Open Forum Infectious Diseases MAJOR ARTICLE A Phase 2 Randomized, Double-Blind, Placebo-Controlled Trial of the Monoclonal Antibody MHAA4549A in Patients With Acute Uncomplicated Influenza A Infection Jeremy J. Lim,1 Sadia Dar,2 Dirk Venter,3 Juan P. Horcajada,4 Priya Kulkarni,1 Allen Nguyen,1 Jacqueline M. McBride,1 Rong Deng,1 Joshua Galanter,1 Tom Chu,1 Elizabeth M. Newton,1 Jorge A. Tavel,1 and Melicent C. Peck1; on behalf of the NIGHTHAWK investigators 1 Early Clinical Development, Genentech, Inc., South San Francisco, California, USA, 2Clinical Research Solutions, LLC, Smryna, Tennessee, USA, 3Henderson Medical Centre, Auckland, New Zealand, and 4Department of Infectious Diseases, Hospital del Mar, Institut Hospital del Mar d’Investigacions Mèdiques, Universitat Autònoma, Universitat Pompeu Fabra, Barcelona, Spain Background. MHAA4549A, a human monoclonal antibody targeting the influenza A hemagglutinin stalk, neutralizes influenza A virus in animal and human volunteer challenge studies. We investigated the safety and tolerability, efficacy, and pharmacokinetics of MHAA4549A in outpatients with acute, uncomplicated influenza A infection. Methods. This was a phase 2, randomized, double-blind, placebo-controlled trial of single intravenous (IV) doses of 3600 mg or 8400 mg of MHAA4549A or IV placebo in adult outpatients testing positive for influenza A. Patients were enrolled across 35 sites in 6 countries. Randomization and dosing occurred within ≤72 hours of symptom onset; the study duration was 14 weeks. The primary end point was the nature and frequency of adverse events (AEs). Secondary end points included median time to alleviation of all in- fluenza symptoms, effects on nasopharyngeal viral load and duration of viral shedding, and MHAA4549A serum pharmacokinetics. Results. Of 125 randomized patients, 124 received study treatment, with 99 confirmed positive for influenza A by central testing. The frequency of AEs between the MHAA4549A and placebo groups was similar; nausea was most common (8 patients; 6.5%). MHAA4549A serum exposure was confirmed in all MHAA4549A-treated patients and was dose-proportional. No hospitalizations or deaths occurred. Between the MHAA4549A and placebo groups, no statistically significant differences occurred in the median time to alleviation of all symptoms, nasopharyngeal viral load, or duration of viral shedding. Conclusions. While MHAA4549A was safe and well tolerated with confirmed exposure, the antibody did not improve clinical outcomes in patients with acute uncomplicated influenza A infection. Keywords. antiviral agents; influenza A virus; MHAA4549A; monoclonal antibody. Seasonal influenza is a highly contagious airborne disease laboratory-confirmed influenza, NAIs reduce both the time caused by influenza A and B viruses. Influenza can cause a to alleviation of symptoms by ~1–2 days and the risk of hos- range of clinical outcomes from self-limited upper respiratory pitalization [3–5]. However, influenza resistance to NAIs re- tract infection to severe disease with life-threatening compli- mains a concern [6, 7], especially in immunocompromised cations, including respiratory failure. Particularly vulnerable individuals due to prolonged viral shedding [8]. Even with populations include children, the elderly, pregnant and post- a seasonal influenza vaccine and NAIs, there were 37.4–42.9 partum women, people with chronic medical conditions, and million cases of influenza, 531 000–647 000 influenza-related those who are immunosuppressed. hospitalizations, and 36 400–61 200 influenza-related deaths The mainstay of treatment in influenza-infected patients in the United States during the 2018–2019 influenza season is neuraminidase inhibitors (NAIs) that act against influ- [9]. Globally, seasonal influenza results in ~3–5 million cases enza A and B subtypes [1, 2]. If given within the first 36–48 of severe illness and up to 650 000 deaths each year [10, 11]. hours of symptom onset in patients with uncomplicated Thus, a significant unmet need exists for developing novel antiviral agents for use with NAIs in patients with severe influenza. Received 