% BSA on ice for 25 min. The cells were washed twice and analyzed by flow cytometry on Accuri C6 system (BD Biosciences). The results are shown in  FIG.  1   . 
     Antibody-F23-4k and antibody-F23-32k, as well as two control antibodies 11D4 and OX40mAb24 at different concentrations were used to incubate Jurkat-hOX40 cells. The antibodies were each 3-fold diluted in gradient from 50 nM for a total of nine concentration points, MFI values were collected, and the data was treated with SoftMax Pro to obtain EC50 values of 1.5 nM, 1.0 nM, 1.5 nM and 5 nM, respectively. 
     PBMC cells from healthy humans (purchased from Leide Biosciences) were activated with anti-CD3/CD28 magnetic beads (purchased from Invitrogen) for 48 h, and 0.5×10 6  cells were co-incubated with 50 nM experimental antibody in PBS for 40 min. The cells were then washed twice and incubated with the anti-FC-PE secondary antibody (purchased from eBioscience) in PBS on ice for 30 min. The cells were washed twice and analyzed by flow cytometry, and MFI values were calculated. The results are shown in Table 5. 
     
       
         
           
               
             
               
                 TABLE 5 
               
             
            
               
                   
               
               
                 Binding of experimental antibodies to 
               
               
                 OX40 on activated T cells (human PBMCs) 
               
            
           
           
               
               
               
            
               
                   
                 Binding percentage % 
                 MFI (ten thousand) 
               
               
                   
                   
               
            
           
           
               
               
               
            
               
                 IgG1 
                 23 
                 0.7 
               
               
                 OX40mAb24 
                 81 
                 6.0 
               
               
                 Antibody-F23-32K 
                 79 
                 5.8 
               
               
                   
               
            
           
         
       
     
     Example 4: Specificity of Anti-Human OX40 Antibodies 
     Similar to the method in Example 3.2, 100 nM experimental antibodies were each incubated with Jurkat cells overexpressing different antigens (Jurkat-TIM3, Jurkat-CTLA4 and Jurkat-TIGIT), CHO cells and Raji cells and then detected by flow cytometry. The results are shown in  FIG.  2   . The results show that antibody-F23-32k did not bind significantly to any of these antigens or cell lines, which indicates that it has good specificity. 
     10 ng of mouse OX40-his (mOX40-his), hCD27-FC and hOX40-his were coated overnight at 4° C. by ELISA, washed, and then incubated with antibody-F23-32K and control antibody, and finally labeled for color developing with HRP-labeled secondary antibody. The OD values detected are shown in Table 6. Similar to the method in Example 3.2, the affinity of antibody-F23-32K and control antibody for rhesus monkey OX40 (Rh-OX40) was detected by Fortebio according to the protein A sensor-antibody-OX40-his (100 nM) program settings. The results are shown in Table 6. The above results show that antibody-F23-32K neither bound to hCD27 (a protein in the same family with hOX40) nor mouse OX40, but it significantly bound to rhesus monkey OX40. 
     
       
         
           
               
             
               
                 TABLE 6 
               
             
            
               
                   
               
               
                 Binding of antibody-F23-32k to hCD27, 
               
               
                 mouse OX40 and rhesus monkey OX40 
               
            
           
           
               
               
               
               
               
            
               
                   
                 Antibody-F23-32k 
                   
                 OX40mAb24 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                 ELISA (OD value) 
                   
                   
                   
                   
               
               
                 mOX40-his 
                 0.17 
                 0.20 
                 0.17 
                 0.17 
               
               
                 hCD27-FC 
                 0.15 
                 0.13 
                 0.20 
                 0.2 
               
               
                 hOX40-his 
                 3.68 
                 3.48 
                 3.10 
                 3.20 
               
               
                 Fortibio(K D ) 
               
            
           
           
               
               
               
               
               
            
               
                 Rh-OX40-his 
                 9 nM 
                   
                 3 nM 
               
               
                   
               
            
           
         
       
     
