α-fetoprotein - specific tumor immynity induced by plasmid DNA vaccination

使用肿瘤特异性抗原基因的DNA疫苗是一种很有前途的癌症免疫治疗策略。鉴于甲胎蛋白(AFP)基因在小鼠肝癌细胞中特异表达，并可作为肝癌的肿瘤标志物，本研究探讨了甲胎蛋白(AFP)基因表达载体DNA疫苗对小鼠肝癌细胞生长的抑制作用。我们分别构建了小鼠AFP表达载体pCMAFP和腺病毒载体AdAFP。将这些表达小鼠AFP的载体导入HeLa细胞后，虽然AdAFP的表达明显好于pCMAFP，但仍能在HeLa细胞中得到充分表达。为探讨pCMAFP疫苗对小鼠肝癌细胞生长的抑制作用，用100μg的pCMAFP皮下注射免疫小鼠。2周后，将5×10~(-6)MH134小鼠肝癌细胞接种于每只小鼠背部皮下，测量肿瘤生长情况。单独接种pCMAFP对肿瘤生长仅有轻微的抑制作用，但将表达造血生长因子基因的GMCSF和MCSF与PCMAFP共导入可有效抑制肿瘤的生长。此外，在第一次接种后一周以10^9pfu的AdAFP加强接种也显示出明显的抑制肿瘤生长的作用。我们使用另一种小鼠肝癌细胞Hepal-6进行了类似的实验，该细胞比MH134产生更多的AFP。PCMAFP疫苗对Hepl-6细胞生长的抑制作用强于MH134，这可能与这两种细胞AFP产量的差异有关。这些结果提示甲胎蛋白DNA疫苗在治疗肝癌方面有潜在的治疗潜力。

DNA vaccination using the tumor specific antigen gene is a promising strategy for cancer immunotherapy. In the present study, we examined whether the vaccination with plasmid DNA expressing a -fetoprotein (AFP) gene could inhibit the growth of mouse hepatoma cells since AFP is specifically expressed in hepatoma cells and used clinically as a tumor marker of hepatoma. We have constructed the mouse AFP expressing plasmid vector, pCMAFP, and adenovirus vector, AdAFP, respectively. The transduction of these mouse AFP expressing vehicles into HeLa cells resulted in the adequate expression of mouse AFP although AdAFP showed much better expression than pCMAFP. To examine the inhibitory effect of pCMAFP vaccination on the growth of mouse hepatoma cells, mice were immunized by the subcutaneous injection with 100 μg of pCMAFP. Two weeks later, 5 x 10^6 of MH134 mouse hepatoma cells were inoculated into back subcutaneous of each mouse, and the tumor growth was measured. pCMAFP vaccination alone showed only a slight inhibition of tumor growth, however, co-introduction of plasmids expressing hematopoietic growth factor genes such as GMCSF and MCSF with PCMAFP effectively inhibited the tumor growth. More over, a booster vaccination with 10^9 PFU of AdAFP one week after first vaccination also showed the apparent inhibition of tumor growth. We performed the similar experiments using another mouse hepatoma cells, Hepal-6, which produce AFP more abundantly than MH134. The growth of Hepl-6 was more effectively inhibited by PCMAFP vaccination than that of MH134, which may be relevant to the differences of AFP productivity in these cells. These results suggest that AFP DNA vaccination may have a therapeutic potential in the treatment of hepatoma.