Comparison of a Novel Human Rabies Monoclonal Antibody to Human Rabies Immunoglobulin for Postexposure Prophylaxis: A Phase 2/3, Randomized, Single-Blind, Noninferiority, Controlled Study

The use of proteins and peptides-based therapy in managing and preventing pathogenic viruses

Therapeutic proteins have been employed for centuries and reached approximately 50 % of all drugs investigated. By 2023, they represented one of the top 10 largest-selling pharma products ($387.03 billion) and are anticipated to reach around $653.35 billion by 2030. Growth hormones, insulin, and interferon (IFN α, γ, and β) are among the leading applied therapeutic proteins with a higher market share. Protein-based therapies have opened new opportunities to control various diseases, including metabolic disorders, tumors, and viral outbreaks. Advanced recombinant DNA biotechnology has offered the production of therapeutic proteins and peptides for vaccination, drugs, and diagnostic tools. Prokaryotic and eukaryotic expression host systems, including bacterial, fungal, animal, mammalian, and plant cells usually applied for recombinant therapeutic proteins large-scale production. However, several limitations face therapeutic protein production and applications at the commercial level, including immunogenicity, integrity concerns, protein stability, and protein degradation under different circumstances. In this regard, protein-engineering strategies such as PEGylation, glycol-engineering, Fc-fusion, albumin conjugation, and fusion, assist in increasing targeting, product purity, production yield, functionality, and the half-life of therapeutic protein circulation. Therefore, a comprehensive insight into therapeutic protein research and findings pave the way for their successful implementation, which will be discussed in the current review.

Isolation and characterization of rabies monoclonal antibody charge variants

Current postexposure prophylaxis of rabies includes vaccines, human rabies immunoglobulin (RIG), equine RIG, and recombinant monoclonal antibodies (mAb). In the manufacturing of rabies recombinant mAb, charge variants are the most common source of heterogeneity. Charge variants of rabies mAb were isolated by salt gradient cation exchange chromatography (CEX) to separate acidic and basic and main charge variants. Separated variants were further extensively characterized using orthogonal analytical techniques, which include secondary and tertiary structure determination by far and near ultraviolet circular dichroism spectroscopy. Charge and size heterogeneity were evaluated using CEX, isoelectric focusing (IEF), capillary-IEF, size exclusion chromatography, sodium dodecyl sulfate polyacrylamide gel electrophoresis, and western blotting. Antigen binding affinity was assessed by enzyme linked immuno-sorbent assay and rapid florescence foci inhibition test. Results from structural and physicochemical characterizations concluded that charge variants are formed due to posttranslational modification demonstrating that the charge heterogeneity, these charge variants did neither show any considerable physicochemical change nor affect its biological function. This study shows that charge variants are effective components of mAb and there is no need of deliberate removal, until biological functions of rabies mAb will get affected.

Safety and immunogenicity of a serum-free purified Vero rabies vaccine in comparison with the rabies human diploid cell vaccine (HDCV; Imovax® Rabies) administered in a simulated rabies post-exposure regimen in healthy adults

A new generation, serum-free, antibiotic-free, purified Vero rabies vaccine (PVRV-NG; Sanofi) has been developed based on the same Pitman-Moore viral strain used for the currently licensed purified Vero cell rabies vaccine (PVRV; Verorab®, Sanofi) and human diploid cell vaccine (HDCV; Imovax® Rabies, Sanofi). PVRV-NG has demonstrated a satisfactory safety profile and induces robust immune responses, with non-inferiority demonstrated versus PVRV when given as a three-dose pre-exposure prophylaxis (PrEP) regimen in healthy children and adults. Here, we evaluated the safety and immunogenic non-inferiority of PVRV-NG compared to HDCV when administered as simulated post-exposure prophylaxis (PEP), with concomitant administration of human rabies immunoglobulin (HRIG), in healthy adults in the USA. Participants were vaccinated according to the 5-dose Essen intramuscular regimen (4-week, 1-injection site regimen, with a single dose given on days 0, 3, 7, 14 and 28) for PEP, with concomitant HRIG administered on day 0. Rabies virus neutralising antibodies (RVNA) were evaluated on days 0, 14, 28 and 42. Non-inferiority of PVRV-NG compared with HDCV was shown if the lower limit of the 95 % confidence interval (CI) for the difference in seroconversion rates (RVNA titers ≥ 0.5 IU/mL on day 14) between PVRV-NG and HDCV was above the non-inferiority margin of -5 %. Safety was evaluated after each vaccination and monitored throughout the study. The difference in seroconversion rate between the PVRV-NG and HDCV groups was -2.8 % (95 % CI, -8.08 to 4.20), indicating that non-inferiority was not demonstrated. The seroconversion rate was < 99 % in both study groups on day 14. There were no major safety concerns identified, and PVRV-NG demonstrated a similar safety profile to HDCV.

Monoclonal antibody applications in travel medicine

For decades, immunoglobulin preparations have been used to prevent or treat infectious diseases. Since only a few years, monoclonal antibody applications (mAbs) are taking flight and are increasingly dominating this field. In 2014, only two mAbs were registered; end of October 2023, more than ten mAbs are registered or have been granted emergency use authorization, and many more are in (pre)clinical phases. Especially the COVID-19 pandemic has generated this surge in licensed monoclonal antibodies, although multiple phase 1 studies were already underway in 2019 for other infectious diseases such as malaria and yellow fever. Monoclonal antibodies could function as prophylaxis (i.e., for the prevention of malaria), or could be used to treat (tropical) infections (i.e., rabies, dengue fever, yellow fever). This review focuses on the discussion of the prospects of, and obstacles for, using mAbs in the prevention and treatment of (tropical) infectious diseases seen in the returning traveler; and provides an update on the mAbs currently being developed for infectious diseases, which could potentially be of interest for travelers.

