A new type of dual-function oncolytic virus that simultaneously kills cancer cells while increasing levels of leptin to support T cells is showing promise in melanoma mouse models, researchers reported in Immunity.  

Standard oncolytic viruses spark tumor cells to release proteins that attract a T-cell response. But the tumor environment is toxic and can eventually stop T cells from functioning, and researchers have found that what many of those T cells are lacking is leptin, a hormone that supports immune function. 

The new virus is engineered to carry the gene for leptin production. When injected directly into tumors, the virus shrank the cancer substantially; approximately 25% of the mice had a complete response and lived longer than the control mice. Of note, the virus did not increase survival in mice whose tumors already had a T-cell-supporting environment, potentially indicating that leptin was the trigger.