Vaccination with the repeat β-hCG C-terminal peptide carried by heat shock protein-65 (HSP65) for inducing antitumor effects

The β-subunit of human chorionic gonadotropin (β-hCG) is ectopically expressed in various types of cancer and has been utilized as an antigenic target in anti-cancer vaccines. In view of the low immunogenicity of this self-peptide, we designed a method based on the isocaudamer technique to generate 14 tandem repeats of the 10-residue sequence X of β-hCG (109-118). These tandemly repeated copies were then combined with β-hCG C-terminal 37 peptides (CTP37) and finally fused to mycobacterial heat-shock protein 65 (HSP65) to construct a fusion protein HSP65-X14-βhCGCTP37 as an immunogen. In this study, BALB/c female mice were immunized via subcutaneous injection of the designed protein. Humoral immune and cellular immune responses were effectively elicited. A high titer of anti-β-hCG antibody was detected in immunized mice sera by enzyme-linked immunosorbent assay and verified by Western blot analysis. The fusion protein, HSP65-X14-β-hCGCTP37, effectively inhibited the growth of Ehrlich ascites carcinoma in mice. These results suggest that HSP65-X14-βhCGCTP37 may be an effective tumor vaccine, and the use of multiple tandem repeats of a certain epitope is an effective method to overcome the low immunogenicity of self-peptide antigens.