The efficacy of neutralizing monoclonal antibodies in transplant recipients with mild-to-moderate COVID-19

Introduction Transplant recipients (TRs) are at high risk for severe coronavirus disease 2019 (COVID-19). Neutralizing monoclonal antibodies (mAbs) are used for treating mild-to-moderate COVID-19. However, reports comparing the efficacy of COVID-19 treatment without/with mAbs in TRs are limited. We assessed the efficacy of casirivimab/imdevimab against mild-to-moderate COVID-19 in TRs. Methods Forty-one patients were retrospectively evaluated. The duration until defervescence, oxygen (O2) requirement ≥5 L, and neutralizing antibody levels were compared in TRs with COVID-19 without/with casirivimab/imdevimab. Results Casirivimab/imdevimab was correlated with shorter duration until defervescence and non-requirement of O2 ≥ 5 L in TRs with COVID-19 [mean: without/with: 6 vs. 2; P = 0.0002, hazard ratio (HR) = 0.3333, 95% confidence interval (CI) = 0.1763–0.6301; 15 vs. 8; P < 0.0001, HR = 0.5333, 95% CI = 0.2878–0.9883; P = 0.0377, HR = 0.1502, 95% CI = 0.02511–0.8980]. Casirivimab/imdevimab was associated with early defervescence after adjusting for sex and age (P = 0.013, HR = 0.412, 95% CI = 0.205–0.826). The antibody levels between patients without/with casirivimab/imdevimab on the day of hospitalization were not significantly different (P = 0.1055), including 13 TRs with vaccination. Antibody levels were higher in patients with casirivimab/imdevimab at 3–5 days after hospitalization than in those without, at 7–9 days after hospitalization (P < 0.0001, mean, without/with: 414.9/40000 AU/mL). Conclusion Casirivimab/imdevimab was effective and increased the neutralizing antibody in TRs with mild-to-moderate COVID-19, it may contribute toward preventing the progression.


Objective or hypothesis
We hypothesized that therapy with neutralizing mAb would be more effective to treat COVID-19 in TRs than therapy without neutralizing mAbs. In this study, we aimed to retrospectively assess the clinical impact of treatment with and without casirivimab/imdevimab neutralizing mAbs in TRs with COVID-19.

Ethical considerations
This retrospective study was conducted using data retrieved from patients' medical records from September 2020 to September 2021 at the Tokyo Women's Medical University Hospital. This study was approved by the institutional review board (date of approval: January 5, 2022; approval number: 2021-0175) at Tokyo Women's Medical University. The board disclosed details of this study on the institution website. Informed consent was obtained from all patients at the time of hospitalization.

Patients
All patients were eligible for therapy with neutralizing mAbs. The included patients were TRs with mild-to-moderate COVID-19 who were hospitalized within 1 week of the onset of symptoms as previous casirivimab/imdevimab study provided a protocol [14]. All patients in this study were hospitalized since TRs were at high risk for severe COVID-19 due to comorbidities and immunosuppression [5]. One group received casirivimab/imdevimab intravenously within 6 h after hospitalization. The other group was eligible for neutralizing mAbs therapy; however, they were not administered casirivimab/imdevimab because they were infected with SARS-CoV-2 before the appearance of neutralizing mAbs. Mild-to-moderate COVID-19 was defined according to the Food and Drug Administration criteria [25]. Briefly, the symptoms and clinical signs of mild-to-moderate COVID-19 included fever, cough, sore throat, headache, malaise, muscle pain, nausea, vomiting, diarrhea, loss of taste or smell, respiratory rate ≥ 20 breaths per min, heart rate ≥ 90 beats per min, and saturation of oxygen (SpO 2 ) ≥ 94% on room air at sea level. Discharge from the hospital was decided when the clinical symptoms disappeared, including maximum body temperature < 37 • C for 72 h and SpO 2 ≥ 94% on room air [25].

