Abstract:
This invention provides antibodies or functional fragments thereof that bind to PD-1 with high affinity. The invention provides nucleic acid molecules encoding the antibodies or the fragments thereof according to the present invention, expression vectors and host cells for expressing the antibodies or the functional fragments thereof according to the present invention, as well as methods for producing the antibodies or the functional fragments thereof according to the present invention. The present invention also provides immunoconjugates and pharmaceutical compositions comprising the antibodies or the functional fragments thereof according to the present invention. The present invention additionally provides methods for treating a plurality of diseases (comprising cancers, infectious diseases and inflammatory diseases) by using the antibodies or the functional fragments thereof disclosed herein.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Technical Field 
         [0002]    The present invention belongs to the field of biomedicine and relates to antibodies or functional fragments thereof that bind specifically to PD-1 with high affinity. The invention provides nucleic acid molecules encoding the antibodies or the fragments thereof according to the present invention, expression vectors and host cells for expressing the antibodies or the functional fragments thereof according to the present invention, as well as methods for producing the antibodies or the functional fragments thereof according to the present invention. The present invention also provides immunoconjugates and pharmaceutical compositions comprising the antibodies or the functional fragments thereof according to the present invention. The present invention additionally provides methods for treating a plurality of diseases (comprising cancers, infectious diseases and inflammatory diseases) by using the antibodies or the functional fragments thereof disclosed herein. 
         [0003]    2. Description of Related Art 
         [0004]    The programmed cell death 1 protein, PD-1, is a member of CD28 family and an immunosuppressive receptor expressed on the surfaces of the activated T cells and B cells (Yao, Zhu et al., Advances in targeting cell surface signaling molecules for immune modulation.  Nat Rev Drug Discov,  2013, 12(2): 130-146). This receptor can bind to its ligands PD-L1 and PD-L2 to effectively reduce the immune response involving T cells. Tumor cells can escape the immune surveillance inside the body via high expression of PD-L1 (Okazaki and Honjo, PD-1 and PD-1 ligands: from discovery to clinical application.  International Immunology,  2007, 19(7): 813-824 2007). The interaction between PD1 and PD-L1 can be blocked to significantly improve the tumor-killing activity of the CD8+ cytotoxic T cells. 
         [0005]    PD-1 is primarily expressed on the surface of CD4+ T cells, CD8+ T cells, NKT cells, B cells, and the activated monocytes. The expression of PD-1 is primarily induced by the signals of T cell receptor (TCR) or B cell receptor (BCR). TNF can enhance the expression of PD-1 on the surfaces of these cells (Francisco, Sage et al., The PD-1 pathway in tolerance and autoimmunity.  Immunol Rev,  2010, 236: 219-242). Human PD-1 is encoded by the gene Pdcd1, which is located on 2q37.3 and is 9.6 kb. It comprises five exons and four introns and its upstream comprises a promoter of 663 bp. The molecular structure of PD-1 comprises extracellular region, trans-membrane region and intracellular region. The amino acid sequences in the extracellular region has 24% homology with CTLA-4 and 28% homology with CD28. Its gene has primarily seven single-nucleotide polymorphic sites. The extracellular region comprises one structural domain of immuno-globulin variable IgV. The intracellular region comprises two signal transduction motifs based on tyrosine—ITIM (immunoreceptor tyrosine-based inhibitory motif) and ITSM (immunoreceptor tyrosine-based conversion motif). Once T cells are activated, PD-1 will associate with tyrosine phosphatase SHP2 primarily via the ITSM motif to cause the de-phosphorylation of the effector molecules including CD3ζ PKCθ and ZAP70, etc. 
         [0006]    There are two PD-1 ligands: PD-L1 and PD-L2. PD-L1 is also referred to as B7H1 or CD274 and PD-L2 is referred to as B7DC or CD273. The PD-L gene is located on the locus of 9p24.2 of human chromosome with a size of 42 kb. These ligands have 21-27% homology in amino acid sequence and structural similarity with B7-1, B7-2 and ICOSL. The PD-1 ligands all comprise one structural domain of immuno-globulin-like variable region, one constant-region-like structural domain, one trans-membrane region, and one short cytoplast tail. The cytoplast tail of PD-L1 is more conservative than that of PD-L2. PD-L1 and PD-L2 are expressed on different cell populations (Shimauchi, Kabashima et al., Augmented expression of programmed death-1 in both neoplastic and non-neoplastic CD4+ T cells in adult T cell leukemia/lymphoma.  Int J Cancer,  2007, 121(12): 2585-2590). These cells include non-hematopoietic tissue and a variety of tumor types. PD-L1 is mainly expressed on T cells, B cells, dendritic cells, macrophages, mesenchymal stem cells and mast cells derived from bone marrow. PD-L1 is also expressed on the cells not derived from bone marrow, such as vascular endothelial cells, epithelial cells, skeletal muscle cells, hepatocytes, renal tubular epithelial cells, islet cells, brain astrocytes, and various types of non-lymphoid tumors such as melanoma, liver cancer, stomach cancer, renal cell carcinoma, as well as expressed on the cells at the immunologically privileged sites such as placenta, eyes. It has been suggested that PD-L1 can be extensive to some degree in regulating the auto-reactive T cells, B cells and immune tolerance and can play a role in response of peripheral tissue T cells and B cells. Nevertheless, the PD-L2 has very limited expressed region and exists only in macrophages and dendritic cells. PD-L1 is believed to play a role mainly in the immune presentation. 
         [0007]    PD-1 and PD-L1 interact with each other to regulate and control the activation of T cells, which has been validated by much in tumors and viral infections. PD-L1 is expressed on the surfaces of various tumor cells which include lung cancer, liver cancer, ovarian cancer, cervical cancer, skin cancer, bladder cancer, colon cancer, breast cancer, glioma, renal carcinoma, stomach cancer, esophageal cancer, oral squamous cell cancer, and head/neck cancer. There are large amount of CD8+ T cells expressing PD-L1 found around these cancers. The clinical statistics reveal that the high level of expression of PD-L1 on cancer cells is related to the poor prognosis of cancer patients (Okazaki and Honjo 2007. Supra.). 
         [0008]    Many chronic and acute viruses also escape the body&#39;s immune surveillance via the signals of PD-1 and PD-L1. For example, the expression level of PD-1 in HIV-infected patients is closely related to the degree of depletion of T cells and can be used as one of the markers of AIDS progression (Trabattoni, Saresella et al., B7-H1 is up-regulated in HIV infection and is a novel surrogate marker of disease progression. Blood, 2003, 101(7): 2514-2520). It is the same case for the patients diagnosed with chronic hepatitis B (Evans, Riva et al., Programmed death 1 expression during antiviral treatment of chronic hepatitis B: Impact of hepatitis B e-antigen seroconversion,  Hepatology,  2008, 48(3): 759-769). The animal tests revealed that the mice whose PD-1 gene has been knocked out can control virus infection better than the normal mice; and hepatitis can be induced if the HBV-specific T cells are transferred into the HBV transgenic animals. 
       BRIEF SUMMARY OF THE INVENTION 
       [0009]    The present invention relates to an anti-PD-1 antibody or a functional fragment thereof which can bind to the programmed cell death 1 (PD-1). 
         [0010]    In one aspect, the antibody or the functional fragment thereof comprises a heavy chain CDR selected from the amino acid sequence SEQ ID NO: 1, 2, 3, 7, 8, 9, 13, 14, 15 or any variant of said sequence, and/or a light chain CDR selected from the amino acid sequence SEQ ID NO: 4, 5, 6, 10, 11, 12, 16, 17, 18 or any variant of said sequence. 
         [0011]    In some preferred embodiments, the antibody or the functional fragment thereof comprises a) heavy chain CDR1, CDR2 and CDR3 sequences selected from any of the following groups of various amino acid sequences or their variants: 
         [0000]                                                                  HCDR1   HCDR2   HCDR3                                    A   SEQ ID NO: 1   SEQ ID NO: 2   SEQ ID NO: 3       B   SEQ ID NO: 7   SEQ ID NO: 8   SEQ ID NO: 9       C   SEQ ID NO: 13   SEQ ID NO: 14   SEQ ID NO: 15                    
and/or light chain CDR1, CDR2 and CDR3 sequences selected from any of the following groups of various amino acid sequences and their variants:
 
