Figure 2.

Virus preinfection of tumors in vivo does not preclude superinfection by heterologous virus. Subcutaneous A549 human lung carcinoma xenografts were implanted in both flanks of nude mice. When tumors had formed, the graft on the right flank was injected intratumorally with either PBS or with 1 × 10⁸ PFU Ad5/3-Δ24 or with 1 × 10⁷ PFU VV-tdTomato. Forty-eight hours later, an i.v. injection was made with either 1 × 10⁸ PFU Ad5/3-Δ24 or with 1 × 10⁷ PFU VV virus. Forty-eight hours after that, tumors and liver were excised and virus was titered by plaque assay/TCID50. (a,b) Vaccinia virus (black triangles) is able upon systemic administration to enter and infect tumors preinfected with adenovirus with equal efficiency as noninfected tumors. (c,d) Infectious adenovirus (empty circles) can only be recovered from tumors preinjected by PBS or vaccinia virus (*P < 0.05, Student’s t-test on log-transformed virus titers). For quantitative genomic virus titers, see Supplementary Figure 3.