16 August 2021; editorial decision 6 December 2021; accepted 9 December 2021; published online 10 December 2021. MHAA4549A is a human monoclonal immunoglobulin Correspondence: Melicent Peck, MD, PhD, Genentech, Inc., 1 DNA Way, South San Francisco, G1 (IgG1) antibody that binds conserved epitopes in the HA CA 94080 (peck.melicent@gene.com). stalk of human influenza A viruses and neutralizes all tested Open Forum Infectious Diseases®2022 © The Author(s) 2022. Published by Oxford University Press on behalf of Infectious Diseases seasonal human influenza A strains [12]. MHAA4549A has 2 Society of America. This is an Open Access article distributed under the terms of the Creative complementary mechanisms of action: (1) it directly neutral- Commons Attribution-NonCommercial-NoDerivs licence (https://creativecommons.org/ licenses/by-nc-nd/4.0/), which permits non-commercial reproduction and distribution of the izes influenza virus by binding to the HA stalk, preventing HA work, in any medium, provided the original work is not altered or transformed in any way, and that maturation and blocking HA-mediated membrane fusion in the the work is properly cited. For commercial re-use, please contact journals.permissions@oup.com https://doi.org/10.1093/ofid/ofab630 endosome and release of influenza particles, and (2) and it binds Anti-influenza A in Acute Influenza • OFID • 1 HA on the surface of infected cells and recruits immune cells to research was conducted, whichever afforded the greater protec- lyse the virus-infected cells through antibody-dependent cel- tion to the individual. The study complied with ICH E2A guide- lular cytotoxicity (ADCC) [13, 14]. MHAA4549A was well tol- lines, US Food and Drug Administration regulations, applicable erated in 2 phase 1 studies and in a phase 2a nasal influenza local, state, and federal laws, and the EU Clinical Trial Directive challenge study [15, 16]. (2001/20/EC). All patients provided written informed con- Preclinical studies have raised the possibility that monoclonal sent. Clinical trial registries: ClinicalTrials.gov: NCT02623322; anti-HA stalk antibodies may promote antibody-dependent EudraCT 2016-000425-40. enhancement (ADE) of infection [17–19]. Specifically, non- neutralizing antiviral antibodies may facilitate virus entry into Participants host cells, causing enhanced viral replication, shedding, and Enrolled participants were otherwise healthy adults, 18–65 potentially more severe clinical symptoms [17, 18, 20–23]. years old, who tested positive for influenza A infection using a However, the phase 2a intranasal challenge study showed none rapid polymerase chain reaction (PCR) test or rapid antigen test, of these effects in subjects receiving MHAA4549A vs pla- had ≤72 hours (3 days) between onset of influenza-like illness cebo [16]. To date, there is no clinical evidence of ADE with and start of study treatment, and had clinical evidence of influ- anti-HA monoclonal antibodies with similar mechanisms to enza infection during screening: at least 1 moderate or severe MHAA4549A [24, 25]. constitutional symptom (eg, headache, myalgias, fever, chills, This phase 2 study (NIGHTHAWK) assessed the safety and fatigue, anorexia, nausea) and 1 moderate or severe respiratory tolerability of MHAA4549A in otherwise healthy outpatients symptom (eg, cough, sore throat, rhinorrhea). Participant ex- with naturally occurring influenza A infection. We also ex- clusion criteria are described in the Supplementary Data. plored the effects of MHAA4549A on time to resolution of in- fluenza symptoms and viral load in the upper respiratory tract. Outcomes The primary end point was the nature, frequency, and severity METHODS of adverse events (AEs) and serious adverse events (SAEs), ef- fects on laboratory values, vital signs, electrocardiogram (ECG) Study Design parameters, and other safety biomarkers in patients receiving a This was a randomized, double-blind, placebo-controlled single IV dose of MHAA4549A or placebo. study to assess the safety and tolerability of single IV doses of Secondary end points included the median time to allevia- MHAA4549A (3600 or 8400 mg) compared with placebo for tion of all influenza symptoms (nasal congestion, sore throat, treatment of acute uncomplicated seasonal influenza A infec- cough, aches, fatigue, headaches, and chills/sweats) with reso- tion in otherwise healthy adults in an outpatient setting. The lution maintained for 24 hours (without use of symptom relief 3600 mg MHAA4549A dose was selected based on the phase medications), defined by a rating of 0 (none) or 1 (mild) for 2a challenge study, which demonstrated significant decreases in each symptom on a 4-point scale (0–3). For patients with mild virology and symptom end points [16, 26]. The 8400 mg dose symptoms, the symptom score had to be reduced by 1 point was selected to mirror the dose used in a trial in hospitalized during the study. Other secondary end points included the in- patients [27] who are likely to have higher viral loads and longer cidence of influenza reinfection/relapse at 100 days after the durations of viral shedding and therefore would need higher end of treatment, hospital admission rate, duration of hospital doses of MHAA4549A [28, 29]. stay, antibiotic usage for secondary bacterial respiratory infec- The study was conducted at 35 investigational sites in 6 coun- tions, influenza reinfection rate, and the incidence of death. tries. Study duration was ~14 weeks; randomization and study MHAA4549A serum pharmacokinetic (PK), nasopharyngeal drug dosing occurred ≤72 hours (3 days) from the onset of viral load by quantitative PCR and TCID50, and the duration of influenza-like illness (as determined by the investigator). Clinic viral shedding in upper respiratory samples were also assessed. visits were conducted on days 3, 5, and 7; telephone follow-ups occurred on days 2, 14, 30, and 100. The end of the study was Procedures defined as the first day when all patients had a study comple- A single dose of MHAA4549A or placebo was diluted in 0.9% tion visit, early termination visit, or had otherwise been discon- normal saline and delivered intravenously over ~120 minutes. tinued from the study. All patients were monitored for study drug reactions during and for at least 30 minutes after study drug administration. Patient Consent Patients recorded symptoms of influenza-like illness, use This study was conducted in full conformance with the of symptom relief medications, and oral temperature in paper International Council for Harmonization (ICH) E6 guideline diaries twice daily: once upon waking in the morning and ~12 for Good Clinical Practice and the principles of the Declaration hours later. Patients recorded entries until day 14 or symptom of Helsinki or the laws and regulations of the country where the resolution (symptom score of 0–1 for 24 hours without use 2 • OFID • Lim et al of symptom relief medications). Temperature was taken be- concentration–time curve from time 0 to day 6 (AUC0–6) are fore administration of acetaminophen/paracetamol and/or reported, with estimates summarized as mean and SD. All sta- nonsteroidal anti-inflammatory drugs. The day 1 entry was tistical analyses were performed using SAS (version 9.2) and R completed within 6 hours before starting study infusion. (version 3.3.2). Sample collection and assays for assessing serum and naso- pharyngeal MHAA4549A pharmacokinetics and viral load are Data Sharing described in the Supplementary Data. Qualified researchers may request access to individual patient- level data through the clinical study data request platform Statistical Analysis (https://vivli.org/). Further details on Roche’s criteria for el- The planned sample size was ~47 patients per treatment group igible studies are available here (https://vivli.org/members/ to obtain 120 evaluable patients (estimated dropout rate de- ourmembers/). For further details on Roche’s Global Policy on rived from country and site feasibility assessments performed the Sharing of Clinical Information and how to request access by our clinical operations group and CRO = 15%). Safety ana- to related clinical study documents, see https://go.gene.com/ lyses included all randomized patients who received the