Cytokines mediate increased endothelial-leukocyte interaction and brain capillary plugging during CAR T cell neurotoxicity

CAR-T cells treat cancer, but also cause systemic cytokine release and immune effector cell associated neurotoxicity syndrome (ICANS). In an immunocompetent mouse model, we show by in vivo two-photon imaging that CD19-CAR T treatment causes brain capillary plugging by circulating CAR-T cells and other CD45+ leukocytes, as well as cortical hypoxia. This is accompanied by increased endothelial ICAM-1 and VCAM-1 expression in the brain capillary-venule transition zone, where most of the capillary stalls occur. In the mouse model, circulating CAR-T cells strongly upregulate integrin α4β1 affinity to VCAM-1, but not affinity of integrin αLβ2 to ICAM-1. Blockade of integrin α4 but not integrin αL improves locomotion behavior. In vitro, human brain microendothelial cells upregulate ICAM-1 more than VCAM-1 in response to TNF, IFN-γ, and IL-1β. In a 3D brain human microvessel model, treatment with TNF and IFN-γ is sufficient to induce adhesion of CAR T cells under flow conditions, which is blocked synergistically by antibodies against integrins α4 and αL. Finally, patients with the highest levels of TNF and IFN-γ also have the highest blood levels of soluble ICAM-1 and VCAM-1, which in turn correlate with ICANS. Integrin α4 but not αL increases in CAR-T cells after they are infused into patients. Combined data from patients, mouse models and in vitro microvessels indicate differential regulation of interactions of ICAM-1 and VCAM-1 with their respective leukocyte integrins. Overall, our study supports the hypothesis that cytokine-driven upregulation of endothelial-leukocyte adhesion is sufficient to induce acute, reversible neurotoxicity.