What Oncolytic viruses (OVs) are new class of immunotherapeutic agents. They are naturally occurring or genetically engineered viruses that have selective tumor killing capacity. One major advantage is that they are antigen agnostic, meaning that they are not restricted to one type of tumor. A therapy based on oncolytic viruses has already been approved for inoperable melanoma (T-VEC) and many more are in clinical trials. The mechanisms of anti-tumor effects consist of direct cell lysis and recruitment of the body’s immune system against the cancer, making “cold tumors” hot. The goal of my project is to map the inducers and inhibitors of OV therapy within tumors and healthy tissue, and thus identify novel genes and factors that can be harnessed in development of novel improved OV-based therapies. Why Oncolytic viruses are a new and promising type of immunotherapy where tumors are eradicated by infection with a virus. However, some treatments are non-responsive because of antiviral mechanisms in certain tumors. These can for example be expression of antiviral genes in the tumor or the lack of proviral transcription factors. Understanding these mechanisms in greater detail allows for development of new OVs. Because OVs can be genetically engineered, we are able to produce viruses that deliver essential proviral genes to the tumor, and thus overcoming the resistance to treatment. How We will use bidirectional whole-genome CRISPR screens on human and mouse cancer cell lines, meaning that in each cell, one gene is silenced or activated. Second, we will infect cells with OVs, and using sequencing we will map how every single gene in tumor cells contribute to or inhibit viral infection. By molecular cloning, the important genes can be engineered into the viral genome such that the virus delivers its own inducers or inhibitors of tumor’s viral silencers. To test our lead viral candidates we will develop a novel mouse model transplanted with tumors that harbor specific mutations that make them either highly susceptible or resistant to infections with oncolytic viruses. This allows us to test and improve genetically modified oncolytic viruses that will function as next-generation immunotherapy.