Receptor on the surface of activated T-cells: ACT-4

Abstract

The invention provides purified ACT-4 receptor polypeptides, antibodies against these polypeptides and nucleic acids encoding ACT-4 receptor polypeptides. Also provided are methods of diagnosis and treatment using the same. ACT-4 receptors are preferentially expressed on the surface of activated CD4 + T-cells. ACT-4 receptors are usually expressed at low levels on the surface of activated CD8 + cells, and are usually substantially absent on resting T-cells, and on monocytes and B-cells (resting or activated). An exemplary ACT-4 receptor, termed ACT-4-h-1, has a signal sequence, an extracellular domain comprising three disulfide-bonded intrachain loops, a transmembrane domain, and an intracellular domain.

What is claimed is:  
     
         1 . A purified ACT-4 receptor polypeptide that comprises at least five contiguous amino acids from an amino acid sequence shown in FIG. 5.  
     
     
         2 . The polypeptide of    claim 1    that exhibits at least eighty percent sequence identity to the amino acid sequence of FIG. 5.  
     
     
         3 . The polypeptide of    claim 2    having an antigenic determinant common to a protein comprising the amino acid sequence shown in FIG. 5.  
     
     
         4 . The polypeptide of    claim 3    that is a full-length polypeptide.  
     
     
         5 . The polypeptide of    claim 4    comprising a domain selected from a group of domains consisting of a signal sequence, an intracellular domain, a transmembrane domain, and an extracellular domain.  
     
     
         6 . The polypeptide of    claim 5    that comprises an extracellular domain.  
     
     
         7 . The polypeptide of    claim 6   , wherein said extracellular domain comprises an intrachain loop formed by disulfide bonding of two cysteine residues.  
     
     
         8 . The polypeptide of    claim 7   , wherein said extracellular domain comprises three intrachain loops, each formed by disulfide bonding of two cysteine residues.  
     
     
         9 . The polypeptide of    claim 8   , wherein said polypeptide is present on the surface of activated CD4 +  T-cells, and is substantially absent on activated CD8 +  T cells and resting T-cells.  
     
     
         10 . The polypeptide of    claim 9    that is naturally occurring.  
     
     
         11 . The polypeptide of    claim 10    that is human.  
     
     
         12 . The polypeptide of    claim 11    that has a molecular weight of about 50 kDa before deglycoslyation and about 27 kDa thereafter.  
     
     
         13 . The polypeptide of    claim 12    comprising the amino acid sequence of FIG. 5.  
     
     
         14 . An extracellular domain of a polypeptide of    claim 3   .  
     
     
         15 . The extracellular domain of    claim 14    comprising an intrachain loop formed by disulfide bonding of two cysteine residues.  
     
     
         16 . The extracellular domain of    claim 15    comprising three intrachain loops, each formed by disulfide bonding of two cysteine residues.  
     
     
         17 . The extracellular domain of    claim 16    that is soluble.  
     
     
         18 . The extracellular domain of    claim 17    that is capable of specifically binding to an ACT-4 ligand.  
     
     
         19 . The extracellular domain of    claim 18    that is immunogenic.  
     
     
         20 . The extracellular domain of    claim 19    that competes with an ACT-4-h-1 receptor polypeptide for specific binding to an antibody.  
     
     
         21 . The extracellular domain of    claim 20    that is fused to a second polypeptide.  
     
     
         22 . The extracellular domain of    claim 21   , wherein the second polypeptide is a constant region of an immunoglobulin heavy chain.  
     
     
         23 . A polypeptide consisting essentially of an epitope specifically bound by an antibody designated L106.  
     
     
         24 . An antibody that specifically binds to an ACT-4-h-1 receptor polypeptide.  
     
     
         25 . The antibody of    claim 24    that is a monoclonal antibody.  
     
     
         26 . The antibody of    claim 25    that inhibits activation of CD4 +  T-cells.  
     
     
         27 . The monoclonal antibody of    claim 25    that stimulates activation of CD4 +  T-cells.  
     
     
         28 . The antibody of    claim 25    that competes with an antibody designated L106 for specific binding to an ACT-4-h-1 receptor polypeptide.  
     
     
         29 . The antibody of    claim 25    that competes with an antibody designated L106 for specific binding to activated CD4 +  T-cells.  
     
     
         30 . The antibody of    claim 25    that is fused to a coat protein of a filamentous phage.  
     
     
         31 . The antibody of    claim 29    that is L106.  
     
     
         32 . A humanized antibody comprising a humanized heavy chain and a humanized light chain: 
 (1) the humanized light chain comprising three complementarity determining regions (CDR1, CDR2 and CDR3) having amino acid sequences from the corresponding complementarity determining regions of a L106 antibody light chain, and having a variable region framework sequence substantially identical to a human light chain variable region framework sequence; and    (2) the humanized heavy chain comprising three complementarity determining regions (CDR1, CDR2 and CDR3) having amino acid sequences from the corresponding complementarity determining regions of a L106 antibody heavy chain, and having a variable region framework sequence substantially identical to a human heavy chain variable region framework sequence;    wherein the humanized antibody specifically binds to an ACT-4-h-1 receptor polypeptide with a binding affinity that is within three-fold of the binding affinity of a L106 antibody.    
     