         [0000]                                                                  LCDR1   LCDR2   LCDR3                                    A   SEQ ID NO: 4   SEQ ID NO: 5   SEQ ID NO: 6       B   SEQ ID NO: 10   SEQ ID NO: 11   SEQ ID NO: 12       C   SEQ ID NO: 16   SEQ ID NO: 17   SEQ ID NO: 18                    
In some preferred embodiments, the amino acid sequences of the heavy chain CDR1, CDR2 and CDR3 as well as the light chain CDR1, CDR2 and CDR3 of the antibody or the functional fragment thereof according to the present invention are selected from any of the following groups of various amino acid sequences or their variants:
 
         [0000]    
       
         
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 HCDR1 
                 HCDR2 
                 HCDR3 
                 LCDR1 
                 LCDR2 
                 LCDR3 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 A 
                 SEQ ID 
                 SEQ ID 
                 SEQ ID 
                 SEQ ID 
                 SEQ ID 
                 SEQ ID 
               
               
                   
                 NO: 1 
                 NO: 2 
                 NO: 3 
                 NO: 4 
                 NO: 5 
                 NO: 6 
               
               
                 B 
                 SEQ ID 
                 SEQ ID 
                 SEQ ID 
                 SEQ ID 
                 SEQ ID 
                 SEQ ID 
               
               
                   
                 NO: 7 
                 NO: 8 
                 NO: 9 
                 NO: 10 
                 NO: 11 
                 NO: 12 
               
               
                 C 
                 SEQ ID 
                 SEQ ID 
                 SEQ ID 
                 SEQ ID 
                 SEQ ID 
                 SEQ ID 
               
               
                   
                 NO: 13 
                 NO: 14 
                 NO: 15 
                 NO: 16 
                 NO: 17 
                 NO: 18 
               
               
                   
               
             
          
         
       
     
