Cancer cells cast a sweet spell on the immune system
Cancer cells have surface proteins and sugars that link with immune cells to quiet their reaction to the cancer. Current immune therapies block interactions between PD-L1 proteins (light green) on tumor cells and PD-1 proteins (teal) on T cells to awaken the immune system to the tumor. A new wave of therapies could target parallel interactions between sialic acid sugars (orange) on the tumor and sugar-binding Siglec proteins (purple) on natural killer cells and other innate immune cells. But so far, these drugs, called checkpoint blockers, work only against some cancers, such as melanoma, kidney cancer and non-small cell lung cancer, and not for all patients. An estimated 10 to 20 percent of cancer patients who get the drugs show improvement. Sugar-targeting drugs, on the other hand, would alert cells of the innate immune system, such as natural killer cells, or NK cells, and macrophages. Innate immune cells also help defend the body against bad guys, be they flu viruses or cells that have turned cancerous, but the innate cells kick into action more quickly and with less specialized responses than T cells. The two systems are complementary.
Sugars far outnumber proteins among surface molecules responsible for distinguishing tumor from norma so you’d think they would make easier drug targets. Trouble is, sugars are immensely harder to study than proteins. Both proteins and sugars adopt three-dimensional shapes to do their work. Once researchers have a protein’s genetic blueprints in hand, they can predict its structure. Sugars, on the other hand, have no clear templates. To further complicate matters, sugars such as sialic acid are just one part of a tumor’s cell-surface barcode. Other players such as proteins also tell immune cells whether to attack or move on. The good news is that current immune therapies awaken immune cells to fight cancer by disrupting some of these proteins.
For more details: - https://www.sciencenews.org/article/cancer-cells-cast-sweet-spell-immune-system