Prophylactic Administration of the Monoclonal Antibody Adintrevimab Protects against SARS-CoV-2 in Hamster and Non-Human Primate Models of COVID-19

ABSTRACT

Adintrevimab is a human immunoglobulin G1 monoclonal antibody engineered to have broad neutralization against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants and other SARS-like coronaviruses with pandemic potential. In both Syrian golden hamster and rhesus macaque models, prophylactic administration of a single dose of adintrevimab provided protection against SARS-CoV-2/WA1/2020 infection in a dose-dependent manner, as measured by significant reductions in lung viral load and virus-induced lung pathology, and by inhibition of viral replication in the upper and lower respiratory tract.

INTRODUCTION

The spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and new variants of concern (VOCs) are ongoing global public health concerns (1). Vaccines are highly effective in preventing severe COVID-19, but both waning immunity and the emergence of highly transmissible VOCs (2–4) have highlighted the need for additional treatment and prevention options that are broadly neutralizing and easily administered across diverse health care settings.

Adintrevimab (formerly ADG20) is a fully human IgG1 monoclonal antibody derived from a survivor of the 2003 SARS-CoV epidemic and engineered to have improved potency and broad neutralization against SARS-CoV-2 and other SARS-like coronaviruses with pandemic potential (5–7). The crystallizable fragment (Fc) region of adintrevimab has a modification to extend its half-life (7). Adintrevimab binds to a distinct epitope in the receptor-binding domain of the spike glycoprotein of SARS-CoV-2 that partially overlaps the angiotensin-converting enzyme 2 binding site and is highly conserved among sarbecoviruses (7). In vitro, adintrevimab has demonstrated potent neutralizing activity against most variants and sublineages of SARS-CoV-2 (including Alpha, Beta, Gamma, and Delta) as well as other SARS-like viruses. Adintrevimab displays reduced in vitro activity against Omicron BA.1/BA.1.1 and lacks activity against BA.2, BA.3, BA.4, and BA.5 (5–9). Prophylactic and therapeutic administration of ADG-2 (the parent antibody of adintrevimab without the half-life extension modification in the Fc region) provided protection against respiratory burden, viral replication in the lungs, and lung pathology in mice infected with mouse-adapted SARS-CoV and SARS-CoV-2 (7). Treatment with ADG-2 after viral exposure was also effective against SARS-CoV-2 Beta infection in mice (10).

Here, we report two studies that evaluated the in vivo prophylactic efficacy of adintrevimab on the diverse range of COVID-19 manifestations in Syrian golden hamsters and nonhuman primates (rhesus macaques) infected with SARS-CoV-2/WA1/2020.

Animal research was conducted at the U.S. Army Medical Research Institute of Infectious Diseases in compliance with the Animal Welfare Act and other applicable federal statutes and regulations relating to experiments involving animals (11). Detailed methodology for both studies is provided in the supplemental material.

Hamster study.

Briefly, 60 Syrian golden hamsters (5- to 6-week-old females; body weight 75 to 125 g) were dosed with a single intraperitoneal injection of either adintrevimab at 9.25, 55, 333, or 2,000 μg (average range: 0.1 to 20 mg/kg) or an isotype-matched control IgG (at the highest and lowest dose) 24 h before intranasal challenge with SARS-CoV-2/WA1/2020 (1 × 10⁵ PFU; Fig. 1A). The animals were monitored and weighed daily over 6 days. At days 3 and 6 post-exposure, five to six animals from each dose group were euthanized, and their lungs were collected to evaluate infectious viral titers (determined by plaque assay), viral RNA load (determined by envelope [E] gene reverse transcriptase PCR [RT-PCR]), histopathology, immunohistochemistry (IHC) for SARS-CoV-2 nucleocapsid protein, and in situ hybridization (ISH) staining for detecting SARS-CoV-2 genomic RNA in the lung. The total lung pathology score was obtained by adding individual severity scores for five indicators of pulmonary damage ranging from zero (no change) to five (severe, ≥80% of the tissue is affected). Statistical comparisons for body weight, viral titers, and viral RNA loads were calculated using unpaired, two-sided t tests, and comparisons for lung pathology were calculated using unpaired 2-sided Mann-Whitney tests with GraphPad Prism version 9.0 software.

FIG 1.

Prophylactic efficacy of adintrevimab in the Syrian golden hamster model of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)/WA1/2020 infection. (A) Study design. (B) Total lung pathology scores on days 3 and 6 in adintrevimab-treated animals versus controls. (C) Lung viral titers on days 3 and 6 in adintrevimab-treated animals versus controls. (D) Lung viral load (subgenomic RNA [sgRNA]) on days 3 and 6 in adintrevimab-treated animals versus controls. Any values below the limit of detection (LOD) were assigned a value half that of the limit. Bars represent mean and standard error of the mean (SEM). Horizontal dotted lines represent LOD. Statistical significance defined as *, P < 0.05; **, P < 0.01; ***, P < 0.001; ****, P < 0.0001 versus control 2,000 μg.

Human IgG antibody concentrations were confirmed in individual animals 24 h after dosing (Fig. S1). Animals not demonstrating detectable human IgG titers (n = 20) were excluded from the study. A total of 27 animals in the adintrevimab group and 13 animals in the control group were assessed.

The results showed minimal weight change in the control animals post-SARS-CoV-2 exposure, while animals treated with 55, 333, and 2,000 μg adintrevimab gained significantly (P < 0.05) more weight by day 6 (Fig. S2). The propensity for weight gain rather than protection from weight loss may reflect the expected weight change in healthy young hamsters of this age (12, 13).