study datasharing. drug. Efficacy analyses were performed on the intent-to-treat infected (ITTI) population, defined as all randomized patients RESULTS with confirmed influenza A infection by a central PCR test. Day 1 samples were used when available; otherwise, the next Patients available time point sample was used. Time to event data were The study was conducted from March 2016 until November analyzed using Kaplan-Meier methodology and were summar- 2017. Two hundred sixty-five patients were screened, and 124 ized using medians and 80% CIs. Patients who were lost to fol- were randomized to receive study treatment (Supplementary low-up (while event-free) were censored at the time that they Figure 1). The mean age of patients (range) was 37.0 (18–65) were last known to be event-free. MHAA4549A serum PK was years (Table 1). There was a higher proportion of women summarized by estimating total serum drug exposure. Because (57.3%), and most patients were White (61.3%). All patients PK samples were only collected until day 7 (PK day 6), only had influenza A infection by local rapid antigen test (RAT) maximum concentration (Cmax) and area under the serum (91.9% of patients) or PCR, with ≤72 hours between symptom Table 1. Patient Demographics and Baseline Characteristics (Safety-Evaluable Population) MHAA4549A MHAA4549A Placebo (n = 43) 3600 mg (n = 41) 8400 mg (n = 40) All Patients (n = 124) Age, y 39.3 ± 10.8 36.5 ± 12.5 35.0 ± 13.6 37.0 ± 12.4  Age group, ≥65 y 0 0 1 (2.5) 1 (0.8) Sex, female 27 (62.8) 22 (53.7) 22 (55.0) 71 (57.3) Race  Asian 2 (4.7) 4 (9.8) 1 (2.5) 7 (5.6)  Black or African American 13 (30.2) 7 (17.1) 15 (37.5) 35 (28.2)  Native Hawaiian or other Pacific Islander 1 (2.3) 2 (4.9) 0 3 (2.4)  White 27 (62.8) 26 (63.4) 23 (57.5) 76 (61.3)  Multiple 0 0 1 (2.5) 1 (0.8)  Unknown 0 2 (4.9) 0 2 (1.6) Influenza confirmation test  Rapid antigen test 39 (90.7) 38 (92.7) 37 (92.5) 114 (91.9)  Rapid PCR test 4 (9.3) 3 (7.3) 3 (7.5) 10 (8.1) Influenza symptom onset time category—calculated  ≤36 hours 11 (25.6) 11 (26.8) 8 (20.0) 30 (24.2)  >36 hours 32 (74.4) 30 (73.2) 32 (80.0) 94 (75.8) Influenza subtypea  H1 4/33 5/35b 2/31 11/99b b  H3 25/33 29/35 28/31 82/99b  Negative for H1 and H3 4/33 2/35 1/31 7/99 Data are mean ± SD or No. (%). Abbreviations: ITTI, intent-to-treat infection; PCR, polymerase chain reaction. a ITTI population; data are number/total for each cohort. b One subject in the 3600 mg group tested positive for H1 and H3. Anti-influenza A in Acute Influenza • OFID • 3 onset and study drug administration. Most patients (75.8%) MHAA4549A-treated patients (8.1%) had treatment-related were dosed >36 hours from symptom onset. AEs (nausea and dry skin, 2 patients each; n = 1 for all other Of 124 patients who were randomized at a 1:1:1 ratio and treatment-related AEs), as deemed by the site investigator, and received IV doses of placebo, 3600 mg of MHAA4549A, or no treatment-related AEs occurred in the placebo group. No 8400 mg of MHAA4549A, 121 patients (97.6%) completed the patients were hospitalized, had influenza reinfection, or died study, with 3 patients (2.4%) lost to follow-up (Supplementary through day 100 post-treatment (end of study). There were no Figure 1). In the placebo group, study treatment infusion was clinically significant changes in laboratory parameters, ECGs, stopped in 1 patient due to an infusion-related reaction. Of the or vital signs. One patient (8400 mg MHAA4549A) had an SAE 124 safety-evaluable patients, 99 were confirmed positive for of atrial fibrillation that self-resolved without treatment and influenza A by a central PCR test (ITTI population). Eight pa- was not considered related to study drug. The only influenza- tients had missing virology samples, and 17 patients were as- related complication was a respiratory tract infection in 1 sumed to be false positive RAT or because there was ~24 hours placebo-treated patient (3.0%), who was treated with the anti- between the sample collections. A majority of subjects (82 out biotic clarithromycin. of 99 subjects) in the ITTI population tested positive for the H3 subtype. One subject in