Since the beginning of the Corona pandemic, researchers have been working on mucosal vaccines that are administered through the nose. Now, scientists from Berlin, including researchers from Charité – Universitätsmedizin Berlin, have developed and tested a live attenuated vaccine for the nose. In the current issue of the journal Nature Microbiology*, the interdisciplinary team describes the special immune protection it triggers.
Coronaviruses spread mainly through the air. When an infected person talks, coughs, sneezes or laughs, he or she excretes droplets containing viruses with the air they breathe. In this way, the pathogens can enter the respiratory tract of other people and infect them. A Berlin research team wants to fight the virus exactly where it first attacks: on the mucous membranes of the nose, mouth, throat and lungs. To this end, the scientists have developed a nasally administered, attenuated live vaccine against SARS-CoV-2 and have been able to show how it provides even better immunity than conventional vaccines.
Two preparations for vaccination through the nose were already approved in India and China last autumn. They are based on attenuated adenoviruses, i.e. viruses that trigger respiratory or gastrointestinal diseases, among others, but no longer reproduce or reproduce poorly themselves and thus do not cause any disease. Other live nasal vaccines are being developed and tested worldwide.
Protects where the infection starts and beyond
The benefits of a vaccine in the form of a nasal spray go far beyond allowing people with a fear of injections to breathe a sigh of relief. When a vaccine is injected, immunity builds up primarily in the blood and throughout the body. However, this means that the immune system detects and fights coronaviruses relatively late in an emergency – because they enter the body via the mucous membranes of the upper respiratory tract. “This is exactly where we need local immunity if we want to catch a respiratory virus early,” says co-lead author of the study Dr Jakob Trimpert, working group leader at the Institute of Virology at Free University of Berlin.
“Nasal vaccines manage to do this much better than vaccines that are injected and reach the mucous membranes only with difficulty or not at all,” says Dr Emanuel Wyler, also co-lead author. He has been researching the coronavirus since the outbreak of the pandemic in the RNA Biology and Posttranscriptional Regulation group headed by Prof. Dr. Markus Landthaler at the Berlin Institute for Medical Systems Biology of the Max Delbrück Center (BIMSB-MDC).
Ideally, a live nasal vaccine stimulates the formation of antibodies, immunoglobulins A (IgA), directly on site, thus preventing infection in the first place. IgA is the most abundant immunoglobulin in the mucous membranes of the respiratory tract. It has the ability to neutralise pathogens by binding to them and thus preventing them from infecting airway cells. At the same time, vaccination also stimulates systemic immune responses, which overall contributes to effective protection against infection.
“Similar to antibodies in the mucosa, memory T cells resident in lung tissue are also beneficial. These white blood cells can remember pathogens and remain in the respective tissue after an infection. Their positioning in the lungs enables them to react quickly to pathogens that enter via the airways,” says Dr. Geraldine Nouailles, immunologist and working group leader at the Clinic for Pneumology, Respiratory Medicine and Intensive Care Medicine at Charité. The co-first author refers to an observation that the team was able to make during the study: “We were able to prove that with previous intranasal vaccination, there is also an increased reactivation of these local memory cells in the case of a SARS-CoV-2 infection. Of course, we were particularly pleased about this.”
Local immunity prevents virus infection
The scientists tested the effect of the newly developed nasal COVID-19 vaccine on hamster models, which Dr Trimpert and his team had already established at the beginning of the pandemic at the Free University of Berlin. The animals are currently the most important non-transgenic model organism for COVID-19, as they are infected with the same virus variants as humans and develop similar disease symptoms. After two administrations of the vaccine, the virus was no longer able to replicate in the model organism. “The immune memory was very well stimulated and the mucous membranes were very well protected due to the high antibody concentration,” Dr Trimpert states. The transmissibility of the virus could also be significantly reduced in this way.
