[Epitopic multiple antigen peptide from α-fetoprotein elicit antitumor immune response in vitro and ex vivo].

Objective: To explore the antitumor effects of multiple antigen peptide (MAP) vaccine from α-fetoprotein (AFP) through AFP-specific cytotoxic T lymphocyte (CTL) against hepatoma in vitro and ex vivo.
Methods: Dendritic cells (DC) were generated from human peripheral blood mononuclear cells (PBMC) and HLA-A2.1-transgenic murine bone marrow. The AFP-specific CTL were induced by MAP-loaded DC and the corresponding linear peptides from human AFP. The lysis rate of effectors to hepatoma cells were tested by 4 h (51)Cr release assay. And enzyme-linked immunosorbent spot (ELISPOT) was used to test the interferon (IFN)-γ release of effector cells.
Results: The specific lysis rate of effectors induced by AFP epitopic MAP vaccines to Hep3B cells (AFP(+), HLA-A2.1(+)) at the highest effector/target (E/T) ratio was significantly higher than linear peptide vaccine (73.5% ± 7.9% vs 45.6% ± 6.9%, P < 0.01). The effectors induced by AFP epitopic MAP vaccine and linear peptide vaccine could not lysis the AFP-negative PLC/PRF/5 liver cancer cells versus the negative control group at the highest E/T (9.3% ± 3.9%, 8.1% ± 2.8% vs 8.3% ± 2.6%, both P > 0.05). But the effectors induced by AFP epitopic MAP vaccine and linear peptide vaccine could lyse PLC/PRF/5 liver cancer cells transfected with cDNA of AFP versus the negative control group (74.8% ± 10.5%, 51.4% ± 12.6% vs 4.2% ± 1.3%, both P < 0.01). And the specific lysis rate of effectors induced by AFP epitopic MAP vaccines was significantly higher than the corresponding linear peptide vaccine (P < 0.01). Compared with the negative control group, the effectors could not lyse HepG2 liver cancer cells, a HLA-A2.1 negative cell line (both P > 0.05). But the effectors could lyse HepG2 cells transfected with cDNA of HLA-A2.1 (71.8% ± 8.6%, 46.5% ± 6.5% vs 4.1% ± 1.1%, both P < 0.01). And the specific lysis rate of effectors induced by MAP vaccine was significantly higher than the corresponding linear peptide vaccine (P < 0.01). ELISPOT test showed that the capability of enhancing IFN-γ release of human AFP MAPs was stronger than that of the AFP linear peptides. The spots count of MAP vaccine group ((158 ± 23) spots/10(5) cells) or linear peptide vaccine group ((78 ± 12) spots/10(5) cells) were significantly higher than the negative control group ((3 ± 1) spots/10(5) cells) (all P < 0.01). The spots count of the positive control group ((166 ± 32) spots/10(5) cells) showed no significant difference with the AFP MAP vaccine group (P > 0.05). And the spots count of MAP vaccine group were significantly higher than the corresponding linear peptide vaccine group ((78 ± 12) spots/10(5) cells, P < 0.01).
Conclusions: AFP multiple antigen peptides elicit not only more powerful specific anti-tumor immune responses but also stronger non-specific anti-tumor immune activities than their corresponding linear peptides. These findings will provide theoretical rationales for their clinical applications.