An Overview of MDSCs

The human immune system is incredibly complex. It has many functions and jobs that are still being studied. Even this well-developed system has its flaws; sometimes it can go overboard in getting rid of an invader. For example, when someone has a 104-degree fever, it may kill off a virus, but it also may be fatal to the host. In order to prevent this, the body has developed a system of “checks and balances”, of which myeloid-derived suppressor cells (MDSCs) are a vital part. In a normally functioning immune system, MDSCs work to regulate the immune system, effectively turning it off once a virus or disease has been destroyed (Gabrilovich & Nagaraj, 2009).  MDSCs are often separated into two categories, each doing essentially the same job but in different ways.  Both possess the ability to suppress T cells and upregulate Tregs, and are essentially the same for the purposes of this research.
Usually MDSCs work for the body, protecting it from its own immune system. For example, during pregnancy, the immune system seeks to attack the fetus, recognizing it as foreign, but MDSCs suppress that reaction. Studies show that the presence of MDSCs in human and mice greatly increases during pregnancy, in both the blood and placenta (Ostrand-Rosenberg et al 2017). The presence of MDSCs signals a successful pregnancy, proving they prevent the immune system from attacking something, even if it identifies that something as foreign or harmful. Similarly, there is an increase in MDSCs in cancer patients, from less than 1% in a healthy patient to almost 40% of neutrophils in tumor tissues (Figure 1) (Veglia, Perego & Gabrivolich, 2018). Despite cancer being extremely harmful to the body, it isn’t attacked by the immune system. In fact, the presence of MDSCs shows that the immune system is suppressed in a cancer patient, especially near tumors. The MDSCs are directly involved in immunosuppression in relation to cancer cells, allowing them to thrive despite the harm they cause.