Immunogenic regions of the GA733-2 tumour-associated antigen recognised by autoantibodies of patients with colorectal carcinoma.
The tumour-associated antigen (TAA) GA733-2 is overexpressed by >90% of human colorectal carcinomas (CRC). The antigen has previously been shown to be recognised by B and T cells. The aim of the present study was to define B cell epitopes of GA733-2. Fifteen percent of CRC patients with no previous immunotherapy have recently been shown to elicit an anti-GA733-2 IgG antibody response. Sera of these patients ( n=136) were analysed by enzyme-linked immunosorbent assay (ELISA) for immunoglobulin G (IgG) antibodies against 23 partly overlapping synthetic peptides (18 amino acids: aa) derived from the extracellular domain of GA733-2. An 18-aa long sequence at the N-terminal region of the antigen (peptide 2) was found to be an immunodominant B cell epitope. Fifty percent of the patients had antibodies against peptide 2, while 8% to 9% had antibodies against peptides 1, 4, 7, 8 or 20. In healthy donors ( n=30) antibodies against peptides 2 and 8 were also detected in 13% and 3% of cases respectively, while no antibodies were found against the other peptides and the complete protein. Thirteen percent of CRC patients ( n=30) with no IgG antibodies against the GA733-2 antigen elicited antibodies against peptide 2. The specificity of peptide-reactive sera was verified by inhibition ELISA. The binding of sera to GA733-2 was significantly inhibited by peptides to which CRC sera bound, but not by control peptides. Binding to peptide 2 of sera showing both peptide 2 and GA733-2 reactivity was specifically inhibited by the complete GA733-2 antigen, while binding of peptide 2-reactive sera showing no GA733-2 reactivity was not inhibited. CRC sera interfered with the binding of monoclonal antibody (mAb) 17-1A and mAb C215 that recognise distinct epitopes of GA733-2. No significant correlation was found between the presence of anti-peptide antibodies in CRC patients and clinical stage or overall survival. The results provide additional evidence for immune recognition of CRC by the host.
Mosolits
Szilvia
S
Immune and Gene Therapy Laboratory, Cancer Centre Karolinska, Karolinska Hospital, 171 76 Stockholm, Sweden.
Steinitz
Michael
M
Harmenberg
Ulrika
U
Ruden
Ulla
U
Eriksson
Emma
E
Mellstedt
Håkan
H
Fagerberg
Jan
J
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000595:Amino Acid Sequence; D000911:Antibodies, Monoclonal / Q000276:immunology; D000951:Antigens, Neoplasm / Q000276:immunology*; D001323:Autoantibodies / Q000276:immunology*; D015815:Cell Adhesion Molecules / Q000276:immunology*; D015179:Colorectal Neoplasms / Q000276:immunology / Q000401:mortality; D004797:Enzyme-Linked Immunosorbent Assay; D000071858:Epithelial Cell Adhesion Molecule; D005260:Female; D006801:Humans; D007074:Immunoglobulin G / Q000097:blood; D008297:Male; D008875:Middle Aged; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000276:immunology*
D000911:Antibodies, Monoclonal; D000951:Antigens, Neoplasm; D001323:Autoantibodies; D015815:Cell Adhesion Molecules; D000071858:Epithelial Cell Adhesion Molecule; D007074:Immunoglobulin G; D010446:Peptide Fragments