About a third of the world’s population carries Toxoplasma gondii, a parasite that puts people with weakened immune systems at risk and can trigger uterine malformations. The single-celled pathogen also leads to economic losses in agriculture, with toxoplasmosis, for example, increasing the risk of miscarriage among sheep.
The parasite has a complex life cycle and attacks almost all warm-blooded creatures, including wild rodents and birds. In livestock, and thus in humans, it is introduced exclusively through cats. Only in this main form of the host are the infectious phases that are excreted into the environment as encapsulated oocysts and from there enter the food chain.
“If we can prevent the formation of these oocysts, we can reduce the incidence of toxoplasmosis among humans and animals,” said Adrian Hehl, a professor of parasitology and vice dean for research and career development at the University of Zurich’s Vetsuisse University. He and his research group have developed methods that enable this type of intervention.
The live vaccine protects cats from natural infections
In previous research, the team has already identified various genes responsible for creating oocysts. This has allowed them to develop a live toxoplasmosis vaccine: researchers can use CRISPR-Cas9 gene scissors to rule out these essential genes and infect or inoculate cats with modified parasites. These pathogens do not produce infectious oocysts, but cats still protect against natural infection Toxoplasma in the wild.
Manipulation without side effects
To make sterile parasites, the researchers used scissors to edit the CRISPR-Cas9 gene. Although this allows for precise modifications of the genetic material, depending on the protocol, the method commonly used may also have drawbacks. Errors and unintentional genetic changes can be introduced. Now a research group around Hehl reports that in Toxoplasma, such side effects can be avoided by using a modified technique.
To edit the CRISPR-Cas9 gene, scientists usually insert a ring-shaped piece of DNA, a so-called plasmid, into a cell. It contains all the information needed to create genetic scissors and elements that recognize the desired place in the genetic material. Thus, the cell itself produces all the components of gene scissors. However, after that, the plasmid remains in the cell and can trigger additional, unplanned genetic changes.
Gene scissors disappear without a trace
The method used by the Zurich team works differently. Researchers assemble pre-programmed gene scissors outside the cell and then insert them directly into the parasites. After the manipulation of the genetic material, the components are completely decomposed very quickly, and only the desired editing remains.
“Our approach is not only faster, cheaper and more efficient than conventional methods. It also allows the genomic sequence to be changed without leaving traces in the cell,” explains Hehl. “That means we can now produce experimental live vaccines without plasmids or implantation of resistance genes.”
Genetic engineering laws are lagging behind
Given these results, Hehl questions the federal government’s plans to subject the CRISPR-Cas9 genome to the existing law on genetic engineering (and the moratorium, which has been extended until 2025): “Our method is a good example of how this new technology differs. from conventional approaches to genetic engineering. ”He says it is now possible to inactivate a gene without leaving unwanted traces in the genetic material, in a way no different from natural mutations. Unlike many other controversial applications of genetic engineering, this process does not affect food production either, and therefore does not represent a direct intervention in the food chain.
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