Abstract: The invention features new helper virus-free methods for making herpesvirus amplicon particles that can be used in immunotherapies, including those for treating any number of infectious diseases and cancers (including chronic lymphocytic leukemia, other cancers in which blood cells become malignant, lymphomas (e.g. Hodgkin's lymphoma or non-Hodgkin's type lymphomas). Described herein are methods of making helper virus-free HSV amplicon particles; cells that contain those particles (e.g., packaging cell lines or patients' cells, infected in vivo or ex vivo); particles produced according to those methods; and methods of treating a patient with an hf-HSV particle made according to those methods.