Taming Toxoplasma gondii for therapeutic protein delivery across the blood brain barrier

Studentship Priority area: Industrial collaborative research
Keywords: Toxoplasma, Rett, Synthetic biology, therapy delivery, brain

Abstract:
One of the main challenged in the development of effective treatments for neurological diseases is the lack of robust methods for delivering macromolecules past the blood brain barrier (BBB) and into the cells of the central nervous system (CNS) (DiNunzio and Williams, 2008). Developing a solution to this challenge would therefore have far-reaching consequences for the translatability of macromolecular therapeutics for neurological diseases, and in particular for protein replacement therapies. This includes wide variety of currently untreatable neurological diseases including neurodegenerative (including some of the leading causes of morbidity in developed countries, such as Alzheimer's and Parkinson's) and various monogenetic human diseases (many of whom considered orphan diseases). Toxoplasma gondii, a highly prevalent eukaryotic parasite that infects humans, has an intrinsic ability to pass the BBB and subsist inside the neurons of its host indefinitely without symptoms. To evade the hosts immune response, and facilitate its persistence in the host, T. gondii secretes an array of effector molecules into the intracellular space of the host cells (Weiss and Kim, 2011). Using an array of advanced techniques developed in Dr. Lilach Sheiner's lab, it was shown that T. gondii can be engineered to secrete human therapeutic proteins into various mammalian cells including neurons. The developed engineered T. gondii can act as a robust vector for targeted delivery of therapeutic proteins to the CNS and mediate the delivery of protein-based treatments for various human neurological disease such as Rett syndrome and a range of neurodegenerative and lysosomal diseases. In particular, it was recently shown that T. gondii which secrete the therapeutic protein MeCP2, (a critical protein missing in Rett syndrome patients) can deliver the functional protein into the neurons of mice. These results highlight the vast and exciting potential of using T. gondii as an effective vector for delivery of therapeutic proteins directly into their site of action in neurons (Bracha et al., in review).
Nevertheless, an important next step in the development of T. gondii as a therapeutic vector is the development of attenuated strains which can pass the stringent safety and regulatory standards required for any live vector aimed for clinical use (Moe-Behrens, 2013). In addition, to expand the range of indications which can be targeted with this new delivery system, additional protein targets should be tested.


The aims of this project are:

1. Develop a method to restrict T. gondii's replication and/or persistence in the brain, by manipulating known endogenous genes involved in virulence, or by implementing an inducible kill switch in T. gondii which can be triggered at either the acute or chronic phase of infection.
2. Examine an array of additional therapeutic proteins that could be delivered upon expression and secretion in T. gondii.
3. Characterize the in vivo efficiency of the protein delivery platform, through examination of T. gondii's spread, levels of protein secretion, localization and functionality of secreted proteins in vivo.