     Example 5: Biological Activity Assays of Anti-OX40 Antibodies 
     5.1 In Vitro Activation Activities of Candidate Antibodies Detected by Using the NFκB Reporter Gene System 
     pGL6-NFkB-lufiferas-reporter plasmid (purchased from Beyotime) was electrotransfected into the Jurkat-hOX40 obtained based on Example 3.2, and finally the cells were subjected to pressurized screening with antibiotics to obtain a stable monoclonal strain named Jurkat-hOX40-NFκB. The cells were thawed, passaged three times, and then plated at 20×10 4  cells/well, wherein each well had 60 μL of medium. Corresponding 1 μg/mL experimental antibody and 2.5 μg/mL anti-FC antibody (goat anti-human, purchased from invitrogen) were added, and the mixture was incubated for 5 h and then added with 50 μL of fluorescent reactant per well (ONE-Glo™ Luciferase Assay System, purchased from promega corporation). The results are shown in  FIG.  3   . The data indicates that the activation signals of the experimental antibodies are all stronger than that of the control antibody at a concentration of 1 μh/mL. 
     Jurkat-hOX40-NFκB-2 cells with a larger window value were reconstructed according to the methods described previously to validate the activation activity of the antibodies. Studies have shown that antibodies directed to activating target receptors require the involvement of Fc-R if the activation activity is to be exerted strongly. Similar to the above method, Jurkat-hOX40-NFκB-2 cells were thawed, passaged three times, and then plated at 4×10 4  cells/well, wherein each well had 60 μL of medium. Corresponding experimental antibodies and 40,000 Raji cells (which naturally have certain Fc-receptors (i.e., Fc-R) on surface) were added, and the mixture was incubated for 4.5 h and then added with 50 μL of fluorescent reactant per well. The results are shown in Table 7. The data indicates that the activation activities of the candidate antibodies can be significantly improved in the presence of Raji cells. 
     
       
         
           
               
             
               
                 TABLE 7 
               
             
            
               
                   
               
               
                 In vitro activation activities of candidate antibodies detected by 
               
               
                 using the NFκB reporter gene system in the presence of Raji cells 
               
            
           
           
               
               
               
               
               
            
               
                   
                 Antibody- 
                   
                 Antibody-F23- 
                   
               
               
                   
                 F23-32k 
                 +Raji 
                 32K + Raji 
                 OX40L 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                 Luciferase IFM 
                 3700 
                 1.6 × 10 4   
                 1.5 × 10 5   
                 5.9 × 10 4   
               
               
                   
               
            
           
         
       
     
     Similar to the above method, Jurkat-hOX40-NFκB-2 cells were thawed, passaged three times, and then plated at 4×10 4  cells/well, wherein each well had 60 μL of medium. The experimental antibody and protein A/G were incubated in a ratio of 1:1 for 2 min, and then the mixture was diluted in gradient from an initial concentration of 1.5 μg/mL. The results are shown in  FIG.  4   . The EC50 values of antibody-F23-32k and 11D4 were 0.1405 μg/mL and 0.2261 mg/mL, respectively. 
     5.2 Detection of Effect of Antibodies on Secretion of IL-2 from Activated PBMCs 
     The agonist activity of the anti-OX40 antibodies described herein was assessed by measuring inflammatory cytokines released by T cells after T cell activation. PBMCs were obtained and plated at 200,000 cells/well on a 96-well plate, wherein each well had 200 μL of medium. Then 80 μg/mL SEB was added to activate the PBMCs. After 2 days, the PBMCs were collected, washed and plated at 200,000 cells/well, wherein each well had 200 μL of medium. Then 1 μg/mL candidate or control antibody and 2 μg/mL anti-FC antibody (goat anti-human, purchased from invitrogen) were added. After 3 days, the secretion level of IL-2 in the medium was determined by ELISA kit. The results are shown in  FIG.  5   . Similar to the above procedure, 1 μg/mL candidate or control antibody was coated on the plate, incubated overnight at 4° C. and then washed three times. The activated PBMCs were plated at 200,000 cells/well, wherein each well had 200 μL of medium. After 3 days, the secretion level of IL-2 in the medium was determined by ELISA kit (purchased from Neobioscience). The results are shown in  FIG.  5   . The data indicates that antibody-F23-32k of the present invention is comparable to the positive control. 
     Example 6: Enhanced Biological Activity of Anti-OX40 Antibodies By Fc Mutation 
     Two IgG1-Fc mutant sequences (mutations RY (E345R and S440Y) and R (E345R)), which were named IgG1-FC-RY (SEQ ID NO: 88) and IgG1-FC-R (SEQ ID NO: 89), respectively, were obtained by artificial synthesis, and the sequences are shown in Table 8 (underline indicates the mutation position). Antibody-F23-32k was subjected to RY or R mutation, and the resulting antibodies were named as 32k-RY and 32k-R, respectively. Furthermore, it was confirmed by HPLC that in the free state, the antibodies were mainly present in the form of a monomer. Jurkat-hOX40-NFκB-2 and Jurkat-hOX40-NFκB cells were thawed and each used in the following experiment. Similar to the procedure in Example 5.1, the cells were passaged three times and then plated at 4×10 4  or 200,000 cells/well. The mixture was added with the corresponding antibody (1 μg/mL), antibody mutant (1 μg/mL), Raji cells (10,000 cells/well) or protein A (1 μg/mL, purchased from Sangon Biotech). The protocols and combinations of samples for addition to the 96-well plate are shown in  FIG.  6   , and the results are also shown in  FIG.  6   . The antibodies comprising the RY or R mutation also significantly activate the OX40 signals in the absence of protein A, and are about ten times stronger than wild-type antibodies. 
     
