Oncolytic Virotherapy and the Tumor Microenvironment.

Oncolytic viral therapy is a promising approach to treat many malignancies, including breast, colorectal, hepatocellular, and melanoma. The best results are seen when using "targeted and armed" viruses. These are viruses that have been genetically modified to selectively replicate within cancer cells and express specific transgenes that alter the tumor microenvironment to inhibit tumor progression. The products of these transgenes induce cell death, make the virus less virulent, compromise tumor vascularity, and are capable of modulating or enhancing the immune system-such as cytokines and chemokines. In addition, oncolytic viruses can induce anti-vascular effects and disrupt the extracellular matrix to improve viral spread within the tumor. Oncolytic viruses also improve crosstalk between fibroblasts, cytokine-induced killer cells, and cancer cells within the microenvironment, leading to enhanced tumor cell death.