SARS-CoV-2, the virus that causes COVID-19, is a novel coronavirus never before seen in humans. To date, it has caused 60,000 deaths in the United States – 56,000 of those in the last month alone. There does not yet exist an FDA-approved treatment for it. While existing antivirals and anti-inflammatory drugs are undergoing clinical testing against COVID-19 now, biopharmaceutical companies are taking a variety of approaches to develop new therapies.
One type of treatment being pursued is called antibody therapy. Antibodies are a type of protein produced by the immune system that specifically target foreign molecules from an invading pathogen. By binding their target, they either physically block the activity of the protein (“neutralizing antibodies”) or send a signal to the immune system to recruit further defenses. While a patient’s immune system will generate its own antibodies to fight off infection by SARS-CoV-2, providing it with antibodies earlier can help combat the disease or even prophylactically prevent illness entirely.
The most straightforward way to transfer anti-SARS-CoV-2 antibodies to a patient is with convalescent plasma therapy, a technique that has been in use since the 19th century. This is essentially a blood transfusion from a person who’s recovered from COVID-19 — and therefore has created antibodies against it — to the recipient being treated. Blood cells are separated out from the liquid portion of blood (plasma), which contains antibodies. This plasma can be transfused, or it can be further processed to concentrate the antibodies, resulting in a more potent product called hyperimmune globulin. This type of treatment has the advantage of being available now, but it is less consistent than a well-defined drug would be and is not easily scalable.
Convalescent plasma therapy in the United States is being coordinated nationally by the American Red Cross and the Mayo Clinic. Treatments based on hyperimmune globulin are being developed worldwide by companies with experience in plasma-derived therapies, and notably a group including Takeda and CSL Behring are collaborating to co-develop a hyperimmune therapy.
Antibody therapy is not limited to treatments from donated blood: antibodies can also be generated in the lab. For example, portions of SARS-CoV-2 proteins can be injected into a lab animal to provoke an immune response, and the resulting anti-SARS-CoV-2 antibodies can then be harvested from that animal’s blood and purified. One such process is being pursued by Regeneron, which uses transgenic mice with a human immune system, so that the antibodies they produce are human proteins and will not be attacked by a patient’s immune system. These antibodies will be tested for how well they neutralize SARS-CoV-2, and the best candidates will be mass produced by specialized cell lines. Regeneron plans to select two candidates out of these antibodies and antibodies found in convalescent plasma and use them together as a multi-antibody cocktail treatment, to increase the chances of effectiveness.
Many more companies are developing their own antibody therapies, often in collaborations between smaller biotechnology companies specializing in identifying antibody candidates and larger pharmaceutical companies experienced in drug development and equipped for mass production. Examples include AbCellera Biologics in collaboration with Eli Lilly, Adaptive Biotechnologies in collaboration with Amgen, and Vir Biotechnology with several partners, including Biogen, Samsung Biologics and GlaxoSmithKline.
While antibody-based therapies have a long history of medical use, a new and growing source of hope is the field of stem cell therapy. A stem cell is a type of cell in the body that can reproduce itself indefinitely and can differentiate into various kinds of specialized cells. As such, stem cells given to a patient have the potential to assist in replacing damaged tissue from injuries or disease. For example, this is the basis of bone marrow transplantation, which replaces a patient’s own hematopoietic (blood) stem cells that have been killed by chemotherapy with donor stem cells. Hematopoietic stem cell transplantation is the only approved use of stem cell therapy to date, but other indications are being tested.
One such indication is the use of stem cells to modulate the immune system, for example to prevent the harmful over-activation that causes autoimmune diseases like rheumatoid arthritis. Some infectious diseases like COVID-19 cause illness not only through the direct effects of the virus but also indirectly by causing an over-reaction from the immune system, also called a cytokine storm. Stem cells that may help reduce the severity of this reaction — and can help in other ways, such as promoting lung repair — are now undergoing clinical trials, or being given to patients as treatments through compassionate use programs. These come from stem cell-focused companies, including Hope Biosciences, Celltex and Athersys. Other cell therapy companies like Celularity and NantKwest are testing the transplantation of immune cells to boost patients’ immune defenses against the virus.
The odds are overwhelmingly against any new drug becoming an effective treatment for its indicated disease. For this reason, it is vital and reassuring that a wide variety of different approaches are being developed simultaneously in order to maximize the chances of quickly finding a treatment that does work. Whether it’s repurposing existing drugs or developing new antivirals, anti-inflammatory drugs, antibody therapies, or stem cell therapies, the biopharmaceutical industry is working at full speed to provide ammunition in the fight against COVID-19.