       
         
           
               
             
               
                 TABLE 8 
               
             
            
               
                   
               
               
                 Two IgG1-Fc mutant sequences 
               
            
           
           
               
               
               
               
            
               
                   
                   
                 SEQ 
                   
               
               
                   
                   
                 ID 
                   
               
               
                   
                   
                 NO 
                 Sequence 
               
               
                   
                   
               
               
                   
                   
                 88 
                 ASTKGPSVFPLAPSSKSTSG 
               
               
                   
                   
                   
                 GTAALGCLVKDYFPEPVTVS 
               
               
                   
                   
                   
                 WNSGALTSGVHTFPAVLQSS 
               
               
                   
                   
                   
                 GLYSLSSVVTVPSSSLGTQT 
               
               
                   
                   
                   
                 YICNVNHKPSNTKVDKKVEP 
               
               
                   
                   
                   
                 KSCDKTHTCPPCPAPELLGG 
               
               
                   
                   
                   
                 PSVFLFPPKPKDTLMISRTP 
               
               
                   
                   
                   
                 EVTCVVVDVSHEDPEVKFNW 
               
               
                   
                   
                   
                 YVDGVEVHNAKTKPREEQYN 
               
               
                   
                   
                   
                 STYRVVSVLTVLHQDWLNGK 
               
               
                   
                   
                   
                 EYKCKVSNKALPAPIEKTIS 
               
               
                   
                   
                   
                 KAKGQPR   R   PQVYTLPPSRDE 
               
               
                   
                   
                   
                 LTKNQVSLTCLVKGFYPSDI 
               
               
                   
                   
                   
                 AVEWESNGQPENNYKTTPPV 
               
               
                   
                   
                   
                 LDSDGSFFLYSKLTVDKSRW 
               
               
                   
                   
                   
                 QQGNVFSCSVMHEALHNHYT 
               
               
                   
                   
                   
                 QK   Y   LSLSPGK 
               
               
                   
                   
               
               
                   
                   
                 89 
                 ASTKGPSVFPLAPSSKSTSG 
               
               
                   
                   
                   
                 GTAALGCLVKDYFPEPVTVS 
               
               
                   
                   
                   
                 WNSGALTSGVHTFPAVLQSS 
               
               
                   
                   
                   
                 GLYSLSSVVTVPSSSLGTQT 
               
               
                   
                   
                   
                 YICNVNHKPSNTKVDKKVEP 
               
               
                   
                   
                   
                 KSCDKTHTCPPCPAPELLGG 
               
               
                   
                   
                   
                 PSVFLFPPKPKDTLMISRTP 
               
               
                   
                   
                   
                 EVTCVVVDVSHEDPEVKFNW 
               
               
                   
                   
                   
                 YVDGVEVHNAKTKPREEQYN 
               
               
                   
                   
                   
                 STYRVVSVLTVLHQDWLNGK 
               
               
                   
                   
                   
                 EYKCKVSNKALPAPIEKTIS 
               
               
                   
                   
                   
                 KAKGQPR   R   PQVYTLPPSRDE 
               
               
                   
                   
                   
                 LTKNQVSLTCLVKGFYPSDI 
               
               
                   
                   
                   
                 AVEWESNGQPENNYKTTPPV 
               
               
                   
                   
                   
