People with melanoma who develop vitiligo – a condition characterized by white patches of skin – often have a better prognosis than those without vitiligo.
New research finds that this may be due to a greater abundance of cancer-fighting memory T cells in their skin.
That discovery could lead to new treatments for melanoma.
Mary Jo Turk, Ph.D., of the Dartmouth-Hitchcock Medical Center in New Hampshire and a study leader, and her colleagues published their findings today in the journal Science Immunology.
The characteristics of melanoma
Melanoma is a cancer that begins in skin cells called melanocytes.
These cells are responsible for producing melanin, the pigment that protects the deeper skin layers from the damaging effects of sun exposure.
While melanoma is not the most common skin cancer in the United States, it is one of the deadliest. This year, it is estimated that 9,730 people in the U.S. will die from the disease.
However, studies have shown that people with metastatic melanoma – that is, melanoma that has spread to other areas of the body – may survive for longer if they also have vitiligo.
Vitiligo is a skin disorder that researchers believe is triggered by an immune system attack on melanocytes, which causes white patches to appear on the skin and particularly on the face, lips, arms, hands, and feet.
For their study, Turk and colleagues set out to determine why vitiligo seems to improve the prognosis of patients with melanoma.
Cancer-fighting T cell discovery
The researchers came to their findings by analyzing the skin of mouse models with vitiligo and melanoma.
The team found that skin affected by vitiligo consists of resident memory T cells, which are immune cells that provide an initial response against infection in tissue surfaces.
While resident memory T cells are known to prevent viral infections in skin, the researchers were surprised to find that they also have cancer-fighting abilities.
Turk and colleagues note that cancer-fighting T cells were thought to only be present in the blood, the spleen, lymph nodes, and other immune system organs, and that they launch an attack on foreign invaders by entering the bloodstream.
"Our studies challenge this long-held belief by showing that tumor-killing T cells already reside in skin, where they can rapidly respond and kill melanoma cells,” says Turk.
Although this study was conducted in mouse models, the researchers believe that their findings may help to explain why vitiligo appears to extend the life of patients with melanoma.
The next step for Turk and colleagues is human studies.
"While we have shown that these T cells can kill melanoma in skin, we still need to determine whether they exist in other organs such as lung, where metastatic melanoma grows,” says Turk.
The hope is that their findings will pave the way for new treatments for melanoma.
"Since our study identifies that resident memory T cells are critical for protection against tumors, and that T cells in skin provide long-term immunity to melanoma, the generation of such cells should be the goal of future cancer therapies,” Turk adds.