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."
Will religious people reject organ transplants from pigs?
Scientists are getting better at transplanting pig organs into humans. But religious followers of prohibitions on consuming pork may reject these organs, even if their bodies could accept them.
The first successful recipient of a human heart transplant lived 18 days. The first artificial heart recipient lived just over 100.
Their brief post-transplant lives paved the way toward vastly greater successes. Former Vice President Dick Cheney relied on an artificial heart for nearly two years before receiving a human heart transplant. It still beats in his chest more than a decade later.
Organ transplantation recently reached its next phase with David Bennett. He survived for two months after becoming the first recipient of a pig’s heart genetically modified to function in a human body in February. Known as a xenotransplant, the procedure could pave the way for greatly expanding the use of transplanted vital organs to extend human lives.
Clinical trials would have to be held in the U.S. before xenotransplants become widespread; Bennett’s surgery was authorized under a special Food and Drug Administration program that addresses patients with life-threatening medical conditions.
German researchers plan to perform eight pig-to-human heart transplants as part of a clinical trial beginning in 2024. According to an email sent to Leaps.org by three scholars working on the German project, these procedures will focus on one of the reasons David Bennett did not survive longer: A porcine infection from his new heart.
The transplant team will conduct more sensitive testing of the donor organs, “which in all likelihood will be able to detect even low levels of virus in the xenograft,” note the scientists, Katharina Ebner, Jochen Ostheimer and Jochen Sautermeister. They are confident that the risk of infection with a porcine virus in the future will be significantly lower.
Moreover, hearts are not the only genetically modified organs that are being xenotransplanted. A team of surgeons at the University of Alabama at Birmingham successfully transplanted genetically modified pig kidneys into a brain-dead human recipient in September. The kidneys functioned normally for more than three days before the experiment ended. The UAB team is now moving forward with clinical trials focusing on transplanting pig kidneys into human patients.
Some experts believe the momentum for xenotransplantation is building, particularly given the recent successes. “I think there is a strong likelihood this will go mainstream,” says Brendan Parent of NYU Langone Health.
Douglas Anderson, a surgeon who is part of that kidney xenotransplant team, observes that, “organ shortages have been the major issue facing transplantation since its inception” and that xenotransplantation is a potential solution to that quandary. “It can’t be understated the number of people waiting for a kidney on dialysis, which has a significant mortality rate,” he says. According to the advocacy group Donate Life America, more than 100,000 people in the U.S. alone are waiting for a donated organ, and 85 percent of them need a kidney.
Other experts believe the momentum for xenotransplantation is building, particularly given the recent successes. “I think there is a strong likelihood this will go mainstream,” says Brendan Parent, director of transplant ethics and policy at NYU Langone Health, a New York City-based hospital system. Like the UAB team, surgeons at NYU Langone have had success coaxing modified pig kidneys to work in deceased humans.
“There is a genuinely good chance that within a generation, (xenotransplantation) might become very common in reasonably wealthy countries,” says Michael Reiss, professor of science education at University College in London. In addition to his academic position, Reiss sits on the Nuffield Council on Bioethics, a nonprofit that is one of Britain’s most prominent watchdogs regarding medical and scientific issues. Reiss is also an Anglican priest and has studied xenotransplantation from both a scientific and religious point of view.
Moreover, genetic modifications could one day lead to organs being specifically optimized for their recipients. That could ensure issues like donor rejection and the calculated risk of artificially suppressing recipient immune systems become concerns of the past.
Major bioethical, religious concerns
Despite the promise of xenotransplantation, numerous bioethical issues swirl around the procedure. They could be magnified if xenotransplantation evolves from one-off experiments to a routine medical procedure.
One of the biggest is the millennia-long prohibitions Islam and Judaism have had regarding the consumption of pork. Will followers of these religions assume such rules extend to those taboo materials being inserted into a human body?
“Initially, one’s instinctual reaction is that, oh, crumbs! – how are Jews and Muslims going to react to that?” Reiss says. But in a world where science and secularism are accepted on an everyday basis, he notes it is not a significant issue. Reiss points out that valves from pig hearts have been used in human patients for decades without any issues. He adds that both Islam and Judaism waive religious dietary restrictions if a human life is at risk.