     
         33 . An immunotoxin comprising the antibody of    claim 31    fused to a toxin polypeptide.  
     
     
         34 . The antibody of    claim 25    that specifically binds to a different epitope on an ACT-4-h-1 receptor polypeptide than that specifically bound by an L106 antibody.  
     
     
         35 . A fragment of the antibody of    claim 31    that specifically binds to an ACT-4-h-1 receptor polypeptide.  
     
     
         36 . A hybridoma producing antibody L106, said hybridoma deposited as ATCC______.  
     
     
         37 . A method of screening an antibody for specific binding to the same epitope as that bound by an L106 antibody, said method comprising: 
 providing a solution comprising an antibody to be screened, said L106 antibody, and an ACT-4-h-1 receptor polypeptide, said polypeptide specifically binding to said L106 antibody; and    measuring specific binding between said polypeptide and said L106 antibody, or between said polypeptide and said antibody to be screened, to indicate whether said antibody to be screened reacts with the same epitope as said L106 antibody.    
     
     
         38 . A method of localizing an epitope specifically bound by an L106 antibody, said method comprising: 
 providing a family of ACT-4-h-1 receptor polypeptides, each member of said family comprising a contiguous segment of at least four amino acids; and    measuring specific binding between a polypeptide from said family and said L106 antibody to indicate the presence of said epitope within said polypeptide.    
     
     
         39 . A nucleic acid fragment encoding a heavy chain of an antibody of    claim 31   .  
     
     
         40 . A nucleic acid fragment encoding a light chain of an antibody of    claim 31   .  
     
     
         41 . A nucleic acid fragment encoding an ACT-4 polypeptide of    claim 1   .  
     
     
         42 . The nucleic acid fragment of    claim 41    that exhibits at least eighty percent sequence identity with the nucleic acid sequence shown in FIG. 5.  
     
     
         43 . The nucleic acid fragment of    claim 42    that encodes a full-length ACT-4 polypeptide.  
     
     
         44 . The nucleic acid fragment of    claim 43    comprising the translated region of the nucleic acid sequence shown in FIG. 5.  
     
     
         45 . An isolated cell line containing a nucleic acid fragment of    claim 41   .  
     
     
         46 . The isolated cell line of    claim 45   , wherein the ACT-4 receptor polypeptide is expressed on the surface of said cell.  
     
     
         47 . The isolated cell line of    claim 46    that is stable.  
     
     
         48 . The isolated cell line of    claim 47   , wherein said nucleic acid fragment is incorporated in the gonome of said cell line.  
     
     
         49 . The isolated cell line of    claim 48   , wherein said cell line is COS-7.  
     
     
         50 . A method of screening for immunosuppressive agents, said method comprising: 
 contacting an ACT-4-h-1 receptor polypeptide with a potential immunosuppressive agent; and    detecting specific binding between said ACT-4-h-1 receptor polypeptide and said agent, said specific binding indicative of immunosuppressive activity.    
     
     
         51 . The method of    claim 50   , wherein said ACT-4 receptor polypeptide is immobilized to a solid surface.  
     
     
         52 . A method for screening for an ACT-4 ligand, said method comprising: 
 contacting a biological sample containing said ACT-4 ligand with an ACT-4-h-1 receptor polypeptide;    isolating a complex formed between said ligand and said ACT-4-h-1 receptor polypeptide; and    dissociating said complex to obtain said ligand.    
     
     
         53 . A method of suppressing an immune response in a patient suffering from an immune disease or condition, said method comprising administering to a patient a therapeutically effective dose of a pharmaceutical composition comprising a pharmaceutically active carrier and a monoclonal antibody of    claim 26   .  
     
     
         54 . A method of inducing an immune response to a selected antigen comprising: 
 administering a monoclonal antibody of    claim 27    to a patient; and    exposing said patient to said selected antigen.    
     
     
         55 . A method of detecting activated CD4 +  T-cells, said method comprising: 
 contacting a tissue sample from a patient with a monoclonal antibody of    claim 24    and    detecting specific binding between said monoclonal antibody and said tissue sample to reveal the presence of said activated CD4 +  T-cells.    
     
     
         56 . The method of    claim 55   , wherein the presence of activated T-cells revealed by said specific binding is diagnostic of a disease or condition of the immune system.  
     
     
         57 . A pharmaceutical composition comprising a monoclonal antibody of    claim 26    and a pharmaceutically acceptable excipient.  
     
     
         58 . An ACT-4 ligand that specifically binds to an ACT-4-h-1 receptor polypeptide.