         [0012]    In some embodiments, the antibody or the functional fragment thereof according to the present invention comprises a) a variable region of the heavy chain selected from the group consisting of amino acid sequences SEQ ID NOs: 19, 21, 23, and any variant of SEQ ID NO: 19, 21, or 23, and/or b) a variable region(s) of the light chain selected from the amino acid sequence SEQ ID NO: 20, 22, 24 or any variant of said sequence. 
         [0013]    In one preferred embodiment, said variable region of the heavy chain is SEQ ID NO: 19 or any variant thereof and said light chain is SEQ ID NO: 20 or any variant thereof. 
         [0014]    In another preferred embodiment, said variable region of the heavy chain is SEQ ID NO: 21 or its variant and said variable region of the light chain is SEQ ID NO: 22 or any variant thereof. 
         [0015]    In another more preferred embodiment, said variable region of the heavy chain is SEQ ID NO: 23 or any variant thereof and said variable region of the light chain is SEQ ID NO: 24 or any variant thereof. 
         [0016]    The antibody or the functional fragment thereof according to the present invention can be a chimeric antibody, a humanized antibody or a fully human antibody. 
         [0017]    The antibody or the functional fragment thereof according to the present invention can be humanized. Methods of preparing humanized antibody are generally known by the skilled in the art. For example, the CDR sequence according to the present invention can be transferred into the variable region of a human antibody to prepare the humanized anti-PD-1 antibody of the present invention. Said humanized antibody will not produce anti antibody response (AAR) and human anti-mouse antibody (HAMA) response, and will not be removed quickly due to neutralization by anti antibody and will play a role of immunological effect such as ADCC and CDC effects. 
         [0018]    In some preferred embodiments, the humanized PD-1 antibody or the functional fragment thereof according to the present invention comprises a) a variable region of the heavy chain selected from the group consisting of amino acid sequences SEQ ID NO: 33, 35, 36 and any variant of SEQ ID NO: 33, 35, or 36, and/or b) a variable region of the light chain selected from SEQ ID NO: 34, 37 and any variant of SEQ ID NO: 34 or 37. 
         [0019]    In one preferred embodiment of the humanized antibody or the functional fragment thereof according to the present invention, said variable region of the heavy chain is SEQ ID NO: 33 or its variant and said variable region of the light chain is SEQ ID NO: 34 or its variant. 
         [0020]    In another preferred embodiment of the humanized antibody or the functional fragment thereof according to the present invention, said variable region of the heavy chain is SEQ ID NO: 35 or its variant and said variable regions of the light chain is SEQ ID NO: 34 or its variant. 
         [0021]    In another preferred embodiment of the humanized antibody or the functional fragment thereof according to the present invention, said variable region of the heavy chain is SEQ ID NO: 36 or its variant and said variable region of the light chain is SEQ ID NO: 34 or its variant. 
         [0022]    In another more preferred embodiment of the humanized antibody or the functional fragments thereof according to the present invention, said variable region of the heavy chain is SEQ ID NO: 35 or its variant and said variable region of the light chain is SEQ ID NO: 37 or its variant. 
         [0023]    The present invention also provides a separate nucleic acid molecule encoding the antibody or the functional fragment thereof according to the present invention. In one preferred embodiment, said nucleic acid molecule comprises the nucleotide sequence as shown by any of SEQ ID NO: 25-30, 38-42 or any combination thereof. 
         [0024]    The present invention also provides an expression vector comprising said nucleic acid molecule as well as a host cell comprising said expression vector. 
         [0025]    The present invention provides methods of producing anti-PD-1 antibodies or the functional fragments thereof, which comprises: culturing said host cells according to the present invention under the condition of allowing it to produce said antibodies or the functional fragments thereof, as well as recovering said antibodies or the functional fragments thereof produced in this way. 
         [0026]    In another aspect, the present invention relates to an immunoconjugate comprising the antibody or the functional fragment according to the present invention that conjugates with a therapeutic agent. Said therapeutic agent is preferably toxin, radioisotope, drug or cytotoxic agent. 
         [0027]    The present invention also relates to a pharmaceutical composition comprising the antibody or the functional fragment thereof according to present invention as well as a pharmaceutical carrier. 
         [0028]    On the other hand, the present invention provides a method used to prevent or treat diseases or conditions through removing, inhibiting or lowering the activity of PD-1, which comprises administration of an effective treatment dose of the antibody or the functional fragment thereof according to the present invention, nucleic acid, expression vector, host cell, immunoconjugate or pharmaceutical composition to a subject in need, wherein: said diseases or conditions are selected from the group consisting of cancers, infectious diseases and inflammatory diseases. Said cancers are preferably selected from the group consisting of melanoma, renal cancer, prostate cancer, breast cancer, colon cancer, lung cancer, bone cancer, pancreatic cancer, skin cancer, head or neck cancer, cutaneous or intraocular malignant melanoma, uterine cancer, ovarian cancer, rectal cancer, anal region cancer, stomach cancer, testicular cancer, uterine cancer, fallopian tube cancer, endometrial cancer, cervical cancer, vaginal cancer, vulva cancer, Hodgkin&#39;s disease, non-Hodgkin&#39;s lymphoma, esophagus cancer, small intestinal cancer, cancer of endocrine system, thyroid cancer, parathyroid cancer, adrenal cancer, soft tissue sarcoma, urethra cancer, penile cancer, chronic or acute leukemia which includes acute myeloid leukemia, chronic myeloid leukemia, acute lymphoblastic leukemia, chronic lymphocytic leukemia, solid tumors during childhood, lymphocytic lymphoma, bladder cancer, kidney or ureter cancer, renal pelvis cancer, vegetation of central nervous system, primary central nervous system lymphoma, tumor angiogenesis, spinal axis tumors, brain stem glioma, pituitary adenoma, Kaposi&#39;s sarcoma, epidermoid carcinoma, squamous cell cancer, T cell lymphoma, environmentally induced cancers which include those induced by asbestos and the combination of said cancers, said infectious diseases are preferably selected from HIV, influenza, herpes, giardiasis, malaria, leishmaniasis, pathogenic infections caused by the following viruses: hepatitis viruses (hepatitis A, B and C), herpes virus (such as VZV, HSV-1, HAV-6, HSV-II, and CMV, Epstein Barr virus), adenovirus, influenza virus, flaviviruses, echovirus, rhinovirus, coxsackie virus, coronavirus, respiratory syncytial virus, mumps virus, rotavirus, measles virus, rubella virus, parvovirus, vaccinia virus, HTLV virus, dengue virus, papilloma virus, molluscum virus, polio virus, rabies virus, JC virus and arboviral encephalitis virus, pathogenic infections by the following bacteria:  chlamydia, rickettsia , mycobacteria,  staphylococcus, streptococcus , pneumococcus, meningococcus and conococci,  klebsiella, proteus, serratia, pseudomonas, legionella , diphtheria,  salmonella , tuberculosis, cholera, tetanus, botulism, anthrax, plague, leptospirosis and Lyme disease bacteria, pathogenic infections by the following fungi:  Candida  ( Candida albicans, Candida krusei, Candida glabrata, Candida tropicalis , etc.),  Cryptococcus neoformans, aspergillus  ( Fumigatus, Aspergillus niger , etc.), genus of  Mucor  ( mucor, absidia, rhizopus ),  Sporothrix schenckii , dermatitis yeast bud, paracoccidiodes  brasiliensis, Coccidioides immitis  and  Histoplasma capsulatum , pathogenic infections by the following parasites:  Entamoeba histolytica , Colon  balantidium , fernando&#39;s worms, amoeba spine, suction blow Giardia,  cryptosporidium, Pneumocystis carinii, P. vivax , voles  Babesia, Trypanosoma brucei , Cruz  trypanosoma, Leishmania donovani, Toxoplasma gondii  and Nippostrongylus  brasiliensis , said inflammatory diseases are preferably selected from acute disseminated encephalomyelitis, Addison&#39;s disease, ankylosing spondylitis, antiphospholipid antibody syndrome, autoimmune hemolytic anemia, autoimmune hepatitis, arthritis, Behcet&#39;s disease, bullous blistering day sores, celiac disease, Chagas disease, Crohn&#39;s disease, dermatomyositis, type-1 diabetes, pulmonary hemorrhage—nephritic syndrome, graft versus host disease, Graves&#39; disease, Guillain-Barre syndrome, Hashimoto&#39;s disease, hyperimmunoglobulin E syndrome, idiopathic thrombocytopenic purpura, lupus erythematosus, multiple sclerosis, myasthenia gravis, pemphigus, pernicious anemia, polymyositis, primary biliary cirrhosis, psoriasis disease, rheumatoid arthritis, Sjogren&#39;s syndrome, temporal arteritis, vasculitis, and Wegener&#39;s granulomatosis. 
         [0029]    The present invention also provides the uses of the antibody or the functional fragment thereof according to the present invention, nucleic acid, expression vector, host cell, immunoconjugate or pharmaceutical composition in preparing the drugs for treating the diseases or conditions. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0030]      FIG. 1  shows the protein size of the extracellular structural region of PD-1 derived from human (hu) and  Macaca fascicularis  (cyno) as indicated by SDS-PAGE. 
           [0031]      FIG. 2  shows the combination of biotin-labeled rh-PD-L1 and human T cells measured by flow cytometry. 
           [0032]      FIG. 3  shows that the PD-L1 control, Clone 1, 10, 11, 55 and 64 block the binding between the PD-1 on cell surface with the ligand PD-L1 as measured by flow cytometry. 
           [0033]      FIG. 4  shows the binding of the antibody control, Clone 1, 10, 11, 55 and 64 with the PD-1 as well as other CD28 family members (ICOS, CTLA-4 and CD28). 
           [0034]      FIG. 5  shows the results of the tetanus toxin stimulation experiments measuring the in vitro stimulation of chimeric antibody on T cells. 
           [0035]      FIG. 6  shows the secretion levels of IL2 by Clones hu38 (“38”), hu39 (“39”), hu41 (“41”) and hu48 (“48”) (control (conIgG4)) of the humanized antibody measured by the CD8+ cytokine assay kit. 
           [0036]      FIG. 7  shows the values of the GFP fluorescence of Clones 38, 39, and 41 relative to Clone 48 (control IgG4) of the humanized anti-PD-1 antibody in experiments where dendritic cells and the modified MD-MAB-453 cells were cultured together for 3 days followed by the addition of extracted T cells and each of the Clones to culture together for an additional 3 days. 
           [0037]      FIG. 8  shows the binding between the humanized antibody according to the present invention with the PD-1 proteins derived from human,  Macaca fascicularis  and mouse. 
           [0038]      FIG. 9  shows the comparison between the PD-1 sequences of human,  Macaca fascicularis  (Cyno) and mouse, wherein the major differences between the mouse PD-1 protein and the human/ Macaca fascicularis  PD-1 protein are boxed. 
           [0039]      FIG. 10  shows the experiment result of T cell proliferation in vitro stimulated by humanized antibody—tetanus antigen memory response. 
           [0040]      FIG. 11  shows the experiment result of T cell proliferation in vitro stimulated by humanized antibody—viral polypeptides antigen memory response. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0041]    Unless otherwise defined, all the technical terms used in this patent have the same meanings understandable by the ordinary technicians in the art. As for the definitions and terms in the art, the professionals can specifically refer to Current Protocols in Molecular Biology (Ausubel). The abbreviation of amino acid residues employs a form of the standard code of 3 letters and/or 1 letter used in the field for each of the 20 commonly-used L-amino acids. 
         [0042]    The present invention provides an anti-PD-1 antibody and a functional fragment thereof, which can bind to the programmed cell death 1 (PD-1). The antibody and the functional fragment thereof according to the present invention has at least one of the following features: the ability to block the interaction between PD-1 and PD-L1 via high affinity, or bind to PD-1 with high specificity but not to other CD28 family members (such as ICOS, CTLA-4 and CD28), or activate tumor-specific T cells to kill the tumor cells and promote CD8+ to enter the tissue of solid tumor so as to increase greatly the levels of the immune effectors such as IFNγ. 
         [0043]    The present invention also provides a humanized anti-PD-1 antibody and a functional fragment thereof. Said humanized antibody is obtained by computer simulation design of the mouse-derived antibody produced by immunized mouse in combination with bacteriophage display technology. Its binding epitopes are also identified accordingly based on its binding characteristics with PD-1 proteins of various species. Except the advantageous characteristics of the anti-PD-1 antibody and the functional fragment thereof described above, said humanized anti-PD-1 antibody and the functional fragment thereof according to the present invention also binds to PD-1 proteins of human or  Macaca fascicularis  via high affinity, but does not interact with the mouse-derived PD-1 protein. 
         [0044]    On the premise of not substantially influencing the activity of the antibody, those skilled in the art can replace, add and/or remove one or more (such as 1, 2, 3, 4, 5, 6, 7, 9 or 10 or more) amino acids of the sequence according to the present invention so as to produce a variant of the sequence of said antibody or the functional fragment thereof. They are all deemed to be included in the protection scope of the present invention. For example, the amino acid in the variable region can be replaced with that of similar property. The sequence of said variant according to the present invention can have an identity of at least 95%, 96%, 97%, 98% or 99% to its source sequence. Said sequence identity described in the present invention can be measured by sequence analysis software, for example, the computer program BLAST using default parameter, especially BLASTP or TBLASTN. 
         [0045]    The antibody according to the present invention can be full length (for example, IgG1 or IgG4 antibody) or comprises only the part that binds an antigen (for example, Fab, F(ab′) 2  or scFv fragment), or an antibody that has been modified to affect its function. The present invention comprises the anti-PD-1 antibody comprising modified glycosylation pattern. In some applications, it is useful to conduct modification to remove the undesirable glycosylation sites or avoid the part of fucose on the oligosaccharide chain to, for example, enhance the antibody of antibody-dependent cellular cytotoxicity (ADCC) function. In some other applications, the modification of galactosylation can be conducted to change the complement-dependent cytotoxcity (CDC). 