“While nobody's saying an individual patient is to be forced to have these, the very high proportion of people who identify as Jews or Muslims when given this option are content with it,” he says.
Concurring with Reiss is Michael Gusamano, professor of health policy at Lehigh University and director of its Center for Ethics. He is currently performing research on the ethics of xenotransplantation for the National Institutes of Health.
“Leaders from all major religions have commented on this and have indicated that this is not inconsistent with religious doctrine,” Gusamano says in written remarks to Leaps.org. “Having said that, it is plausible to believe that some people will assume that this is inconsistent with the teaching of their religion and may object to…receiving a xenotransplant as part of routine medical care.”
A history of clashes
Despite those assurances, science has long clashed with theology. Although Galileo proved the planets revolved around the sun, the Catholic Church found him guilty of heresy and rewarded his discovery with house arrest for the last decade of his life. A revolt occurred in mid-19th century India after native-born soldiers believed the ammunition supplied by their British occupiers had been lubricated with pork and beef tallow. Given they had to use their mouths to tear open ammunition pouches, this violated both the tenets of Islam and Hinduism. And one of the conspiracy theories hatched as a result of COVID-19 was that the vaccines developed to fight the disease were the “mark of the beast” – a sign of impending Armageddon under evangelical Christian theology.
The German xenotransplant research team has encountered such potential concerns when the procedure is regarded through a religious lens. “The pastors in our research suspected that many recipients might feel disgust and revulsion,” they write. “Even beyond these special religious reservations, cultural scripts about pigs as inferior living beings are also generally widespread and effective in the western world, so that here too possible disgust reactions cannot be ruled out.”
The German researchers add that “Jewish and Muslim hospital pastoral workers believe possible considerable problems in this respect, which must be dealt with psychosocially, religiously, and pastorally prior to a possible transplantation in order to strengthen the acceptance of the received organ by the patients and their relatives.”
Parent, the director at NYU Langone, shares a concern that xenotransplantation could move “too fast,” although much of his worry is focused on zoonotic disease transmission – pig viruses jumping into humans as a result of such procedures.
Another ethical issue
Moreover, the way pigs and other animals are raised for transplants could pose future ethical dilemmas.
Reiss notes that pigs raised for medical procedures have to be grown and kept in what are known as a designated pathogen-free facility, or DPF. Such facilities are kept painstakingly antiseptic so as to minimize the risk of zoonotic transmissions. But given pigs are fond of outdoor activities such as wallowing in mud and sleeping on hay, they lead “stunningly boring lives” that they probably do not enjoy, Reiss observes.
Ethical concerns with using pigs may push transplantation medicine into its next logical phase: Growing functional organs for transplant in a laboratory setting.
“There’s no doubt that these research pigs have gotten much better veterinary care, et cetera, (compared to farmed pigs). But it’s not a great life,” Reiss says. “And although it hasn’t so far dominated the discussion, I think as the years go by, rather as we’ve seen with the use of apes and now monkeys in medical research, more and more theologians will get uncomfortable about us just assuming we can do this with…pigs.”
The German research team raises the same concerns, but has taken a fairly sanguine view on the topic. “The impairments of the species-typical behavior will certainly provoke criticism and perhaps also public protest. But the number of animals affected is very small in relation to slaughter cattle,” the German researchers note. “Moreover, the conditions there and also in several animal experiments are far worse.”
Observers say that may push transplantation medicine into its next logical phase: Growing functional organs for transplant in a laboratory setting. Anderson, the UAB transplant surgeon, believes such an accomplishment remains decades away.
But other experts believe there is a moral imperative that xenotransplantation remain a temporary solution. “I think we have a duty to go in that direction,” Parent says. “We have to go that way, with the xenotransplantation process (as) a steppingstone and research path that will be useful for bioengineered organs.”
The Friday Five: Scientists treated this girl's disease before she was born
In this week's Friday Five, scientists treated this girl's rare diseases in utero. Plus, how to lift weights in half the time, electric shocks help people regain the ability to walk, meditation is found to work as well as medication, and much more.
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:
- Kids treated for diseases before they're born
- How to lift weights in half the time
- Electric shocks help people regain the ability to walk
- Meditation just as good as medication?
- These foods could pump up your motivation