Purpose: The possibility of tumor rejection antigen, encoded by the MAGE-1 gene, being a target for immunotherapy in hepatocellular carcinoma (HCC) patients and the cloning of the full-length cDNA of this gene for subsequent studies were explored with the aim of discovering new immunotherapeutic strategies for HCC.
Methods: Expression of the MAGE-1 gene in HCC specimens and HCC cell lines was examined by the reverse transcription/polymerase chain reaction (RT-PCR) with a pair of specific primers, which gave a 421-bp fragment. Another pair of primers were then used to amplify the full-length MAGE-1 cDNA by the same method. The PCR products were then digested by restriction endonucleases and inserted into the plasmid PUC19. After primary selection of the recombinants by endonuclease digestion, the sequences of the inserted gene fragments were confirmed by DNA sequence analysis.
Results: In 45 HCC patients, MAGE-1 mRNA was expressed in 27 tumor tissues (60%) and 5 paratumor tissues (11.1%). All the four HCC cell lines positively expressed the MAGE-1 gene. Owing to the high homology of the MAGE gene family, we obtained three clones of different MAGE genes using the same pair of cloning primers. The three clones were confirmed to be a full-length MAGE-1 gene, a 750-bp fragment of the MAGE-3 gene and a fragment highly homologous to MAGE-6 and MAGE-12 but not identical to any known MAGE genes.
Conclusion: The high expression frequency of MAGE-1 gene in HCC suggests the possibility of using it as a target for immunotherapy in HCC patients. Some MAGE genes other than MAGE-1 may also be expressed in HCC together with an unknown MAGE gene that might introduce new targets for immune attacks. The three gene clones obtained in this study can be used in further investigations and especially in the development of new liver cancer vaccines.