Abstract: Described herein are chimeric Newcastle disease viruses comprising a packaged genome comprising a transgene encoding interleukin-12. The chimeric Newcastle disease viruses and compositions thereof are useful in combination with an antagonist of programmed cell death protein 1 (“PD-1”) or a ligand thereof in the treatment of cancer. In particular, described herein are methods for treating cancer comprising administering the chimeric Newcastle disease viruses in combination with an antagonist of PD-1 or a ligand thereof, wherein the chimeric Newcastle disease virus comprises a packaged genome comprising a transgene encoding interleukin-12.