                 LDSDGSFFLYSKLTVDKSRW 
               
               
                   
                   
                   
                 QQGNVFSCSVMHEALHNHYT 
               
               
                   
                   
                   
                 QKSLSLSPGK 
               
               
                   
                   
               
            
           
         
       
     
     Example 7: Validation of Ability of Anti-OX40 Antibodies to Inhibit Tumor Growth in Humanized Mouse MC38 Tumor Graft Models 
     The anti-tumor efficacy of the anti-OX40 antibodies of the present invention was studied in OX40 humanized mouse models (purchased from Biocytogen). MC38 tumor cells were seeded subcutaneously on the right side of B-hOX40 humanized female mice at a concentration of 5×10 5  cells/0.1 mL, and the mice were randomly grouped (6 mice per group) by tumor volume when tumors grew to about 119 mm 3 . The antibodies were administered intraperitoneally at a frequency of Q3D (once every 3 days) at 3 mg/kg for a total of 6 administrations. PBS was used as the negative control. 
     The tumor volume and body weight were measured twice a week throughout the study, and the mice were euthanized when the tumors reached an endpoint or when the mice had more than 20% of body weight loss. For each group, mean tumor volume was estimated with a digital caliper, and the tumor volume (mm 3 ) was calculated to be about 50 mm 3  by using the following formula: (width) 2 ×length/2. The results are shown in  FIG.  7   . In  FIG.  7   , TGI % is the inhibition rate for relative tumor volume, which is calculated by the formula: TGI %=(1−(mean RTV administration group)/(mean RTV control group))×100%, wherein the mean RTV administration group represents mean RTV of administration group and the mean RTV control group represents mean RTV of control group; RTVn=Vnt/Vn0, wherein the Vnt represents tumor volume at day t for a mouse numbered n, the Vn0 represents tumor volume at day 0 for a mouse numbered n, and the RTVn represents relative tumor volume at day t for a mouse numbered n. The heavy chain of antibody 4K-RY was obtained by FC mutation of antibody-F23-4k (E345R and 5440Y). 
     To further understand the effect of experimental antibodies on tumor-infiltrating T cells (TILs) after administration, four suitable mice were selected from each group at the end of the above experiment. Tumor-infiltrating T lymphocytes and T lymphocytes in the blood were obtained by conventional dissection method. The cells were further fluorescently labeled by different labels, and finally fluorescence detection was conducted by using a flow sorter. The results show that the experimental antibodies of the present invention can increase the ratio of CD4+ and CD8+ T cells in tumor, and have no effect on the ratio of CD4+ and CD8+ T cells in blood. 
     Example 8 
     1) Affinity Maturation and Affinity Determination of Candidate Antibodies 
     Table 9 shows some mutations in the CDRs of antibody-F23-32K, wherein the underlined amino acids are the mutation sites. Table 10 illustrates the CDRs of eight full antibodies containing these amino acid mutations, and the rest of the sequences are the same as those of antibody-F23-32K. Their affinity was determined by BIACORE, and the specific process was binding the antibodies to probes and then detecting the binding and dissociation of 20 nM OX40-his. The results are shown in Table 11, wherein the affinity of antibody M is increased by about 70-fold to 0.16 nM, which is about 21-fold higher than that of OX40mAb24, and about 9-fold higher than that of 11D4. Similar to the method described above, Jurkat cells overexpressing OX40 were incubated with WEST+VGTD and ST+VGTD antibodies at different concentrations, and the resulting EC50 values were 1.2 nM and 1.3 nM, respectively. The results are shown in  FIG.  8   . The sequences of the anti-OX40 antibody (antibody M) are shown in Table 12; wherein, the expression cells used for the antibodies above (including antibody M) are CHO-S cells, and the method for preparing the antibody M-KF is as follows: the antibody M was identical to the antibody M-KF in terms of amino acid sequence and was expressed by the CHO cell line in which the fut8 gene was knocked out (the content of fucose in antibody M-KF was about 0%). 
     