         [0046]    The terms used in this patent—“functional fragment” refers to especially the antibody fragment such as Fv, scFv (sc refers to single strand), Fab, F(ab′)2, Fab′, scFv-Fc fragment or diabody, or any fragment whose half life should be possibly increased by means of chemical modification or incorporating into the liposome. Said chemical modification is, for example, adding polyalkylene glycol such as polyethylene glycol (“pegylation, PEGylated”) (referred to as a pegylated fragment such as Fv-PEG, scFv-PEG, Fab-PEG, F(ab′)2-PEG or Fab′-PEG) (“PEG” is polyalkylene glycol) and said fragment has EGFR binding activity. Preferably, said functional fragment comprises a partial sequence of the heavy or light variable chain of their source antibody. Said partial sequence maintains sufficient antigen-binding specificity and affinity, which are the same as those of its source antibody. As for PD-1, the affinity is preferably at least 1/100, and more preferably at least 1/10, of the affinity of its source antibody. Said functional fragment comprises at least 5 amino acids and preferably comprises 10, 15, 25, 50 and 100 continuous amino acids of its source antibody sequence. 
         [0047]    Technicians skilled in the art can clone the DNA molecule encoding said anti-PD-1 antibody according to the present invention into a vector and then transform to host cell. In this way, the present invention can also provide a type of recombinant DNA vector, which comprises a DNA molecule encoding said anti-PD-1 antibody according to the present invention. 
         [0048]    Preferably, said recombinant DNA vector is a type of expression vector. Technicians skilled in the art can clone the DNA molecule of said antibody into the expression vector and transform it into host cell to get antibody by means of induction expression. The expression vector according to the present invention comprises the encoding DNA sequence of the variable region of the heavy chain, the variable region of the light chain and/or constant region of the anti-PD-1 antibody. Nevertheless, two types of expression vectors can also be constructed separately: one comprising the variable region of the heavy chain and constant region and another comprising the variable region of the light chain and constant region. The two types of expression vectors are then introduced into the same mammal. In one preferred embodiment, said expression vector further comprises a promoter and a DNA sequence encoding the secreting signal peptide as well as at least one type of drug-resistant gene used to screen. 
         [0049]    The host cells according to the present invention can be prokaryotic host cell, eukaryotic host cell or bacteriophage. Said prokaryotic host cell can be  Escherichia coli, Bacillus subtilis, Streptomyces  or  Proteus mirabilis , etc. Said eukaryotic host cell can be fungi such as  Pichia pastoris, Saccharomyces cerevisiae , fission yeast and  Trichoderma , insect cells such as  Spodoptera frugiperda , plant cells such as tobacco, mammalian cells such as BHK cell, CHO cell, COS cell and myeloma cell. In some embodiments, the host cells according to the present invention are preferably mammalian cells, more preferably, BHK cells, CHO cells, NSO cells or COS cells. 
         [0050]    The term “pharmaceutical composition” used herein refers to the combination of at least one kind of drug and randomly selected pharmaceutical carriers or excipients for a special purpose. In some embodiments, said pharmaceutical composition includes the combinations, which are separated in time and/or space provided that they can function synergistically to realize the purpose of the present invention. For example, the ingredients contained in said pharmaceutical composition (for example, the antibody, nucleic acid molecule, combination and/or conjugate of nucleic acid molecule) can be administered to the subject as a whole or separately. In the case that the ingredients contained in said pharmaceutical composition are administered separately to the subject, they can be used simultaneously or in turn. Preferably, said pharmaceutical carrier is water, buffer aqueous solution, isotonic saline solutions such as PBS (phosphate buffer), glucose, mannitol, dextrose, lactose, starch, magnesium stearate, cellulose, magnesium carbonate, 0.3% glycerol, hyaluronic acid, ethanol or polyalkylene glycols such as polypropylene glycol, triglyceride and others. The type of the pharmaceutical carrier can be selected based on whether the composition according to the present invention is formulated to be administered via oral, intranasal, intradermal, subcutaneous, intramuscular or intravenous route. The composition according to the present invention can comprise a wetting agent, an emulsifier or a buffer solution as additive. 
         [0051]    The pharmaceutical composition according to the present invention can be administered via any appropriate route, for example, oral, intranasal, intradermal, subcutaneous, intramuscular or intravenous. 
         [0052]    In one relevant aspect, the present invention provides a pharmaceutical composition comprising an anti-PD-1 antibody and a second therapeutic agent. In one embodiment, the second therapeutic agent is any agent advantageous to combine with anti-PD-1 antibody. Examples of such agent advantageous to combine with anti-PD-1 antibody include, but are not limited to, other agents that can inhibit the activity of PD-1 (including the fragments, the peptide inhibitor, the small molecule antagonists, etc., binding to other antibodies or antigens) and/or the agents that can interfere with the transduction of upstream or downstream signals of PD-1. 
         [0053]    The terms “prevent or treat diseases or conditions through removing, inhibiting or lowering the activity of PD-1” refers to the diseases or conditions caused by expression of PD-1 or those diseases or conditions with the symptoms/features of PD-1 expression. In some embodiments, said diseases or conditions are cancers or infectious diseases. Said cancers include, but are not limited to, lung cancer, liver cancer, ovarian cancer, cervical cancer, skin cancer, bladder cancer, colon cancer, breast cancer, glioma, renal cancer, gastric cancer, esophageal cancer, oral squamous cell carcinoma, head/neck cancer. Said infectious diseases include, but are not limited to, HIV infection and Hepatitis B virus infection. 
         [0054]    The term “effective treatment dose” used in this patent refers to a dose sufficient to confer benefit to the application target. The dose administered, the administration rate and the duration may depend on the conditions and severity of the target to treat. The prescription of treatment (for example, determination of dose) is determined by a physician, who may consider the factors such as the disease to treat, the condition of individual patient, the administration site, and the administration method. 
         [0055]    The term “subject” used in this patent refers to mammals such as human or other animals, for example, wild animals (heron, stork, crane, etc), livestock (duck, goose, etc) or laboratory animals (orangutan, monkey, rate, mouse, rabbit and guinea pig, etc) 
         [0056]    The following Examples are provided to prove and further explain some preferred embodiments according to the present invention. Nevertheless, they should not be interpreted as limiting the scope of the present invention. 
       EXAMPLES 
     Example 1 
     Clone Human PD1 Extracellular Structural Region into Eukaryotic Expression Plasmid 
       [0057]    Total RNA from human peripheral blood cells (Beijing Red Cross Blood Center) was extracted with Trizol RNA extraction kit (Invitrogen) and cDNA was obtained with reverse transcription kit by Invitrogen. The PD1 extracellular fragment was obtained by PCR amplification of the cDNA using the upstream primer 5′-GTACGCTAGCCACCATGCAGATCCCACAGGC-′3 (SEQ ID NO.31) and the downstream primer 5′-GATCCTCGAGCCACCAGGGTTTGGAACTG-′3 (SEQ ID NO.32). The amplified product was digested by Nhe I and Xho I and cloned into the eukaryotic expression plasmid system of pCDNA3.1. 293T cells (ATCC) were transfected with this plasmid for 3 days, the supernatant of the cell culture was collected to purify h-PD1. Total RNA from the peripheral blood cells of  Macaca fascicularis  were also extracted and the produced cDNA was cloned into the a eukaryotic expression vector. 
         [0058]    As shown in  FIG. 1 , due to the posttranslational modification such as glycosylation, the protein sizes of PD-1 extracellular structural regions of human-derived (hu) and  Macaca fascicularis  derived (cyno) PD-1 were about 50K Dalton after Coomassie blue staining. 
       Example 2 
     Test the Combination of the PD-1 on Cells and the Ligand PD-L1 
       [0059]    1. Isolate T cells from human peripheral blood cells 
         [0060]    When the suspension of peripheral blood cells (Beijing Blood Institute) flows through nylon-fiber column (Beijing Hede Biotechnology Company), the B cells, plasma cells, mononuclear cells and some ancillary cells will adhere selectively to the nylon fiber although most T cells pass through nylon-fiber column and hence yield the enriched T cell population. The procedure is simply described as follows: take a 50-ml glass syringe, pull out the syringe core and fit a rubber hose with clip into the syringe nozzle. Tie up some nylon fibers and insert them into the syringe. Fix the syringe on the support and pour RPMI cell culture fluid at 37° C. to pre-treat the nylon fibers. Close the valve, open the valve after 0.5 hours to release the cell culture fluid. Dilute the cell fluid to be separated with pre-heated RPMI culture fluid to an appropriate concentration about 5.00×10 7  cells/ml. Pour the cell fluid into the syringe and submerge the nylon-fiber column. Cover the syringe and incubate at 37° C. for 1 hour. Open the lower opening, release the fluid slowly (1 drip/min) and collect in a centrifuge tube. Centrifuge at 1000×g for 10 minutes to yield the desired T lymphocytes. 
         [0000]    2. Conjugate Rh-PD-L1 Recombinant Protein with Biotin 
         [0061]    Mix 100 ug rh-PD-L1 recombinant protein (purchased from Beijing Sino Biological Inc.) with the biotin-amino-caproic acid-NHS (Thermo) dissolved in DMSO at a molar ratio of 1:4 and keep the mixture still at room temperature for 1 hour. Then pass the reaction mixture through G25 gel column (Thermo) to separate the biotin-marked rh-PD-L1 and the free biotins. 
         [0000]    3. Combine the Biotin-Marked Rh-PD-L1 with Human T Cells 
         [0062]    rh-PD-L1 recombinant protein conjugated with different concentrations of biotins was mixed with 10 5  T cells isolated according to the method above. The mixture was incubated at 4° C. for 15 minutes. After washing three times with PBS, a streptavidin-allophycocyanin (Thermo) (SA-APC) to 0.2 ug/ml was added and incubated with the mixture at 4° C. for 20 minutes. After washing three more times with PBS, samples were measured at 660 nm using the Beckman Dickson FACSCalibur. As shown in  FIG. 2 , the result shows that the PD-L1 protein conjugated with biotin can bind to T cells. 
       Example 3 
     Preparation of Anti Rh-PD-1 Antibody 
     1. Animal Immunization 
       [0063]    10 ug rh-PD-1 recombinant protein of 1 mg/ml as antigen was mixed with equivalent immune adjuvants (Freund adjuvant (Sigma-Aldrich)) and immunized subcutaneously three female FVB mice of 6-week old. After the first immunization, the same dose is administered once per week to boost the immunization. 
       2. Cell Fusion 
       [0064]    After the last shot of enhanced immunization, lymph nodes at the thigh root of mice were collected and milled in the normal saline. The produced suspension, enriched with B cells, was fused with the SP2/0 cells via the conventional method of electrophoretic transfer (see BTX electroporator manual). The fusion cells were cultured at the condition of 5% CO 2  and 37° C. in the RPMI-1640 whole culture medium containing HAT (Sigma) to culture. 
       Example 4 
     Experiment of Blocking Ligand and Receptor 
       [0065]    From 20000 of monoclonal hybridoma cell lines, the enzyme label (Elisa) reaction was employed to screen out the 1220 clones of secreted antibodies, which can bind to PD-1 proteins. Five of these 1220 clones of antibodies had the ability to inhibit the binding between the biotin-marked PD-L1 and the PD-1 receptor on T cells to various degrees. 
         [0066]    1 ug/ml of each of the five antibodies described as above were incubated with 312 ng/ml of biotin-marked rh-PD-L1 (concentration) at room temperature for 20 minutes. The mixture was then incubated with T cells isolated from human peripheral blood cells at 4° C. for 15 minutes. After washing three times with normal saline and 0.2 ug/ml of SA-APC was added to the mixture and incubated at 4° C. for 15 minutes. After washing three times with normal saline, samples were measured with BD&#39;s flow cytometer to verify whether the antibodies can inhibit the binding of rh-PD-L1 and PD-1 receptor on the surface of T cell. 
         [0067]    As shown in  FIG. 3 , Clones 1, 10 and 11 can block the binding of PD-1 with the ligand PD-L1 on the cell surface, whereas Clones 55 and 64 can only play a weak inhibition role. 
       Example 5 
     Binding of the Antibody Candidates to Other CD28 Family Members 
       [0068]    In order to further test the binding specificity of antibody candidate Clones 1, 10, 11, 55 and 64, 1 ug/ml of rh-PD-1 or the other CD28 family members, i.e., ICOS, CTLA-4 and CD28 (R&amp;D System) in the carbonate buffer solution (0.05M PH9) was used to coat a 96-well enzyme-label plate and kept at 4° C. overnight. The next day, solution was removed from the wells and the wells were washed three times with a washing buffer (PBS+0.5% TWEEN). PBS solution containing 3% BSA was added to the wells to block for 20 minutes. After washing three times with the washing buffer, 100 ul of each antibody clone was added at 1 ug/ml and incubated at room temperature for 1 hour. After three washes with the washing buffer, HRP cross-linked goat anti mouse antibody (Jackson Immunoresearch) was diluted in the washing buffer 1:0000, and added to the sample wells and incubated at room temperature for 1 hour. After three washes with the washing buffer, 50 ul TMB (tetramethyl benzidine) substrate solution was added to develop the color. The color reaction was terminated after the reaction was continued for 10 minutes at room temperature by adding 25 ul of 0.5M sulfuric acid solution to the reaction mixture. The absorbance was then measured at 450 nm. 
         [0069]    As shown in  FIG. 4 , all the antibody candidate clones tested can recognize and bind to rh-PD-1 but not other CD28 family members. 
       Example 6 
     The Variable Region Sequence of the Antibody Candidates 
       [0070]    Candidate hybridoma cells were cultured until reaching a total count of 10 7 . The cells were collected by centrifugation at 1000 rpm for 10 minutes and total RNA from the cells was extracted with Trizol reagent kit (Invitrogen). The total RNA was used as the template to synthesize the first strand cDNA (Qiagen), which, in turn, was used as a template to amplify the DNA sequence of the variable region of the respective hybridoma cells. The primer sequence used in the amplification reaction is complementary to the first framework region and the constant region of the variable region of antibody (Larrick, J. W., et al., (1990) Scand. J. Immunol., 32, 121-128 and Coloma, J. J. et al., (1991) BioTechniques, 11, 152-156 et al.). In a 50 μl reaction system, 1 μl of cDNA, 5 μl of 10×PCR buffer solution, each 1 μl (25 pmol) of upstream and downstream primer, 1 μl of dNTP, 1 μl of 25 mmol/L MgCl 2 , 39 μl of H 2 O, were added separately. The initial denaturation of the template was conducted at 95° C. for 10 minutes. 1 μl of Taq enzyme (Invitrogen) was added to the reaction to start temperature cycles of the PCR amplification. The reaction conditions are as follows: denaturing at 94° C. for 1 minute, annealing at 58° C. for 1 minute, and extending at 72° C. for 115 minutes. The cycle was repeated 30 times before the reaction mixture was kept at 72° C. for 10 minutes. 
         [0071]    The amplified product is sequenced and the sequences of variable regions of the heavy chain and light chain of Clone 1, 10 and 11 of hybridoma are shown below: 
         [0000]    
       
