In vivo experiments

Animal protocols were approved by the Mayo Clinic Institutional Care and Use Committee. Four- to 5-week-old female C57BL/6J mice (Harlan Laboratories) received 2 × 10⁶ C1498 cells implanted subcutaneously on the right flank. Fourteen days later, mice received 1 IV dose of VSV-mIFNβ-NIS (10⁶, 10⁷, or 10⁸ TCID₅₀) or phosphate-buffered saline. Three days later, some mice received 200 μg of anti-PD-L1 Ab (10F.9G2; BioXCell) given intraperitoneally (IP) on days 17, 20, and 23. Isotype control rat immunoglobulin G2b (IgG2b) Ab (LTF-2; BioXCell) was used in the control group. Tumors were harvested on day 30 (16 days postvirus).

AML was established by IV injection of 2 × 10⁶ C1498.GFP cells into mice. Twelve days post-C1498.GFP administration, mice were treated with VSV-mIFNβ-NIS (10⁸ TCID₅₀; IV). Three days later, some mice received anti-PD-L1 Ab IP (200 μg per dose) 3 times, given 3 days apart. Rat IgG2b Ab was used as the isotype control. Mice were euthanized when they lost ≥10% of their body weight, demonstrated inactivity, or exhibited paralysis of both hindlimbs. T-cell depletion studies were performed to determine the impact of CD4, CD8, or natural killer (NK) cells on virotherapy. Details of the experiment and the associated immune cell analysis (enzyme-linked immunospot [ELISPOT] and IFN-γ staining) are in supplemental Methods (available on the Blood Web site).