the 3600 mg group tested positive for Efficacy both the H1 and H3 subtypes, and 7 subjects tested negative for The median time to alleviation of all symptoms (total symptom both the H1 and H3 subtypes. score ≤1) was slightly longer in the active treatment arms (3600 mg MHAA4549A, 154 hours; 80% CI, 125–175 hours; Safety 8400 mg MHAA4549A, 146 hours; 80% CI, 133–157 hours) Similar proportions of patients experienced AEs between compared with placebo (117 hours; 80% CI, 109–157 hours) the MHAA4549A and placebo groups (Table 2). Forty-one (Figure 1), but these differences were not statistically significant. patients (33.1%) had 81 AEs. The most common AEs were Hazard ratios (stratified analysis) for the 3600 and 8400 mg nausea (6.5%) and bronchitis (4%). Bronchitis was not dose- MHAA4549A arms were 0.92 (80% CI, 0.6–1.4) and 0.90 (80% dependent and occurred in 4 (4.9%) MHAA4549A recipients CI, 0.6–1.4), respectively. In the MHAA4549A arms, a trend of and 1 (2.5%) placebo subject with onset within 1 week of enroll- increased cough duration (~1 day longer to resolve than pla- ment in all cases, except 1 where the diagnosis was associated cebo) drove the differences in resolution of the total symptom with sinusitis. All bronchitis events were either mild (grade 1) score, but these differences were not statistically significant. or moderate (grade 2), were not serious, and were not con- The effect of MHAA4549A on influenza A nasopharyngeal sidered related to study drug by the site investigator. Other AEs viral load is shown in Figure 2. We observed no differences included vomiting, oropharyngeal pain, epistaxis, nasal con- by PCR (Figure 2A), but with TCID50, the MHAA4549A arms gestion, and headache, which all occurred in <3% of patients. showed a trend toward faster viral load clearance; however, this Two placebo-treated patients experienced 5 unrelated grade 3 was not statistically significant (Figure 2B). The duration of AEs (nausea, diarrhea, lower respiratory tract infection, drug viral shedding between treatment groups did not differ (data intolerance, and anxiety). All other events were grade ≤2. Ten not shown). Table 2. Safety Profile; AEs in ≥2% of All Patients Are Shown MHAA4549A MHAA4549A Placebo (n = 43) 3600 mg (n = 41) 8400 mg (n = 40) All Patients (n = 124) Total No. of patients with ≥1 AE 13 (30.2) 16 (39.0) 12 (30.0) 41 (33.1) Total No. of AEs 29 32 20 81 Related AE 2 (4.7) 4 (9.8) 4 (10.0) 10 (8.1) Related AE leading to withdrawal from treatment 1 (2.3) 0 0 1 (0.8) Total No. of patients with ≥1 SAE 0 0 1 (2.5)a 1 (0.8) AEs in ≥2% of all patients  Nausea 2 (4.7) 3 (7.3) 3 (7.5) 8 (6.5)  Bronchitis 1 (2.3) 3 (7.3) 1 (2.5) 5 (4.0)  Oropharyngeal pain 1 (2.3) 1 (2.4) 2 (5.0) 4 (3.2)  Vomiting 2 (4.7) 1 (2.4) 1 (2.5) 4 (3.2)  Epistaxis 1 (2.3) 1 (2.4) 1 (2.5) 3 (2.4)  Headache 0 2 (4.9) 1 (2.5) 3 (2.4)  Nasal congestion 0 2 (4.9) 1 (2.5) 3 (2.4) Data are presented as No. (%) unless otherwise indicated. Abbreviations: AE, adverse event; SAE, serious adverse event. a Not considered related to study drug. 4 • OFID • Lim et al A B 300 100 SYMPTOM (0–3) Patients with total symptom score >1 (%) Nasal congestion Time to alleviation of symptoms, h 250 Sore throat Cough 80 Aches/pains 200 Fatigue Headache 60 Chills/sweats 150 40 100 20 Placebo 50 MHAA4549A 3600 mg MHAA4549A 8400 mg 0 0 Placebo MHAA4549A MHAA4549A 1 26 51 76 101 126 151 176 201 226 251 276 (n = 24) 3600 mg 8400 mg Time, h (n = 24) (n = 25) Placebo 24 22 21 19 17 11 10 7 2 1 1 1 MHAA4549A 3600 mg 24 26 22 21 19 14 13 8 5 4 1 1 MHAA4549A 8400 mg 25 24 23 21 18 16 11 7 5 2 NE NE Figure 1. Median time to alleviation of total symptoms, as measured by a total symptom score ≤1. A, Each symptom was scored as none (0), mild (1), moderate (2), and severe (3) and then added for a total symptom score. Horizontal bar and box boundaries indicate median and IQR, respectively; whiskers indicate 1.5 times the IQR from the upper and lower hinges of the box. B, Kaplan-Meyer plot of time to alleviation of symptoms. Abbreviation: IQR, interquartile range. Pharmacokinetics placebo. Similar proportions of patients experienced AEs