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."
Podcast: The Friday Five weekly roundup in health research
The Friday Five covers five stories in research that you may have missed this week. There are plenty of controversies and troubling ethical issues in science – and we get into many of them in our online magazine – but this news roundup focuses on scientific creativity and progress to give you a therapeutic dose of inspiration headed into the weekend.
Here are the promising studies covered in this week's Friday Five:
- Using graphene to repair shoulders
- Testing for PTSD with saliva
- Cancer detection with a microchip
- Best posture for pill taking
- Resilient food for climate change
And an honorable mention goes to research on a new way to induce healthy fat.
Podcast: The Science of Recharging Your Energy with Sara Mednick
If you’re like me, you may have a case of email apnea, where you stop taking restful breaths when you open a work email. Or maybe you’re in the habit of shining blue light into your eyes long after sunset through your phone. Many of us are doing all kinds of things throughout the day that put us in a constant state of fight or flight arousal, with long-term impacts on health, productivity and happiness.
My guest for today’s episode is Sara Mednick, author of The Power of the Downstate, a book about the science of relaxation – why it’s so important, the best ways to go about getting more of it, and the time of day when our bodies are biologically suited to enjoy it the most. As a cognitive neuroscientist at the University of California, Irvine, Mednick has a great scientific background on this topic. After getting her PhD at Harvard, she filled her sleep lab with 7 bedrooms, and this is where she is federally funded to study people sleeping around the clock, with her research published in top journals such as Nature Neuroscience. She received the Office Naval Research Young Investigator Award in 2015, and her previous book, Take a Nap! Change Your Life was based on her groundbreaking research on the benefits of napping.
In our conversation, we talk about how work and society make it tough to get stimulation like food and exercise in ways that support our circadian rhythms, and there just as many obstacles to getting sleep and restoration like our ancestors enjoyed for 99 percent of human history. Sara shares some fascinating ways to get around these challenges, as well as her insights about the importance of exposure to daylight and nature vs nurture when it comes to whether you’re a night owl or an early bird. And we talk about how things could change with work and lifestyles to make it easier to live in accordance with our biological rhythms.
Show notes
3:10 – The definition of “upstates” and “downstates”
5:50 – The power of 6 slow, deep breaths per minute to balance the nervous system
9:05 – Watching out for mouth breathing and email apnea
13:30 – Different ways of breathing for different goals
16:35 – Body rhythms – what is heart rate variability and why is it so important?
21:05 – Are you naturally a morning or night person? Nature vs nurture
27:10 – The perfect storm that gets in the way of following our circadian rhythms
29:15 – The evolution of our pre-bedtime downstates – why it's important to check in with your cave mates
30:10 – The culture shift needed for more people to follow their circadian rhythms and improve their health
35:10 – Employers and communities can build downstates into daily work and life
38:15 – Choosing how we react to the world
41:00 – Being smarter about peak performance
45:09 – The science of pacing yourself for long-term productivity
49:42 – The science of light exposure for circadian rhythms
52:20 – Where to learn more about Sara Mednick’s research and writing
Links:
Sara Mednick’s website https://www.saramednick.com/ and her Twitter
Mednick’s recent book - The Power of the Downstate
Mednick’s book on the benefits of napping - Take a Nap! Change Your Life
The blue light blocking glasses recommended in Mednick’s book https://www.amazon.com/dp/B019C3O2UE?psc=1&ref=ppx_yo2ov_dt_b_product_details
An app for measuring heart rate variability - Elite HRV app https://elitehrv.com/
Thorne take-home Melatonin test