Safety and immunogenicity of three dose levels of an investigational, highly purified Vero cell rabies vaccine: A randomized, controlled, observer-blinded, Phase II study with a simulated post-exposure regimen in healthy adults

A serum-free, highly purified rabies vaccine produced in Vero cells is under development. The initial formulation, PVRV-NG, was evaluated in five Phase II studies and subsequently reformulated (PVRV-NG2). This multicenter, observer-blinded Phase II study investigated the safety and immune response of three different doses (antigen content) of PVRV-NG2 versus a licensed human diploid cell rabies vaccine (HDCV; Imovax rabies®). Healthy adults (N = 320) were randomized to receive PVRV-NG2 (low, medium, or high dose), PVRV-NG, or HDCV (2:2:2:1:1 ratio), according to a five-dose Essen simulated post-exposure regimen (Days [D] 0, 3, 7, 14, and 28). All participants received human rabies immunoglobulin intramuscularly on D0. Immunogenicity was assessed at D0, 14, 28, 42, and 6 months after the final injection using the rapid fluorescent focus inhibition test. Seroconversion rates were calculated as the percentage of participants achieving rabies virus neutralizing antibody titers ≥0.5 IU/mL. All analyses were descriptive. At each timepoint, geometric mean titers (GMTs) increased with antigen content (measured using an enzyme-linked immunosorbent assay). High-dose PVRV-NG2 GMTs were the highest at all timepoints, medium-dose PVRV-NG2 GMTs were similar to those with HDCV, and low-dose PVRV-NG2 GMTs were similar to PVRV-NG. The safety profile of PVRV-NG2 was comparable to PVRV-NG; however, fewer injection site reactions were reported with PVRV-NG2 or PVRV-NG (range 36.7-47.5%) than with HDCV (61.5%). This study demonstrated a dose-effect of antigen content at all timepoints. As post-exposure prophylaxis, the safety and immunogenicity profiles of the high-dose PVRV-NG2 group compared favorably with HDCV. Clinicaltrials.gov number: NCT03145766.

Comparing recombinant human rabies monoclonal antibody (ormutivimab) with human rabies immunoglobulin (HRIG) for postexposure prophylaxis: A phase III, randomized, double-blind, non-inferiority trial

OBJECTIVES

To evaluate the immunogenicity and safety of an anti-rabies monoclonal antibody (mAb), ormutivimab, compared with human rabies immunoglobulin (HRIG).

METHODS

This phase III trial was designed as a randomized, double-blind, non-inferiority clinical trial in patients aged ≥18 years with suspected World Health Organization category Ⅲ rabies exposure. The participants were randomized 1:1 to ormutivimab and HRIG groups. After thorough wound washing and injection of ormutivimab/HRIG on day 0, the vaccination was administered on days 0, 3, 7, 14, and 28. The primary endpoint was the adjusted geometric mean concentration (GMC) of rabies virus-neutralizing activity (RVNA) on day 7. The endpoint of safety included the occurrence of adverse reactions and serious adverse events.

RESULTS

A total of 720 participants were recruited. The adjusted-GMC of RVNA (0.41 IU/ml) on day 7 in ormutivimab group was not inferior to that in the HRIG group (0.41 IU/ml), with ratio of adjusted-GMC of 1.01 (95% confidence interval: 0.91, 1.14). The seroconversion rate of the ormutivimab group was higher than that of the HRIG group on days 7, 14, and 42. Most local injection sites and systemic adverse reactions reported from both groups were mild to moderate in severity.

CONCLUSION

ormutivimab + vaccine can protect victims aged ≥18 years with category Ⅲ suspected rabies exposure as a component of postexposure prophylaxis. ormutivimab has a weaker influence on the immunity response of rabies vaccines.

CLINICAL TRIALS REGISTRATION

ChiCTR1900021478 (the Chinese Clinical Trial Registry of World Health Organization).

Antiviral mechanisms of two broad-spectrum monoclonal antibodies for rabies prophylaxis and therapy

Rabies is an acute and lethal encephalomyelitis caused by lyssaviruses, among which rabies virus (RABV) is the most prevalent and important for public health. Although preventable through the post-exposure administration of rabies vaccine and immunoglobulins (RIGs), the disease is almost invariably fatal since the onset of clinical signs. Two human neutralizing monoclonal antibodies (mAbs), RVC20 and RVC58, have been shown to be effective in treating symptomatic rabies. To better understand how these mAbs work, we conducted structural modeling and in vitro assays to analyze their mechanisms of action, including their ability to mediate Fc-dependent effector functions. Our results indicate that both RVC20 and RVC58 recognize and lock the RABV-G protein in its pre-fusion conformation. RVC58 was shown to neutralize more potently the extra-cellular virus, while RVC20 mainly acts by reducing viral spreading from infected cells. Importantly, RVC20 was more effective in promoting effector functions compared to RVC58 and 17C7-RAB1 mAbs, the latter of which is approved for human rabies post-exposure treatment. These results provide valuable insights into the multiple mechanisms of action of RVC20 and RVC58 mAbs, offering relevant information for the development of these mAbs as treatment for human rabies.

Hyperimmune Globulins for the Management of Infectious Diseases

This review is focused on the use of hyperimmune globulin therapy to treat some infectious diseases of viral or bacterial origin. Despite the introduction of antibiotics and vaccines, plasma immunoglobulin therapy from whole blood donation can still play a key role. These treatments provide passive transfer of high-titer antibodies that either reduces the risk or the severity of the infection and offer immediate but short-term protection against specific diseases. Antibody preparations derived from immunized human donors are commonly used for the prophylaxis and treatment of rabies, hepatitis A and B viruses, varicella-zoster virus, and pneumonia caused by respiratory syncytial virus, Clostridium tetani, Clostridium botulinum. The use of hyperimmune globulin therapy is a promising challenge, especially for the treatment of emerging viral infections for which there are no specific therapies or licensed vaccines.

Active safety surveillance of rabies monoclonal antibody and rabies vaccine in patients with category III potential rabies exposure

Background

A vero cell-based inactivated Rabies Vaccine (Rabivax-S) and Rabies Human Monoclonal Antibody (Rabishield) have been approved since 2016. A post-marketing surveillance was conducted in India from 2020 to 2021 to gather real world safety data on Rabivax-S and Rabishield.

Methods

This was non-interventional active surveillance in patients with category III potential rabies exposure who were administered a post-exposure prophylaxis (PEP) regimen (Rabishield and Rabivax-S) by their healthcare providers (HCPs) as per the dosages and regimens mentioned in the package insert approved by the Indian regulators. The approved schedule for PEP was local infiltration of Rabishield on Day 0 and five doses of Rabivax-S on Day 0, 3, 7, 14, and 28 (Intramuscular route, IM) or four doses of Rabivax-S on Day 0, 3, 7, and 28 (Intradermal route, ID). The primary objective of this surveillance was to generate real-world evidence on the safety and tolerability of Rabishield and Rabivax-S. All patients enrolled in the surveillance were required to report any adverse events (AEs) occurring up to Day 31 after initiation of PEP (administration of Rabishield and the first dose of Rabivax-S) to their HCP.

