Jin Kim ^1,7, Kyung-Tae Lee ^1,7, Jong Seung Lee¹, Jisoo Shin¹, Baofang Cui¹, Kisuk Yang¹, Yi Sun Choi ¹, Nakwon Choi ^2,3,4, Soo Hyun Lee², Jae-Hyun Lee ^5,6, Yong-Sun Bahn^1,* and Seung-Woo Cho^1,5,6 ,*

¹Department of Biotechnology, Yonsei University, Seoul, Republic of Korea.
²Brain Science Institute, Korea Institute of Science and Technology (KIST), Seoul, Republic of Korea.
³KU-KIST Graduate School of Converging Science and Technology, Korea University, Seoul, Republic of Korea.
⁴Division of Bio-Medical Science and Technology, KIST School, Korea University of Science and Technology (UST), Seoul, Republic of Korea.
⁵Institute for Basic Science (IBS), Center for Nanomedicine, Seoul, Republic of Korea. ⁶Graduate Program of Nano Biomedical Engineering (NanoBME), Advanced Science Institute, Yonsei University, Seoul, Republic of Korea.
⁷These authors contributed equally: Jin Kim, Kyung-Tae Lee.

^*Corresponding author.

The neurovascular unit, which consists of vascular cells surrounded by astrocytic end-feet and neurons, controls cerebral blood flow and the permeability of the blood–brain barrier (BBB) to maintain homeostasis in the neuronal milieu. Studying how some pathogens and drugs can penetrate the human BBB and disrupt neuronal homeostasis requires in vitro microphysiological models of the neurovascular unit. Here we show that the neurotropism of Cryptococcus neoformans—the most common pathogen causing fungal meningitis—and its ability to penetrate the BBB can be modelled by the co-culture of human neural stem cells, brain microvascular endothelial cells and brain vascular pericytes in a human-neurovascular-unit-on-a-chip maintained by a stepwise gravity-driven unidirectional flow and recapitulating the structural and functional features of the BBB. We found that the pathogen forms clusters of cells that penetrate the BBB without altering tight junctions, suggesting a transcytosis-mediated mechanism. The neurovascular-unit-on-a-chip may facilitate the study of the mechanisms of brain infection by pathogens, and the development of drugs for a range of brain diseases.