Oncolytic viruses improve cancer immunotherapy by reprogramming solid tumor microenvironment

Immunotherapies using immune checkpoint inhibitors (ICIs) and chimeric antigen receptor (CAR) T-cell therapy have achieved successful results against several types of human tumors, particularly hematological malignancies. However, their clinical results for the treatment of solid tumors remain poor and unsatisfactory. The immunosuppressive tumor microenvironment (TME) plays an important role by interfering with intratumoral T-cell infiltration, promoting effector T-cell exhaustion, upregulating inhibitory molecules, inducing hypoxia, and so on. Oncolytic viruses are an encouraging biocarrier that could be used in both natural and genetically engineered platforms to induce oncolysis in a targeted manner. Oncolytic virotherapy (OV) contributes to the reprogramming of the TME, thus synergizing the functional effects of current ICIs and CAR T-cell therapy to overcome resistant barriers in solid tumors. Here, we summarize the TME-related inhibitory factors affecting the therapeutic outcomes of ICIs and CAR T cells and discuss the potential of OV-based approaches to alleviate these barriers and improve future therapies for advanced solid tumors.