Findings

A total of 1000 patients with category III potential rabies exposure were enrolled across India. 991 patients received the PEP regimen with IM Rabivax-S while 9 received a PEP regimen with the ID regimen. While 32% of the patients were <12 years of age, 11.8% were ≥12 to <18 years of age and 56.2% were ≥18 years of age. The entire PEP regimen was completed by 97.3% of the enrolled patients. A total of 69 AEs were reported in 64 patients. Out of these, 49 AEs in 47 patients were assessed as causally related to the study products (26 with Rabishield and 23 with Rabivax-S). The majority of the AEs were mild and all recovered without any sequelae. One serious adverse event (SAE) of fracture of the hand was reported which was not related to either Rabishield or Rabivax-S. No case of rabies was reported.

Interpretation

Rabishield and Rabivax-S have an excellent safety profile and are well tolerated. No participant developed rabies during 31 day follow up.

Funding

The PMS was funded by Serum institute of India Private Limited which is the manufacturer of the study products.

Monoclonal antibodies for prophylaxis and therapy of respiratory syncytial virus, SARS-CoV-2, human immunodeficiency virus, rabies and bacterial infections: an update from the World Association of Infectious Diseases and Immunological Disorders and the Italian Society of Antinfective Therapy

Monoclonal antibodies (mABs) are safe and effective proteins produced in laboratory that may be used to target a single epitope of a highly conserved protein of a virus or a bacterial pathogen. For this purpose, the epitope is selected among those that play the major role as targets for prevention of infection or tissue damage. In this paper, characteristics of the most important mABs that have been licensed and used or are in advanced stages of development for use in prophylaxis and therapy of infectious diseases are discussed. We showed that a great number of mABs effective against virus or bacterial infections have been developed, although only in a small number of cases these are licensed for use in clinical practice and have reached the market. Although some examples of therapeutic efficacy have been shown, not unlike more traditional antiviral or antibacterial treatments, their efficacy is significantly greater in prophylaxis or early post-exposure treatment. Although in many cases the use of vaccines is more effective and cost-effective than that of mABs, for many infectious diseases no vaccines have yet been developed and licensed. Furthermore, in emergency situations, like in epidemics or pandemics, the availability of mABs can be an attractive adjunct to our armament to reduce the impact. Finally, the availability of mABs against bacteria can be an important alternative, when multidrug-resistant strains are involved.

Neutralizing antibody activity, safety and immunogenicity of human anti-rabies virus monoclonal antibody (Ormutivimab) in Chinese healthy adults: A phase Ⅱb randomized, double-blind, parallel-controlled study

OBJECTIVE

This study was a randomized, double-blind, parallel-controlled trail to evaluate the rabies virus neutralizing activity（RVNA）, safety and immunogenicity of Ormutivimab + rabies vaccine in Chinese healthy adults.

METHODS

Subjects were randomly and equally assigned to 4 groups (20 IU/kg Omtv + vaccine, 40 IU/kg Omtv + vaccine, 20 IU/kg HRIG + vaccine, and placebo + vaccine). Subjects received vaccine as the WHO Essen regime combined with Omutivimab、HRIG or placebo on Day 0. The study lasted for 43 days.

RESULTS

A total of 240 subjects were simultaneously assigned to both FAS and SS. Fifty subjects with baseline RVNA > 0.05 IU/ml (detection limit) were excluded, 190 were included into mITT. All the subjects from 40 IU/kg Omtv + vaccine group had a protection level of RNVA (≥0.5 IU/ml, WHO) on Day 14, and those in 20 IU/kg Omtv + vaccine group and placebo + vaccine group converted positive 100 % on Day 28. In contrast to 20 IU/kg HRIG + vaccine and placebo + vaccine, Ormutivimab + vaccine provided a higher RVNA during Days 0 to 7. And RVNA in 40 IU/kg Omtv + vaccine and 20 IU/kg Omtv + vaccine groups were always higher than 20 IU/kg HRIG + vaccine group during the whole study. Although anti-Omtv antibody were detected in some subjects, it did not influence the RVNA. The incidence of adverse reactions was significantly lower in 20 IU/kg Omtv + vaccine group (17.2 %) than in 40 IU/kg Omtv + vaccine (36.7 %) and 20 IU/kg HRIG + vaccine groups (40.3 %).

CONCLUSION

Compared with HRIG + vaccine and placebo + vaccine, Omtv + vaccine provided higher RNVA for earlier immune protection. The interference of Ormutivimab on the long-term immune protection induced by rabies vaccine is weaker than HRIG. At the same dose, the adverse reactions of Omtv + vaccine group were less than HRIG + vaccine group.

REGISTRATION

ClinicalTrials.gov #NCT02559921.

Structure of trimeric pre-fusion rabies virus glycoprotein in complex with two protective antibodies

Rabies virus (RABV) causes lethal encephalitis and is responsible for approximately 60,000 deaths per year. As the sole virion-surface protein, the rabies virus glycoprotein (RABV-G) mediates host-cell entry. RABV-G's pre-fusion trimeric conformation displays epitopes bound by protective neutralizing antibodies that can be induced by vaccination or passively administered for post-exposure prophylaxis. We report a 2.8-Å structure of a RABV-G trimer in the pre-fusion conformation, in complex with two neutralizing and protective monoclonal antibodies, 17C7 and 1112-1, that recognize distinct epitopes. One of these antibodies is a licensed prophylactic (17C7, Rabishield), which we show locks the protein in pre-fusion conformation. Targeted mutations can similarly stabilize RABV-G in the pre-fusion conformation, a key step toward structure-guided vaccine design. These data reveal the higher-order architecture of a key therapeutic target and the structural basis of neutralization by antibodies binding two key antigenic sites, and this will facilitate the development of improved vaccines and prophylactic antibodies.

