Analysis of factors involved in the antineoplastic activity of IFN-α. (A) Analysis of IL-6 and IL-10 release in culture supernatants of transduced CRO-AP/3 cells. Histograms resume data obtained by analyzing different time points in 2 independent transduction experiments using mIFN-α₁-LV in parallel with EGFP-LV and in 2 independent experiments using hIFN-α₂b-LV and EGFP-LV. Data refer to infections performed at MOI 2 and are reported as ratio between the mean of different time points of LV-transduced cells and the mean of control mock-transduced cells; SD of the ratio was calculated as stated in Figure 1. *Statistically significant differences between hIFN-α₂b-LV–transduced cells and the other groups (Student t test). IL-6 and IL-10 secretion was significantly up-regulated in CRO-AP/3 cells expressing hIFN-α₂b in vitro, whereas EGFP-LV– and mIFN-α₁-LV–transduced cells released comparable levels of these cytokines. (B) Measurement of VEGF levels in supernatants from transduced CRO-AP/3 cells and ascites. Data are expressed in picograms per milliliter, and each histogram in the left panel represents the mean and SD of data obtained in the transduction experiments described above, at the time points shown below each column. Data in the in vivo panel report the mean and SD of VEGF measured in the cell-free fraction of ascites from 8 control mice (medium and EGFP-LV), 3 mIFN-α₁-LV–treated mice, 2 hIFN-α₂b-LV–treated mice with a fully developed effusion, and 2 hIFN-α₂b-LV–treated animals with regressed ascites. *Statistically significant differences between hIFN-α₂b-LV–transduced cells and the other groups, and between hIFN-α₂b-LV–treated mice with regressed ascites and the other groups (Student t test). The murine cytokine did not affect VEGF secretion by PEL cells in vitro and in vivo, whereas human IFN-α significantly down-regulated VEGF release in vitro and was found to be consistently reduced in regressed ascites (volumes ≤ 0.5 mL).