Cancer cells 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.

The work, "Exosomal PD-L1 contributes to immunosuppression and is associated with anti-PD-1 response" published in the journal 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 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.
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