COVID-19 convalescent plasma: Mechanisms of action and rationale for use: A narrative review

The use of convalescent plasma (CP) transfusions for patients with coronavirus disease 2019 (COVID-19) has gained great interest during the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) pandemic. This review aims at summarizing the literature on the potential mechanisms of action of COVID-19 CP (CCP) and the rationale for use. A narrative review of the literature was conducted using PubMed, Google Scholar, and the Cochrane Database through October 2020. The rationale of CCP deployment was based on historical use in other outbreaks and pandemics and the emergent need at the time of lack of proven therapies and vaccines. There are many proposed mechanisms of action including direct neutralization and suppression of viremia, antibody-dependent cellular cytotoxicity, modification of the inflammatory response, restoration of the coagulation factors, immunomodulation of the hypercoagulable state and the potential role of ABO naturally occurring iso-agglutinins. Many donor, product, and patient factors can impact the response to CCP, such as antibody titer in the CCP product, CCP dose, frequency of administration, the severity of underlying illness, and the timing of administration from time of disease onset. Based on current evidence, CCP appears to be safe. However, it remains unknown whether it impacts the improvement of clinical symptoms, time to death, and all-cause mortality. In conclusion, the use of CCP offers quick access as an empirical therapy when specific therapies are not available or under development. Ongoing clinical trials are expected to add to the breadth of knowledge on the safety and efficacy of CCP use in patients with COVID-19.