Convalescent plasma therapy in COVID-19 critically ill patients during advanced phases of clinical trials and their preliminary results

ABSTRACT The objective of this study was to highlight the global scientific effort to fight the SARS-CoV-2, addressing the preliminary results of passive immunization through convalescent plasma. We performed a search at the major databases of interventional clinical trial protocols about the transfusion of convalescent plasma in patients with COVID-19, as well as, published articles (n≥25), using the following search strategy: [(COVID-19 OR SARS-CoV-2 OR nCoV-2019) AND (Convalescent plasma OR Plasma exchange) AND (Treatment OR Therapy)]. A total of 24 interventional clinical trial protocols (advanced in phases II-III, III, and IV) were included in this review, as well as three studies that had enough outcomes to evaluate the efficacy of convalescent plasma therapy for patients with COVID-19. All interventional clinical trial protocols applied approximately 500mL of convalescent plasma (from single or more donations) in hospitalized patients, mainly in patients with severe disease associated with standard therapy for COVID-19, and compared to placebo or standard therapy plus specific drugs. Most of interventional clinical trial protocols are multicenter, and the phase IV studies are recruiting at intercontinental centers of North America, Oceania, Europe, but most are recruiting center inside their own county. The three studies published reported similar approach of convalescent plasma intervention with decrease in length of stay, mortality, with less than 4% of adverse events, mainly for treating critical cases with life-threatening disease. All advanced clinical trials focused on convalescent plasma therapy in patients with COVID-19 hospitalized in severe conditions, and the preliminary results provide strong evidence for therapy for the COVID-19 patients.

Descritores: COVID-19; Infecções por coronavírus; SARS-CoV-2; Betacoronavírus; Imunização; Imunização passiva; Plasma; Plasma convalescente ❚ INTRODUCTION At the end of 2019, the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) emerged, resulting in the coronavirus disease 2019 (COVID- 19), which caused an unprecedented health emergency and declared a pandemic by the World Health Organization (WHO) on March 11, 2020. (1) Up to September 2020, this pandemic had affected approximately 28 million and killed roughly 920 thousand people worldwide. (2) In Brazil, more than 5 million cases and more than 130 thousand deaths have occurred so far. (3) New approaches to the development of immunity transfer were quickly implemented in preclinical studies, and currently interesting results of clinical trials are beginning to emerge, aiming to improve the symptoms of COVID-19, a heterogeneous disease caused by SARS-CoV-2. (2) Simultaneously, different vaccines are being developed and tested for effective disease prevention. (4) Before SARS-CoV-2, the use of convalescent plasma (CP) had been investigated, with positive outcomes, in outbreaks of other viral infections, (5) such as the pandemic influenza A (H1N1), in 2009, (6) avian influenza A (H5N1), (7) among others. Furthermore, some studies have demonstrated that CP antibodies can limit virus proliferation during the infection and support viral clearance, which is favorable for fast recovery of the disease. (8) A recent review on plasma therapy in COVID-19 patients reported low frequency of severe adverse event, and improvement in clinical symptoms in some participants after plasma therapy, but the authors judged the risk of reporting bias. (9) The high or low titers of neutralizing antibodies against COVD-19 can be managed to reduce patient's symptoms and mortality. There are 24 advanced clinical trials in phases II-III, III, and IV reported in several countries using CP to treat these patients, and answer this question.  Although passive immunization has been used for over a century to treat infectious diseases, the recent results pose challenges to set the best time of plasma extraction and donor choice, in addition to the cost of this whole procedure. This lack of information empowers the movements of antivaccine and antiplasma groups. (34) ❚ OBJECTIVE To highlight the global scientific effort in the fight against SARS-CoV-2, addressing passive immunization through convalescent plasma and their preliminary results.

Inclusion and exclusion criteria
This review included clinical trial protocols (CTP) phases III and IV that addressed the development of therapies based on CP to treat COVID-19 patients by passive immunization, and studies that showed the efficacy of CP therapy applied in more than 25 COVID-19 patients. The reasons for excluding studies were as follows: CTP for observational studies, CTP involving vaccines, and CTP canceled, or not approved, until the searching date in the databases. einstein (São Paulo). 2021;19:1-11 Study eligibility, data extraction, data collection, and risk of bias assessment The study eligibility followed the Preferred. Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. (35)

Data analysis
All results were described and presented using the percentage distribution for all variables analyzed in the tables.

