Photo credit: Image by Dr. Hiroshi Kiyono, CC BY 4.0
A new vaccine to protect against deadly cholera was made by grinding genetically modified grains of rice. The first attempt on humans showed no obvious side effects and a good immune response. Researchers from the University of Tokyo and Chiba University have released peer-reviewed results from the Phase 1 clinical trial of the vaccine MucoRice-CTB The Lancet Microbe.
Vaccine manufacturing has made tremendous strides in 2020, fueled by COVID-19. However, the complexity of mRNA-based SARS-CoV-2 vaccines has highlighted the value of vaccinations that can be inexpensively manufactured, transported and stored without refrigeration.
The MucoRice-CTB vaccine is stable from start to finish at room temperature.
“I am very optimistic about the future of our MucoRice-CTB vaccine, especially given the results of the dose escalation. Participants responded to the vaccine at the low, medium, and high dose, with the strongest immune response at the highest dose, ”said Professor Hiroshi Kiyono, DDS, Ph.D. from the Institute of Medical Science at the University of Tokyo who run the MucoRice project. Dr. Kiyono is also a faculty member at Chiba University in Japan and the University of California, San Diego, in the United States
Thirty volunteers received a placebo and groups of 10 volunteers received a total of four doses of either 3 milligrams (mg), 6 mg, or 18 mg of the vaccine every two weeks. Tests two and four months after receiving the last dose showed that volunteers who responded to the vaccine had IgA and IgG antibodies – two types of proteins that the immune system makes to fight infections – specific for cholera toxin B ( CTB). Participants who received a higher vaccine dose were more likely to have CTB-specific antibodies.
An independent review committee found no evidence of significant side effects.
Breeding a new type of vaccine
Vibrio cholerae bacteria are most commonly transmitted through drinking water contaminated with wastewater. Without medical attention, cholera can kill in a matter of hours due to diarrhea with severe dehydration. Cholera infects 1.3 million to 4 million people and causes 21,000 to 143,000 deaths each year, according to the World Health Organization.
There are four modern needle-free cholera vaccines, all of which are placed on the tongue as drops but must be refrigerated and made from whole killed or live weakened (weakened) cholera cells; https: /
The new cholera vaccine grows in genetically modified Japanese short grain rice plants that produce a non-toxic part of the CTB that can be recognized by the immune system. CTB is similar in structure to a toxin produced by some types of disease-causing E. coli bacteria, so cholera vaccines often offer cross-protection against diarrhea in travelers.
The researchers grow the rice plants in a purpose-built indoor hydroponics farm that meets WHO good medical practice standards, ensuring the vaccine remains uncontaminated and the plants are isolated from the natural environment.
The plants produce the CTB subunit in their seeds, the edible rice grains, and store the antigens in droplets called protein bodies with membranes made of fat.
“The rice protein bodies act like a natural capsule to deliver the antigen to the gut’s immune system,” said Dr. Kiyono.
Other drugs have been grown in plants, mostly in the leaves – including treatments for Ebola, lymphoma, and flu – but the drugs must be extracted and purified before use. The grain-based aspect of the MucoRice system avoids these extra steps, the need for cold storage, and protects the antigens on their way through the aggressive stomach acid.
When the plants are ripe, the rice is harvested and ground to a fine powder, then sealed in aluminum packets for storage. When people are ready to be vaccinated, the powder is mixed with about 90 milliliters (1/3 US cup) of liquid and then drunk. Researchers only tested the vaccine with saline (a saline solution that is equivalent to body fluids), but they believe it would work just as well with plain water.
Gut immunity is strong, but the microbiome complicates it
“The nice thing about our vaccine is that it makes good use of the immune system of the body’s mucous membranes via the intestines to induce antigen-specific antibodies,” said Dr. Kiyono.
MucoRice-CTB penetrates the body through the intestinal lining and mimics a natural way of encountering and responding to germs. The stimulation of the mucosal immune system produces two classes of antibodies that identify and specifically remove germs, IgG and IgA. Vaccines that are injected under the skin or into a muscle generally only raise IgG, not IgA, antibodies.