be- MHAA4549A serum exposure was confirmed in all tween the MHAA4549A and placebo groups, and there were no MHAA4549A-treated patients (Figure 3A) and was dose- treatment-related SAEs, cases of influenza reinfection, hospital- proportional (Figure 3B). The maximum observed serum con- izations, or deaths through day 100 post-treatment. The most centrations (mean ± SD) for MHAA4549A were 1050 ± 299 µg/ common AEs were nausea and dry skin. MHAA4549A serum mL and 2190 ± 58 µg/mL for the 3600 and 8400 mg groups, re- exposure was confirmed in all MHAA4549A-treated patients spectively (Figure 3C). and with expected dose-proportional PK. In MHAA4549A-treated patients, there was a trend of cough persisting ~1 day longer compared with placebo-treated pa- DISCUSSION tients. While bronchitis was reported as one of the most MHAA4549A was tested as adjunctive therapy to NAIs for common AEs (4% of patients), there were no significant dif- hospitalized patients with severe influenza A. This study ferences between the treatment and placebo groups, and only 1 evaluated single IV doses of MHAA4549A in adults with placebo-treated patient received an antibiotic. The cause of pro- uncomplicated seasonal influenza A. MHAA4549A dem- longed cough in MHAA4549A recipients is unknown; one hy- onstrated acceptable safety and tolerability compared with pothesis is that it could be due to antibody-mediated irritation A 0 ● B 1 in TCID50 , log10TCID50/mL Median change from baseline Median change from baseline in viral load, log10vp/mL ● 0 ● ● −2 ● ● ● −1 ● −4 −2 ● Placebo MHAA4549A 3600 mg MHAA4549A 8400 mg −3 1 3 5 7 1 3 5 7 Visit day Visit day Figure 2. Median (±SD) change in nasopharyngeal viral load as measured by (A) qPCR and (B) TCID50 in the ITTI population. For (A), LLOQ = 2.18 log10[vp/mL]. For (B), LLOQ = 0.75 log10[TCID50/mL]. Assay results below the LLOQ were imputed as the LLOQ. Abbreviations: ITTI, intent-to-treat-infected; LLOQ, lower limit of quantification; qPCR, quantitative polymerase chain reaction; TCID50, 50% tissue culture infectious dose; vp, viral particles. Anti-influenza A in Acute Influenza • OFID • 5 A 10000 B 1 MHAA4549A concentration concentration, µg/mL Dose-normalized MHAA4549A 1000 0.1 MHAA4549A 3600 mg MHAA4549A 8400 mg 100 0 2 4 6 0 2 4 6 Time, d Time, d C MHAA4549A MHAA4549A 3600 mg 8400 mg n = 40 n = 37 Cmax, mean (SD), µg/mL 1050 (299) 2190 (581) n = 37 n = 34 AUC0–6, mean (SD), d•µg/mL 3990 (943) 8880 (2360) Figure 3. A, MHAA4549A serum concentration–time curve. B, MHAA4549A serum concentration normalized to dose. C, Summary of serum MHAA4549A pharmacokinetic parameters in PK-evaluable subjects. in pleural fluid. In a phase 2 outpatient study with MEDI8852, a lack of ADE of infection or influenza disease. We also saw a human IgG1 monoclonal antibody that binds the influenza no evidence of viral resistance to MHAA4549A, based on the A hemagglutinin stalk epitope, bronchitis occurred at a higher resolution of viral shedding and clinical symptoms, although 3 rate in MEDI8852 recipients than oseltamivir recipients (11.8% MHAA4549A-resistant viruses that either abolished or reduced and 3.1%, respectively), with most events starting around day 7 HA binding have been previously isolated in vitro [13]. and resolving by day 15 [24]. The cause of the bronchitis event It is unclear why MHAA4549A did not demonstrate clin- is unknown; however, most of the bronchitis events occurred ical activity in patients with uncomplicated influenza infection, at a single study site. Additionally, prolonged postinfectious though a number of factors can be considered. First, unlike cough from influenza infection is common due to epithelial neuraminidase inhibitors, there are limited data to determine damage and inflammation in the airway tract. Patients with in- the appropriate time-to-treatment window with monoclonal fluenza infections commonly report cough lasting more than antibodies, and patients may have received MHAA4549A too a week [30], and 11%–25% of patients with upper respiratory late in the course of disease. While we saw no differences among infections develop persistent cough (>3 weeks