Is a wasp virus the new wonder vector?

Researchers think they may have a new means of designing transfer vectors for gene therapy - and it is based on an immune dodging technique used by the parasite wasp.

Braconid parasite wasp utilise immusupressant viral particles when invading a caterpillar. © IRBI-CNRS, Annie Bézier

The team - from the Institut de recherche sur la biologie de l'insecte - have found that the wasps release viral particles, and that genes from these viral particles are contained in the wasp's own genome. These genes came from a virus captured by a common ancestor of these wasps 100 million years ago. The wasps have therefore "domesticated" a virus to turn it into a vector for transferring their genes.

Wasps of the family Braconidae reproduce by laying their eggs in caterpillars, which then serve as food for the developing wasp larvae. However, the body of a caterpillar is a hostile environment, with an efficient defense system that forms a capsule of immune cells around foreign objects. To get around these defenses, when the wasp lays her eggs in the caterpillar, she also injects these viral particles made in her ovaries. These particles then enter the caterpillar's cells where they induce immunosuppression and control development, allowing the wasp larvae to survive.

More that twenty different genes coding for characteristic components of nudiviruses - insect viruses often used in biological pest control - are expressed in the wasps' ovaries. Furthermore, these genes are conserved in the different kinds of wasp that make these particles. The results indicate that the ancestor of the braconid wasps integrated the genome of a nudivirus into its own genome. Although these genes continue to produce viral particles, the particles now deliver the wasp's own virulence genes into the parasitised host.

Although many examples of symbiotic bacteria are known, the present case of a parasitic species using a virus to control its host's physiology is unique. To improve our understanding of the phenomenon, researchers are studying these viral particles in detail.Understanding how they work could therefore be very useful for the design of new therapeutic vectors.