         
               
               
             
           
               
                 Clone 1: 
                   
               
               
                 Heavy chain 
               
               
                 
                   
                             
                     
                         
                         
                     
                   
                 
               
               
                 
                   
                             
                     
                         
                         
                     
                   
                 
               
               
                 Nucleic acid sequence 
               
               
                 CACGGGTCAACTGCAGCAGTCTGGGGCTGAGCTGGTGAGGCCTGGGGCTTCAGTGACGCTGACCTGCAA 
               
               
                   
               
               
                 GGCTTCGGGCTACACATTTACTGACTATGAAATGCACTGGGTGAAGCAGACACCTATACATGGCCTGGAA 
               
               
                   
               
               
                 TGGATTGGAGTTATTGAATCTGAAACTGGTGGTACTGCCTACAATCAGAAGTTCAAGGGCAAGGCCAAA 
               
               
                   
               
               
                 CTGACTGCAGACAAATCCTCCAGCACAGCCTACATGGAGCTCCGCAGCCTGACATCTGAGGACTCTGCCG 
               
               
                   
               
               
                 TCTATTACTGTACAAGAGAGGGTATTACTACGGTAGCAACTACGTACTACTGGTACTTCGATGTCTGGGG 
               
               
                   
               
               
                 CACAGGGACCACGGTCACCGTCTCCTCA 
               
               
                   
               
               
                 Light chain 
               
               
                 
