In conversation with First Author, Namrata Baruah
On her recent publication
Stable Recombinant Invasion Plasmid Antigen C (IpaC)-Based Single Dose Nanovaccine for Shigellosis. Baruah N, Halder P, Koley H, Katti DS. Mol Pharm. 2022.
MFCEM: Congratulations on this publication. It follows your previous study on Ipa-based nasal vaccine for Shigellosis. What was the motivation to engineer this vaccine and further improvise it?
Namrata Baruah: Thank you! This is year 2022 and hundreds of people are still dying due to shigellosis- a diarrheal disease, for which a commercial vaccine is unfortunately, not available. The situation is grim because most strains of Shigella, the bacterial pathogen, have become multi-drug resistant. There may soon be an outbreak we do not have antibiotics for. Therefore, the requirement of a vaccine is paramount.
Although there have been considerable research, a vaccine passing all the phases of clinical trials is still not available mainly because of low immunogenicity of the antigen(s) or serotype specific narrow-range protection of the vaccine candidates. Instability of immunogenic, potential vaccine antigens, exacerbates the problem. Therefore, we first stabilized a potential immunogen –IpaC, a protein found in all Shigella strains. We then assessed its vaccine potential with the available resources, and surprisingly found it to be cross-protective (heterologous protection) without any adjuvant. To further reduce dosing and increase eventual patient compliance, we encapsulated the minimum protective amount of the stabilized protein into PLGA (polymer with several FDA approved applications) nanoparticles to obtain a minimalistic single dose nanovaccine for shigellosis which is expected to protect against all Shigella strains.
MFCEM: Can you explain for the larger scientific community the technology used to develop this vaccine. How do the improvisations implemented by you push the field of vaccine development forward?
Namrata Baruah: To develop the nanovaccine, we first stabilized an immunogenic recombinant Shigella protein-IpaC (origin- Shigella dysenteriae 1, the most harmful Shigella with the most unstable IpaC) which resulted in a self-adjuvanting single-antigen nasal vaccine. Nasal immunization can provide protection at a different site such as the intestine because of the common mucosal immune system (CMIS).
Further, compared to oral, nasal vaccines provide higher protection with lesser dose and thus, most Shigella vaccine candidates currently being explored are intranasally administered. The stabilized IpaC vaccine could protect the immunized mice against a high dose challenge of a heterologous Shigella (S. flexneri 2a, the most common type around the globe) whereas, all the unimmunized control mice died after severe diarrhea. Therefore, we obtained a cross-protective vaccine. Cross-protection against Shigella dysenteriae is difficult to achieve and there are only few reports showing minimal protection. Therefore, we chose IpaC protein of S. dysenteriae origin (most vaccine candidates currently being explored are from S. flexneri origin), as it is bound to show homologous protection. Therefore, as expected, it protected immunized mice from bloody diarrhea. However, the vaccine needed to be administered in 3 doses which meant that eventually, patients would be required to visit a hospital or care facility for 3 times at regular intervals. As the disease mainly affects the infants and the elderly, decreasing hospital visits was a priority. Therefore, we explored a single-dose nasal vaccine. As biodegradable polymeric nanoparticles are known to show a depot effect leading to slow release of the encapsulants, we chose a nanoparticle system which was expected to result in greater circulation time of the stabilized IpaC in the body and hence, equivalent immunogenicity at 1/3rd the dose. We chose the biodegradable polymer PLGA with established safety (FDA approved for multiple applications) as it is expected to shorten the entire process of lab to the market.
Since, the current vaccine candidate is a single antigen, single dose, cross-protective, facile formulation, therefore, our work should accelerate the progress towards a protective commercial Shigella vaccine.
MFCEM: Could you comment on the possibility of translating this technique for developing vaccines for human use. Do you envisage it happening in the near future?
Namrata Baruah: The minimalistic, cross-protective, single dose nanovaccine is amenable to translation at a large scale because of the following reasons-
First, being recombinant, IpaC protein purification omits pathogenic Shigella culture requiring a BSL 2 facility. Second, the stabilized IpaC protein was found to be stable at a multitude of temperatures, which would ultimately reduce the cost of storage and/or transportation of the protein. Third, the nanovaccine is minimalistic requiring only a few elements to complete the whole process after which it can be lyophilized and stored for years at room temperature. Fourth, as it is an intranasal vaccine, trained personnels for vaccine administration would not be required. Finally, due to a single dose, it is expected to increase patient compliance and overall acceptance. All of these factors can reduce cost and effort and therefore, after rigorous testing, I expect the nanovaccine to at least be part of the solution especially in low and middle income countries where the disease causes greater harm.