All animals in the control group and those in the lower adintrevimab dose groups (9.25 and 55 μg) exhibited various degrees of pulmonary inflammation consistent with an acute SARS-CoV-2 infection (14). Lung tissues from these animals were positive by IHC and ISH in the areas of inflammation and within the respiratory epithelium. Animals in the higher adintrevimab dose groups (333 and 2,000 μg) had significantly lower total lung pathology scores (P < 0.01 and P < 0.05, respectively) than the controls at day 3 (Fig. 1B) and displayed limited histopathological evidence of pneumonia at days 3 and 6 post-exposure. In the 2,000-μg adintrevimab dose group, lung tissue was negative by IHC and ISH in 4 of 5 animals tested at day 3 and in 3 of 5 animals tested at day 6 post-exposure, respectively.

On day 3, lung viral titers (determined by plaque assay) were below the limit of detection (LOD) in all animals in the 2,000-μg adintrevimab group and in 3 of 5 animals in the 333-μg adintrevimab group (Fig. 1C). Compared with control animals, day 3 viral titers were significantly lower in animals which received the higher adintrevimab doses (333 and 2,000 μg; P < 0.01) but not in those which received the lower adintrevimab doses (9.25 and 55 μg). A similar dose-response trend was seen on day 3 for levels of viral subgenomic E RNA (sgRNA; Fig. 1D), which has been used as a marker for actively replicating virus and levels of total E RNA (sgRNA and genomic RNA; Fig. S3). By day 6, both control and treated animals had reduced lung viral titers and sgRNA viral loads, consistent with other studies showing natural clearance of SARS-CoV-2 infection within a week in the hamster model (15).

NHP study.

In a separate study, 12 rhesus macaques (5.6 to 8.8 years old; 6 females [4.4 to 6.3 kg] and 6 males [6.1 to 8.5 kg]) were dosed with a single intravenous injection of either adintrevimab (n = 8; 5 or 25 mg/kg) or an isotype-matched control IgG (n = 4; 25 mg/kg) 72 h before intranasal and intratracheal challenge with SARS-2-CoV-2/WA1/2020 (4.24 × 10⁵ PFU; Fig. 2A). Viral RNA loads were assessed in nasopharyngeal (NP) and oropharyngeal (OP) swabs (daily) and in bronchoalveolar lavage fluid (BALF; days 1, 3, and 5) by E gene RT-PCR (all samples). Infectious viral titers in NP and OP swabs were assessed by plaque assay. Histopathological examination and IHC were performed on lung tissue collected on day 5 post-exposure following scheduled euthanasia. Whole-genome sequencing (WGS) was used to evaluate the emergence of resistance to study drugs.

FIG 2.

Prophylactic efficacy of adintrevimab in the rhesus macaque model of SARS-CoV-2/WA1/2020 infection. (A) Study design. (B) Viral load (sgRNA) in nasopharyngeal (NP), oropharyngeal (OP), and bronchoalveolar lavage fluid (BALF) samples in adintrevimab-treated animals versus controls. (C) Viral load (total E RNA) in NP, OP, and BALF samples in adintrevimab-treated animals versus controls. Any values below the LOD were assigned a value half that of the limit. Horizontal solid lines represent mean values. Horizontal dotted lines represent LOD.

The results showed that on day 5 post-exposure, all control animals demonstrated pulmonary inflammation with positive SARS-CoV-2 IHC in areas of inflammation and within the respiratory epithelium, supporting SARS-CoV-2 infection as the underlying cause for the histopathology. Animals in both adintrevimab dose groups had reduced pulmonary inflammation compared with the controls, predominantly exhibiting multifocal minimal to mild inflammation and IHC-negative lung tissue (Fig. S4).

All control animals had high levels of SARS-CoV-2 sgRNA in NP and OP swabs until day 3 post-exposure. Animals in the 25-mg/kg adintrevimab dose group had undetectable sgRNA viral loads in all respiratory compartments across all time points assessed (Fig. 2B). A similar trend in the reduction of total E RNA was also observed, with total E RNA viral loads below the LOD by day 4 post-exposure in all animals in the 25-mg/kg adintrevimab dose group (Fig. 2C). Furthermore, no infectious virus was detected in NP and OP compartments via plaque assay at any time points in the 25-mg/kg adintrevimab dose group (Fig. S5).

In the 5-mg/kg adintrevimab group, OP sgRNA viral loads were comparable to controls, NP sgRNA viral load was detected in one animal, and BALF sgRNA viral loads were reduced compared with controls (Fig. 2B); total E RNA viral loads were reduced in OP and NP swabs but comparable to the controls in BALF (Fig. 2C). In the 5-mg/kg adintrevimab group, infectious viral titers at 1 day post-exposure in OP swabs were reduced more than 100-fold compared with controls. These results suggest a dose-dependent response in this model, with animals in the 5-mg/kg adintrevimab group achieving partial protection compared with those prophylactically treated with the higher dose.

In rhesus macaques, no mutations or single nucleotide polymorphisms in the binding region of adintrevimab (spike glycoprotein amino acid positions 403 to 505) at a variant allele frequency greater than 10% were detected by WGS.

In summary, these studies demonstrated the in vivo prophylactic efficacy of adintrevimab in two different animal models of SARS-CoV-2 infection. In the Syrian golden hamster and rhesus macaque models, protection from SARS-CoV-2/WA1/2020 infection was demonstrated in a dose-dependent manner through substantial reduction in lung viral load and lung inflammation and pathology scores and by inhibition of viral replication in the upper and lower airways. No emergence of resistance to adintrevimab in rhesus macaques was detected by WGS.

The overall results continue to add to the body of growing evidence of the efficacy of monoclonal antibodies targeting the receptor binding domain. Given the evolution of SARS-CoV-2, these data support the development of new potent monoclonal antibodies which have potential to retain activity against future circulating variants.