Convalescent Plasma: A Potential Treatment for COVID-19

Currently, there are no specific antiviral agents available to treat patients suffering from the coronavirus. However, in a recent study conducted by the National Academy of Sciences, researchers explored the effects of convalescent plasma (CP) transfusion.

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By Andrea Huang

In recent months, the COVID-19 pandemic has ravaged cities, nations, and continents all over the world. It has taken over 145,000 lives as of April 16, uprooted hospitals and clinics, and pressured scientists to scramble for a cure. This growing burden on our world’s medical workers has forced them to work tirelessly around the clock, looking for something that can stop the spread and save lives. Scientists previously thought that no antiviral agents existed to treat patients suffering from the coronavirus because the virus’s strategy of hijacking the host’s cells makes it more difficult to find drugs that target the virus but don’t attack the host in the process. This assumption changed, however, with a recent study conducted by the National Academy of Sciences (NAS), in which researchers explored the promising effects of convalescent plasma (CP) transfusion, a procedure commonly performed on severe influenza patients.

CP therapy is a classic adaptive immunotherapy technique used for the prevention and treatment of many infectious diseases—most notably, severe acute respiratory syndrome (SARS). According to the NAS, CP therapy was successfully utilized in the treatments of SARS, MERS, and the 2009 H1N1 pandemic with “satisfactory efficacy and safety” over the past two decades. All three of these potentially fatal diseases have one thing in common: like COVID-19, they are highly contagious respiratory illnesses. Analysis derived from 32 separate studies of the SARS infection as well as severe influenza revealed a significant reduction in the likelihood of death following CP therapy compared to no therapy or a placebo. Researchers observed that the virological and clinical characteristics of SARS, MERS, and COVID-19 shared several similarities and thus drew the conclusion that CP therapy might be a promising treatment option for severe coronavirus patients.

There are many components of CP therapy, the most crucial being a convalescent blood product from coronavirus survivors: plasma. Blood plasma is the liquid component of blood that suspends blood cells and carries proteins throughout the body. More importantly, it contains antibodies, proteins that chemically combine with foreign invaders in the blood, such as viruses, that counteract the foreign invaders’ adverse effects by binding to a specific antigen. Antigens are “red flag” molecules present on the surface of a virus that alert the immune system of an invader in the body.

Antibodies play a key role in CP therapy because individuals who have recovered from COVID-19 have the very antibodies needed to combat the virus floating through their own plasma. Thus, COVID-19 survivors contain the antibodies necessary to neutralize the virus and are considered valuable donor sources for CP therapy.

In a NAS study, 10 severe COVID-19 patients were each given 200 mL of CP derived from recently recovered donors. Within a few days, the results were promising: the disappearance of viremia (the presence of the virus in the bloodstream) in seven days, the improvement in clinical symptoms within three days, and varying disappearance of lung lesions (as shown by radiological examination) within seven days. If the therapy had not taken place, the patients would have attained maximum concentration of viremia in the blood, rapid worsening in clinical symptoms, and uncontrolled growth of lung lesions.

Moreover, after CP transfusion, the level of neutralizing antibodies in the patients themselves increased rapidly, demonstrating the ability of the patients to use antibodies from donors as “templates” to create their own. In addition to a significant improvement in clinical symptoms, there was an increase in oxyhemoglobin (combination of oxygen atoms with oxygen-carrying hemoglobin proteins) saturation within three days. This increase is significant because oxyhemoglobin is the molecule responsible for carrying and distributing oxygen throughout the body. Compared to pretransfusion, the patients also exhibited an increased lymphocyte (white blood cell) count and decreased amounts of C-reactive protein, a protein produced by the liver during increased inflammation in response to severe diseases. “Severe diseases” are illnesses that place the patient in a life-threatening situation. The study’s outcome showed that “CP therapy was well tolerated and could potentially improve the clinical outcomes through neutralizing viremia in severe COVID-19 cases.”

Nevertheless, whether the risks of CP therapy outweigh the potential clinical benefits is still to be determined. Though no severe adverse effects were observed in this particular study, there have been reports of inadvertent infection with undetected pathogens present in the donor’s plasma. There have also been reports of the potential worsening of immune-mediated tissue damage when antibodies target the body’s own tissues by mistakenly recognizing itself as a pathogen. But thus far, evidence for these unfavorable outcomes remains largely theoretical.

The Food and Drug Administration (FDA) is currently collaborating with a number of organizations in order to move thousands of units of plasma to the patients who need them in the coming weeks. Moreover, the agency is working with the healthcare industry and its government partners to develop hyperimmune globulin, a biological product manufactured from CP. The FDA is working to get hyperimmune globulin on the market and encourages people who have fully recovered from COVID-19 for at least two weeks to consider donating plasma. One of the problematic elements of CP therapy is that each “package” of donor plasma contains a different number of antibodies. This is because every donor has a unique immune system, and scientists have no way of controlling the concentration of antibodies in the plasma. Regardless, in partnership with the Red Cross, the government organization plans to conduct additional testing and urges survivors to donate and potentially help save the lives of those suffering from the virus.

Despite some of the concerns raised by CP therapy, this potential treatment for severe coronavirus cases does offer hope for patients and researchers alike. There is so much information scientists don’t know yet about this relatively new discovery, such as its optimal dose, clinical benefits, and age restrictions. However, the fruitful results of the NAS study and the past successes of CP therapy indicate that scientists are well on their way to a groundbreaking discovery. Though this recently-surfaced treatment for COVID-19 leaves several questions unanswered, it may play a critical role in the world’s everlasting fight against disease.