What is convalescent plasma therapy?
The concept of convalescent plasma therapy involves procurement of blood from survivors of a disease, processing it and transfusing it into patients with the same disease. The basis of it is that the survivor’s blood has antibodies against the Ebola virus that would help the patient recover.
The therapeutic strategy has been around for a while, but has revived due to research into alternative Ebola treatments as there are no readily available drugs or vaccine for the highly contagious and deadly virus. Even though news about Ebola has simmered down, there is still an urgent need to develop a viable therapy as countries in West Africa are still being ravaged by the disease.
What is the science behind it?
The immune response
When the body is infected with a pathogen such as a virus, our bodies naturally mount an immune response against it. This adaptive immunity is an additional line of defense that our bodies have, in addition to our innate immune response, to fight against pathogens we have yet to cross paths with.
Lymphocytes, which are white blood cells, can recognise the invading pathogen and produce antibodies unique to the pathogen. The binding surface of the antibody has a complementary shape to that of the pathogen, which allows the two components to bind together. As a result, the pathogen is destroyed and engulfed by macrophages.
Once the pathogen has been defeated and the patient recovers, immune cells have a ‘memory’ for the pathogen. If the individual is exposed to the same pathogen again, their bodies can respond to the invasion much quicker and more efficiently to hopefully prevent them from falling ill again.
The blood transfusion
Whilst blood transfusion has become a standard procedure, there is a limit on the amount of blood a person can donate each time. Blood can be separated by centrifugation, such that the plasma can be extracted. The benefits of this, as opposed to whole blood transfusion, is that it allows recycling of the red blood cells back to the donor. It therefore increases the amount of blood a donor can donate, and the frequency of allowed donations. Plasma can also be stored for much longer than whole blood.
Historical outlook on convalescent plasma therapy
Emil von Behring published a paper in 1890 describing antitoxins that the body produced to neutralise diphtheria and tetanus. The discovery of convalescent plasma therapy for the diseases secured him the first Nobel Prize in Physiology or Medicine in 1901. Despite the effectiveness of the treatment, it fell out of favour to antibiotics, antiviral drugs and vaccines.
Since the late nineteenth century, the concept has been used for an array of diseases, such as H1N1, H5N1 and SARS, amongst others. Drugs and vaccines superseded convalescent plasma therapy in previous attempts, as they are easier to mass-produce and administer. For example, the availability of antiviral drugs such as Tamiflu rendered convalescent plasma therapy unnecessary for H1N1.
However in the case of Ebola, convalescent plasma therapy is a worthwhile avenue of investigation as drugs and vaccines are unavailable. In the Ebola outbreak of 1995 in the Congo, seven of eight patients treated with convalescent plasma made full recoveries. Similarly, the therapy was used in the Ebola outbreak of 2014. These cases are promising, but further investigation is necessary to probe the benefits of the treatment.
Junin, a hemorrhagic fever in Latin America is treated using convalescent plasma therapy. Furthermore, the 2012 outbreak of MERS-CoV (Middle East Respiratory Syndrome Corona virus) in Saudi Arabia has prompted clinical trials for convalescent plasma therapy as a potential therapy.
So, is it plausible?
In the 2014 pandemic, the therapy seemingly worked on several cases, but there was a lack of scientific method in that there was a lack of control groups, and patients were also treated with other medicine. Thus, further work needs to investigate the efficacy of the treatment, and risk-benefit assessments.
Clinical trials for convalescent plasma therapy has recently started in West Africa to assess its benefits. If the treatment is proven effective, it can be easily scaled up quickly in hospitals and clinics due to its low cost, and can have substantial impact. WHO has deemed experimental therapies ethical for Ebola due to the lack of effective treatments, and has issued guidelines for it. However, implementations of the treatment has to be standardised, as there is the danger of transmitting other diseases such as Hepatitis B and HIV.