       
         
           
               
             
               
                 TABLE 9 
               
             
            
               
                   
               
               
                 Mutation sites of antibody-F23-32K 
               
            
           
           
               
               
               
               
               
            
               
                   
                 VH-CDR2 
                 VH-CDR3 
                 VL-CDR2 
                 VL-CDR3 
               
               
                   
               
               
                 Antibody- 
                 V ISYD GSNQ 
                 DNQD S S 
                 AA SSL QS 
                 QQY NS YPL 
               
               
                 F23-32K 
                 YYADSVKG 
                 PDVGI 
                   
                   
               
               
                   
                   
                 DY 
                   
                   
               
               
                   
               
               
                 Amino acid 
                 WED, SED, 
                 T 
                 VGL, VAL, 
                 TD, ND, 
               
               
                 mutation at 
                 AEV 
                   
                 VGS 
                 DD, SD 
               
               
                 underlined 
                   
                   
                   
                   
               
               
                 sites 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 10 
               
             
            
               
                   
               
               
                 CDR sequences of 8 mutated 
               
               
                 anti-OX40 antibodies 
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                 VH 
                 VH  
                 VH  
                 VL  
                 VL  
                 VL  
               
               
                   
                 CDR1 
                 CDR2 
                 CDR3 
                 CDR1 
                 CDR2 
                 CDR3 
               
               
                   
               
               
                 Antibody M 
                 SYGM 
                 VIWE 
                 DNQD 
                 RASQ 
                 AAVG 
                 QQYT 
               
               
                   
                 H 
                 DGSN 
                 TSPD 
                 NIS 
                 LQS 
                 DYP 
               
               
                   
                   
                 Q 
                 VGID 
                 PFLN 
                   
                 LT 
               
               
                   
                   
                 YYAD 
                 Y 
                   
                   
                   
               
               
                   
                   
                 SVKG 
                   
                   
                   
                   
               
               
                   
               
               
                 T + VGL + TD 
                 SYGM 
                 VISY 
                 DNQD 
                 RASQ 
                 AAVG 
                 QQYT 
               
               
                   
                 H 
                 DGSN 
                 TSPD 
                 NIS 
                 LQS 
                 DYP 
               
               
                   
                   
                 Q 
                 VGID 
                 PFLN 
                   
                 LT 
               
               
                   
                   
                 YYAD 
                 Y 
                   
                   
                   
               
               
                   
                   
                 SVKG 
                   
                   
                   
                   
               
               
                   
               
               
                 WEST + VL 
                 SYGM 
                 VIWE 
                 DNQD 
                 RASQ 
                 AASS 
                 QQYN 
               
               
                   
                 H 
                 DGSN 
                 TSPD 
                 NIS 
                 LQS 
                 SYP 
               
               
                   
                   
                 Q 
                 VGID 
                 PFLN 
                   
                 LT 
               
               
                   
                   
                 YYAD 
                 Y 
                   
                   
                   
               
               
                   
                   
                 SVKG 
                   
                   
                   
                   
               
               
                   
               
               
                 VH + VGTD 
                 SYGM 
                 VISY 
                 DNQD 
                 RASQ 
                 AAVG 
                 QQYT 
               
               
                   
                 H 
                 DGSN 
                 SSPD 
                 NIS 
                 LQS 
                 DYP 
               
               
                   
                   
                 Q 
                 VGID 
                 PFLN 
                   
                 LT 
               
               
                   
                   
                 YYAD 
                 Y 
                   
                   
                   
               
               
                   
                   
                 SVKG 
                   
                   
                   
                   
               
               
                   
               
               
                 WEST VG 
                 SYGM 
                 VIWE 
                 DNQD 
                 RASQ 
                 AAVG 
                 QQYN 
               
               
                   
                 H 
                 DGSN 
                 TSPD 
                 NIS 
                 LQS 
                 SYP 
               
               
                   
                   
                 Q 
                 VGID 
                 PFLN 
                   
                 LT 
               
               
                   
                   
                   
                 Y 
                   
                   
                   
               
               
                   
               
               
                 WEST + TD 
                 SYGM 
                 VIWE 
                 DNQD 
                 RASQ 
                 AASS 
                 QQYT 
               
               
                   
                 H 
                 DGSN 
                 TSPD 
                 NIS 
                 LQS 
                 DYP 
               
               
                   
                   
                 Q 
                 VGID 
                 PFLN 
                   
                 LT 
               
               
                   
                   
                 YYAD 
                   
                   
                   
                   
               
               
                   
                   
                 SVKG 
                 Y 
                   
                   
                   
               
               
                   
               
