Figure 3.

IAV Infection Mediates Oncolysis of B16-F10 Melanoma Lung Metastases

(A) Schematic representation of IAV infection, tumor score, and BALF analysis of C57BL/6 mice after i.v. injection of syngeneic B16F10 melanoma cells. (B–D) B16-F10 cells (2 × 10⁵ per mouse) were injected intravenously to establish pulmonary metastases. After 7 days, animals were infected with 300 plaque-forming units (PFU) of influenza A/PR8/8/34 (PR8) H1N1 strain (red symbols) or mock-infected with PBS (black symbols) and the lung tumor burden was determined each third day after infection. (B) Numbers of tumor foci on the surface of right lungs at indicated days after IAV infection. (C) Content of tumor tissue in lungs was calculated as a ratio of MC1R-positive tumor area normalized to the whole-lung section area after different days of IAV infection. (D) The expression of melanoma-specific Dct mRNA in lung tissues was measured by TaqMan qRT-PCR. The values are normalized to Dct mRNA levels of control animals that had not been injected with B16-F10 cells or infected with PR8. (E) Control (open symbols) or B16-F10-implanted (filled symbols) mice were infected with 300 PFU of PR8 IAV, and virus titers in BALFs were determined by plaque assay at times indicated. Values of individual animals and mean values (black lines) per group are shown. (F) Paraffin lung sections of tumor-bearing mice infected for 3 or 6 days with PR8 IAV were stained for expression of viral NP protein (red) and counterstained with hematoxylin (blue). Most melanoma cells show characteristic melanin inclusions. Scale bars, 50 μm. ∗p < 0.05, ∗∗p < 0.01, ∗∗∗p < 0.001 (B–D, Mann-Whitney U test; E, two-way ANOVA followed by Sidak’s multiple comparisons test)