Population Pharmacodynamic Analyses of Human Anti-Rabies Virus Monoclonal Antibody (Ormutivimab) in Healthy Adult Subjects

Ormutivimab is the first recombinant human anti-rabies monoclonal antibody (rhRIG) approved for clinical application in China. In this study, a population pharmacodynamic (PPD) model was established to compare the neutralizing antibody activities of Ormutivimab and human rabies immunoglobulin (HRIG), alone or combined with human rabies vaccine (Vero), in a phase II clinical trial, and to recommend a target dose for the phase III trial. The model was verified to fit the PPD data well. The stability of the model was verified by the bootstrap method. The level of neutralizing antibodies in vivo increased rapidly after administration of Ormutivimab or HRIG. Neutralizing antibodies with a strong activity were produced at 7 days (Ormutivimab + vaccine) or 10 days (HRIG + vaccine) after induction by the vaccine in vivo. Compared to that induced by HRIG + vaccine, the level of the neutralizing antibodies induced by Ormutivimab + vaccine peaked higher and faster. The levels of neutralizing antibodies induced by Ormutivimab + vaccine and HRIG + vaccine were similar within 21 days after administration. According to these results and the safety data, 20 IU·kg^-1 was recommended as the target dose in the confirmatory study of Ormutivimab. Registration: ClinicalTrials.gov #NCT02559921.

Safety and clinical efficacy of human rabies immunoglobulin in post exposure prophylaxis for category III animal exposures

The human rabies immunoglobulin (HRIG) is a life-saving immune biological essential for all category III animal exposures. It provides neutralizing antibodies at the site of exposure until the body can produce vaccine-mediated antibodies. We conducted this study to determine the safety and clinical efficacy of an HRIG being used presently for post-exposure prophylaxis (PEP) and to strengthen the existing evidence for its further usage. We conducted a prospective cohort study in 123 subjects with category III animal exposures at the KIMS Hospital and Research Center, Bangalore, India. Post-exposure prophylaxis (PEP) with wound toilet, a single application of HRIG, and a full course of anti-rabies vaccination were provided to all the study subjects. The volume of HRIG was calculated according to the body weight, and all the wounds were infiltrated as was anatomically feasible. All the study subjects were followed up for immediate and delayed adverse events (AE), both local and systemic. Subsequently, all the subjects were followed up for 6 months to demonstrate the clinical efficacy of PEP. The incidence of AEs was 11.4% including local pain, erythema, itching, headache, body ache, fever, and malaise. All AEs were mild and subsided without any complications. All the study subjects were healthy and alive after 6 months following the administration of HRIG, along with a full course of anti-rabies vaccine. Our study provides evidence of safety and clinical efficacy of HRIG for category III animal exposures and supports its continued usage.

Inhibitory effect of concomitantly administered rabies immunoglobulins on the immunogenicity of commercial and candidate human rabies vaccines in hamsters

The World Health Organization protocol for rabies post-exposure prophylaxis (PEP) recommends extensive wound washing, immediate vaccination, and administration of rabies immunoglobulin (RIG) in severe category III exposures. Some studies have shown that RIG can interfere with rabies vaccine immunogenicity to some extent. We investigated the interference of RIG on a next generation highly purified Vero cell rabies vaccine candidate (PVRV-NG) versus standard-of-care vaccines in a previously described hamster model. The interference of either human (h) or equine (e) RIG on the immune response elicited by PVRV-NG, Verorab^® (purified Vero cell rabies vaccine, PVRV), and Imovax^® Rabies (human diploid cell rabies vaccine; HDCV) was evaluated using the 4-dose Essen PEP regimen. The anti-rabies seroneutralizing titers and specific serum IgM titers were measured by fluorescent antibody virus neutralization test and enzyme-linked immunosorbent assay, respectively, for the vaccines administered with or without RIG. The RIG interference on PVRV-NG, observed transiently at Day 7, was similar to that on PVRV and tended to be lower than that on HDCV using both read-outs. In summary, the results generated in the hamster model showed that RIG induced similar or less interference on PVRV-NG than the standard-of-care vaccines.

Rabies in the Tropics

Purpose of Review

Rabies is an ancient yet still neglected tropical disease (NTD). This review focuses upon highlights of recent research and peer-reviewed communications on the underestimated tropical burden of disease and its management due to the complicated dynamics of virulent viral species, diverse mammalian reservoirs, and tens of millions of exposed humans and animals – and how laboratory-based surveillance at each level informs upon pathogen spread and risks of transmission, for targeted prevention and control.

Recent Findings

While both human and rabies animal cases in enzootic areas over the past 5 years were reported to PAHO/WHO and OIE by member countries, still there is a huge gap between these “official” data and the need for enhanced surveillance efforts to meet global program goals.

Summary

A review of the complex aspects of rabies perpetuation in human, domestic animal, and wildlife communities, coupled with a high fatality rate despite the existence of efficacious biologics (but no therapeutics), warrants the need for a One Health approach toward detection via improved laboratory-based surveillance, with focal management at the viral source. More effective methods to prevent the spread of rabies from enzootic to free zones are needed.

A One Medicine Mission for an Effective Rabies Therapy

Despite the disease's long history, little progress has been made toward a treatment for rabies. The prognosis for patient recovery remains dire. For any prospect of survival, patients require aggressive critical care, which physicians in rabies endemic areas may be reluctant or unable to provide given the cost, clinical expertise required, and uncertain outcome. Systematic clinical research into combination therapies is further hampered by sporadic occurrence of cases. In this Perspective, we examine the case for a One Medicine approach to accelerate development of an effective therapy for rabies through the veterinary care and investigational treatment of naturally infected dogs in appropriate circumstances. We review the pathogenesis of rabies virus in humans and dogs, including recent advances in our understanding of the molecular basis for the severe neurological dysfunction. We propose that four categories of disease process need to be managed in patients: viral propagation, neuronal degeneration, inflammation and systemic compromise. Compassionate critical care and investigational treatment of naturally infected dogs receiving supportive therapy that mimics the human clinical scenario could increase opportunities to study combination therapies that address these processes, and to identify biomarkers for prognosis and therapeutic response. We discuss the safety and ethics of this approach, and introduce the Canine Rabies Treatment Initiative, a non-profit organization with the mission to apply a One Medicine approach to the investigation of diagnostic, prognostic, and therapeutic options for rabies in naturally infected dogs, to accelerate transformation of rabies into a treatable disease for all patients.

Advances in the progress of monoclonal antibodies for rabies

Rabies is a highly fatal zoonotic disease caused by the rabies virus invading the central nervous system. When suspected of exposure to the rabies virus, post-exposure prophylaxis should be administered as soon as possible. Monoclonal antibodies (mAbs) neutralizing the rabies virus could be better in human rabies post-exposure prophylaxis than equine or human rabies immune globulin in terms of supply, cost, and efficacy. This article reviews anti-rabies mAbs produced by multiple techniques, and the results of clinical trials for anti-rabies mAbs cocktails recognizing non-overlapping epitopes are also discussed.

