Cell Biology – An estimated one third of the world’s population is infected with the parasite called Toxoplasma gondii. In the “Journal of Biological Methods” researchers have presented a modified gene scissors that can be used to develop a live vaccine against the parasite.
The tiny parasite, which also affects farm animals and wild animals, slumbers in a quarter of the Swiss population. Healthy people hardly experience any symptoms. However, an initial infection during pregnancy is dangerous for the unborn child and can cause permanent neurological damage, among other things. Infection can even be fatal for people with immunodeficiency.
According to the University of Zurich, it is mainly cats that transmit the parasite. It migrates to your intestines, where it multiplies and forms so-called oocsysts. These end up in the environment with the faeces, where they remain infectious for several years and end up in the food chain.
The aim of the research team led by Adrian Hehl, molecular cell biologist at the University of Zurich: to prevent the production of these oocysts in cats. In previous work, they identified various genes that make the parasite sterile if they are eliminated using the Crispr / Cas9 gene scissors.
No difference to natural mutations
However, with the gene editing method, unintended gene changes can creep in. Normally, researchers smuggle ring-shaped DNA molecules (plasmids) into cells that contain the blueprint for the gene scissors and the information about the interface. After the work is done, however, the plasmid is not broken down and can trigger unplanned genetic changes. In the case of zoonotic toxoplasms, this leads to more virulent variants in the worst case.
The Zurich team used a trick: They assembled the gene scissors outside of the toxoplasma cells and smuggled them directly into the parasite in a test tube. There the gene scissors remove the desired gene and are then completely broken down. Only the sterile parasite remains without leaving any other traces in its cells. The inactivation of the gene is no different from naturally occurring mutations, said Hehl.
Elimination of infectious oocysts
In the laboratory, the researchers administered these gene-edited single-cell organisms as a vaccine to several cats, who then built up immune protection. When the cats were infected again with parasites from the wild, they no longer produced infectious oocysts.
Accordingly, the method enables live vaccines to be developed without building plasmids or resistance genes into the parasite, as Hehl concluded.