Spray-on gel slows down the regrowth of tumours after cancer surgery

A way of destroying cancers with our own immune system is a long-held goal of medicine. Now a new twist on such immunotherapy has given promising results in mice.

The treatment is a gel sprayed on to the wound left when a tumour is cut out. The targeted delivery means nearby immune cells start killing cancer cells, both at the wound and elsewhere in the body – but it doesn’t cause a potentially harmful body-wide immune reaction

Several kinds of immunotherapy have been developed into treatments in the past few years. Most give people just a few extra months of life rather than being a cure. But the immune system has many different arms, so the search continues for an approach that more effectively harnesses its power.

Don’t eat me

Several ongoing trials are looking at ways to block a molecule called CD47, which is present on many tumour cells and helps them evade the immune system by giving off a “don’t eat me” signal. But antibodies against this molecule lead not only to death of tumour cells but also to destruction of red blood cells, which normally have CD47 on their surface.

Zhen Gu at the University of California, Los Angeles and colleagues have found a way to make the immune reaction more targeted. They took mice with skin cancer and cut out most but not all of the tumour, as can happen when human patients have cancer surgery. Then they sprayed the wound with a gel containing antibodies against CD47, as well as a chemical that makes the tissue less acidic, a way of revving up immune cells called macrophages.

The tumour cells at both the wound site and in a metastatic tumour elsewhere in the body regrew more slowly in mice treated this way than they did in animals who got just inert gel sprayed on their wound. The strategy “awakens” the immune system, says Gu, although he adds that the fact that it works in mice is no guarantee it would work in people. The team’s next step is further trials in larger animals.