Monoclonal antibodies against rabies: current uses in prophylaxis and in therapy

Rabies is a severe viral infection that causes an acute encephalomyelitis, which presents a case fatality of nearly 100% after the manifestation of neurological clinical signs. Rabies can be efficiently prevented with post-exposure prophylaxis (PEP), composed of vaccines and anti-rabies immunoglobulins (RIGs); however, no treatment exists for symptomatic rabies. The PEP protocol faces access and implementation obstacles in resource-limited settings, which could be partially overcome by substituting RIGs for monoclonal antibodies (mAbs). mAbs offer lower production costs, consistent supply availability, long-term storage/stability, and an improved safety profile. Here we summarize the key features of the different available mAbs against rabies, focusing on their application in PEP and highlighting their potential in a novel therapeutic approach.

Defining the volume of rabies immunoglobulins/ rabies monoclonal antibodies requirement for wound infiltration of category III animal exposures - an exploratory study

WHO recommends infiltration of rabies immunoglobulins/rabies monoclonal antibodies as anatomically possible, into or close to all category III animal bite wound(s)/exposures for post exposure prophylaxis. The volume required for wound infiltration depending upon the site/size/severity of wound is yet to be defined for guiding the treating physicians. This study aimed to determine the volume of rabies immunoglobulin/rabies monoclonal antibody required for wound infiltration depending upon the site, size, and severity. A prospective cohort study was conducted including category III animal exposures at the anti-rabies clinic, KIMS hospital and Research Center, Bangalore, India. The volume of rabies immunoglobulins/rabies monoclonal antibodies required for wound infiltration, depending on site, severity, and size was determined. All the subjects were followed for 6 months to demonstrate the safety and clinical efficacy of post exposure prophylaxis. The present study included 717 subjects having 1428 bite wounds. There was a significant difference in the median volume required for wound infiltration based on site, size, and severity of bite wounds. However, on pairwise comparison; the median volume among all the pairs for only wound size was found to be statistically significant. Supportively, a strong positive correlation was seen with the size of wound and volume infiltrated. The volume of rabies immunoglobulin/rabies monoclonal antibodies required for wound infiltration shall be determined according to size of wounds, i.e. 1 ml for <1 cm wound, 3 ml for 1-5 cm wound, and 5 ml for >5 cm wound.

Rabies virus neutralizing activity, pharmacokinetics, and safety of the monoclonal antibody mixture SYN023 in combination with rabies vaccination: Results of a phase 2, randomized, blinded, controlled trial

BACKGROUND

SYN023-002 is a randomized, blinded, controlled study comparing rabies virus neutralizing activity (RVNA) and safety of SYN023, a monoclonal anti-rabies antibody mixture, to human-serum derived anti-rabies immunoglobulin (RIG) when administered with commercially available vaccines to healthy adult volunteers.

METHODS

Participants were randomized among 4 treatment groups (SYN023 + Imovax, SYN023 + RabAvert, HyperRab + Imovax, HyperRab + RabAvert). On Day 0, subjects received 1 dose of RIG (0.3 mg/kg SYN023 or 20 IU/mL HyperRab) and their first of 5 vaccine doses. The primary objective was to compare cumulative RVNA between SYN023 and HyperRab recipients. Secondary objectives were to compare safety and to assess SYN023 pharmacokinetics and immunogenicity.

RESULTS

All 164 randomized subjects initiated treatment and were included in safety analyses. At least 34 subjects/treatment group received all treatment and had complete RVNA results, thus were included in the primary endpoint analysis. Mean RVNAs were approximately ten-fold higher in SYN023 recipients compared to HyperRab recipients until Day 14. From Day 14 onwards, mean RVNA was lower in SYN023 recipients, but remained above the RVNA level widely considered adequate (≥0.5 IU/mL) through Day 112 (study end). The point estimate of the cumulative RVNA (83.22% SYN023/HyperRab), but not the lower CI bound (90% CI: 66.06%, 104.83%), fell within the protocol-defined similarity margin. Each RIG + vaccine regimen appeared safe with mostly mild AEs and no serious or severe related events observed. Except injection site pain (22% HyperRab recipients vs. 6% SYN023 recipients), treatment-related AEs incidences were similar between RIGs. Anti-SYN023 antibodies were observed but had no apparent effects on PK or safety.

CONCLUSIONS

SYN023 administered with commercially available vaccines provides adequate antibody coverage beginning earlier than other commercially available RIGs with an acceptable safety profile. Some suppression of vaccine response occurred, but RVNA levels ≥ 0.5 IU/mL were maintained throughout the relevant period.

REGISTRATION

ClinicalTrials.gov #NCT02956746.

FUNDING

Synermore biologics.

A broad-spectrum and highly potent human monoclonal antibody cocktail for rabies prophylaxis

Post-exposure prophylaxis (PEP) is highly effective in preventing disease progression of rabies when used in timely and appropriate manner. The key treatment for PEP is infiltration of rabies immune globulin (RIG) into lesion site after bite exposure, besides wound care and vaccination. Unfortunately, however, RIG is expensive and its supply is limited. Currently, several anti-rabies virus monoclonal antibody (mAb) products are under development as alternatives to RIG, and two recently received regulatory approval in India. In this study, fully human mAbs that recognize different rabies virus glycoprotein conformational antigenic site (II and III) were created from peripheral blood mononuclear cells of heathy vaccinated subjects. These mAbs neutralized a diverse range of lyssavirus types. As at least two anti-rabies virus mAbs are recommended for use in human PEP to ensure broad coverage against diverse lyssaviruses and to minimize possible escape variants, two most potent mAbs, NP-19-9 and 11B6, were selected to be used as cocktail treatment. These two mAbs were broadly reactive to different types of lyssaviruses isolates, and were shown to have no interference with each other. These results suggest that NP-19-9 and 11B6 are potent candidates to be used for PEP, suggesting further studies involving clinical studies in human.

