Enhancing immunogenicity of a CTL epitope from carcinoembryonic antigen by selective amino acid replacements.
OBJECTIVE
Many epitopes from tumor antigens recognized by CTLs canbe poorly immunogenic. This low immunogenicity can be improved by carrying out amino acid replacements in their sequence. We have applied this strategy to enhance the immunogenicity of the HLA-A2-restricted CTL epitope CEA691 (IMIGVLVGV) from carcinoembryonic antigen (CEA), which is expressed by a wide variety of tumors.


METHODS
Substituted peptides from CEA691 were synthesized and tested in HLA-A2-binding assays, and in recognition by CEA691-specific CTL. Selected peptides were used to induce CTL responses in vivo in HLA-A2Kb transgenic mice and in vitro with human cells.


RESULTS
Our experiments afforded several peptides with enhanced binding and/or recognition by CTL specific of CEA691. However, when HLA-A2Kb mice were immunized with these peptides only a few induced a CTL response that cross-reacted with CEA691. Additional replacement of their NH(2)-terminal amino acid by Y (tyrosine) afforded peptides YMIGMLVGV and YMIGVLLGV with enhanced in vivo and in vitro immunogenicity than CEA691. Indeed, they activated a greater number of precursor cells that recognized CEA691-pulsed cells and tumor cells expressing CEA.


CONCLUSIONS
Our results widen the possibility of treating CEA-expressing tumors with enhanced efficacy.
Huarte
Eduardo
E
Department of Internal Medicine, University of Navarra, 31008 Pamplona, Spain.
Sarobe
Pablo
P
Lu
Jun
J
Casares
Noelia
N
Lasarte
Juan José
JJ
Dotor
Javier
J
Ruiz
Marta
M
Prieto
Jesús
J
Celis
Esteban
E
Borrás-Cuesta
Francisco
F
D000818:Animals; D019496:Cancer Vaccines / Q000276:immunology; D002272:Carcinoembryonic Antigen / Q000276:immunology*; D003602:Cytotoxicity, Immunologic; D003713:Dendritic Cells / Q000276:immunology; D000939:Epitopes / Q000276:immunology*; D018984:Epitopes, T-Lymphocyte / Q000276:immunology; D015789:HLA-A2 Antigen / Q000276:immunology*; D006801:Humans; D066298:In Vitro Techniques; D051379:Mice; D008822:Mice, Transgenic; D010446:Peptide Fragments / Q000138:chemical synthesis / Q000276:immunology*; D011485:Protein Binding; D013602:T-Lymphocytes, Cytotoxic / Q000276:immunology*; D014443:Tyrosine / Q000276:immunology; D014611:Vaccination
D019496:Cancer Vaccines; D002272:Carcinoembryonic Antigen; D000939:Epitopes; D018984:Epitopes, T-Lymphocyte; D015789:HLA-A2 Antigen; D010446:Peptide Fragments; D014443:Tyrosine