Scientists Are Growing an Edible Cholera Vaccine in Rice
The world's attention has been focused on the coronavirus crisis but Yemen, Bangladesh and many others countries in Asia and Africa are also in the grips of another pandemic: cholera. The current cholera pandemic first emerged in the 1970s and has devastated many communities in low-income countries. Each year, cholera is responsible for an estimated 1.3 million to 4 million cases and 21,000 to 143,000 deaths worldwide.
Immunologist Hiroshi Kiyono and his team at the University of Tokyo hope they can be part of the solution: They're making a cholera vaccine out of rice.
"It is much less expensive than a traditional vaccine, by a long shot."
Cholera is caused by eating food or drinking water that's contaminated by the feces of a person infected with the cholera bacteria, Vibrio cholerae. The bacteria produces the cholera toxin in the intestines, leading to vomiting, diarrhea and severe dehydration. Cholera can kill within hours of infection if it if's not treated quickly.
Current cholera vaccines are mainly oral. The most common oral are given in two doses and are made out of animal or insect cells that are infected with killed or weakened cholera bacteria. Dukoral also includes cells infected with CTB, a non-harmful part of the cholera toxin. Scientists grow cells containing the cholera bacteria and the CTB in bioreactors, large tanks in which conditions can be carefully controlled.
These cholera vaccines offer moderate protection but it wears off relatively quickly. Cold storage can also be an issue. The most common oral vaccines can be stored at room temperature but only for 14 days.
"Current vaccines confer around 60% efficacy over five years post-vaccination," says Lucy Breakwell, who leads the U.S. Centers for Disease Control and Prevention's cholera work within Global Immunization Division. Given the limited protection, refrigeration issue, and the fact that current oral vaccines require two disease, delivery of cholera vaccines in a campaign or emergency setting can be challenging. "There is a need to develop and test new vaccines to improve public health response to cholera outbreaks."
A New Kind of Vaccine
Kiyono and scientists at Tokyo University are creating a new, plant-based cholera vaccine dubbed MucoRice-CTB. The researchers genetically modify rice so that it contains CTB, a non-harmful part of the cholera toxin. The rice is crushed into a powder, mixed with saline solution and then drunk. The digestive tract is lined with mucosal membranes which contain the mucosal immune system. The mucosal immune system gets trained to recognize the cholera toxin as the rice passes through the intestines.
The cholera toxin has two main parts: the A subunit, which is harmful, and the B subunit, also known as CTB, which is nontoxic but allows the cholera bacteria to attach to gut cells. By inducing CTB-specific antibodies, "we might be able to block the binding of the vaccine toxin to gut cells, leading to the prevention of the toxin causing diarrhea," Kiyono says.
Kiyono studies the immune responses that occur at mucosal membranes across the body. He chose to focus on cholera because he wanted to replicate the way traditional vaccines work to get mucosal membranes in the digestive tract to produce an immune response. The difference is that his team is creating a food-based vaccine to induce this immune response. They are also solely focusing on getting the vaccine to induce antibodies for the cholera toxin. Since the cholera toxin is responsible for bacteria sticking to gut cells, the hope is that they can stop this process by producing antibodies for the cholera toxin. Current cholera vaccines target the cholera bacteria or both the bacteria and the toxin.
David Pascual, an expert in infectious diseases and immunology at the University of Florida, thinks that the MucoRice vaccine has huge promise. "I truly believe that the development of a food-based vaccine can be effective. CTB has a natural affinity for sampling cells in the gut to adhere, be processed, and then stimulate our immune system, he says. "In addition to vaccinating the gut, MucoRice has the potential to touch other mucosal surfaces in the mouth, which can help generate an immune response locally in the mouth and distally in the gut."
Cost Effectiveness
Kiyono says the MucoRice vaccine is much cheaper to produce than a traditional vaccine. Current vaccines need expensive bioreactors to grow cell cultures under very controlled, sterile conditions. This makes them expensive to manufacture, as different types of cell cultures need to be grown in separate buildings to avoid any chance of contamination. MucoRice doesn't require such an expensive manufacturing process because the rice plants themselves act as bioreactors.
The MucoRice vaccine also doesn't require the high cost of cold storage. It can be stored at room temperature for up to three years unlike traditional vaccines. "Plant-based vaccine development platforms present an exciting tool to reduce vaccine manufacturing costs, expand vaccine shelf life, and remove refrigeration requirements, all of which are factors that can limit vaccine supply and accessibility," Breakwell says.
Kathleen Hefferon, a microbiologist at Cornell University agrees. "It is much less expensive than a traditional vaccine, by a long shot," she says. "The fact that it is made in rice means the vaccine can be stored for long periods on the shelf, without losing its activity."