                   
                             
                     
                         
                         
                     
                   
                 
               
               
                 Nucleic acid sequence 
               
               
                 GATGTTTTGATGACCCAGACTCCACTCTCCCTGCCTGTCAGTCTTGGAGATCAAGCCTCCATCTCTTGCAG 
               
               
                   
               
               
                 ATCTAGTCAGAGCATTGTACATAGTAATGGAAACACCTATTTAGAATGGTACCTGCAGAAACCAGGCCAG 
               
               
                   
               
               
                 TCTCCAGAGCTCCTGATCTACAAAGTTTACAACCGATTTTCTGGGGTCCCAGACAGGTTCAGTGGCAGTG 
               
               
                   
               
               
                 GATCAGGGACAGATTTCACACTCAAGATCAGCAGAGTGGAGGCTGAGGATCTGGGAGTTTATTACTGCT 
               
               
                   
               
               
                 TTCAAGGTTCACATGTTCCATTCACGTTCGGCTCGGCTCGGGGACAAAGTTGGAAATAAAA 
               
               
                   
               
               
                 Clone 10: 
               
               
                 Heavy chain 
               
               
                 
                   
                             
                     
                         
                         
                     
                   
                 
               
               
                 
                   
                             
                     
                         
                         
                     
                   
                 
               
               
                 Nucleic acid sequence 
               
               
                 CAGGTTCAACTGCAGCAGTCTGGGGCTGAGCTGGTGAGGCCTGGGGCTTCAGTGACGCTGTCCTGCAAGGC 
               
               
                   
               
               
                 TTCGGGCTACACATTTACTGACTATGAAATGCACTGGGTGAAGCAGACACCTGTGCATGGCCTGGAATGGA 
               
               
                   
               
               
                 TTGGAGCTATTGATCCTGAAACTGGTGGTGCTGCCTACAATCAGAAGTTCAAGGGCAAGGCCATACTGACT 
               
               
                   
               
               
                 GCAGACAAATCCTCCAGCACAGCCTACATGGAGCTCCGCAGCCTGACATCTGAGGACTCTGCCGTCTATTA 
               
               
                   
               
               
                 CTGTACAAGAGAGGGTATTACTACGTCAGTGGTTACGTACTACTGGTACTTCGATGTCTGGGGCACAGGGA 
               
               
                   
               
               
                 CCACGGTCACCGTCTCCTCA 
               
               
                   
               
               
                 Light chain 
               
               
                 
                   
                             
                     
                         
                         
                     
                   
                 
               
               
                 
                   
                             
                     
                         
                         
                     
                   
                 
               
               
                 Nucleic acid sequence 
               
               
                 GATGTTTTGATGACCCAAACTCCACTCTCCCTGCCTGTCAGTCTTGGAGATCAAGCCTCCATCTCTTGCAG 
               
               
                   
               
               
                 ATCTAGTCAGAGCATTGTACATAGTAATGGAAACACCTATTTAGAATGGTACCTGCAGAAACCAGGCCAGT 
               
               
                   
               
               
                 CTCCAAAGCTCCTGATCTACAAAGTTTCCAACCGATTTTCTGGGGTCCCAGACAGGTTCAGTGGCAGTGGA 
               
               
                   
               
               
                 TCAGGGACAGATTTCACACTCAGGATCAGCAGAGTGGAGCCTGAGGATCTGGGAGTTTATTACTGCTTTCA 
               
               
                   
               
               
                 AGGTTCACATGTTCCACTCACGTTCGGCTCGGGGACAAAGTTGGAAATAAAA 
               
               
                   
               
               
                 Clone 11: 
               
               
                 Heavy chain 
               
               
                 
                   
                             
                     
                         
                         
                     
                   
                 
               
               
                 
                   
                             
                     
                         
                         
                     
                   
                 
               
               
                 Nucleic acid sequence 
               
               
                 CAGGTTACTCTGAAAGAGTCTGGCCCTGGGATATTGCAGCCCTCCCAGACCCTCAGTCTGACTTGTTCTTT 
               
               
                   
               
               
                 CTCTGGGTTTTCACTGAGCACTTTTGGTATGGGTGTCGGCTGGATTCGTCAGCCTTCAGGGAAGGGTCTGG 
               
               
                   
               
               
                 AGTGGCTGGCACACATTTGGTGGGATGATGATAAGTACTATAATCCCGCCCTGAAGAGTCGGCTCACAATC 
               
               
                   
               
               
                 TCCAAGAATACCTCCAAAAACCAGGTTCCGCTGGTACTTCGATGTCTGGGGCACAGGGACCACGGTCACCG 
               
               
                   
               
               
                 TCTCCTCA 
               
               
                   
               
               
                 Light chain 
               
               
                 
                   
                             
                     
                         
                         
                     
                   
                 
               
               
                 
                   
                             
                     
                         
                         
                     
                   
                 
               
               
                 Nucleic acid sequence 
               
               
                 AGGGCTGGTTGGACTCAGGAATCTGCACTCACCACATCACCTGGTGAAACAGTCACACTCACTTGTCGCT 
               
               
                   
               
               
                 CAAGTACTGGGGCTATTACAACTAGTAACTATGCCAACTGGGTCCAAGAAAAACCAGATCATTTATTCAC 
               
               
                   
               
               
                 TGGTCTAATAGGTGGTACCAACAACCGAGCTCCAGGTGTTCCTGCCAGATTCTCAGGCTCCCTGATTGGA 
               
               
                   
               
               
                 GACAAGGCTGCCCTCACCATCACAGGGGCACAGACTGAGGATGAGGCAATATATTTCTGTGCTCTATGGT 
               
               
                   
               
               
                 ACAGCAACCACTGGGTGTTCGGTGGAGGAACCAAACTGACTGTCCTA 
               
             
          
         
       
     
       Example 7 
     Construct the Expression Vector of Chimeric Antibody 
       [0072]    The Fc fragment of the constant region of the heavy chain and the κ/λ constant region of the light chain from human blood cells (Beijing Blood Institute) were cloned into the plasmid pCDNA3.1 (see Walls M A, Hsiao H and Harris L J (1993), Nucleic Acids Research, Vol. 21, No. 12 2921-2929) for modification. Said sequence fragments of the heavy chain and light chain described in Example 6 were synthesized by Genscript Corporation. The heavy chain sequence fragment, after digestion by Xho I and Age I enzymes, and the light chain sequence fragment, after digestion by Sma I and Dra III enzymes, were cloned into the plasmid pCDNA3.1 and sequenced to confirm the sequence of cloned DNA. The experimental materials in the description below were all obtained through transfecting the cells with this series of plasmids and purifying the products generated by the transfected cells. 
       Example 8 
     In Vitro Stimulation of T Cells by Chimeric Antibody-Tetanus Toxin Stimulation Test 
       [0073]    Freshly prepared peripheral blood mononuclear cell (PBMC) were placed into 96-well flat-bottom plate. After an overnight incubation, various concentrations of antibodies and 100 ng/ml of tetanus toxin (TT) (List Biological Laboratories) were added. Supernatant was collected from each of the sample well three days later. The content of IFNγ in the supernatant was measured by ELISA using the INFNy kit (R&amp;D System). As shown in  FIG. 5 , after the PD-1 signal is blocked, the cytokine secretion by the immune cells activated by the TT stimulation increased significantly. In addition, the titers of the candidate antibodies are higher than EH12.2H7, an antibody described in the Chinese patent application CN 200980147059.0 and purchased from Biolegend Corporation. 
       Example 9 
     Interaction of Various Antibodies with PD-1 after Exchange of Heavy and Light Chains of the Former 
       [0074]    Using the method described in Example 7, the light and heavy chains of the antibodies 1 and 10 were recombined reciprocally to generate recombinant antibodies H1L10 (heavy chain 1, light chain 10) and H10L1 (heavy chain 10, light chain 1). These antibodies, the original antibody 1 (heavy chain 1, light chain 1) and the original antibody 10 (heavy chain 10, light chain 10) were tested by ELISAs and the results of EC50s for these antibodies are shown in the table below: 
         [0000]    
       
         
               
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 Sample 
                 H1L1 
                 H10L10 
                 H1L10 
                 H10L1 
               
