These “memory killer cells” can also contribute to the inflammatory skin disorders vitiligo and psoriasis.

High levels of memory killer cells in cancer tissue may boost survival in people with melanoma, a new study shows.

Certain immune T cells called tissue-resident memory cells are formed locally in the skin and other tissue and protect against infections that they have encountered before. Some express proteins that enable them to kill infected cells. These “memory killer cells” can also contribute to the inflammatory skin disorders vitiligo and psoriasis. Recent research has shown that they are also involved in the body’s immune response to various cancers.

The memory killer cells have been shown to respond to immunotherapy. “We don’t know so much about how and why memory killer cells are formed in the skin and what it means for cancer patients,” says Professor Yenan Bryceson at the Department of Medicine (Huddinge), Karolinska Institutet, in a news release.“Finding out how these cells develop enables us to contribute to the development of more efficacious immunotherapy for diseases like melanoma.”

The study charted the development of memory killer cells in human skin, performed as a collaborative effort between reseechers at the Karolinska Institutetand the University of Copenhagen in Denmark. The researchers isolated T cells from the skin and blood of healthy volunteers and used advanced techniques to examine gene activity and expression of different proteins. This allowed them to identify T cells in the blood with the potential to develop into memory killer cells in skin or other tissues. After knocking out specific genes, they could also demonstrate which genes are required for the maturation of memory killer cells in tissue.

The researchers then went on to study tumour samples from melanoma patients and found that those with a higher rate of survival also had a larger accumulation of epidermal memory killer cells.

“We’ve been able to identify several factors that control the formation of memory killer cells, which play an important part in maintaining a healthy skin,” adds Liv Eidsmo, dermatologist and professor at the University of Copenhagen in Denmark and researcher at Karolinska Institutet in Sweden. “There’s a fine balance between effective protection against tumours and infections in the skin and contribution to inflammatory diseases like vitiligo and psoriasis.”

The researchers now aim to harness their findings to optimize the immunotherapy-induced T-cell response to make it even better at eliminating cancer cells in tissues.

The study is published in Immunity.