Cancer cells are more than a lump of cells growing out of control; they participate in active combat with the immune system for their own survival. Being able to evade the immune system is a hallmark of cancer. Cancer cells release biological "drones" to assist in that fight--small vesicles called exosomes circulating in the blood and armed with proteins called PD-L1 that cause T-cells to tire before they have a chance to reach the tumor and do battle, according to researchers from the University of Pennsylvania (Penn). The work, published online on August 8, 2018 in Nature, is a collaboration between Wei Guo, PhD, a Professor of Biology in the School of Arts and Sciences, and Xiaowei Xu, MD, PhD, a Professor of Pathology and Laboratory Medicine in the Perelman School of Medicine. While primarily focused on metastatic melanoma, the team found that breast and lung cancer also release the PD-L1-carrying exosomes. The article is titled “Exosomal PD-L1 Contributes to Immunosuppression and Is Associated with Anti-PD-1 Response.” The research offers a paradigm-shifting picture of how cancers take a systemic approach to suppressing the immune system. In addition, it also points to a new way to predict which cancer patients will respond to anti-PD1 therapy that disrupts immune suppression to fight tumors and a means of tracking the effectiveness of such therapies. "Immunotherapies are life-saving for many patients with metastatic melanoma, but about 70 percent of these patients don't respond," said Dr. Guo. "These treatments are costly and have toxic side effects so it would be very helpful to know which patients are going to respond.
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