Loading CAR-T cells with oncolytic virus can address two major challenges that make solid tumours difficult to treat with CAR-T cell therapy alone. First, the oncolytic virus can break down the molecular shield that some solid tumours use to avoid an immune system attack. Second, the virus can invade into the core of the cancer cells — a near-impossible feat for immune cells alone, which often lose their power in the attempt. The combination approach, published in Science Translational Medicine, involves loading CAR-T cells, which are engineered to look for antigens on cancer cells, with an oncolytic virus. Oncolytic viruses are naturally occurring viruses that can infect and break down cancer cells. They either naturally replicate well in cancer cells or can be engineered to selectively target cancer cells. The latest study by Mayo Clinic researchers suggests CAR-T cells can deliver the oncolytic virus to the tumour. Then the virus can infiltrate tumour cells, replicate to bust the cells open, and stimulate a potent immune response.