According to the WHO, influenza causes between 290,000 and 650,000 deaths each year. This is why vaccination against the disease is strongly recommended, particularly for people over the age of 65.
“Today, conventional vaccines target a viral protein called hemagglutinin," explains Louis Bourlon, research engineer at CEA-Leti. “The problem is that this part of the virus mutates frequently from one year to the next, preventing antibodies from recognizing the virus and effectively protecting against it. As a result, new mutations must be anticipated every year in order to produce an effective updated vaccine."
This approach requires annual revaccination and proves inadequate in the event of a pandemic, where the virus undergoes major mutations.
Grafting the M2e Peptide Onto Lipidots®
A better solution would therefore be to target another, more stable part of the virus. This is the case for the “M2e" peptide, a fragment of the M2 protein that changes very little across strains and over time, making it an ideal candidate for a universal vaccine.
Unfortunately, unlike hemagglutinin, M2e has insufficient immunogenicity, meaning it triggers only a weak immune response.
As part of a CIFRE PhD project involving Sanofi, CEA-Leti, and Institut pour l'Avancée des Biosciences (IAB), Louis Bourlon aimed specifically to improve the immunogenicity of M2e in order to develop a universal influenza vaccine.
This objective relied on a technology developed at CEA-Leti for more than 15 years:
Lipidots®.
“These are lipid nanoparticles, similar in nature to those used in mRNA vaccines against COVID-19," explains Louis Bourlon. “One of the main differences lies in their core, which is more solid than that of mRNA vaccine nanoparticles, significantly improving their stability. In addition, instead of encapsulating the molecule of interest inside the nanoparticle, Lipidots® allow it to be grafted onto the surface. Finally, thanks to their lipid composition, which is close to that of biological systems, they offer high biocompatibility and safety compared with other types of nanoparticles and do not contain synthetic lipids."
The manufacturing process is simple and based on shear forces, enabling easier industrial scale-up through a well-established high-pressure homogenization process.
A Method That Enhances the Immune Response to M2e
The key challenge of the PhD work was the following: how can M2e be grafted onto Lipidots® in a controlled manner while preserving the peptide's natural structure?
The answer came through a method known as “click chemistry."
“We modified the surface of the Lipidots® by adding a specific chemical function called 'DBCO'. At the same time, we sourced commercially available M2e peptides carrying the complementary 'azide' chemical function."
The method consists of bringing the two elements together: a chemical reaction occurs between the nanoparticles and the modified peptides, which “click" together and bind.
The result is Lipidots® displaying the M2e peptide on their surface.
“Click chemistry enabled us to graft unmodified M2e with a high surface density. This allows the peptide to be presented to immune cells in a way that closely resembles what happens during a natural influenza infection. This greatly increases the likelihood that the antibodies induced by our formulation will be protective."
“To refine the process, we also applied several analytical methods," adds Louis Bourlon. “The goal was to measure the number of peptides per nanoparticle depending on conditions, verify that the surface-grafted M2e remained recognizable and accessible to anti-M2e antibodies, determine the injection dose, and so on."
Both in vitro and in vivo tests confirmed that the method increased the immunogenicity of M2e. Researchers observed a strong improvement in the immune response thanks to the vectorization of M2e by Lipidots®, by measuring both the presence and quality of antibodies and T lymphocytes.
Cationic Lipidots® With Multiple Applications
During this work, other formulations of Lipidots®, known as cationic Lipidots®, were used to vectorize an adjuvant.
In previous projects, these formulations demonstrated significant added value in both human and veterinary healthcare applications, particularly for nucleic acid delivery.
Highly promising preclinical results have been obtained in several models using messenger RNA (mRNA) vaccines complexed with Lipidots®.
Unlike the encapsulation of mRNA by conventional lipid nanoparticles (LNPs), which is complex to control, the complexation between mRNA and Lipidots® is achieved through a simple extemporaneous mixing process.
This technology, protected by 15 patents, also benefits from an optimized manufacturing process enabling large-scale industrial production without solvents.
“Their high stability, versatility, natural tropism for immune cells, and the possibility of active targeting make Lipidots® ideal vectors for vaccination and many other promising therapeutic applications," concludes Louis Bourlon.