A promising area of cancer therapeutic development involves utilizing the immune system to preferentially target tumour cells. Cancer immunotherapies encompass numerous strategies including administering oncolytic viruses to preferentially infect and kill cancer cells and administering adeno-associated virus (AAV)-based gene therapies to produce a therapeutic transgene in vivo. The aim of this doctoral thesis was to improve therapeutic efficacy by optimizing dosing and delivery strategies in intracranial melanoma and ovarian cancer preclinical models. Here we explore how altering dosing protocols for the oncolytic rhabdovirus vesicular stomatitis virus (VSV) influences neutrophil and T cell populations in the blood and tissue of infected mice. VSV iv administration caused neutrophils to rapidly egress from the bone marrow and accumulate in the lungs. A dramatic increase in immature neutrophils was observed in the lungs, as was an increase in the antigen presentation potential of these cells within the spleen. Multi-dosing protocols cause both CD4+ and CD8+ T cells to become infected by VSV and reduce efficacy in a murine intracranial B16F10 melanoma model. In vitro modelling demonstrated that most activated T cells become infected and die, while an alteration in the VSV glycoprotein (G) protein prevents off-target infection. Ovarian cancer remains a highly lethal gynecological disease. One option to improve existing vasculature normalizing therapeutic options is to engineer the proteins to be expressed in vivo using AAV gene therapy vectors. Three AAV-vectored gene therapeutics that affected tumour vasculature (3TSR, Fc3TSR, and Bevacizumab) were tested in a murine model of epithelial ovarian carcinoma to analyze impact on survival and influences on natural killer and T cell numbers. Therapies were combined with the oncolytic avian orthoavulavirus-1 to assess whether the combination therapies altered tumour size or the number of metastases compared to AAV monotherapies. This thesis advances knowledge within three areas of cancer immunotherapy: the impacts VSV administration has on neutrophil populations, the mechanisms resulting in off-target infections of activated T cells, and the use of gene therapeutics to extend efficacy in a preclinical model of ovarian cancer. This information can be used to modify existing therapeutics to ultimately improve the health outcomes of cancer patients.