Convalescent Plasma as a Cure for COVID-19

As COVID-19 illness spreads, the authorities are pressing all buttons to stop the spread, treat those who are infected, save lives and develop strategies to prevent future spread of the virus. All of these steps are essential in fighting the pandemic.

On the treatment front, we at least have one anti-viral drug that has been given the green light by the FDA. Over the next coming weeks and months, the drug remdesivir will be supplied to many hospitals treating severe cases of COVID-19.

Another treatment is being tested is the convalescent plasma. Since thousands of people have recovered from the coronavirus infection, they can be the source of this plasma.

What is convalescent plasma?

Our blood has cells that float in a liquid medium called plasma. It has everything in it like water, proteins, sugar, nutrients, enzymes, and hormones to name a few. These materials are transported from one place in the body to the destination organs by the powerful pump, the heart. Our body is constantly replacing and reconstituting the plasma. As noted above, the plasma also contains the proteins produced by our immune system. When we encounter an infection, the immune system mounts a robust counterattack. The immune system unleashes killer cells (T-Cell Lymphocytes) and proteins (antibodies) to fight off the invading contagion (germ).

The immune proteins (antibodies) are produced in two phases. One (IgM type of proteins) are made within a week and protect us for a month or so. In the second phase, immune proteins of the IgG class are produced that can last in the plasma for many months. The individuals who have recovered from COVID-19 now have the proteins (IgG class of antibodies) in their plasma that can neutralize the virus.  It is called convalescent plasma because it comes from those who are convalescing or have fully recovered from the illness.

The processed and purified convalescent plasma can  be further processed to extract a specific protein (antibody) called Hyperimmune Globulin. Similar product is used prophylactically in individuals who were exposed to Hepatitis virus or HIV infection through a needle stick. 

The process is rather simple and for the donor, it is just like donating blood. The difference is that the donor only donates the liquid portion (plasma) and not the whole blood. The donor is hooked to a machine. The needle is inserted in the vein just like when donating blood. The blood is then spun in a centrifuge machine that separates the cells from the plasma. The cells are reconstituted with appropriate sterile solutions and returned to the patient through another vein. The harvesting of convalescent plasma therefore takes somewhat longer than just donating blood. 

The average blood donor donates a pint of blood at a time. There is enough plasma in the one pint of blood to serve as one dose for the COVID-19 patient. The donor suffers no harm. Donor’s body quickly replaces the lost fluid and proteins. Similar to blood donation, an individual can donate convalescent plasma over and over again as long the antibody level in the plasma remain in the therapeutic range. 

The donated plasma is then processed to remove unintended ingredients. The residual solution that is rich in the immune proteins (antibodies) is then readied for infusion as a treatment. Like blood transfusion, the donor and the recipient are matched for the blood type to avoid reaction. However the specific protein called Hyperimmune Globulin extracted from the convalescent plasma can be given across the various blood types. 

In some of the published studies, it appears that only one dose (~200 ml) of convalescent plasma is needed. Based on the strength of the immune proteins (antibodies) in the donated plasma, the virus could be eliminated or at least weakened so that the patient can recover sooner and with less complications.

The level of the antibodies (called the titer in medical lingo) in the convalescent plasma needs to be measured. The quality and quantity of the antibodies produced by a recovering patient depend on their own immune system and the dose of the virus (that they were exposed to. Hence, each sample of the donated plasma may not have the same quantity and quality of the immune proteins in it. The pharmaceutical companies or the laboratories that have been or will be certified by the FDA to process and produce the plasma have the responsibility to make a product that meets the clinical standards.