               
                 T + VG 
                 SYGM 
                 VISY 
                 DNQD 
                 RASQ 
                 AAVG 
                 QQYN 
               
               
                   
                 H 
                 DGSN 
                 TSPD 
                 NIS 
                 LQS 
                 SYP 
               
               
                   
                   
                 Q 
                 VGID 
                 PFLN 
                   
                 LT 
               
               
                   
                   
                 YYAD 
                 Y 
                   
                   
                   
               
               
                   
                   
                 SVKG 
                   
                   
                   
                   
               
               
                   
               
               
                 T + TD 
                 SYGM 
                 VISY 
                 DNQD 
                 RASQ 
                 AASS 
                 QQYT 
               
               
                   
                 H 
                 DGSN 
                 TSPD 
                 NIS 
                 LQS 
                 DYP 
               
               
                   
                   
                 Q 
                 VGID 
                 PFLN 
                   
                 LT 
               
               
                   
                   
                 YYAD 
                 Y 
                   
                   
                   
               
               
                   
                   
                 SVKG 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 11 
               
             
            
               
                   
               
               
                 Affinity of the 8 mutated anti-OX40 antibodies 
               
            
           
           
               
               
               
               
               
            
               
                   
                 Antibody 
                 K D  (M) 
                 K a  (1/Ms) 
                 K d  (1/s) 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 11D4 
                 1.31 × 10 −09   
                 353000 
                 0.000461 
               
               
                   
                 OX40mAb24 
                 3.45 × 10 −09   
                 408100 
                 0.001410 
               
               
                   
                 Antibody-F23-32K 
                 1.15 × 10 −08   
                 841000 
                 0.00965 
               
               
                   
                 Antibody M 
                  1.6 × 10 −10   
                 610000 
                 0.0000977 
               
               
                   
                 T + VGL + TD 
                 2.66 × 10 −10   
                 448000 
                 0.000119 
               
               
                   
                 WEST + VL 
                 1.93 × 10 −09   
                 371000 
                 0.000714 
               
               
                   
                 VH + VGTD 
                 5.65 × 10 −10   
                 431000 
                 0.000243 
               
               
                   
                 WEST + VG 
                  7.7 × 10 −10   
                 452000 
                 0.000348 
               
               
                   
                 WEST + TD 
                 6.53 × 10 −10   
                 491000 
                 0.000321 
               
               
                   
                 T + VG 
                 4.54 × 10 −09   
                 292000 
                 0.00133 
               
               
                   
                 T + TD 
                 5.01 × 10 −09   
                 278000 
                 0.00139 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 12 
               
             
            
               
                   
               
               
                 Sequences of the anti-OX40 
               
               
                 antibody (antibody M) 
               
            
           
           
               
               
               
               
            
               
                   
                 SEQ 
                   
                   
               
               
                   
                 ID 
                   
                   
               
               
                   
                 NO 
                 Name 
                 Sequence 
               
               
                   
                   
               
               
                   
                 86 
                 Heavy 
                 QVQLVESGGGVVQPGESLRL 
               
               
                   
                   
                 chain 
                 SCAASGFTFSSYGMHWVRQA 
               
               
                   
                   
                 of 
                 PGKGLEWVAVIWEDGSNQYY 
               
               
                   
                   
                 antibody 
                 ADSVKGRFTISRDNSKNTLY 
               
               
                   
                   
                 M 
                 LQMNSLRAEDTAVYYCAKDN 
               
               
                   
                   
                   
                 QDTSPDVGIDYWGQGTLVTV 
               
               
                   
                   
                   
                 SSASTKGPSVFPLAPSSKST 
               
               
                   
                   
                   
                 SGGTAALGCLVKDYFPEPVT 
               
               
                   
                   
                   
                 VSWNSGALTSGVHTFPAVLQ 
               
               
                   
                   
                   
                 SSGLYSLSSVVTVPSSSLGT 
               
               
                   
                   
                   
                 QTYICNVNHKPSNTKVDKKV 
               
               
                   
                   
                   
                 EPKSCDKTHTCPPCPAPELL 
               
               
                   
                   
                   
                 GGPSVFLFPPKPKDTLMISR 
               
               
                   
                   
                   
                 TPEVTCVVVDVSHEDPEVKF 
               
               
                   
                   
                   
                 NWYVDGVEVHNAKTKPREEQ 
               
               
                   
                   
                   