Polymerase chain reaction
All TRs were tested for SARS-CoV-2 with polymerase chain reaction (PCR) before hospitalization. Even if the patients had been tested at another institution, they were tested again. PCR was performed as we have previously described [26]. Briefly, specimens were sampled from the nasal cavities of patients with swabs (503CS01-E, BP100; Shin Corporation, Hyogo, Japan). After viral ribonucleic acid was extracted with the QIAamp Viral RNA Mini Kit (QIAGEN, Tokyo, Japan), PCR was conducted as per the manufacturer's instructions using the amplification reagent (BGI Genomics, Shenzhen, China).

Neutralizing antibody levels
Neutralizing antibody levels in the serum were measured using the Alinity SARS-CoV-2 IgG II Quant kit (Abbot, Chicago, IL, USA) in all patients. The effective level of neutralizing antibody as an anti-SARS-CoV-2 threshold was stipulated as ≥4160 AU/mL, as previously described, to correspond to a 95% probability of SARS-CoV-2 neutralization in neutralization tests [27,28]. Neutralizing antibody levels were measured on the day of hospitalization in all patients, 7-9 days after hospitalization in patients who did not receive casirivimab/imdevimab therapy, 3-5 days after hospitalization in patients who received casirivimab/imdevimab therapy, and on the day of discharge for all patients.

Comparison of clinical status
The clinical status of TRs with COVID-19 who received and did not receive casirivimab/imdevimab therapy was compared using medical records. Clinical status included the duration until defervescence (maximum body temperature < 37 • C for 72 h); duration of hospitalization; body temperature at hospitalization; prognosis; requirement of mechanical ventilation; requirement of oxygen (O 2 ) ≥ 5 L (which is the threshold for applying high flow nasal cannula [29]); level of white blood cells, lymphocytes, hemoglobin, aspartate aminotransferase, alanine aminotransferase, γ-glutamyl trans-peptidase, creatinine, surfactant protein D, Krebs von den lungen-6, D-dimer, albumin, interleukin-6, and C-reactive protein; body mass index; and presence of cardiovascular disease and diabetes mellitus.

Data analysis
Analysis of data was conducted with Graph Pad PRISM 9 (GraphPad Software, La Jolla, CA, USA) with t-tests, Kaplan-Meier analysis, calculation of hazard ratio (HR), and 95% confidence intervals (CI), which were used to compare the clinical status, neutralizing antibody levels, and the duration until defervescence. SPSS version 28 (IBM, Armonk, NY, USA) was used for multiple variables Cox proportional hazards analysis, was used to compare the duration until defervescence in TRs with or without casirivimab/imdevimab therapy. A two-sided P < 0.05 was considered statistically significant.
Casirivimab/imdevimab treatment was significantly associated with the duration until defervescence after adjusting for sex and age (P = 0.013, HR = 0.412, 95% CI = 0.205-0.826; Table 2). In addition, there were no casualties, and mechanical ventilation was not required in patients who received casirivimab/imdevimab therapy, whereas in patients who did not receive casirivimab/imdevimab therapy, one patient died and two required mechanical ventilation.

Casirivimab/imdevimab enhances neutralizing antibody levels in TRs with COVID-19
Neutralizing antibody levels in TRs with COVID-19 on each day of hospitalization are presented in Fig. 2a Fig. 3b). Moreover, neutralizing antibody levels were significantly higher in patients with casirivimab/imdevimab therapy than in those without the therapy at the time of discharge (mean antibody level without vs. with casirivimab/imdevimab: 2951 vs. 40,000; P < 0.0001, 95% CI = 34,982-39,116; Fig. 3c).
In this study, we assessed the efficacy of casirivimab/imdevimab therapy in TRs with mild-to-moderate COVID-19. Specifically, we demonstrated that casirivimab/imdevimab therapy correlated with a shorter duration until defervescence and non-requirement of O 2 ≥ 5 L in TRs with mild-to-moderate COVID-19 (Fig. 1). In addition, casirivimab/ imdevimab therapy increased neutralizing antibody levels in TRs with COVID-19 ( Fig. 3b and c), suggesting that it is appropriate to apply casirivimab/imdevimab therapy for such patients. These results should be related to the observation that casirivimab/imdevimab therapy reduced the duration of hospitalization and the rates of acute respiratory failure and death in TRs with COVID-19, as previously described [5,[17][18][19][20][21][22]. Furthermore, neutralizing antibody levels in TRs with COVID-19 who received casirivimab/imdevimab therapy (Fig. 3a) including 13 vaccinated patients (Table 1a) were not high enough on the day of hospitalization compared with those in patients who did not mABs, monoclonal antibodies; 95% CI, 95% confidence interval.

