Interferon alpha (IFN alpha) is a cytokine approved for the treatment of several types of cancer. However, the modest effect on overall survival and the high toxicity associated with the treatment has reduced the clinical use of this cytokine. In this study, we have developed a tumor model that reproduces this clinical setting. A high dose of an adeno-associated virus encoding IFN alpha (AAV-IFN alpha) was able to eradicate a liver metastases model of colon cancer but induced lethal pancytopenia. On the other hand, a safe dose of AAV-IFN alpha was not able to eliminate the liver metastases of colon cancer. In this IFN alpha-resistant tumor model, administration of an adeno-associated vector encoding apolipoprotein A-1 fused to IFN alpha was able to fully eradicate the tumor in 43% of mice without toxicity. This antitumor effect was limited by suboptimal long-term CD8+ T cell activation and the expansion of T regulatory cells. In contrast, IFN alpha upregulated suppressor molecules such as PD-1 and interleukin 10 on CD8(+) T lymphocytes. In conclusion, we show that apolipoprotein A-1 fused to IFN alpha is a novel antitumor drug that differs from IFN alpha in the modulation of suppressor mechanisms of the immune response. These differential properties pave the way for rational combinations with other immunomodulatory drugs.