Developing Recombinant Antibodies by Phage Display Against Infectious Diseases and Toxins for Diagnostics and Therapy

Antibodies are essential molecules for diagnosis and treatment of diseases caused by pathogens and their toxins. Antibodies were integrated in our medical repertoire against infectious diseases more than hundred years ago by using animal sera to treat tetanus and diphtheria. In these days, most developed therapeutic antibodies target cancer or autoimmune diseases. The COVID-19 pandemic was a reminder about the importance of antibodies for therapy against infectious diseases. While monoclonal antibodies could be generated by hybridoma technology since the 70ies of the former century, nowadays antibody phage display, among other display technologies, is robustly established to discover new human monoclonal antibodies. Phage display is an in vitro technology which confers the potential for generating antibodies from universal libraries against any conceivable molecule of sufficient size and omits the limitations of the immune systems. If convalescent patients or immunized/infected animals are available, it is possible to construct immune phage display libraries to select in vivo affinity-matured antibodies. A further advantage is the availability of the DNA sequence encoding the phage displayed antibody fragment, which is packaged in the phage particles. Therefore, the selected antibody fragments can be rapidly further engineered in any needed antibody format according to the requirements of the final application. In this review, we present an overview of phage display derived recombinant antibodies against bacterial, viral and eukaryotic pathogens, as well as microbial toxins, intended for diagnostic and therapeutic applications.

Isolation and Characterization of Cross-Reactive Human Monoclonal Antibodies That Potently Neutralize Australian Bat Lyssavirus Variants and Other Phylogroup 1 Lyssaviruses

Australian bat lyssavirus (ABLV) is a rhabdovirus that circulates in four species of pteropid bats (ABLVp) and the yellow-bellied sheath-tailed bat (ABLVs) in mainland Australia. In the three confirmed human cases of ABLV, rabies illness preceded fatality. As with rabies virus (RABV), post-exposure prophylaxis (PEP) for potential ABLV infections consists of wound cleansing, administration of the rabies vaccine and injection of rabies immunoglobulin (RIG) proximal to the wound. Despite the efficacy of PEP, the inaccessibility of human RIG (HRIG) in the developing world and the high immunogenicity of equine RIG (ERIG) has led to consideration of human monoclonal antibodies (hmAbs) as a passive immunization option that offers enhanced safety and specificity. Using a recombinant vesicular stomatitis virus (rVSV) expressing the glycoprotein (G) protein of ABLVs and phage display, we identified two hmAbs, A6 and F11, which completely neutralize ABLVs/ABLVp, and RABV at concentrations ranging from 0.39 and 6.25 µg/mL and 0.19 and 0.39 µg/mL respectively. A6 and F11 recognize overlapping epitopes in the lyssavirus G protein, effectively neutralizing phylogroup 1 lyssaviruses, while having little effect on phylogroup 2 and non-grouped diverse lyssaviruses. These results suggest that A6 and F11 could be effective therapeutic and diagnostic tools for phylogroup 1 lyssavirus infections.

Safety, Pharmacokinetics, and Neutralizing Activity of SYN023, a Mixture of Two Novel Antirabies Monoclonal Antibodies Intended for Use in Postrabies Exposure Prophylaxis

SYN023 is a mixture of 2 humanized monoclonal antirabies antibodies (CTB011, CTB012). Two first-in-human studies evaluated ascending intramuscular (IM) injected doses (Study SYN023-001; N = 15) and IM vs subcutaneous (SC) administration (Study SYN023-003; N = 35) in healthy adults. In both studies, end points were safety, pharmacokinetics (PK), pharmacodynamics/rabies virus neutralizing activity (RVNA), and immunogenicity (anti-SYN023 antibodies). Adverse events were mild and infrequent at all doses tested by IM injection (0.3 mg/kg, 1.0 mg/kg, 2.0 mg/kg), or by SC injection (0.3 mg/kg). There were no apparent trends in adverse event frequency or nature with increased dose or with administration route. Serum PK of SYN023 component antibodies appeared comparable to each other at each dose tested and when administered IM versus SC with serum exposure doubling over the second week after administration. At the lowest dose tested (0.3 mg/kg) by either IM or SC injection, RVNA levels exceeded the concentration generally accepted as protective against rabies (≥0.5 IU/mL) by day 1 after administration. Supra-inhibitory levels persisted >42 days. RVNA increased with higher doses. Anti-CTB011 and anti-CTB012 antibodies occurred with no apparent effect on PK or safety. These data support the potential use of SYN023 in antirabies postexposure prophylaxis.

Deep Sequencing of B Cell Receptor Repertoires From COVID-19 Patients Reveals Strong Convergent Immune Signatures

Deep sequencing of B cell receptor (BCR) heavy chains from a cohort of 31 COVID-19 patients from the UK reveals a stereotypical naive immune response to SARS-CoV-2 which is consistent across patients. Clonal expansion of the B cell population is also observed and may be the result of memory bystander effects. There was a strong convergent sequence signature across patients, and we identified 1,254 clonotypes convergent between at least four of the COVID-19 patients, but not present in healthy controls or individuals following seasonal influenza vaccination. A subset of the convergent clonotypes were homologous to known SARS and SARS-CoV-2 spike protein neutralizing antibodies. Convergence was also demonstrated across wide geographies by comparison of data sets between patients from UK, USA, and China, further validating the disease association and consistency of the stereotypical immune response even at the sequence level. These convergent clonotypes provide a resource to identify potential therapeutic and prophylactic antibodies and demonstrate the potential of BCR profiling as a tool to help understand patient responses.

Understanding the dynamics of COVID-19; implications for therapeutic intervention, vaccine development and movement control

The COVID-19 disease is caused by the SARS-CoV-2 virus, which is highly infective within the human population. The virus is widely disseminated to almost every continent with over twenty-seven million infections and over ninety-thousand reported deaths attributed to COVID-19 disease. SARS-CoV-2 is a single stranded RNA virus, comprising three main viral proteins; membrane, spike and envelope. The clinical features of COVID-19 disease can be classified according to different degrees of severity, with some patients progressing to acute respiratory distress syndrome, which can be fatal. In addition, many infections are asymptomatic or only cause mild symptoms. As there is no specific treatment for COVID-19 there is considerable endeavour to raise a vaccine against SARS-CoV-2, in addition to engineering neutralizing antibody interventions. In the absence of an effective vaccine, movement controls of varying stringencies have been imposed. Whilst enforced lockdown measures have been effective, they may be less effective against the current strain of SARS-CoV-2, the G614 clade. Conversely, other mutations of the virus, such as the Δ382 variant could reduce the clinical relevance of infection. The front runners in the race to develop an effective vaccine focus on the SARS-Co-V-2 Spike protein. However, vaccines that produce a T-cell response to a wider range of SARS-Co-V-2 viral proteins, may be more effective. Population based studies that determine the level of innate immunity to SARS-CoV-2, from prior exposure to the virus or to other coronaviruses, will have important implications for government imposed movement control and the strategic delivery of vaccination programmes.