In addition, the scientists compared the effectiveness of the attenuated live vaccine with that of intramuscularly injected vaccines. To do this, they vaccinated the hamsters either twice with the live vaccine, once with an mRNA and then with the live vaccine, or twice with an mRNA- or adenovirus-based vaccine. Using tissue samples from the nasal mucosa and lungs, they checked how strongly the viruses were still able to attack the mucosal cells in a subsequent infection with SARS-CoV-2. They also determined the extent of the inflammatory reaction using single cell sequencing.
“The live attenuated vaccine performed better than the comparator vaccines in all parameters,” Dr Wyler summarises. The decisive factor is probably that the nasally administered vaccine builds up immunity directly at the entry site of the virus. In addition, the live vaccine contains all the virus components and not just the spike protein, as is the case with the mRNA vaccine. Spike is the most important antigen of the virus – but the immune system can also recognise the virus from about 20 other proteins.
Protects better than conventional vaccines
The best protection against SARS coronavirus 2 was achieved by a double vaccination via the nose, followed by the combination of an injection of the mRNA vaccine into the muscle and the live vaccine administered nasally afterwards. “This could make the live vaccine particularly interesting as a booster,” says co-first author of the study Julia Adler, a veterinarian and doctoral student at the Institute of Virology at Free University of Berlin.
The principle of live attenuated vaccines is old and is used, for example, in measles or rubella vaccination. In the past, however, scientists produced the attenuation by chance, sometimes by waiting for years for mutations that produced an attenuated virus. The Berlin researchers, on the other hand, have deliberately altered the genetic code of the coronaviruses. “In this way, we want to prevent the attenuated viruses from mutating back into a more aggressive variant,” explains Dr Dusan Kunec, a scientist at the Institute of Virology at Freie Universität Berlin and also a co-lead author. The key co-developer of the vaccine emphasises: “Our live vaccine is therefore safe and can be tailored to new virus variants.”
Next up are safety tests: For this, the researchers are working with RocketVax AG, a Swiss start-up based in Basel. The biotech company is further developing the live attenuated vaccine against SARS-CoV-2 and is preparing a phase 1 clinical trial in humans. “We are very pleased to have a pioneering role in the development and production of the live attenuated SARS-CoV-2 vaccine in the form of a nasal spray. Our goal is to rapidly scale up production and move forward with clinical trials for market access to provide protection from COVID symptoms to all people. We see great potential in the market for seasonal nasal vaccines,” says Dr Vladimir Cmiljanovic, CEO of RocketVax.
Only time will tell which nasal vaccine will ultimately provide the best protection. The manufacturers of the intranasal adenovirus vaccines developed in India and China have not yet applied for approval in Europe. However, according to the researchers, one thing is certain: since they are administered as nasal sprays or drops, nasal vaccines are basically well suited for use with limited access to trained medical personnel. They are also inexpensive to produce and easy to store and transport. Last but not least, live vaccines such as the one used here have been shown to provide cross-protection against related viral strains.
Image: After double vaccination with the attenuated live vaccine (A), the nasal mucosa in the hamster model is very well protected and shows hardly any changes due to SARS-CoV-2 (B). The combination of live and mRNA vaccine (C) is also very effective; however, the virus (coloured brown) still finds small attack surfaces in the nasal mucosa (D). Double intramuscular vaccinations perform significantly worse in protecting the nasal mucosa in comparison (E+F and G+H). The virus can damage the upper tissue layers. © Free University of Berlin l Anne Voß
*Nouailles G et al. A live attenuated vaccine confers superior mucosal and systemic immunity to SARS-CoV-2 variants. Nature Microbiology 2023 Apr 03. doi: 10.1038/s41564-023-01352-8
About the study
The work was funded by the German Research Foundation (DFG), funding code OS 143/16-1 and SFB-TR84/Z01b, among others. For the further development of the vaccine, the Berlin researchers are collaborating with the Swiss company RocketVax AG.
Clinic for Pneumology, Respiratory Medicine and Intensive Care with the Sleep Medicine Unit of the Charité
AG Landthaler, RNA Biology and Posttranscriptional Regulation
Department of Veterinary Medicine at the Free University of Berlin
Understanding lung injury in COVID-19 disease – Press release Publication Nat Comms 2021