Oncolytic virus (OV) therapy is an experimental form of biological therapy has shown increasing potential over the last decade, culminating with the first FDA approval of an OV therapy, the Herpes simplex virus Talimogene laherparepvec (T-VEC), in 2015. Newcastle disease virus (NDV), a promising OV with a strong safety record, preferentially replicates in and kills established cancer cells, while leaving normal cells untouched. While NDV can activate and prime the immune system to recognize malignant cells, cytotoxic T cells can ultimately be inhibited in the highly immune suppressive milieu of the tumor microenvironment. To counter these immune suppressive roadblocks, we hypothesize that arming NDV with immune checkpoint blockades, including a humanized CTLA-4 antibody and soluble PD-1, will prevent T cell shutdown and localize expression of these biologics to the tumor. Described herein are methods and experiments to test this hypothesis. We optimized a protocol for efficient rescue of rNDV in embryonated chicken eggs and found that both tangential flow filtration and interference chromatography are feasible methods for the purification of high-titer, ultra-clean suitable for systemic delivery in murine cancer models. Additionally, we characterized a panel of murine cancer cell lines to determine the most appropriate model to test vectorization of NDV. We discovered that murine melanoma (B16-F10) cells are most susceptible to NDV oncolysis, but die too quickly to support much transgene expression, whereas a cell line like the murine colon carcinoma CT26LacZ cells, which are not able to produce or respond to IFN, are less susceptible to NDV-mediated oncolysis but can support reasonable levels of virus replication and transgene expression. Finally, we evaluated rNDVs expressing immune checkpoint blockades in vivo in CT26LacZ and B16-F10 cancer models and observed a promising increase in the ratios of activated CD8+ T cells to suppressive T regulatory and myeloid derived suppressor cells, which have been shown to be important indicators of outcome, in mice treated with rNDV expressing checkpoint inhibitors compared to controls. These results demonstrate that arming NDV with immune checkpoint blockades warrants further investigation as a potential therapeutic agent for cancer treatment in humans.