Patient-specific BBB-on-Chip Enables Predictive Personalized Medicine Applications

The blood brain barrier (BBB) comprises a multicellular neurovascular unit (NVU) in which pericytes, astrocytes, and neurons directly interact with brain microvascular endothelial cells (BMECs). In turn, BMECs form a specialized transporter barrier created by tight junctions and polarized efflux pumps. This fine-tuned cellular architecture permits the blood-to-central nervous system (CNS) passage of crucial nutrients and metabolic molecules while prohibiting the entry of deleterious factors and most drugs. Several neurological disorders involve BBB dysfunction, creating the need to understand BBB physiology and transport mechanisms in both health and disease. Marked differences in BBB substrate specificity and transporter activity across species limit the relevance of animal models. Therefore, a human-specific BBB model is crucial to study human diseases and for the discovery of new CNS permeable drugs.

One challenge to be addressed when engineering a human BBB model is the source of human BMECs. Primary human BMECs have a low yield (<0.1% of CNS cells), a tendency to de-differentiate in culture and donor to donor variability. Immortalized human BMECs overcome these limitations, but display poor barrier properties that severely limit their use for permeability assays. Human induced pluripotent stem cells (iPSCs) were recently introduced as an attractive source for BMECs (iBMECs). These cells are highly scalable and exhibit remarkable functional barrier properties that are well suited for BBB modeling.

A further challenge in current in vitro BBB models, is the poor representation of the physiological NVU, in which the multicellular context and organization as well as the applied physical forces are important both, for the development and function of the BBB.

Here, combining iPSC and organ-on-chip technologies we developed a novel platform in which isogenic (cells derived from a single patient) iPSC-derived iBMECs, iAstrocytes and iNeurons mimic human BBB functionality. iBMECs form a bioengineered vessel-like structure on the Organ-Chip and human astrocytes, pericytes and neurons form direct cell-to-cell interactions that mimic functionality at the level of an organ. The BBB-Chip exhibits physiologically relevant transendothelial electrical resistance and faithfully predicts BBB permeability of molecules. Whole human blood perfusion through the ‘blood vessel’ introduces another physiological interphase and demonstrates that iBMECs can protect spontaneously active neurons from cytotoxicity. Finally, genetic neurological disease modeling in the context of a functional organ reveals substrate transport variability across individual BBB, demonstrating the feasibility of this approach for predictive personalized medicine applications.