                 YNSTYRVVSVLIVLHQDWLN 
               
               
                   
                   
                   
                 GKEYKCKVSNKALPAPIEKT 
               
               
                   
                   
                   
                 ISKAKGQPREPQVYTLPPSR 
               
               
                   
                   
                   
                 DELTKNQVSLTCLVKGFYPS 
               
               
                   
                   
                   
                 DIAVEWESNGQPENNYKTTP 
               
               
                   
                   
                   
                 PVLDSDGSFFLYSKLTVDKS 
               
               
                   
                   
                   
                 RWQQGNVFSCSVMHEALHNH 
               
               
                   
                   
                   
                 YTQKSLSLSPGK 
               
               
                   
                   
               
               
                   
                 87 
                 Light 
                 DIQMTQSPSSLSASVGDRVT 
               
               
                   
                   
                 chain 
                 ITCRASQNISPFLNWYQQKP 
               
               
                   
                   
                 of 
                 GKAPKLLIYAAVGLQSGVPS 
               
               
                   
                   
                 antibody 
                 RFSGSGSGTDFTLTISSLQP 
               
               
                   
                   
                 M 
                 EDFATYYCQQYTDYPLTFGG 
               
               
                   
                   
                   
                 GTKVEIKRTVAAPSVFIFPP 
               
               
                   
                   
                   
                 SDEQLKSGTASVVCLLNNFY 
               
               
                   
                   
                   
                 PREAKVQWKVDNALQSGNSQ 
               
               
                   
                   
                   
                 ESVTEQDSKDSTYSLSSTLT 
               
               
                   
                   
                   
                 LSKADYEKHKVYACEVTHQG 
               
               
                   
                   
                   
                 LSSPVTKSFNRGEC 
               
               
                   
                   
               
            
           
         
       