               
                   
                   
               
             
             
               
                   
                 EC50 (pM) 
                 338.1 
                 426.3 
                 270.1 
                 528.1 
               
               
                   
                   
               
             
          
         
       
     
         [0075]    The result shows that the antibodies produced after recombination can still bind to PD-1 protein effectively. 
       Example 10 
     Humanization Modification of Antibody 
       [0076]    The humanization modification was conducted based on the sequence of variable region of the antibody secreted by the hybridoma cell obtained as described above. In brief, the process of humanization modification involved the following steps: A—comparing the gene sequences of the antibodies secreted by various hybridoma cells with the gene sequence of the human embryonic antibody to find the sequence of high homology; B—analyzing and testing the affinity of HLA-DR in order to select the framework sequence of human embryo with low affinity; C—using computer analog technology to apply molecular docking to analyze the sequences of framework amino acids in the variable region and the surrounding, and examining its spatial stereo binding mode; calculating the electrostatic force, Van der Waals force, hydrophobicity-hydrophilicity and the entropy value to analyze the key individual amino acids in the gene sequences of the antibodies secreted by various hybridoma cell, which are critical for interacting with PD-1 and maintaining the antibodies&#39; spatial configuration, grafting these key amino acids back to the selected gene framework of human embryo. The amino acid sites in the framework region which must be reserved were also identified and random primers were synthesized to construct the phage library. The humanized antibody library was then screened (Pini, A. et al., (1998). Design and Use of a Phage Display Library: HUMAN ANTIBODIES WITH SUBNANOMOLAR AFFINITY AGAINST A MARKER OF ANGIOGENESIS ELUTED FROM A TWO-DIMENSIONAL GEL.,  Journal of Biological Chemistry,  273(34): 21769-21776). A number of humanized antibodies were obtained from the screening, including the following clones. The light chain sequences of Clone 38, 39 and 41 are the same, and the heavy chain sequences of Clone 39 and 48 are the same. 
         [0000]    
       
         
               
               
             
           
               
                 Heavy chain of Clone 38 
                   
               
               
                 
                   
                             
                     
                         
                         
                     
                   
                 
               
               
                 CAGGGCCAGCTGGTGCAGAGCGGCGCCGAGGTGAAGAAGCCCGGCGCCAGCGTGAAGGTGAGCTGCA 
               
               
                   
               
               
                 AGGCCAGCGGCTACACCTTCACCGACTACGAGATGCACTGGGTGAGACAGGCCCCCATCCACGCCTGG 
               
               
                   
               
               
                 AGTGGATCGGCGTGATCGAGAGCGAGACCGGCGGCACCGCCTACAACCAGAAGTTCAAGGGCAGAGTG 
               
               
                   
               
               
                 ACCATCACCGCCGACAAGAGCACCAGCACCGCCTACATGGAGCTGAGCAGCCTGAGAAGCGAGGACAC 
               
               
                   
               
               
                 CGCCGTGTACTACTGCGCCAGAGAGGGCATCACCACCGTGGCCACCACCTACTACTGGTACTTCGACGTG 
               
               
                   
               
               
                 TGGGGCCAGGGCACCACCGTGACCGTGAGCAC 
               
               
                   
               
               
                 Light chain of Clone 38 
               
               
                 
                   
                             
                     
                         
                         
                     
                   
                 
               
               
                 
                   
                             
                     
                         
                         
                     
                   
                 
               
               
                 GATGTGGTGATGACCCAGAGCCCGCTGAGCCTGCCGGTGACCCTGGGCCAGCCGGCGAGCATTAGCTGC 
               
               
                   
               
               
                 CGCAGCAGCCAGAGCATTGTGCATAGCAACGGCAACACCTATCTGGAATGGTATCTGCAGAAACCGGGC 
               
               
                   
               
               
                 CAGAGCCCGCAGCTGCTGATTTATAAAGTGAGCAACCGCTTTAGCGGCGTGCCGGATCGCTTTAGCGGC 
               
               
                   
               
               
                 AGCGGCAGCGGCACCGATTTTACCCTGAAAATTAGCCGCGTGGAAGCGGAAGATGTGGGCGTGTATTAT 
               
               
                   
               
               
                 TGCTTTCAGGGCAGCCATGTGCCGCTGACCTTTGGCCAGGGCACCAAACTGGAAATTAAA 
               
               
                   
               
               
                 Heavy chain of Clone 39 
               
               
                 
                   
                             
                     
                         
                         
                     
                   
                 
               
               
                 
                   
                             
                     
                         
                         
                     
                   
                 
               
               
                 CAGGGCCAGCTGGTGCAGAGCGGCGCCGAGGTGAAGAAGCCCGGCGCCAGCGTGAAGGTGAGCTGCA 
               
               
                   
               
               
                 AGGCCAGCGGCTACACCTTCACCGACTACGAGATGCACTGGGTGAGACAGGCCCCCGGCCAGGGCCTG 
               
               
                   
               
               
                 GAGTGGATGGGCGTGATCGAGAGCGAGACCGGCGGCACCGCCTACAACCAGAAGTTCAAGGGCAGAG 
               
               
                   
               
               
                 CCAAGATCACCGCCGACAAGAGCACCAGCACCGCCTACATGGAGCTGAGCAGCCTGAGAAGCGAGGAC 
               
               
                   
               
               
                 ACCGCCGTGTACTACTGCACCAGAGAGGGCATCACCACCGTGGCCACCACCTACTACTGGTACTTCGACG 
               
               
                   
               
               
                 TGTGGGGCCAGGGCACCACCGTGACCGTGAGCAGC 
               
               
                   
               
               
                 Light chain of Clone 39 
               
               
                 
                   
                             
                     
                         
                         
                     
                   
                 
               
               
                 
                   
                             
                     
                         
                         
                     
                   
                 
               
               
                 GATGTGGTGATGACCCAGAGCCCGCTGAGCCTGCCGGTGACCCTGGGCCAGCCGGCGAGCATTAGCTGC 
               
               
                   
               
               
                 CGCAGCAGCCAGAGCATTGTGCATAGCAACGGCAACACCTATCTGGAATGGTATCTGCAGAAACCGGGC 
               
               
                   
               
               
                 CAGAGCCCGCAGCTGCTGATTTATAAAGTGAGCAACCGCTTTAGCGGCGTGCCGGATCGCTTTAGCGGC 
               
               
                   
               
               
                 AGCGGCAGCGGCACCGATTTTACCCTGAAAATTAGCCGCGTGGAAGCGGAAGATGTGGGCGTGTATTAT 
               
               
                   
               
               
                 TGCTTTCAGGGCAGCCATGTGCCGCTGACCTTTGGCCAGGGCACCAAACTGGAAATTAAA 
               
               
                   
               
               
                 Heavy chain of Clone 41 
               
               
                 
                   
                             
                     
                         
                         
                     
                   
                 
               
               
                 CAGGGCCAGCTGGTGCAGAGCGGCGCGGAAGTGAAAAAACCGGGCGCGAGCGTGAAAGTGAGCTGCA 
               
               
                   
               
               
                 AAGCGAGCGGCTATACCTTTACCGATTATGAAATGCATTGGGTGCGCCAGGCGCCGGGCCAGGGCCTGG 
               
               
                   
               
               
                 AATGGATGGGCGTGATTGAAAGCGAAACCGGCGGCACCGCGTATAACCAGAAATTTCAGGGCCGCGTG 
               
               
                   
               
               
                 ACCCTGACCGCGGATAAAAGCAGCAGCACCGCGTATAIGGAACTGAGCAGCCTGCGCAGCGAAGATACC 
               
               
                   
               
               
                 GCGGTGTATTATTGCACCCGCGAAGGCATTACCACCGTGGCGACCACCTATTATTGGTATTTTGATGTGT 
               
               
                   
               
               
                 GGGGCCAGGGCACCCTGGTGACCGTGAGCAGC 
               
               
                   
               
               
                 Light chain of Clone 41 
               
               
                 
                   
                             
                     
                         
                         
                     
                   
                 
               
               
                 
                   
                             
                     
                         
                         
                     
                   
                 
               