[New aspects of rabies control]

Rabies still causes about 60,000 human deaths per year, mainly in poor populations in Africa and Asia. However, since Louis Pasteur developed the first vaccine 130 years ago, prophylactic measures have been considerably improved and simplified. They now consist of the vaccine combined with purified rabies immunoglobulins of equine or human origin. In general, however, post-exposure prophylaxis protocols are long and expensive. Furthermore, the immunoglobulins used for associated serotherapy are costly and not widely available in developing countries. Approaches have been developed to deal with these two issues that offer hope for a paradigm shift for the benefit of exposed populations. Finally, mass rabies vaccination in dogs, which are the most cost-effective measure for preventing rabies in humans, are difficult to implement and sometimes have moderate effectiveness. The identification and analysis of the epidemiological drivers conditioning the circulation of the virus in dog populations allow a better understanding of the key control points that need to be associated with these campaigns for a better efficacy.

A combination of two human monoclonal antibodies cures symptomatic rabies

Rabies is a neglected disease caused by a neurotropic Lyssavirus, transmitted to humans predominantly by the bite of infected dogs. Rabies is preventable with vaccines or proper post-exposure prophylaxis (PEP), but it still causes about 60,000 deaths every year. No cure exists after the onset of clinical signs, and the case-fatality rate approaches 100% even with advanced supportive care. Here, we report that a combination of two potent neutralizing human monoclonal antibodies directed against the viral envelope glycoprotein cures symptomatic rabid mice. Treatment efficacy requires the concomitant administration of antibodies in the periphery and in the central nervous system through intracerebroventricular infusion. After such treatment, recovered mice presented good clinical condition, viral loads were undetectable, and the brain inflammatory profile was almost normal. Our findings provide the unprecedented proof of concept of an antibody-based therapeutic approach for symptomatic rabies.

An update on antiviral antibody-based biopharmaceuticals

Due to the vastness of the science virology, it is no longer an offshoot solely of the microbiology. Viruses have become as the causative agents of major epidemics throughout history. Many therapeutic strategies have been used for these microorganisms, and in this way the recognizing of potential targets of viruses is of particular importance for success. For decades, antibodies and antibody fragments have occupied a significant body of the treatment approaches against infectious diseases. Because of their high affinity, they can be designed and engineered against a variety of purposes, mainly since antibody fragments such as scFv, nanobody, diabody, and bispecific antibody have emerged owing to their small size and interesting properties. In this review, we have discussed the antibody discovery and molecular and biological design of antibody fragments as inspiring therapeutic and diagnostic agents against viral targets.

Potent neutralizing antibodies from COVID-19 patients define multiple targets of vulnerability

The rapid spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has had a large impact on global health, travel, and economy. Therefore, preventative and therapeutic measures are urgently needed. Here, we isolated monoclonal antibodies from three convalescent coronavirus disease 2019 (COVID-19) patients using a SARS-CoV-2 stabilized prefusion spike protein. These antibodies had low levels of somatic hypermutation and showed a strong enrichment in VH1-69, VH3-30-3, and VH1-24 gene usage. A subset of the antibodies was able to potently inhibit authentic SARS-CoV-2 infection at a concentration as low as 0.007 micrograms per milliliter. Competition and electron microscopy studies illustrate that the SARS-CoV-2 spike protein contains multiple distinct antigenic sites, including several receptor-binding domain (RBD) epitopes as well as non-RBD epitopes. In addition to providing guidance for vaccine design, the antibodies described here are promising candidates for COVID-19 treatment and prevention.

A novel ELISA for quantification of glycoprotein in human rabies vaccines using a clinically proven virus neutralizing human monoclonal antibody

Global efforts on the replacement of the in vivo rabies vaccine potency test (NIH method) with in vitro methods for quantification of immunodominant glycoprotein (GP) in rabies vaccine have made significant progress. We report here, a sandwich ELISA method based on the use of a neutralizing rabies GP site III directed human monoclonal antibody (RAB-1) and a polyclonal GP specific antibody recognizing the intact form of viral GP. The method was shown to be robust, specific, linear, precise and accurate in the quantification of intact GP in vaccine samples. The assay was able to differentiate between potent and sub-potent vaccine samples. The assay was shown to be linear over the range of 0.07-2.25 IU/mL with LOD and LLOQ values of 0.035 and 0.070 IU/mL, respectively. The assay was able to quantify the GP content of rabies vaccines derived from rabies vaccine strains, e.g., Pittman-Moore, Pasteur and Flury LEP with acceptable precision (CV < 20%) and also showed good agreement with NIH potency estimates. The binding kinetics of RAB-1 with intact and modified vaccine samples were also characterized using biolayer interferometry (BLI). The developed method may be used as an alternative to the NIH method in quality control testing of human rabies vaccines.

A Phase 3, Randomised, Open-Label, Non-inferiority Trial Evaluating Anti-Rabies Monoclonal Antibody Cocktail (TwinrabTM) Against Human Rabies Immunoglobulin (HRIG)

BACKGROUND

Limited supply, cost and potential for severe adverse effects observed with the blood derived rabies immunoglobulin products has led to search for alternative therapies. This issue has been addressed by developing an antirabies monoclonal antibody cocktail.

METHODS

This is a phase 3, randomized, open-label, noninferiority trial conducted in patients with WHO category III exposure with suspected rabid animal. Eligible patients were assigned to either the test arm, TwinrabTM (docaravimab and miromavimab) or the reference arm, Human rabies immunoglobulin (HRIG; Imogam® Rabies-HT), in a ratio of 1:1. The primary endpoint was the comparison of responder rates between the two arms assessed as percentage of those with rabies virus neutralizing antibodies titers ≥ 0.5 IU/mL on day 14.

RESULTS

A total of 308 patients were equally randomized into the two arms. In the per-protocol (PP) population, there were 90.21% responders in the TwinrabTM arm and, 94.37% in the HRIG arm. The Geometric Mean of RFFIT titres in the PP on day 14 were 4.38 and 4.85 IU/mL, for the TwinrabTM and HRIG arms, respectively. There were no deaths or serious adverse events reported.

CONCLUSIONS

This study confirmed that TwinrabTM is non-inferior to HRIG in terms of providing an unbroken window of protection up to day 84. This trial in healthy adults with WHO category III exposure from suspected rabid animal also establishes the safety of TwinrabTM in patients with one WHO approved vaccine regimen (Essen).