after acute symp- patients based on time to treatment (≤ or >36 hours from toms disappear) [31–33]. Given the lack of associated influenza symptom onset; data not shown), most patients (76%) were symptoms, lack of increase in influenza virus shedding the dosed >36 hours from symptom onset due to operational con- MHAA4549A vs placebo groups, and similar number of bron- straints associated with diagnostic testing and delivery of an IV chitis cases between the MHAA4549A and placebo recipients, therapy. Accordingly, we could not fully assess efficacy trends the finding of prolonged cough by 1 day is not considered to regarding timing of therapy with respect to symptom onset. be consistent with ADE of influenza disease or to be clinically Previous influenza outpatient studies with the polymerase significant. inhibitors baloxivir, marboxil, and pimodivir [34, 35] that dem- MHAA4549A displayed PK properties consistent with pre- onstrated efficacy required a 48-hour window from symptom vious observations [15, 16, 26], indicating that therapeutic onset for enrollment, allowing for treatment within 24–48 serum concentrations were reached. Despite expected exposure hours with respect to symptom onset in the majority of pa- to study drug, MHAA4549A did not significantly improve the tients. In studies with the anti-HA stalk antibodies MEDI8852 time to resolution of signs and symptoms of influenza compared and VIS410 [24, 25], most patients were treated within 24–48 with placebo. Similarly, MHAA4549A did not reduce the time hours of symptom onset. The median time to treatment from to clearance of viral load over placebo. The absence of increased symptom onset in the VIS410 study was 42 hours, with favor- viral loads, persistent viral shedding, and prolonged clinical able effects on symptom resolution seen early (~day 2) and symptoms in the MHAA4549A arm vs the placebo arm suggests decreasing by day 7 in the trial (end points were not presented 6 • OFID • Lim et al based on time to treatment). MEDI8852 did not demonstrate constraints, and the seasonal variability of influenza [43, 44]. a treatment benefit even in those who received drug within 48 In particular, patients were required to have PCR- or RAT- hours. Based on the data from these influenza trials, a 72-hour confirmed influenza and be dosed within 72 hours of symptom treatment window after symptom onset may be too long for in- onset. From an operational standpoint, this was challenging fluenza therapy to reverse signs and symptoms of clinical influ- and slowed trial enrollment. During the trial, patients were re- enza, especially in otherwise healthy patients with mild disease quired to receive a 120-minute IV infusion in an outpatient set- where the viral load typically peaks on the day of symptom ting followed by postinfusion monitoring for 30 minutes. This onset or within 1–2 days [30] as seen in this study. was a less attractive option to patients as compared with oral Second, the use of monoclonal antibodies for the treatment oseltamivir, which was readily available during the trial period of influenza is challenging from a drug exposure perspective. and was prohibited in this study. There are many uncertainties surrounding the PK and distri- End point selection is critical to the effective evaluation of bution of a systemically administered antibody at the respira- novel therapeutic agents, and there were no standardized out- tory epithelial surface. Failure to achieve adequate and potent comes across influenza trials at the time of this trial. While concentrations at the site of action early in the course of dis- symptom duration has been used for registrational trials of ease progression may contribute to lack of efficacy [36]. In an acute uncomplicated influenza [45], these studies are subject to influenza challenge study in healthy volunteers, MHAA4549A reporting bias, and it is challenging to quantify differences be- showed dose-proportional serum PK with a long terminal half- tween patients. Virologic end points are not considered appro- life and slow clearance, though nasopharyngeal swab PKs were priate measures of