A plant-based vaccine may even be able to address vaccine hesitancy, which has become a growing problem in recent years. Hefferon suggests that "using well-known food plants may serve to reduce the anxiety of some vaccine hesitant people."
Challenges of Plant Vaccines
Despite their advantages, no plant-based vaccines have been commercialized for human use. There are a number of reasons for this, ranging from the potential for too much variation in plants to the lack of facilities large enough to grow crops that comply with good manufacturing practices. Several plant vaccines for diseases like HIV and COVID-19 are in development, but they're still in early stages.
In developing the MucoRice vaccine, scientists at the University of Tokyo have tried to overcome some of the problems with plant vaccines. They've created a closed facility where they can grow rice plants directly in nutrient-rich water rather than soil. This ensures they can grow crops all year round in a space that satisfies regulations. There's also less chance for variation since the environment is tightly controlled.
Clinical Trials and Beyond
After successfully growing rice plants containing the vaccine, the team carried out their first clinical trial. It was completed early this year. Thirty participants received a placebo and 30 received the vaccine. They were all Japanese men between the ages of 20 and 40 years old. 60 percent produced antibodies against the cholera toxin with no side effects. It was a promising result. However, there are still some issues Kiyono's team need to address.
The vaccine may not provide enough protection on its own. The antigen in any vaccine is the substance it contains to induce an immune response. For the MucoRice vaccine, the antigen is not the cholera bacteria itself but the cholera toxin the bacteria produces.
"The development of the antigen in rice is innovative," says David Sack, a professor at John Hopkins University and expert in cholera vaccine development. "But antibodies against only the toxin have not been very protective. The major protective antigen is thought to be the LPS." LPS, or lipopolysaccharide, is a component of the outer wall of the cholera bacteria that plays an important role in eliciting an immune response.
The Japanese team is considering getting the rice to also express the O antigen, a core part of the LPS. Further investigation and clinical trials will look into improving the vaccine's efficacy.
Beyond cholera, Kiyono hopes that the vaccine platform could one day be used to make cost-effective vaccines for other pathogens, such as norovirus or coronavirus.
"We believe the MucoRice system may become a new generation of vaccine production, storage, and delivery system."
Dec. 17th Event: The Latest on Omicron, Boosters, and Immunity
This virtual event will convene leading scientific and medical experts to discuss the most pressing questions around the new Omicron variant, including what we know so far about its ability to evade COVID-19 vaccines, the role of boosters in eliciting heightened immunity, and the science behind variants and vaccines. A public Q&A will follow the expert discussion.
EVENT INFORMATION:
Date: Friday Dec 17, 2021
2:00pm - 3:30pm EST
Dr. Céline Gounder, MD, ScM, is the CEO/President/Founder of Just Human Productions, a non-profit multimedia organization. She is also the host and producer of American Diagnosis, a podcast on health and social justice, and Epidemic, a podcast about infectious disease epidemics and pandemics. She served on the Biden-Harris Transition COVID-19 Advisory Board.
Dr. Theodora Hatziioannou, Ph.D., is a Research Associate Professor in the Laboratory of Retrovirology at The Rockefeller University. Her research includes identifying plasma samples from recovered COVID-19 patients that contain antibodies capable of neutralizing the SARS-CoV-2 coronavirus.
Dr. Onyema Ogbuagu, MBBCh, is an Associate Professor at Yale School of Medicine and an infectious disease specialist who treats COVID-19 patients and leads Yale’s clinical studies around COVID-19. He ran Yale’s trial of the Pfizer/BioNTech vaccine.
Dr. Eric Topol, M.D., is a cardiologist, scientist, professor of molecular medicine, and the director and founder of Scripps Research Translational Institute. He has led clinical trials in over 40 countries with over 200,000 patients and pioneered the development of many routinely used medications.
This event is the fourth of a four-part series co-hosted by Leaps.org, the Aspen Institute Science & Society Program, and the Sabin–Aspen Vaccine Science & Policy Group, with generous support from the Gordon and Betty Moore Foundation and the Howard Hughes Medical Institute.
Kira Peikoff was the editor-in-chief of Leaps.org from 2017 to 2021. As a journalist, her work has appeared in The New York Times, Newsweek, Nautilus, Popular Mechanics, The New York Academy of Sciences, and other outlets. She is also the author of four suspense novels that explore controversial issues arising from scientific innovation: Living Proof, No Time to Die, Die Again Tomorrow, and Mother Knows Best. Peikoff holds a B.A. in Journalism from New York University and an M.S. in Bioethics from Columbia University. She lives in New Jersey with her husband and two young sons. Follow her on Twitter @KiraPeikoff.