Plasma therapy outcome in COVID-19 patients
The three studies that evaluate the efficacy of plasma therapy also prioritize the evaluation of COVID-19 in severely ill patients or those in life-threatening situation, such as the advanced clinical trials mentioned above. The CP therapy intervention varied a lot among studies, without a consensus about the best CP pattern of application. Regarding the results, the studies showed a reduction by 53% in disease severity (not needing intensive care), (38) 26% in length of hospital stay, (36) and from 35% to 50% in mortality rate, (36)(37)(38) reporting adverse effects in less than 4% of patients after treatment with CP in different doses and volumes associated with standard therapy for COVID-19, (36)(37)(38) as shown in table 2.

DISCUSSION
In the absence of effective treatment for patients with COVID-19, many studies have sought alternatives to treat patients and enhance patient's immune defense, such as the use of CP therapy. The recovery trial (40) provides evidence to support some treatments (for instance, dexamethasone) and improve immunity in critical condition cases, and this trial uses CP therapy as one therapeutic arm. However, many aspects of this therapy are still being explored, such as a timeout/ collection interval for COVID-19, or immunoglobulin G/immunoglobulin M (IgG/IgM) titers from donors, the therapy clinical improvement and efficacy in critical or non-critical patients and adverse effects. Among 170 CTP identified, only 24 CTP were in advanced phase (III/IV) with 33,000 individuals, concentrated in the regions of America, showing the pivotal questions on efficient use of the CP still uncertain or fragile to justify an increased use in critical or non-critical hospital care. In addition, no country, including the United States, has licensed CP as a treatment for COVID-19. The Food and Drug Administration (FDA) judged eligible for wider use under an emergency use authorization, (41) although other countries have granted approval for use on an individual patient basis. One of the first CP clinical trials that analyzed 103 patients with severe and life-threatening COVID-19 (median age 70 years), (37) showed no statistically significance in clinical improvement after 28 days or reduced mortality. However, there was evidence of notable therapeutic effects and possible antiviral activity in group of 60 to 80-year-old patients, at the final stage of the disease course, after 14 days of symptoms, using only units with a very high antibody titers (IgG over 1:50) specific for spike (S)-and receptor-binding domain (RBD). Another study on CP therapy in severe COVID-19 patients (42) showed significant improvement of clinical symptoms, with an increase in oxyhemoglobin saturation after the third day of transfusion, reduction of pulmonary lesions, amelioration of routine laboratory criteria, and pulmonary function accompanied by rapid einstein (São Paulo). 2021;19:1-11 neutralization of viremia, using 200mL of CP derived from recently recovered donors with the neutralizing antibody titers between 1:160-640, approximately 16.5 days after onset of symptoms, associated to standard care and antiviral agents. Only three CTP (14,19,28) mentioned the antibody titers used in the CP therapy (over 1:160), and the studies by Abolghasemi et al., (36) and Li et al., (37) also reported the use of antibody titers above 1.1 in CP therapy associated with clinical improvement and reduction in mortality.
To reduce the variability in therapeutic response of patients, the WHO recommends some care and standardization in the selection of CP donors. (43) Eligibility criterion in relation to donor age does not vary widely: 18-67 years. (36,44) The donors were patients who recovered from COVID-19 and showed no detection of SARS-CoV-2 by real-time Quantitative polymerase chain reaction (qRT-PCR) or any related symptoms after a period that varied among studies. In one study, donors could have recovered after one week, and the short recovery period might have contributed to the death of 5 out of 6 patients. (45) Longer recovery period allowed reports of therapeutic efficacy. This period could be 10 days, with collection performed twice, with a difference of 24 hours, (46) at least 14 days, (36,47) and more than two weeks. (36,42,44) In some cases, qRT-PCR from nasopharyngeal swabs must be tested negative twice, and an interval of 24 hours between tests. (36,42) Regarding the quantification of antibodies, S-RBDspecific IgG titers vary from donor to donor. One study demonstrated that ten out of 25 collected plasma displayed the titer of 1:450, 6/25 1:350, while in the others vary from 1:1 to 1:150. (44) Most of studies employed a CP volume of roughly 500mL, in a single dose or divided into two doses, derived from a single donor, (12,16,20,23) or two different donors. (12,16) Therefore, this lack of standardization regarding donor selection, quality control of the CP, and recipient patients could explain the varied therapeutic effects.