     
     2) Detection of Antigen-Binding Specificity of Antibodies 
     The binding capacities of the antibody M-KF for human and cynomolgus monkey OX40 were determined by ELISA. The test method is as follows: human or cynomolgus monkey OX40 was coated on a plate and incubated overnight at 4° C. at a concentration of 2 μg/mL, and then incubated with antibody M-KF at different concentrations for detection. The antibody M-KF was 2-fold diluted in gradient from an initial concentration of 1 μg/mL or 2 μg/mL. 
     The results show that the antibody M-KF can bind to human and cynomolgus monkey OX40 with EC50 values of about 0.0340 ng/mL and 0.0352 ng/mL, respectively. 
     Example 9: ADCC Effect and In Vitro Activation Activity of Antibodies 
     The content of fucose in the antibody M was about 96%. The content of fucose in the antibody M-KF was about 0%. FC-RIIIA and NF-AT reporter genes were transferred into the Jurkat cells to obtain the Jurkat-ADCC cells. Jurkat-hOX40 cells and Jurkat-ADCC cells were mixed well at a ratio of 1:1, and the mixture was added with the antibody M and the antibody M-KF at corresponding concentration gradients. The results are shown in  FIG.  9   . Similar to the method described above (Example 5), the in vitro activation activities of candidate antibodies were detected by using the NFκB reporter gene system. Jurkat-hOX40-NFκB-2 cells were thawed, passaged three times, and then plated at 4×10 4  cells/well, wherein each well had 60 μL of medium, and the mixture was added with corresponding experimental antibodies and 40,000 Raji cells. The results are shown in  FIG.  10   . The EC50 values of the antibody M and the antibody M-KF were slightly better than that of 11D4, but the activation peaks of the two antibodies were about 2.5-fold greater than that of 11D4. 
     Example 10: In Vitro Efficacy Experiment of Antibodies 
     As describe above, the anti-tumor efficacy of the anti-OX40 antibodies of the present invention was studied in OX40 humanized mouse models (purchased from Biocytogen). MC38 tumor cells were seeded subcutaneously on the right side of B-hOX40 humanized female mice at a concentration of 5×10 5  cells/0.1 mL, and the mice were randomly grouped (6 mice per group) by tumor volume when tumors grew to about 119 mm 3 . A batch of endotoxin-free antibodies, antibody M and antibody M-KF, were obtained by expression and purification, and the antibodies were administrated intraperitoneally at a frequency of Q3D and at three doses of 1 mg/kg, 0.2 mg/kg and 0.04 mg/kg, for a total of 6 administrations. 
     The tumor volume and body weight were measured twice a week throughout the study, and the mice were euthanized when the tumors reached an endpoint or when the mice had more than 20% of body weight loss. For each group, mean tumor volume was estimated with a digital caliper, and the tumor volume (mm 3 ) was calculated to be about 50 mm 3  by using the following formula: (width) 2 ×length/2. The results are shown in  FIG.  11   , and the results at day 21 are shown in  FIG.  12   . The high-dose group of the antibody M and the antibody M-KF can significantly inhibit tumor growth (P&lt;0.05), and the effect is significantly better than that of the high-dose group of 11D4. The medium-dose group of the antibody M-KF can also significantly inhibit tumor growth (P&lt;0.05). 
     Example 11: ADCC Effect of Antibodies (PBMC Method) 
     Jurkat-hOX40 cells were used as target cells, and PBMCs derived from healthy humans were used as effector cells. PBMCs and Jurkat-OX40 cells were mixed in a quantity ratio of 25:1, and the mixture was added with the antibody M-KF or the antibody M (4-fold diluted in gradient from an initial concentration of 1 μg/mL), and incubated at 37° C. for 4 h. Then the corresponding signals were determined by using a kit CytoTox 96® Non-Radioactive Cytotoxicity Assay (Promega), and the ADCC-mediated killing effect on living cells of the antibody was determined by this system. 
     The results are shown in  FIG.  13    and indicate that the antibody M-KF has significant ADCC effect with an EC50 of about 1.891 ng/mL, which is more than 2-fold stronger than that of the antibody M. 
     Example 12: Detection of Effect of Antibodies on Secretion of IL-2 from Activated PBMCs 
     The activation effect of the antibody M-KF on human peripheral blood mononuclear cells (PBMCs) under exogenous stimulation was detected by detecting the release of IL-2 cytokines using ELISA. PBMCs were stimulated by SEB ( Staphylococcus aureus  enterotoxin B) for 24 h, and the mixture was added with the antibody M-KF or the reference antibody 11D4 at different concentrations, and then incubated for 3 days. Finally, IL-2 secreted by PBMCs was detected by a human IL-2 ELISA development kit (HRP) (Mabtech, Cat. No. 3445-1H-20). 
     The results are shown in  FIG.  14    and indicate that the amount of IL-2 secreted by PBMCs under the stimulation of the antibody M-KF at a concentration of 0.32 μg/mL or higher is about 4 times more than that of the negative control IgG1. 
     Example 13: Detection of Effect of Antibodies on Release of PBMC Cytokines Under a Non-Activating Condition 
     The activation effect of the antibody M-KF on human PBMCs without exogenous stimulation was detected by detecting the release of IL-2, INF-γ, IL-6 and TNF-α cytokines using ELISA, thereby examining the safety of the antibody. The final purpose of the action mechanism of the antibody M-KF is to activate T cells and thereby stimulate the immune system and enhance the immune function. For safety, this type of antibodies may cause over-activation of the immune system in body, thereby causing a cytokine storm. Since IL-2, INF-γ, IL-6 and TNF-α are all common factors produced in large quantities when a cytokine storm occurs, these factors are selected for detection. 
     Human PBMCs without activation treatment were incubated with the antibody M-KF or CD28 antibody at different concentrations, and the antibody was 3-fold diluted in gradient from an initial concentration of 200 μg/mL. Finally, IL-2, INF-γ, IL-6 and TNF-α secreted by PBMCs were each detected by using a corresponding cytokine detection kit (Mabtech company). 
     As shown in  FIG.  15   , compared to the positive control anti-CD28 antibody, the antibody M-KF cannot enable PBMCs without exogenous stimulation to produce IL-2, INF-γ, IL-6 and TNF-α at a concentration of 200 μg/mL or lower, indicating the antibody M-KF is safe to some extent. 
     All publications and patent documents cited herein are incorporated herein by reference, as if each of the publication and the documents are specifically and individually indicated to be incorporated herein by reference. Citation of publications and patent documents described above is not intended as an admission that any is pertinent prior art, nor does it constitutes any admission as to the contents or date of the same. Now, the present invention has been described in the written description, and it should be understood by those skilled in the art that the present invention may be practiced in various embodiments. The description and embodiments above are intended to be illustrative rather than limiting the claims of the present invention.