Genomic diversity contributes to the neuroinvasiveness of the Yellow fever French neurotropic vaccine.

Mass vaccination with the live attenuated vaccine YF-17D is the current way to prevent infection with Yellow fever virus (YFV). However, 0.000012-0.00002% of vaccinated patients develop post-vaccination neurological syndrome (YEL-AND). Understanding the factors responsible for neuroinvasion, neurotropism, and neurovirulence of the vaccine is critical for improving its biosafety. The YF-FNV vaccine strain, known to be associated with a higher frequency of YEL-AND (0.3-0.4%) than YF-17D, is an excellent model to study vaccine neuroinvasiveness. We determined that neuroinvasiveness of YF-FNV occured both via infection and passage through human brain endothelial cells. Plaque purification and next generation sequencing (NGS) identified several neuroinvasive variants. Their neuroinvasiveness was not higher than that of YF-FNV. However, rebuilding the YF-FNV population diversity from a set of isolated YF-FNV-N variants restored the original neuroinvasive phenotype of YF-FNV. Therefore, we conclude that viral population diversity is a critical factor for YFV vaccine neuroinvasiveness.

A Human Blood-Brain Interface Model to Study Barrier Crossings by Pathogens or Medicines and Their Interactions with the Brain.

The early screening of nervous system medicines on a pertinent and reliable in cellulo BBB model for their penetration and their interaction with the barrier and the brain parenchyma is still an unmet need. To fill this gap, we designed a 2D in cellulo model, the BBB-Minibrain, by combining a polyester porous membrane culture insert human BBB model with a Minibrain formed by a tri-culture of human brain cells (neurons, astrocytes and microglial cells). The BBB-Minibrain allowed us to test the transport of a neuroprotective drug candidate (e.g., Neurovita), through the BBB, to determine the specific targeting of this molecule to neurons and to show that the neuroprotective property of the drug was preserved after the drug had crossed the BBB. We have also demonstrated that BBB-Minibrain constitutes an interesting model to detect the passage of virus particles across the endothelial cells barrier and to monitor the infection of the Minibrain by neuroinvasive virus particles. The BBB-Minibrain is a reliable system, easy to handle for researcher trained in cell culture technology and predictive of the brain cells phenotypes after treatment or insult. The interest of such in cellulo testing would be twofold: introducing derisking steps early in the drug development on the one hand and reducing the use of animal testing on the other hand.

Zika virus enhances monocyte adhesion and transmigration favoring viral dissemination to neural cells.

Zika virus (ZIKV) invades and persists in the central nervous system (CNS), causing severe neurological diseases. However the virus journey, from the bloodstream to tissues through a mature endothelium, remains unclear. Here, we show that ZIKV-infected monocytes represent suitable carriers for viral dissemination to the CNS using human primary monocytes, cerebral organoids derived from embryonic stem cells, organotypic mouse cerebellar slices, a xenotypic human-zebrafish model, and human fetus brain samples. We find that ZIKV-exposed monocytes exhibit higher expression of adhesion molecules, and higher abilities to attach onto the vessel wall and transmigrate across endothelia. This phenotype is associated to enhanced monocyte-mediated ZIKV dissemination to neural cells. Together, our data show that ZIKV manipulates the monocyte adhesive properties and enhances monocyte transmigration and viral dissemination to neural cells. Monocyte transmigration may represent an important mechanism required for viral tissue invasion and persistence that could be specifically targeted for therapeutic intervention.