TRIALS REGISTRATION

CTRI/2017/07/009038.

Modern biologics for rabies prophylaxis and the elimination of human cases mediated by dogs

Introduction: Rabies is a major viral zoonosis and neglected tropical disease, with a global distribution. Humans, domestic animals, and wild mammals are susceptible to infection. Etiological agents reside in the Order Mononegavirales, Family Rhabdoviridae, Genus Lyssavirus. This acute, progressive encephalitis causes the highest case fatality of any conventional infectious disease. Tens of millions of humans become exposed annually to the bites of infected mammals, predominantly in Asia and Africa. Despite the existence of effective vaccines and immune globulins, tens of thousands of people, typically children in the developing world, succumb. Areas covered: Concentrating upon both historical and major published references from the peer-reviewed literature over the past 5 years, we describe current biologics for rabies prevention, newly recommended principles for prophylaxis, and relevant future products in the developmental pipeline. Expert opinion: Modern human rabies biologics are pure, potent, safe, and efficacious, when used in a timely and appropriate manner. Few individuals survive after clinical signs. Anti-viral compounds are not licensed. Experimental therapy, while obviously desirable, is highly controversial. Education on bite prevention and integrated risk management are critical. Access to affordable care, dose-sparing, and shortened regimens of human rabies biologics remain key.

In Vivo Efficacy of SYN023, an Anti-Rabies Monoclonal Antibody Cocktail, in Post-Exposure Prophylaxis Animal Models

Rabies immune globulin (RIG) is an indispensable component of rabies post-exposure prophylaxis (PEP) because it provides passive immunity to prevent this otherwise inescapably fatal disease in Category III exposed patients. Even with decades of development, RIG products are still criticized for their high cost, lot-to-lot variation, and potential safety issues. They remain largely unattainable in most developing regions of the world, where demand is highest. In recent years, monoclonal antibodies (MAbs) have become widely accepted as safer and more cost-effective alternatives to RIG products. As an example, SYN023 is a 1:1 cocktail of two humanized anti-rabies MAbs previously shown to display extensive neutralizing capabilities. Here, we further assessed the efficacy of SYN023 in animal models of rabies, and found that SYN023 afforded protection equal to a standard dose of human RIG (HRIG) at 0.03 mg/kg in Syrian hamsters and 0.1 mg/kg in beagles. Potential interference with vaccine-induced immunity was analyzed for the MAbs at these concentrations. While individual MAbs did not interfere with vaccine response, SYN023 at dosages of 0.1 mg/kg and above resulted in reduced neutralizing antibody titers similar to HRIG. Thus, the in vivo characterization of SYN023 supports its utility in human rabies PEP as an efficacious alternative to RIG products.

How can monoclonal antibodies be harnessed against neglected tropical diseases and other infectious diseases?

Introduction: Monoclonal antibody-based therapies now represent the single-largest class of molecules undergoing clinical investigation. Although a handful of different monoclonal antibodies have been clinically approved for bacterial and viral indications, including rabies, therapies based on monoclonal antibodies are yet to fully enter the fields of neglected tropical diseases and other infectious diseases. Areas covered: This review presents the current state-of-the-art in the development and use of monoclonal antibodies against neglected tropical diseases and other infectious diseases, including viral, bacterial, and parasitic infections, as well as envenomings by animal bites and stings. Additionally, a short section on mushroom poisonings is included. Key challenges for developing antibody-based therapeutics are discussed for each of these fields. Expert opinion: Neglected tropical diseases and other infectious diseases represent a golden opportunity for academics and technology developers for advancing our scientific capabilities within the understanding and design of antibody cross-reactivity, use of oligoclonal antibody mixtures for multi-target neutralization, novel immunization methodologies, targeting of evasive pathogens, and development of fundamentally novel therapeutic mechanisms of action. Furthermore, a huge humanitarian and societal impact is to gain by exploiting antibody technologies for the development of biotherapies against diseases, for which current treatment options are suboptimal or non-existent.

Priorities in applied research to ensure programmatic success in the global elimination of canine rabies

The elimination of human rabies mediated by dogs is attainable in concept, based upon current sensitive and specific diagnostic methods, existing safe and effective human and veterinary vaccines and a sound virological, pathological and epidemiological understanding of the disease. Globally, all developed countries achieved this goal. Regionally, major progress occurred throughout the Americas. However, less advancement is evident in Africa and Asia. Our objective was to concentrate upon those salient improvements to extant tools and methods over the next five years which could assist and simplify the task for both those developing countries that have already begun the process, as well as other localities in the earlier stages of consideration. We considered several categories of applied research which could be accomplished in the short term, based upon the available scientific evidence and recent recommendations from subject matter experts and key opinion leaders, focused upon perceived major limitations to prior program success. Areas of concentration included: laboratory-based surveillance, pathogen detection and characterization; human rabies prophylaxis; veterinary biologics; implementation of canine vaccination; and oral vaccination of free-ranging community dogs. Further real-time application in these core areas with proven techniques and technology would simplify attaining not only the global goal focused subtly upon human mortality, but the actual elimination of canine rabies as well.

Monoclonal antibodies as anti-infective products: a promising future?

BACKGROUND

The paucity of licensed monoclonal antibodies (mAbs) in the infectious diseases arena strongly contrasts with the ready availability of these therapeutics for use in other conditions.

AIMS

This narrative review aims to assess the potential of monoclonal antibody-based interventions for infectious diseases.

SOURCES

A review of the literature via the Medline database was performed and complemented by published official documents on licensed anti-infective mAbs. In addition, ongoing trials were identified through a search of the clinical trial registration platform ClinicalTrials.gov.

CONTENT

We identified the few infections for which mAbs have been added to the therapeutic armamentarium and stressed their potential in representing a readily available protection tool against biothreats and newly emerging and reemerging infectious agents. In reviewing the historical context and main features of mAbs, we assert a potentially wider applicability and cite relevant examples of ongoing therapeutic developments. Factors hindering successful introduction of mAbs on a larger scale are outlined and thoughts are offered on how to possibly address some of these limitations.

IMPLICATIONS

mAbs may represent important tools in treating or preventing infections occurring with reasonably sufficient prevalence to justify demand and for which existing alternatives are not deemed fully adequate. Future initiatives need to address the prohibitive costs encountered in the development process. The feasibility of more large-scale administration of alternative modalities merits further exploration. In order to ensure optimal prospect of regulatory success, an early dialogue with competent authorities is encouraged.