The present invention relates generally to the fields of oncology, virology and immunotherapy. More particularly, it concerns the use of poxviruses, specifically the replication competent attenuated vaccinia virus with deletion of thymidine kinase (VC-TK−) with and without the expression of human Flt3L or GM-CSF as oncolytic and immunotherapy. The foregoing poxviruses can also be used in combination with immune checkpoint blocking agents. The foregoing poxviruses can also be inactivated via Heat or UV-treatment and the inactivated virus can be used as immunotherapy either alone or in combination with immune checkpoint blocking agents.