“Bubble pig syndrome” is a turn of phrase on what is better known as severe combined immunodeficiency (SCID) or “bubble boy syndrome.” In humans it is typically characterized by a lack of adaptive immune system, according to the National Human Genome Research Institute.
SCID is a genetic defect found in humans, mice, dogs and horses. But with a recent discovery at Iowa State University, SCID has been identified in swine. The real importance of this finding is the potential it holds for finding solutions for numerous human health research and applications.
As noted on a SCID website, in humans “the defining characteristic is usually a severe defect in both the T- & B-lymphocyte systems. This usually results in the onset of one or more serious infections within the first few months of life. These infections are usually serious, and may even be life threatening, they may include pneumonia, meningitis or bloodstream infections.”
As Chris Tuggle, Iowa State animal scientist, points out, “the immune system has two major arms; the innate immune system, which recognizes when there is a foreign object — such as a sliver — in the skin and goes to work immediately. There’s also the adaptive immune system, which responds very specifically to what type of pathogen is present in the body.”
While conducting feed-efficiency research targeted at developing a line of swine that grow faster, the Iowa state scientists discovered SCID. It was something of a “happy accident,” Jack Dekkers, Iowa State animal scientist and one of the researchers on the project.
Researchers were testing that genetic line at Kansas State University facilities and four piglets died early on in the process, raising concern. Following a post-mortem examination, it showed that each piglet had a very poorly developed immune system.
“It’s a finding that was totally unrelated to the [feed efficiency study],” Dekkers notes, “but when we looked at it carefully, we knew it was something completely new and very important.”
Once the Iowa State and Kansas State researchers assessed that SCID was involved, they set out to find the exact nature and cause of the immunodeficiency.
It’s important to note that the disease can only be passed down if both parents carried the gene. Emily Waide, Iowa State graduate student studying quantitative genetics, got involved last October to identify the gene that’s responsible.
The researchers decided to treat the SCID piglets the same way as a human with the disease-- by giving the piglets a bone marrow transplant. Essentially, this gives them an immune system, Dekkers notes.
Matthew Ellinwood, Iowa State associate professor of animal science with a background in veterinary medical genetics, oversaw the bone marrow transplantation of the piglets. Ellinwood said he was excited to do the procedure because he had worked on transplants in SCID dogs. Three SCID piglets from two litters received the procedure.
“We just got the data, and it looks like they are engrafting,” Ellinwood says. “They are all doing clinically well.” This success offers hope for the future uses of this discovery, such as using these swine as a biomedical model for humans.
“This discovery is an incredibly important one,” Ellinwood say.
Jason Ross, Iowa State assistant professor of the animal science, has researched using animals as biomedical models. “The majority of human health research has been in rodent models, but they don’t always replicate the human conditions,” he says.
While it’s more expensive to do research with swine instead of rodents, the pigs’ similarity to humans is worth the extra money. For example, genetic mutations such as cystic fibrosis, which affects the lungs, pancreas, liver and intestines in humans, does not have a good rodent model.
“With the SCID piglets, we can better study how to treat people who have a weakened immune system from things like AIDS to radiation treatments,” Dekkers says. “Availability of SCID pig will make such research much more directly applicable to humans.”
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