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A new vaccine to protect against deadly cholera has been made by grinding up genetically modified grains of rice. The first human trial has shown no obvious side effects and a good immune response.
Researchers have   published the peer-reviewed results of the Phase 1 clinical trial of the vaccine, named MucoRice-CTB, in The Lancet Microbe.
The MucoRice-CTB vaccine is stable at room temperature from start to finish.
There are four modern needle-free cholera vaccines, all of which are given as drops on the tongue, but require cold storage and are made from whole killed or live-attenuated (weakened) cholera cells.

The new cholera vaccine grows in genetically modified Japanese short-grain rice plants that produce a nontoxic portion of CTB that can be recognized by the immune system. CTB is similar in structure to a toxin made by some types of disease-causing E. coli bacteria, so cholera vaccines often provide cross protection against travelers' diarrhea.

Researchers grow the rice plants in a purpose-built, indoor hydroponic farm that meets WHO good manufacturing practice standards for medicines, which ensures that the vaccine remains uncontaminated and that the plants are isolated from the natural environment.

The plants produce the CTB subunit in their seeds, the edible grains of rice, and store the antigens in droplets called protein bodies with membranes made of fat.

"The rice protein bodies behave like a natural capsule to deliver the antigen to the gut immune system.

Other medicines have been grown in plants, most often in the leaves—including treatments for Ebola, lymphoma and flu—but the drugs have to be extracted and purified before being used. The grain-based aspect of the MucoRice system avoids those extra steps, the need for cold storage, and protects the antigens as they travel through the harsh acid of the stomach.

When the plants are mature, the rice is harvested and ground into 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 U.S. cup) of liquid and then drunk. Researchers have only tested the vaccine using saline (a salt solution equivalent to body fluids), but they expect it would work equally well with plain water.

The beautiful part of this vaccine is that it wisely uses the body's mucosal immune system through the gut for the induction of antigen-specific antibodies.

MucoRice-CTB enters the body through intestinal mucosal membranes, mimicking a natural way of encountering and responding to germs. Stimulating the mucosal immune system produces two classes of antibodies that identify germs and target them for removal, IgG and IgA. Vaccines that are injected under the skin or into a muscle generally increase only IgG, not IgA, antibodies.

Volunteers who responded to MucoRice-CTB had their highest blood levels of antigen-specific IgG and IgA after eight to 16 weeks.

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, Takanori Marui, Noritada Yoshikawa, Fumitaka Nagamura, Kohtaro Fujihashi, Hiroshi Kiyono. 24 June 2021. Assessment of Oral MucoRice-CTB vaccine for the safety and microbiota-dependent immunogenicity in humans: A Randomized Trial. The Lancet Microbe.

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