Some possible adverse effects with the use of CP can be avoided, such as CP free of antigens, which could cause transfusion-related acute lung injury (TRALI), such as human leukocyte antigens that protect the embryo. (36) In a multicenter clinical trial, the use of CP was not allowed in pregnant women, aiming to prevent TRALI. (36) The severity of patient's disease transfused with CP varied from mild, moderate, severe to critical. A CTP with severe patients divided the study groups in severe acute respiratory illness and severe community acquired pneumonia. (10) Another CTP compared the effects of the treatment in oncological and non-oncological COVID-19 patients. (27) Admission in the intensive care unit is related in some CTP, (11,18,28,30) although it is presumed that it is applied to all severe patients. In some CTP, the CP treatment was compared to other treatments, such as corticoids, antibiotics, monoclonal antibodies, and anti-viral drugs. (10,22,23,33) Some published results allowed evaluation of different parameters concerning the efficacy of treatment. In a study in which CP was applied, 6 out of 17 patients required mechanical ventilation, mainly elderly patients. (47) In a multicenter study, the mortality rate was 14.8% of the patients (n=115). (36) Similar results were found in another multicenter study (15.7%). (36) Another investigation reported a mortality rate of only 2.2%. (38) A study employed this therapy in patients with hypertension, diabetes or cardiovascular disease, but it was not clear the effect of these comorbidities in the CP treatment effect. (36) The transfusion of CP therapy for COVID-19 must follow some pre-established conditions, such as availability of a population of donors who have recovered from the disease and can donate convalescent serum; blood banks to process serum donations; availability of assays, including serological tests, to detect SARS-CoV-2 in serum and virological assays to measure viral neutralization; laboratory support for virology to carry out these tests; and standardization of phase and condition of COVID-19 patient. (48) The main limitations of the multicenter studies were the reduced number of patients in the control groups compared to the treatment group, usually due to lack of blood group CP match, and concomitant or previous use of another treatment. (36) Another limitation is the lack of standard protocols and training for the study staff, as well as diversity in patients monitoring. (49) In turn, the main limitation of our study is the impossibility of carrying out a meta-analysis, due to the lack of a robust number of studies reporting conclusive therapeutic effects of this modality, such as decrease in SARS-CoV-2 titers. However, few articles published on multicenter studies demonstrated that CP could be a promising therapeutic modality.

❚ AUTHORS' COLLABORATION
The data extraction, collection, and risk of bias assessment was performed by six authors (Fernando Anselmo de Oliveira, Mariana Penteado Nucci, Gabriel Nery de Albuquerque Rego, Arielly da Hora Alves, Leopoldo Penteado Nucci and , Javier Bustamante einstein (São Paulo). 2021;19:1-11 Mamani) organized in pairs, independently and randomly reviewed and evaluated the information recorded from the clinical trial protocols and studies identified by the search strategy in the databases mentioned above. Discrepancies in study selection and data extraction between the authors were discussed with two authors (Luciana Cavalheiro Marti and Lionel Fernel Gamarra) and resolved. The final inclusion of studies in this review was agreed among all authors.

❚ CONCLUSION
Currently, there are no reliable therapeutic options for critically-ill COVID-19 patients. Based on the few consolidated multicenter clinical data results available, we concluded the convalescent plasma therapy studies provided relevant results in severe/critical cases of COVID-19 patients, reducing length of hospital stay, disease severity, and mortality, with low frequency of adverse events in a considerable number of patients. However, it is not possible to state, in a conclusive fashion, about the real relevance of this treatment, considering the lack of data that enable a robust statistics analysis, such as a meta-analysis.