Oncolytic viruses
Oncolytic viruses infect cancer cells and multiply inside them until the cells burst, while normal cells are able to eliminate the virus; the debris of dying tumour cells additionally helps the immune system "see" the cancer. The only FDA-approved therapy of this kind, talimogene laherparepvec (T-VEC), is a modified herpes virus injected directly into melanoma tumours. In some patients tumours that were not injected have also shrunk, and early trials of T-VEC combined with checkpoint inhibitors reported higher response rates than a checkpoint inhibitor alone — the field remains at an early stage of research.
How it works
Oncolytic viruses act through two mechanisms. First, they preferentially infect tumour cells and make copies of themselves until the cell bursts. Second, the burst cell releases tumour antigens — fragments the immune system can learn to recognize — so, as a researcher quoted by NCI puts it, the viruses are "alerting the immune system that something's wrong." This can turn a locally injected treatment into a wider immune response: in some patients treated with T-VEC, tumours that could not be injected have also shrunk.
T-VEC, approved for melanoma, is built on herpes simplex virus type 1 and additionally engineered to produce a protein that stimulates the production of immune cells. It is injected directly into tumours. Researchers are testing oncolytic viruses in combination with other immunotherapies — in early trials in melanoma, T-VEC plus a checkpoint inhibitor gave higher response rates than a checkpoint inhibitor alone — but NCI describes these as still early days for this class of treatment.
Used in
Malignant Melanoma
C43
talimogene laherparepvec injected into lesions is an option in selected advanced cases