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

利用肿瘤特异性抗原基因进行DNA疫苗接种是一种很有前途的肿瘤免疫治疗策略。由于甲胎蛋白（AFP）在肝癌细胞中特异性表达，并可作为临床上肝癌的肿瘤标志物，本研究探讨了用表达AFP基因的质粒DNA疫苗接种小鼠肝癌细胞是否能抑制其生长。我们分别构建了小鼠AFP表达质粒载体pCMAFP和腺病毒载体AdAFP。将这些小鼠AFP表达载体转导到HeLa细胞中导致小鼠AFP的充分表达，尽管AdAFP显示出比pCMAFP好得多的表达。为了检测pCMAFP疫苗接种对小鼠肝癌细胞生长的抑制作用，通过皮下注射100 μg pCMAFP免疫小鼠。两周后，将5x 10^6个MH 134小鼠肝癌细胞接种到每只小鼠的背部皮下，并测量肿瘤生长。单独的pCMAFP疫苗接种仅显示出对肿瘤生长的轻微抑制，然而，表达造血生长因子基因如GMCSF和MCSF的质粒与PCMAFP的共引入有效地抑制了肿瘤生长。此外，在第一次接种后一周用10^9PFU的AdAFP加强接种也显示出明显的肿瘤生长抑制。我们使用另一种小鼠肝癌细胞Hepal-6进行了类似的实验，Hepal-6产生的AFP比MH 134更丰富。PCMAFP疫苗对Hepl-6细胞的生长抑制作用明显强于MH 134细胞，这可能与二者AFP产量的差异有关。这些结果表明，AFP DNA疫苗接种可能具有治疗肝癌的潜力。

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.