Scientists at the German Cancer Research Center have developed a technique that induces the body’s own immune cells to attack and destroy cancerous tumors.
The therapy is part of a new approach in cancer treatment that seeks to mobilize the body’s own immune system to remove the disease, preferably with fewer risks and side effects than more conventional and invasive treatments like surgery, radiation or chemotherapy. Immune therapies are already in use against prostate cancer and melanoma.
In this case, the immune therapy focuses on cells called natural killer (NK) cells, which are specialized for finding and destroying defective bodily cells, including cancer cells. They are effective against a wide variety of cancer types, including cells that are often ignored by other parts of the immune system. But having NK cells obviously doesn’t make us immune to cancer, and that’s because the cells are only effective against small clusters of cancerous cells. Against solid tumors, they quickly lose their aggressiveness and eventually give up.
“The big problem in using NK cells for therapy is their rapid loss of activity, hence their aggressiveness,” researcher Adelheid Cerwenka said. “Although there are good treatment results for certain types of blood cancer, NK cells have been clinically effective in fighting solid tumors only in a few cases.”
Persistent and effective response
The researchers cultured NK cells from mice in a dish, along with a cocktail of three natural immune-boosting mediators (interleukins 12, 15, and 18). The cells were then injected into cancerous mice.
The treated NK cells remained persistently active far beyond the time when they would normally have lost their aggressiveness. Tumor growth significantly slowed in all the injected mice, and in 25 percent of them, the tumors completely regressed. In mice injected with non-treated NK cells, none of these effects were observed.
The researchers then repeated the test with human cell cultures, finding that the treated NK cells remained persistently active there as well.
To the researchers’ surprise, other immune cells in the mice continued to re-stimulate the treated NK cells, allowing them to remain active three months after injection even in cases where the tumors had been completely eliminated. This suggests that somehow, the NK cells were able to “remember” the recent presence of cancer and remained on the alert as a result.
“We previously thought immunological memory exists only in cells of the adaptive immune system,” Cerwenka said.
The adaptive immune system responds to highly individualized threats, such as a specific virus with a unique protein signature. It is known to possess a “memory” of all threats it has previously responded to, but this effect has not before been seen in the innate system, which responds to more general threats.
The researchers noted that even the treated NK cells were only effective in mice that had previously undergone radiation treatment. They could not explain why this was the case.
“The good thing is that we might be able to achieve this effect in a potential clinical application by combining the cocktail-treated NK cells with radiation therapy,” Cerwenka said.