The world has recently seen immense activity in the sphere of vaccine development as a result of the coronavirus disease 2019 (COVID-19) pandemic, because the causative virus, the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), continues to emerge in latest variants with increased transmissibility, immune escape capability and virulence attributes.

Study: Nebulized mRNA-Encoded Antibodies Protect Hamsters from SARS-CoV-2 Infection. Image Credit: Johannes Menge/Shutterstock

A latest paper describes a novel route of prevention using messenger ribonucleic acid (mRNA) molecules that encode protective antibodies throughout the recipient.

Introduction

The usage of mRNA to encode vaccines in the shape of SARS-CoV-2 spike protein was pioneered by the Pfizer/BioNTech and Moderna vaccines. These were amongst the various vaccine technologies pressed into use to counter the relentless spread and the rising death toll of the COVID-19 pandemic.

As well as, monoclonal antibodies were also isolated for his or her neutralizing activity against the virus, each pre-and post-exposure. Emergency use authorization (EUA) was obtained for 4 mAb protocols: the therapeutic mAbs casirivimab + imdevimab, bamlanivimab + etesevimab, and sotrovimab and the prophylactic mAbs tixagevimab + cilgavimab. Of those, the primary two aren’t any longer effective, and their EUA has been withdrawn.

These antibodies have to be given intravenously, necessitating a medical setting. They have to be delivered in relatively large doses of 10–100 mg kg−1 to compensate for the incontrovertible fact that only a small fraction reaches the positioning of interest. This drives up the fee of treatment, limiting their availability, especially in low- and middle-income countries (LMIC).

Alternative methods of mAb production have to be explored. The present paper, published in Advanced Science, discusses such an alternate, where a formulation amenable to nebulization was designed to permit the introduction of antibody-encoding mRNA into the lungs to neutralize the disease. Each in vitro and in vivo results support using this novel technology to fight not only COVID-19 but in addition other respiratory virus infections.

The usage of mRNA is protected in that it doesn’t enter the nucleus, unlike DNA or viral vectors carrying DNA, which relies on their effect on nuclear entry and integration with the host DNA genome. Secondly, the half-life of mRNA in circulation is comparatively short, avoiding long-term consequences. By reducing the required dose to a hundredth of the unique amount, when delivered on to the respiratory tract fairly than systemically, the general cost of therapy is significantly decreased.

Prior research showed that this approach was feasible, using intravenous lipid nanoparticle (LNP)-encapsulated mRNA encoding a neutralizing antibody against the chikungunya virus, which could be expressed within the liver.

Earlier research by the identical authors showed the potential to direct mRNA to the lungs to supply mAbs there. By avoiding the necessity to introduce the recombinant spike protein, the researchers encoded a membrane anchor within the heavy chain of the immunoglobulin G (IgG) antibody molecule. This allowed the tissue to retain the antibody for several weeks.

The present study moved a step further by shifting from the sooner intratracheal administration to nebulization, which might be performed by the person outside a medical setting. This might allow the mAbs to be expressed at high concentrations on the mucosal surface, the principal site of entry of respiratory viruses, while avoiding the necessity to administer large doses systemically.

What did the study show?

The study findings show the flexibility of nebulized mRNA-encoded neutralizing antibody (nAb) to counter SARS-CoV-2 infection within the hamster lung, reducing the viral count and mitigating lung disease signs in addition to infection-related weight reduction within the hamsters.

The glycosylphosphatidylinositol (GPI) membrane anchoring molecule allowed the antibodies to stay linked to the cell membrane. The antibodies tested here comprised six mAbs isolated from B cells taken from SARS-CoV-2-infected individuals.

Direct stochastic optical reconstruction microscopy (dSTORM) enhanced the flexibility to view the antibodies once expressed throughout the cell culture. One formed long strings on the cell surface and was thus disqualified from further testing in vivo.

All of the sure and anchored mAbs retained neutralizing capability, as shown by their cytopathic effect (CPE) in a monolayer cell culture. Though most of them were capable of neutralize the unique variant and the B.1.1.7 variant, one didn’t offset the latter. The protective capability was linked to the particular mRNA-encoded antibodies and never to the GPI anchor, as shown by a control antibody with an attached GPI.

All of the mAbs could neutralize the virus at low concentrations, with low nanomolar half-maximal inhibitory concentration (IC50). Further testing was carried out using two chosen mAbs, COV2-2832 and DH1041.

Hamster model

Following these promising in vitro findings, further testing was carried out in Syrian golden hamsters, which give a sturdy animal model for human COVID-19 infection.

Longer retention in lungs

This demonstrated that the antibodies were, as expected, anchored to the cell membrane within the lung by the GPI molecule. Compared with the secreted or non-anchored form, it was found to stay within the lung tissue. At the identical time, the latter led to increased serum concentrations, the difference in post-transfection serum levels being 27-fold in favor of the secreted form. This occurred despite the efficient translation of each types in lung tissue following nebulization, peaking at 24-48 hours.

The encoded anchor enhanced lung retention from just over at some point to seven days, which could mean a single-dose approach to the post-exposure treatment of COVID-19.

This approach wouldn’t be onerous compared with other nebulizer-based treatments, which usually consist of multiple doses a day or a single dose for as much as 22 h.”

Widespread delivery

The nebulized formulation reached all parts of the lung uniformly and richly, each the alveolar space and the airway epithelium.

Because the virus is usually found throughout the alveolar space, this finding indicates the potential for transfected antibodies to forestall COVID-19 and severe disease. The effective dose delivered to the lungs might be enhanced by increasing the concentration of the formulation.

The ratio of mRNA delivered to the lung to total delivered mRNA is about 12% in hamsters but is more likely to be much higher, nearer to 30-50%, in larger mammals. This might mean that a much smaller amount of the nebulized formulation could be required to realize the required dosage.

 These data indicate that a low dose of mRNA can achieve high expression of durable mAb constructs across much of the hamster lung alveolar and airway epithelial compartments, with minimal pulmonary toxicity.”

Clinical improvement

Furthermore, the hamsters treated with the mRNA-encoded mAbs before being inoculated two days later with the virus showed 1% weight gain by day 5, ranging from the second day of treatment. At the identical time, untreated exposed controls lost 5% of their body weight by the fifth-day post-inoculation.

Examination of the lung tissue from treated hamsters and controls showed lower viral titers by over 80% in the previous, in comparison with controls, with an ~80% decrease within the viral RNA load as measured by quantitative polymerase chain response (qPCR). Lung pathology was also largely mitigated in treated hamsters.

The study also suggested that weight reduction was probably the most reliable correlate of the animal’s health, while lung pathology reflects the strength of the immune response fairly than the intensity of viral replication. The delivery of the mRNA didn’t cause lung inflammation or damage to any lung tissue.

What are the implications?

Despite using human mAbs in a hamster model, which shows sub-optimal Fc-mediated immune functions, the present study demonstrated the flexibility of those antibodies, when expressed by nebulized mRNA throughout the lung tissue, to induce an encouraging degree of protection against the virus. This appears to be a fruitful option for passive immunization that cuts short the time required for the host to neutralize the virus following infection while overcoming any deficiency of the host immune system itself.

The nebulization approach allows for self-administration, ensuring wider distribution in low-resource settings.

Each mRNA-expressed COV2-2832 and DH1041 are a transparent complementary prophylactic technique to the therapies currently in use.”