Volunteers who responded to MucoRice-CTB had the highest blood levels of antigen-specific IgG and IgA after eight to 16 weeks.
However, 11 of the 30 volunteers who received the vaccine had a weak or no measurable immune response. All study participants said they had never traveled outside of Japan, so it is unlikely that they had prior exposure or natural immunity to V. cholerae or pathogenic E. coli.
“When we saw these data on the 11 low- and non-responders, we thought that the intestinal microflora might have an influence on the outcome of the immune response,” recalls Dr. Kiyono.
The microflora or the microbiome is the community of microorganisms that live in our body and are either useful or harmless to us. It is generally accepted that digestive system microflora affects health and immunity, but scientists are only just beginning to understand the exact mechanisms behind this relationship.
Extensive genetic analysis of stool samples from all volunteers identified the thousands of types of bacteria that live in the volunteers’ intestines.
“Put simply, high responders had a more diversified microflora, and in the low-responder group the diversity was much lower,” said Dr. Kiyono.
The researchers warned that the small size of the Phase 1 study – where the vaccine was only given to 30 healthy Japanese male volunteers – means that the relevance and prevalence of non-responders is still unclear and that the overall difference in microflora -Diversity was low. However, the results indicate the greater role microflora played in the effectiveness of the vaccine.
“At the moment this is all speculation, but perhaps higher microflora diversity creates a better situation for a strong immune response to oral vaccines,” said Dr. Kiyono.
The link between the gut microbiome and vaccine effectiveness has already been revealed by the unfortunate fact that most vaccines are developed in developed countries and some are less effective when shipped in developing countries. Mucosal vaccines, including oral vaccines for polio and cholera, appear to be particularly vulnerable to this inequality. Most of the scientific theories explaining the phenomenon focus on chronic bowel inflammation associated with poor hygiene. (https: /
“Probably at present, with any vaccination, even injected vaccines, we should think about the immune status of the individual based on the state of their microflora,” said Dr. Kiyono.
It remains to be seen how the diversity of microflora will affect the global effectiveness of the new edible vaccine system, MucoRice, compared to other oral vaccines.
For now, the researchers plan to work with partners from the pharmaceutical industry to bring MucoRice-CTB to the next phase of clinical trials in Japan and overseas.
Yoshikazu Yuki, Masanori Nojima, Osamu Hosono, Hirotoshi Tanaka, Yasumasa Kimura, Takeshi Satoh, Seiya Imoto, Satoshi Uematsu, Shiho Kurokawa, Koji Kashima, Mio Mejima, Rika Nakahashi-Ouchida, Yohei Uchida, Yohei Yoshigawa, Noritada Kohtoshawa, Takanori Kohtoshawa Fujihashi, Hiroshi Kiyono. June 24, 2021. Evaluation of MucoRice-CTB Oral Vaccine for Safety and Microbiota-Dependent Immunogenicity in Humans: A Randomized Study. The Lancet Microbe.
Mucosal Immunology Department: https: /
Interview with the Society for Mucosal Immunology: https: /
Professor Hiroshi Kiyono, DDS, Ph.D.
IMSUT Distinguished Professor Unit, Division of Mucosal Immunology, International Research and Development Center for Mucosal Vaccines, The Institute of
Medical Science, Tokyo University, 4-6-1 Shirokanedai, Minato-ku, Tokyo 108-8639, Japan
Tel: + 81-03-5449-5271
E-mail: [email protected]
Contact press officer
Mrs. Caitlin Devor
Strategic Public Relations Department, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 133-8654, JAPAN
Tel: + 81-080-9707-8178
E-mail: [email protected]
About the University of Tokyo
The University of Tokyo is Japan’s leading university and one of the world’s leading research universities. The enormous research output of around 6,000 researchers is published in the world’s leading journals in the fields of art and science. Our lively student body of around 15,000 Bachelor and 15,000 PhD students comprises over 4,000 international students. Find out more at http: // www.
Japanese Agency for Medical Research and Development (AMED), Ministry of Education, Culture, Sports, Science and Technology (MEXT), Science and Technology Research Partnership for Sustainable Development (SATREPS)