Plants are like a factory, powered by sunlight to manufacture food using carbon dioxide and water. Now, scientists have found a way to use a tobacco-like plant to create particles for a new polio vaccine.
In a study published in the journal Nature Communications in August, researchers from the John Innes Centre in the United Kingdom report that they successfully produced a polio vaccine using a tobacco-related plant called Nicotiana benthamiana. The plant manufactures virus-like protein particles that can be used to create vaccines.
The team chose the plant, which is native to Australia, because it grows quickly, has an effective plant immune system and is good at synthesizing proteins.
“It just happens to be a workhorse plant that’s been used for decades in plant research,” said Andrew Macadam, co-author of the study and principal scientist at the U.K.’s National Institute for Biological Standards and Control. “The plants are easy to work with.”
Currently, there are two types of polio vaccines in use: the inactivated poliovirus vaccine, or IPV, and the oral poliovirus vaccine, or OPV. The IPV was first developed by Dr. Jonas Salk and introduced for general use in the 1950s. It involves growing the poliovirus and chemically inactivating it before injecting it into a patient. The vaccine then produces antibodies in the patient’s blood.
In the late 1950s, Dr. Albert Sabin developed the OPV, which was approved for use in 1961. The OPV uses a live virus, but prevents it from spreading to the central nervous system and helps people develop an immune response to the poliovirus.
However, the issue with these vaccines is that they both rely on the poliovirus in order to function. Although the viruses are contained in facilities, there’s a risk that they could escape and circulate in the environment.
“What they both have in common is you have to grow the virus,” Macadam said of the two vaccines. “There’s the risk of reintroducing it into the human population. If we could develop a vaccine that doesn’t introduce the live virus, that would be a huge breakthrough.”
The World Health Organization helped fund this research in hopes of fully eradicating polio. Since current vaccines still require the live poliovirus, WHO hopes to seek alternatives.
“These [existing vaccines] have been absolutely effective at controlling polio,” said George Lomonossoff, project leader at the John Innes Centre and co-author of the study. “The problem is they require the production of large amounts of poliovirus and allow the virus to continually circulate. You’ll never eliminate polio entirely without continually vaccinating.”
“If we could develop a vaccine that doesn’t introduce the live virus, that would be a huge breakthrough.”
Polio is an infectious disease that can be fatal or disabling and lead to paralysis. One of the most well-known Americans who suffered from polio was former President Franklin D. Roosevelt, who lost movement in his legs and right hand. Today, polio still circulates in Afghanistan, Pakistan and Nigeria.
WHO has been working to provide polio vaccines to developing countries, but one problem with current vaccination programs is their expense. Lomonossoff says that manufacturing vaccine material in plants would reduce costs.
This new plant-based method also has some costs of its own. To create the vaccine, manufacturers would have to grow the plants and extract the material. Right now, the plants are grown in controlled conditions, so these types of facilities would have to be scaled up.
To create a vaccine using the plant, the researchers put genetic code from the poliovirus’ outer surface into a natural soil bacterium. This bacterium can transfer its own DNA into plant cells, so once the bacterial cells infiltrate the plant, the plant will be infected with genetic instructions from the poliovirus.
Within less than a week, the plant will start making protein particles that look almost identical to and have the same structure as the poliovirus. These particles are empty on the inside, but still mimic the virus in appearance, allowing researchers to create a polio vaccine without using the actual poliovirus.
Polio is just one virus that can be treated using this method. Researchers have also been working on creating vaccines for other diseases, such as a virus that affects sheep in South Africa, the hepatitis B virus and enterovirus 71, a cousin of polio. The method could also potentially be used for the Zika virus, flu, tuberculosis, cancer and more.
The researchers tested the vaccine on mice with successful results, but the next steps for research are to scale up and find ways to produce more of the virus-like particles to create vaccines. The team plans to do more extensive animal trials and eventually clinical trials on humans.
There are currently three types of polio, and this study just treats one. Researchers plan to work on vaccines for the other two types of polio as well.
“I was pleasantly surprised at how relatively straightforward [it was] to make these stabilized captives,” Lomonossoff said. “I thought it was potentially feasible but it actually worked extremely well as a collaboration. It did seem to work exactly as predicted. It’s almost a rarity [when] things work out the way you think things are going to.”