efficacy for influenza therapeutics as there not dose-proportional [26]. MHAA4549A reached concentra- is no established relationship between viral reduction and clin- tions exceeding influenza concentrations in tracheal aspirates ical symptoms. Similar to end points used in this study, trials in hospitalized patients with severe influenza infection with the evaluating viral polymerase inhibitors and anti-HA stalk anti- same doses used in this study [26, 27, 37]. bodies have used end points focusing on the time to symptom Other anti-HA stalk antibodies with the same mechanism of resolution and measures of antiviral activity, including reduc- action as MHAA4549A have shown signs of preliminary effi- tions in viral load or duration of viral shedding. cacy. In patients with acute influenza, MEDI8852 was compa- In conclusion, this study demonstrated that MHAA4549A rable to oseltamivir for time to resolution of symptoms, time to was well tolerated with acceptable PK and likely reached effica- reduction of viral load, and duration of viral shedding [24]. In a cious exposures at the site of activity, but it did not improve clin- trial of outpatients with uncomplicated influenza, VIS410 dem- ical outcomes in patients with acute uncomplicated influenza A onstrated a tendency toward faster symptom resolution by day 3 infection. Even though the sponsor has decided to discontinue and reduced median nasopharyngeal viral load vs placebo [25]. the clinical development of MHAA4549A for reasons unre- Notably, the study used a 32-question FLUPRO patient-reported lated to safety, this study has contributed to our understanding outcome assessment, which may have been more sensitive than of anti-HA stalk monoclonal antibody therapy in patients with the scale used in this study. VIS410 evaluated in combination influenza A and supported the feasibility of this targeting ap- with oseltamivir vs oseltamivir alone in hospitalized adults with proach in future programs. influenza A requiring oxygen showed improvements in time to Supplementary Data normal oxygenation, cessation of virus shedding, and time to Supplementary materials are available at Open Forum Infectious Diseases complete clinical response in subset analyses of patients pre- online. Consisting of data provided by the authors to benefit the reader, senting within 72 hours of symptom onset [38]. In a more recent the posted materials are not copyedited and are the sole responsibility of study, a single dose of VIS410 reduced the median viral load in the authors, so questions or comments should be addressed to the corre- sponding author. healthy volunteers inoculated with H1N1 [39]. A number of promising antibody candidates have emerged Acknowledgments as potential therapeutic agents in the prevention and treatment The authors wish to thank all participating patients and their families as of COVID-19 infection in the outpatient setting. Antibodies well as all the contributing staff at the attending sites. Editing and writing assistance was provided by Genentech, Inc. have demonstrated efficacy in COVID-19 trials, possibly due Financial support. This work was supported by Genentech, Inc. to the longer window of ~5–7 days between onset of symp- Potential conflicts of interest. J.J.L., P.K., A.N., J.M.M., R.D., J.G., T.C., toms and progression to severe illness requiring hospitalization E.M.N., J.A.T., and M.C.P. were employees of Genentech, Inc.. a member of the Roche group, and own/owned Roche stock and/or options at the time [36, 40, 41]. In contrast, antibody-based therapeutics have not this study was performed. Genentech, Inc., provided research funding to the demonstrated widespread efficacy in hospitalized patients with institutions of S.D., D.V., and J.P.H.G. for the conduct of this study. All au- COVID-19. Further, the emergence of resistant variants signifi- thors have submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Conflicts that the editors consider relevant to the content of the cantly threatens the efficacy of nAb-based therapeutics [42]. manuscript have been disclosed. 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