               
                 GATGTGGTGATGACCCAGAGCCCGCTGAGCCTGCCGGTGACCCTGGGCCAGCCGGCGAGCATTAGCTGC 
               
               
                   
               
               
                 CGCAGCAGCCAGAGCATTGTGCATAGCAACGGCAACACCTATCTGGAATGGTATCTGCAGAAACCGGGC 
               
               
                   
               
               
                 CAGAGCCCGCAGCTGCTGATTTATAAAGTGAGCAACCGCTTTAGCGGCGTGCCGGATCGCTTTAGCGGC 
               
               
                   
               
               
                 AGCGGCAGCGGCACCGATTTTACCCTGAAAATTAGCCGCGTGGAAGCGGAAGATGTGGGCGTGTATTAT 
               
               
                   
               
               
                 TGCTTTCAGGGCAGCCATGTGCCGCTGACCTTTGGCCAGGGCACCAAACTGGAAATTAAA 
               
               
                   
               
               
                 Heavy chain of Clone 48 
               
               
                 
                   
                             
                     
                         
                         
                     
                   
                 
               
               
                 CAGGGCCAGCTGGTGCAGAGCGGCGCCGAGGTGAAGAAGCCCGGCGCCAGCGTGAAGGTGAGCTGCA 
               
               
                   
               
               
                 AGGCCAGCGGCTACACCTTCACCGACTACGAGATGCACTGGGTGAGACAGGCCCCCGGCCAGGGCCTG 
               
               
                   
               
               
                 GAGTGGATGGGCGTGATCGAGAGCGAGACCGGCGGCACCGCCTACAACCAGAAGTTCAAGGGCAGAG 
               
               
                   
               
               
                 CCAAGATCACCGCCGACAAGAGCACCAGCACCGCCTACATGGAGCTGAGCAGCCTGAGAAGCGAGGAC 
               
               
                   
               
               
                 ACCGCCGTGTACTACTGCACCAGAGAGGGCATCACCACCGTGGCCACCACCTACTACTGGTACTTCGACG 
               
               
                   
               
               
                 TGTGGGGCCAGGGCACCACCGTGACCGTGAGCAGC 
               
               
                   
               
               
                 Light chain of Clone 48 
               
               
                 
                   
                             
                     
                         
                         
                     
                   
                 
               
               
                 GATGTGGTGATGACCCAGAGCCCGCTGAGCCTGCCGGTGACCCTGGGCCAGCCGGCGAGCATTAGCTGC 
               
               
                   
               
               
                 CGCAGCAGCCAGAGCATTGTGCATAGCAACGGCAACACCTATCTGGAATGGTATCTGCAGAAACCGGGC 
               
               
                   
               
               
                 CAGAGCCCGCGCCTGCTGATTTATAAAGTGAGCAACCGCTTTAGCGGCGTGCCGGATCGCTTTAGCGGC 
               
               
                   
               
               
                 AGCGGCAGCGGCACCGATTTTACCCTGAAAATTAGCCGCGTGGAAGCGGAAGATGTGGGCGTGTATTAT 
               
               
                   
               
               
                 TGCTTTCAGGGCAGCCATGTGCCGCTGACCTTTGGCCAGGGCACCAAACTGGAAATTAAA 
               
             
          
         
       
     
       Example 11 
     In Vitro Stimulation of T Cells by Humanized Antibody 
       [0077]    Freshly prepared PBMCs (Beijing Blood Institute) were placed in the wells of a 96-well flat-bottom plate. After an overnight incubation, 10 ug/ml of antibody and 100 ng/ml of tetanus toxin (TT) were added to the PBMCs. After culturing it for 3 days, the supernatant was collected and the secretion level of IL2 of Clone 38, 39, 41 and 48 (control (conIgG4)) of the humanized antibodies were measured using Luminex® (Thermo Fisher Scientific, Inc.) and CD8+ cytokine assay detection kit (EMD Millipore, Inc.). The result (see  FIG. 6 ) shows that all the humanized antibodies can stimulate the T cells. 
       Example 12 
     Humanized Antibody can Stimulate T Cells to Kill Tumor Cells In Vitro 
       [0078]    MD-MAB-453 cells were infected with the lentivirus (Qiagen) expressing PD-L1 protein to generate a MD-MAB-453 cell line, which stably expresses PD-L1. A GFP gene was also introduced to said cell line to allow the stable expression of the GFP protein. Dendritic cells (DC) isolated from the fresh human peripheral blood cells 300 cells/well were cultured with said MD-MAB-453 cells stably expressing both PD-L1 and GFP (300 cells/well) in a 96-well plate together for three days. T cells (1000 cells/well) isolated from human peripheral blood and 10 ug/ml of the humanized anti-PD-1 antibody Clones 38, 39, 41 or the control antibody clone 48 (“conIgG4”) were added to the mixture and cultured together for 3 days to before the GFP fluorescence was measured. The result (see  FIG. 7 ) shows that all the humanized antibodies can stimulate T cells to kill the tumor cells. 
       Example 13 
     The Binding of Humanized Antibodies with PD-1 Proteins Derived from Various Species 
       [0079]    1 ug/ml of human-derived PD-1,  Macaca fascicularis  PD-1, and mouse-derived PD-1 (Sinobiological) in the carbonate buffer solution (0.05 M PH9) were prepared and used to coat the wells of the 96-well flat-bottom plates at 4° C. overnight. The next day, solution was removed from the wells and the wells were washed three times with a washing buffer. PBS solution containing 3% BSA was added to block the wells for 20 minutes. The wells were then washed three times with the washing buffer before 100 ul of various concentrations of candidate antibodies were added. The mixture was incubated at room temperature for 1 hour and then washed three times with a washing buffer. A HRP conjugated goat anti human antibody (Jackson Immunoresearch) was first diluted to 1:10000 with the washing buffer and then added to the wells to incubate at room temperature for 1 hour. After washing three times with the washing buffer, 50 ul TMB substrate solution was added to the wells to develop the color. After 10 minutes at room temperature, the color development reaction was terminated with 25 ul 0.5M sulfuric acid solution and the absorbance was read at 450 nm. The results ( FIGS. 8A , B and C) show that all clones bind to PD-1 of human or  Macaca fascicularis  with similar affinity, but not with the mouse-derived PD-1. 
         [0080]    Compare PD-1 sequences of human,  Macaca fascicularis  and mouse (see  FIG. 9  in which the main different regions of mouse PD-1 and PD-1 of human/ Macaca fascicularis  are boxed). Experimental results have proved that the epitope of the candidate antibody that binds to PD-1 protein exists in these regions. 
       Example 14 
     Experiment of In Vitro Stimulation by Humanized Antibody to T Cell Proliferation-Tetanus Antigen Memory Response Experiment 
       [0081]    Freshly prepared PBMC (Beijing Blood Institute) were placed into the wells of a 96-well flat-bottom plate. After incubation overnight, the cells were labeled with carboxyflurescein succinimidyl ester (CFSE) and incubated with 10 ug/ml of humanized antibody (38, 39, 41 and 48) and 100 ng/ml of tetanus toxin (TT) (List Biological Laboratories). T cell proliferation at the 6 th , 8 th  and 10 th  day was analyzed based on the dilution ratio of CSFE with the flow cytometry (FACS). As shown by the result of  FIG. 10 , compared with the control IgG, the immune cells activated by TT stimulation induced through blocking the PD-1 signal was under further division and proliferation. Example 15. In vitro stimulation of T cell proliferation by humanized antibody—viral polypeptides antigen memory response experiment 
         [0082]    Freshly prepared PBMCs (Beijing Blood Institute) were placed into the wells of a 96-well flat-bottom plate. After an overnight incubation, the cells were labeled with CFSE. 10 ug/ml of humanized antibody (38, 39, 41 and 48) and 1 ug/ml of peptide mixture of CMV, EBV and Influenza (“CEF”) were added to the wells. Quantitative analysis were conducted on T cell proliferation at the 6 th , 8 th  and 10 th  day with the flow cytometry (FACS) based on the dilution ratio of CSFE. As shown by the result of  FIG. 11 , compared with the control NG; the immune cells activated by CEF mixed polypeptides stimulation induced through blocking the PD-1 signal was under further division and proliferation.