7 Things to Know about the U.S.’s Capability to Detect Omicron
If the new variant Omicron isn’t here already – which many experts suspect that it is – it will be soon. While we wait for scientists to conduct the necessary research to characterize its transmissibility, potential fitness at immune evasion, and disease severity, we wanted to give Leaps.org readers a window into how the U.S. is positioned to detect the variant. So we spoke to Kelly Wroblewski, director of infectious diseases at the Association of Public Health Laboratories, a membership organization that represents state and local government health labs in the United States. Here are seven insights she shared.
1) If you test positive for COVID-19 with a standard PCR test, the diagnostic report will not tell you which variant you have. There are no diagnostic tests available for your doctor to order to identify variants. To find out the variant, the specimen must be sent to a commercial, clinical, academic, or public health laboratory for genetic sequencing.
2) Today, the U.S. sequences about 5 to 10 percent of all diagnostic specimens that test positive for SARS-CoV-2 in order to determine which variants are circulating and where. Last week nationally, for example, labs sequenced about 80,000 samples. This represents a massive increase from last year at this time, when labs were only sequencing about 8,000 specimens per week. Currently, 99.5 percent of circulating SARS-CoV-2 virus in the U.S. is the Delta variant.
3) The U.S. is “very well prepared” to detect Omicron, Wroblewski says, “particularly compared to where we were when the Alpha variant, or B117 first emerged.” Of the hunt for Omicron, she adds, “it’s very reminiscent of that time, except we are doing so much more sequencing and we have so much better coverage with our sequencing geographically, and we're doing it in a much more timely way. We have the ability to find emerging variants that are circulating in 0.01 percent of the population.”
4) Deciding which specimens to sample is not totally random. Samples that have more virus are likely to lead to better sequencing results. Labs also look to have a diverse set of representative samples, meaning across geographic regions and across gender, race, ethnicity, and age groups. Clinical diversity is also important, such as including pregnant women, severe in-patient cases, mild cases, etc.
5) Sequencing more is not necessarily better to find Omicron faster. “We will increase the number of sequences to a certain extent,” Wroblewski says. “Where we exhibit some caution is doing that indiscriminately isn’t the most effective use of time and resources. The important thing is to try to find Omicron, and if you increase your testing capacity too much, right now, it's still predominantly Delta in the U.S. by a long shot. So you’re mostly going to sequence Delta and you run the risk of delaying your discovery of Omicron, if you focus solely on increasing sequencing.”
So besides just ramping up the sheer numbers of sequencing, diagnostic labs across the country are now advised to preferentially use a certain PCR test made by Thermo Fisher that can help hasten the detection of Omicron. It turns out that Omicron’s specific mutations in the Spike protein mean that the Spike is not picked up on this PCR test, which yields a type of result called an S-gene target failure. Yet the test will still accurately pick up a COVID-19 diagnosis, because it detects two other gene targets on Omicron that are not mutated. “That S-gene target failure gives you a good indication that you may have Omicron. It’s a good early screen.”
Labs will then still need to sequence the whole genome to confirm it matches the Omicron sequence. “So right now, the new recommendation is to use [the Thermo Fisher test] as much as possible to give us a better chance of detecting Omicron more quickly.”
6) This Thermo Fisher test is “fairly widely used” in the U.S. already, so many labs are already well positioned to make the shift. “In early to mid 2020,” Wroblewski explains, “when the supply chain issue for testing was acute, many public health labs implemented five, six, seven, eight different tests, just so they could get enough supplies to do all the testing. Now that we're in a much better place supply-chain wise, it's very difficult and time consuming and cumbersome to maintain all those different test methods all the time, and many, many labs scaled back to only one or two. And so this [new recommendation] would just be shifting to two for some labs that will be shifting to them.”
7) Once Omicron is found here, labs will be focused on finding as many cases as possible, and the CDC will be conducting a variety of studies to determine the impact of the variant on diagnostics, therapeutics, and vaccines. Epidemiologists at the local, state, and federal level will analyze which populations it is spreading in, as well as the severity of the disease it causes. They will work to sort out different impacts on vaccinated vs. unvaccinated populations. The ultimate goal, Wroblewski concludes, is to “use all of that information to make better public health decisions and inform the public about what’s going on.”
Kira Peikoff was the editor-in-chief of Leaps.org from 2017 to 2021. As a journalist, her work has appeared in The New York Times, Newsweek, Nautilus, Popular Mechanics, The New York Academy of Sciences, and other outlets. She is also the author of four suspense novels that explore controversial issues arising from scientific innovation: Living Proof, No Time to Die, Die Again Tomorrow, and Mother Knows Best. Peikoff holds a B.A. in Journalism from New York University and an M.S. in Bioethics from Columbia University. She lives in New Jersey with her husband and two young sons. Follow her on Twitter @KiraPeikoff.