Several different types of white blood cells that are able to suppress the immune response to cancer are more abundant in cancer patients than in healthy people, but no one knew which ones actually do this suppressing. Now, researchers have identified the white blood cells that tumors use to suppress the immune response to the tumors and enhance growth.
The group of different white blood cells that can do this are called myeloid-derived suppressor cells (MDSC) and they are known to help cancer grow and to suppress specialized immune cells called T cells. T cells can target and destroy tumor cells. Finding out more precisely which cells are responsible for the immune suppression could give rise to ways to harness the immune system against cancer.
Working with mice, researchers at St. Jude's Children's Research Hospital in Memphis, TN, found that the immune suppression that is associated with MDSCs is primarily the work of a type of white blood cell called a monocyte. Monocytes give rise to cells called macrophages that have the chore of cleaning up dead or damaged tissue in the body, fighting cancer, and regulating the body's immune response.
By manipulating a gene called MCL1 and a protein called FLIP, the researchers showed that monocyte cells are the cells that are primarily responsible for T cell suppression seen around tumors.
"We've known for decades that cancer has harnessed the immune system to keep pumping out large numbers of mature and immature myeloid cells from the bone marrow," said Peter Murray, Ph.D., a member of the departments of Infectious Diseases and Immunology at St. Jude.
"This study marks a significant step in efforts to understand, develop and optimize immunotherapies for treatment of cancer," he said.
The study was published in the journal Immunity.