Table 1b
The organ of transplant.   1. The duration until defervescence since hospitalization in TRs with COVID-19 who did and did not receive casirivimab/imdevimab therapy. Casirivimab/imdevimab therapy correlated with less duration until defervescence in TRs with mild-to-moderate COVID-19 than in TRs who did not receive casirivimab/imdevimab (P = 0.0002, HR = 0.3333, 95% CI = 0.1763-0.6301). COVID-19, coronavirus disease 2019; TRs, transplant recipients; HR, hazard ratio; 95% CI, 95% confidence interval; without, without casirivimab/imdevimab; with, with casirivimab/imdevimab. receive casirivimab/imdevimab therapy to prevent breakthrough SARS-CoV-2 infection [31]. In addition to immunosuppression, poor neutralizing antibody levels similar to that in patients without vaccination or without casirivimab/imdevimab therapy must be one of the reasons for the 13 patients acquiring a breakthrough SARS-CoV-2 infection despite vaccination. A previous study reported that IgG and the neutralizing antibody levels against COVID-19 increased until 4-20 days after COVID-19 onset [32,33]; however, our results demonstrated that TRs with COVID-19 who did not receive casirivimab/imdevimab therapy did not have enough neutralizing antibody levels even 7-9 days after hospitalization (Fig. 3b) and at discharge (Fig. 3c) to prevent the progression of COVID-19 and the subsequent SARS-CoV-2 infection. These results suggested that compared with those who receive casirivimab/ imdevimab therapy, TRs with COVID-19 who do not receive casirivimab/imdevimab therapy may need long duration until defervescence and may experience more severe COVID-19 with O 2 requirement ≥5 L, and may reacquire COVID-19 even right after discharge. Based on these results, casirivimab/imdevimab therapy is more effective against mild-to-moderate COVID-19 in TRs than therapy without casirivimab/imdevimab. This study has some limitations. First, it was retrospectively performed at a single hospital with a small number of TRs, which may have influenced the results, and a randomized controlled study was not conducted to evaluate the results. Second, it was performed only in Tokyo, and the situation may be different in other geographical areas. Third, since the variant of SARS-CoV-2 between the patients with/ without casirivimab/imdevimab were different and 13 patients with casirivimab/imdevimab therapy were vaccinated, the variant of SARS-CoV-2 and vaccination might affect the clinical outcomes between the two groups. Finally, the treatment with neutralizing mAbs was for patients with kidney, liver, and bone marrow TRs. Therefore, another study is needed for patients with lung and heart TRs.
Our results demonstrated that casirivimab/imdevimab therapy involving neutralizing mAbs is effective against mild-to-moderate COVID-19 in TRs compared with treatment without casirivimab/imdevimab. Casirivimab/imdevimab enhanced neutralizing antibody levels against COVID-19 in TRs in whom the levels tended to stay lower despite vaccination with BNT162b2 or mRNA-1273. Therefore, casirivimab/ imdevimab therapy could contribute to preventing the progression of mild-to-moderate COVID-19 in TRs.

Consent for publication
Not applicable.  Neutralizing antibody levels in patients a, who did not receive casirivimab/ imdevimab therapy and b, who received casirivimab/imdevimab therapy. A, day of hospitalization; B1, 7-9 days after hospitalization; B2, 3-5 days after hospitalization; C, day of discharge.

Availability of data and materials
Data that support the conclusions of this study are demonstrated in this manuscript and details are available upon reasonable request from the corresponding author. However, data have not been made available publicly.

Funding
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Author's contributions
KA and HS conceptualized and designed the study. KA, FE, TM, KU, TK, HI, HE, and JT performed data acquisition. KA, YH, HS, and KS analyzed the data. KA, ET, and MK wrote the manuscript KA, KK, TM, ET, and MK revised and edited the manuscript. MK and TK supervised the study. All authors have read and approved the manuscript.

Declaration of Competing Interest
None.

Data availability
No data was used for the research described in the article.