Modelling host- Trypanosoma brucei gambiense interactions in vitro using human induced pluripotent stem cell-derived cortical brain organoids

Background: Sleeping sickness is caused by the extracellular parasite Trypanosoma brucei and is associated with neuroinflammation and neuropsychiatric disorders, including disruption of sleep/wake patterns, and is now recognised as a circadian disorder. Sleeping sickness is traditionally studied using murine models of infection due to the lack of alternative in vitro systems that fully recapitulate the cellular diversity and functionality of the human brain. The aim of this study is to develop a much-needed in vitro system that reduces and replaces live animals for the study of infections in the central nervous system, using sleeping sickness as a model infection. Methods: We developed a co-culture system using induced pluripotent stem cell (iPSC)-derived cortical human brain organoids and the human pathogen T. b. gambiense to model host-pathogen interactions in vitro. Upon co-culture, we analysed the transcriptional responses of the brain organoids to T. b. gambiense over two time points. Results: We detected broad transcriptional changes in brain organoids exposed to T. b. gambiense, mainly associated with innate immune responses, chemotaxis, and blood vessel differentiation compared to untreated organoids. Conclusions: Our co-culture system provides novel, more ethical avenues to study host-pathogen interactions in the brain as alternative models to experimental infections in mice. Although our data support the use of brain organoids to model host-pathogen interactions during T. brucei infection as an alternative to in vivo models, future work is required to increase the complexity of the organoids ( e.g., addition of microglia and vasculature). We envision that the adoption of organoid systems is beneficial to researchers studying mechanisms of brain infection by protozoan parasites. Furthermore, organoid systems have the potential to be used to study other parasites that affect the brain significantly reducing the number of animals undergoing moderate and/or severe protocols associated with the study of neuroinflammation and brain infections.