Figure 3.
(Left) IFN-γ-secreting and IFN-γ-insensitive 6132A-PRO tumor cells grow at similar rates in vitro as do unmodified 6132A-PRO parental cells. The in vitro growth of PRO-DNγR cells, PRO-IFN-γ cells, and 6132A-PRO cells (PRO) was analyzed in a [(3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium] (MTS) assay by measuring absorbance at 490 nm minus background absorbance at 650 nm. All experiments were done in triplicate, and SEM >0.08 are indicated. (Middle) IFN-γ is neither cytotoxic nor cytostatic for 6132A-PRO cells in vitro. The proliferation of 6132A-PRO tumor cells in vitro in the presence of varying amounts of IFN-γ was measured in an MTS assay by reading the absorbance at 490 nm minus the background absorbance at 650 nm. All experiments were performed in triplicate and SEM >0.08 are indicated. (Right) Growth of IFN-γ-secreting 6132A-PRO tumor cells in vivo. SCID mice were inoculated s.c with 105 6132A-PRO (PRO) or 3 × 105 IFN-γ-secreting PRO-IFN-γ, and tumor growth was measured every 3–4 days. Two of the five animals challenged with PRO-IFN-γ were treated with anti-IFN-γ antibodies. The SEM were always <0.03 and therefore are not shown. The tumor growth differs across the three groups (P value = 0.036) by Fisher’s Exact test considering rapid growth in the three PRO-challenged mice or the two mice challenged with PRO-IFN-γ cells but treated with anti-IFN-γ versus the three mice challenged with PRO-IFN-γ cells.