Figure 2.

Schematic illustration of some physical barriers to oncolytic viruses and ways to overcome them. Tumor nests are often surrounded by extracellular matrix (ECM), which prevents viruses from reaching the tumor cells (see also Figure 1). Another problem is that tight junctions hide virus receptors and limit diffusion of viruses into the tumor tissue. Newly developed tight junction openers [40,47,48] may facilitate virus infection by exposing the hidden receptors, and virus-encoded proteases may degrade the stromal shield surrounding tumor nests [26].