Patients with COVID-19 have been observed to experience a wide variety of symptoms, ranging from a mild cough to acute respiratory failure. So, what causes the most severe cases of coronavirus infection? In some instances, COVID-19 fatalities occur when a patient’s own immune system inflicts too much damage on the individual’s infected organs.
In a general sense, the immune system protects the body from pathogens through a series of chemical signaling networks. These signals are received by specific receptor cells which in turn respond by enhancing immune responses like inflammation, fever, and cell death. One type of chemical signal that is prevalent in the immune system’s response to coronavirus is a cytokine. These tiny proteins can carry out many different functions, but the most prevalent type of cytokine in coronavirus research is one that promotes inflammation.
Healthy vs. Unhealthy Immune Systems
In a healthy immune system, the body must be able to recognize and control the intensity of immune responses by signaling for the suppression of a response after its activation. This cycle of enhancing and suppressing immune functions keeps fevers from running too high and inflammation from damaging tissue. As people age, the immune cells that produce cytokines often become less efficient. In some of these patients, there is a lack of balance between signals that promote immune responses and signals that suppress them. When these individuals contract coronavirus, the immune system may be activated in what is called a “cytokine storm.” During this process, cytokines are sent out in a surge that causes severe amounts of inflammation in the lungs, leading to tissue damage. At this point, the virus may have infected other organs where increasing inflammation will lead to even more damage. If there is a lack of signaling to stop this immune response, organ damage may be sufficient to cause death. In patients at risk of experiencing this “cytokine storm,” professionals are considering using mesenchymal stem cells to prevent and repair tissue damage.
What is a Stem Cell?
A stem cell is a specific kind of cell that does not have a specialized function in the body. Instead, they have the potential to differentiate into many specific types of cells, such as red blood cells or neurons. There are three main types of stem cells: embryonic, induced pluripotent, and adult. Adult stem cells, which are found in small quantities in all types of tissue in the human body, are most of interest to researchers seeking to treat COVID-19. These types of cells are only capable of developing into limited types of tissue, likely the type that they already reside in. Mesenchymal stem cells (or MSCs) are a type of adult stem cell that may be derived from several different organs, including the bone marrow, fat, and umbilical cords. They have the potential to become the cells that are responsible for creating bone, cartilage, or fat. Aside from their ability to differentiate into other cell types, MSCs have several other properties that make them of interest in treating COVID-19. First, these stem cells can suppress the activity of certain immune cells. Evidence suggests that through these functions, MSCs may be able to regulate inflammatory responses. Second, MSCs can secrete growth factors that stimulate the development of surrounding cells.
Clinical Trials With Stem Cells
Trials are now taking place to test the efficacy of MSCs to treat severe complications from COVID-19. In these studies, MSCs are injected into a patient experiencing respiratory infection. The MSCs then accumulate in the lungs, where their regulatory properties counteract or prevent the “cytokine storm.” The stem cell’s regenerative properties also serve a purpose to repair and regrow damaged tissue. A recent study conducted in Beijing, China treated seven coronavirus patients who had either critically severe, severe, or normal reactions to the virus. All seven patients exhibited symptoms including shortness of breath, fever, and weakness. Within two days of their MSC transplant, these symptoms had disappeared in all the patients. Many similar trials are now being conducted in multiple different countries.