Convalescent Plasma Therapy

  • With no specific treatment available for novel coronavirus disease and a vaccine, recently, the US Food and Drug Administration (FDA) last week approved use convalescent plasma therapy to treat severely critical COVID-19 patients.

About Convalescent Plasma Therapy (CPT)

  • Patients who have recovered from a disease have permanent antibodies generated by the immune system floating in their blood plasma, the liquid component of blood.
  • To turn that into a drug, the plasma is harvested, tested for safety, and purified to isolate those protective antibodies.
  • When injected into a new patient, the plasma-derived therapy, provides “passive immunity” until the patient’s immune system can generate its own antibodies.

Recent Use of CPT

  • The United States used plasma of recovered patients to treat patients of Spanish flu (1918-1920).
  • Hong Kong used it to treat Severe Acute Respiratory Syndrome (SARS) patients in 2005.
  • In 2009, H1N1(Swine Flu) patients were treated with CPT.
  • Convalescent serum was also used in the 2013 West African Ebola epidemic.
  • A protocol for treatment of Middle East respiratory syndrome (MERS) coronavirus with convalescent plasma was established in

Process

  • The process to infuse plasma in a patient can be completed quickly. It only requires standard blood collection practices, and extraction of plasma.
  • If whole blood is donated (350-450 ml), a blood fractionation process is used to separate the plasma.
  • Otherwise, a special machine called aphaeresis machine can be used to extract the plasma directly from the donor.
  • While blood is indeed extracted from the donor, the aphaeresis machine separates and extracts the plasma using a plasma kit, and the remaining blood components are returned into the donor’s body.

WHO Guidelines Regarding CPT

  • WHO guidelines in 2014 mandate a donor’s permission before extracting plasma.
  • Plasma from only recovered patients must be taken, and donation must be done from people not infected with HIV, hepatitis, syphilis, or any infectious disease.
  • If whole blood is collected, the plasma is separated by sedimentation or centrifugation, then injected in the patient.
  • If plasma needs to be collected again from the same person, it must be done after 12 weeks of the first donation for males and 16 weeks for females.

Chance of Success in case of COVID-19 Treatment

  • The treatment has been successful in other disease outbreaks.
  • As a disease develops, the body has already begun developing antibodies against the virus.
  • Infusing convalescent plasma is essentially like topping with more antibodies hoping that increased amount of antibodies will dampen the disease progression.
  • Antibodies in the plasma bind to the virus and prevent them from entering the cells.
  • But by the time it is given, many cells have already been infected. Hence, convalescent plasma therapy might not prove effective against COVID-19 treatment.

Associated Benefits

  • COVID-19 convalescent sera can be used for either prophylaxis of infection or treatment of disease.
  • In a prophylactic mode, the benefit of convalescent serum administration is that it can prevent infection and subsequent disease in those who are at high risk for disease, such as vulnerable individuals with underlying medical conditions, health care providers, and those with exposure to confirmed cases of COVID-19.
  • Used therapeutically, convalescent serum would be administered to those with clinical disease in an effort to reduce their symptoms and mortality.

Associated Risks

  • Risks of passive administration of convalescent sera fall into two categories, known and theoretical.
  • Known risks are those associated with transfer of blood substances, which include inadvertent infection with another infectious disease agent and reactions to serum constituents, including immunological reactions such as serum sickness.
  • The theoretical risk involves the phenomenon of antibody-dependent enhancement of infection (ADE). ADE can occur in several viral diseases and involves an enhancement of disease in the presence of certain antibodies.
  • Another theoretical risk is that antibody administration to those exposed to SARS-CoV-2 may prevent disease in a manner that attenuates the immune response, leaving such individuals vulnerable to subsequent reinfection.

Implication in India

  • CPT can be done in India, but it is important to control the risk of infection during transfusion, and the patient’s acceptance is required.
  • India has facilities for removing 500 ml of plasma from a donor using aphaeresis.
  • For this experimental therapy to be tried out, the Drug Controller General of India will first have to grant blood banks approval for removal of plasma from recovered COVID-19 patients.
  • However, treatment could be effective for patients in the age group 40-60, but may be less effective for people aged beyond 60 years.

Source : Civil Services Chronicle Online, March, 2020