New breakthrough in mRNA technology: Vaccine efficacy Doubled

New breakthrough in mRNA technology: Vaccine efficacy Doubled. 

Using mRNA as a vaccine has great potential, but its high innate immunogenicity, easy degradation and low delivery efficiency in the body have hindered its progress in vaccine development.

With the chemical modification of N1-methyl pseudouridine (m1ψ) proposed by Drew Weissman and Katalin Karikó, and the invention of lipid nanoparticle (LNP) delivery vehicles, the obstacles for mRNA vaccine development have been cleared.

The success of mRNA COVID-19 vaccines has shown us the powerful potential of this new vaccine platform based on mRNA technology.

Taking the mRNA COVID-19 vaccine as an example, the chemically modified mRNA encoding the spike protein (S protein) of the coronavirus is encapsulated in LNP to protect the mRNA from being rapidly degraded and to help it enter cells.

Once inside cells, its mRNA is translated into spike protein, which is detected by the immune system, resulting in neutralizing antibodies and activating T cell immune responses. If infected with the coronavirus later, the immune system will recognize and mobilize quickly.

However, the chemical modification of mRNA improves its tolerance and translation ability, but also largely impairs the innate immune response. Therefore, scientists around the world are working hard to improve and try to develop more powerful mRNA vaccines that can produce stronger immune responses.

On September 6, 2023, Canada Research Chair, Assistant Professor of Pharmacy at the University of Toronto Bowen Li co-authored a paper titled: Enhancing the immunogenicity of lipid-nanoparticle mRNA vaccines by adjuvanting the ionizable lipid and the mRNA with MIT professors Robert Langer and Daniel Anderson in Nature Biomedical Engineering journal .

The study simultaneously engineered both the mRNA itself and its delivery vehicle LNP, and developed a “self-adjuvanting” mRNA vaccine for the first time by a dual approach, which can greatly improve neutralizing antibody titers and T cell responses by injection or nasal inhalation.

If further applied to humans, this new type of mRNA vaccine may require lower doses, which could help reduce costs and possibly produce more lasting immunity. The vaccine platform may also help enhance the immune response of other types of mRNA vaccines, including cancer vaccines.

In this paper published in Nature Biomedical Engineering journal, Li Bowen and others wanted to further enhance the potential of mRNA technology and enhance the immune response of mRNA vaccines.

Adjuvants are molecules commonly used to enhance vaccine immune responses, but have not yet been applied to mRNA vaccines. In this study, the research team engineered both the mRNA molecule and its delivery vehicle LNP simultaneously, thus developing a “self-adjuvanting” mRNA vaccine for the first time by a dual approach, allowing both internal and external components of the vaccine to act as adjuvants and enhance the immune response of mRNA vaccines.

First, they focused on C3d protein, which is part of the complement system, a branch of the innate immune system. When the complement system is activated by exogenous microbes, C3d in complement attaches to potential antigens, amplifying the immune response generated by these antigens.

Inspired by this innate immune mechanism, the research team constructed an mRNA encoding a fusion protein of antigen (the RBD binding domain of coronavirus S protein) and three C3d proteins. In this way, once inside cells, its mRNA can express a fusion protein that combines both functions of antigen and C3d.

Li Bowen said that in this experiment, although adding C3d repeats slightly reduced the protein expression level of mRNA, under the same dose of mRNA, the immunogenicity of the generated antigen-C3d fusion protein was more than 10 times higher than that of the original antigen.

Importantly, if antigen and C3d are expressed separately in two independent mRNAs, this significant immunoenhancement effect will not occur.

This specificity means that C3d will not blindly enhance the immune activity of other antigens, thus ensuring its safety for application in vaccine enhancement.

This idea was initially inspired by a paper published in Science in 1996 that he read during his graduate studies.

The paper showed that antigens with two and three C3d had immunogenicity 1000 times and 10000 times higher than single antigens alone respectively , while free C3d had no effect on antigen immunity.

The mRNA technology allows us to easily achieve antigen-C3d fusion , quickly verify this paper’s findings within an mRNA framework ,and apply C3d as a molecular adjuvant to an mRNA vaccine for the first time.

In addition to modifying at molecular level ,the research team also tried to optimize lipid nanoparticles (LNP) used to deliver mRNA vaccines ,so that LNP can stimulate immune responses besides delivering mRNA .

Nanoparticles themselves may have immunostimulatory effects ,but it is not clear what components can optimize this stimulation .To identify the most effective components ,the research team constructed a library of 480 ionizable lipids with different chemical properties ,and screened and evaluated the library by high-throughput methods ,from which they found some lipids that may improve immune responses .

Next, the research team tested the novel mRNA vaccine based on the above findings in a mouse model. Its mRNA encodes S protein and C3d fusion protein, and uses LNP delivery vehicle composed of the best performing ionizable lipid (lipid 331) identified from the library.

Compared with mice vaccinated with unadjuvanted COVID-19 mRNA vaccine, mice vaccinated with this novel mRNA vaccine produced more than 10 times higher levels of neutralizing antibodies and also produced stronger T cell responses.

In June this year, Professor Michael J. Mitchell’s team at the University of Pennsylvania (Dr. Xue Xianghan as the first author) published a paper in Nature Nanotechnology, developing a new LNP component-adjuvant-like lipid that can enhance the adjuvanticity of mRNA-LNP vaccines.

Li Bowen said that the purpose of developing a multiple adjuvant platform is to overcome the dose-dependent limitations of single adjuvant-like lipids, which are especially evident at lower vaccine doses. This is not difficult to understand, because higher vaccine doses will bring more adjuvant-like lipids to enhance immune activation, while the effect is limited otherwise.

Considering the shortage of mRNA vaccine supply in the early stage of the epidemic, we hope to achieve superior or at least similar vaccine effects at very low doses, and a single adjuvant scheme cannot achieve this goal.

Therefore, we constructed this vaccine platform with multiple adjuvant properties, which can significantly enhance the immune effect of the vaccine even at very low doses, achieving a “1+1>2” comprehensive effect.

This type of multiple adjuvant mRNA-LNP vaccine design can not only reduce costs and potential side effects by lowering doses, but also has high value in some specific application scenarios (such as children’s vaccines or nasal vaccines).

Nasal vaccines targeting respiratory mucosa may address the shortcomings of intramuscular injection.

Preclinical studies of nasal influenza vaccines have shown that mucosal immunity can enhance protection against different subtypes of influenza viruses by IgA antibodies and tissue-resident T memory cells, and improve the persistence of antiviral immunity.

In addition, nasal vaccines are easier to accept for children and people with needle phobia, and can also avoid shortages of needles and syringes or other materials.

Especially during a pandemic, using nasal vaccines to immunize the entire population will be faster and more cost-effective than intramuscular injection.

Li Bowen also mentioned that this work started in the early stage of COVID-19 epidemic, when it was not clear whether mRNA vaccines could be administered nasally, because their effectiveness might be severely hindered by the mucus cilia barrier covering the upper respiratory tract.

Considering the potential advantages of nasal vaccines, the team further explored the feasibility of administering this novel RNA vaccine platform nasally. When they injected the vaccine into the noses of mice, they observed strong immune responses similar to those seen with injection vaccination in mice.

If this vaccine is developed for humans, this nasal inhalation vaccine may provide stronger protection because it will produce immune responses in mucosal tissues in the nose and lungs, eliminating infectious viruses at mucosal sites before they enter the bloodstream.

The corresponding author of the paper Daniel Anderson said: If you just spray something into your nose instead of lining up for an injection vaccine, nasal vaccines may also be easier for more people to accept.