Endothelial-leukocyte interaction in CAR T cell neurotoxicity

CD19-directed CAR T cells treat cancer, but also cause immune effector cell associated neurotoxicity syndrome (ICANS). Despite strong epidemiologic links between cytokine release syndrome and ICANS, it is uncertain how elevated systemic cytokines and activated immune cells cause brain dysfunction. We previously showed that leukocytes plug brain capillaries in an immunocompetent mouse model of CD19-CAR neurotoxicity. Here, we used the same model to explore how integrin activation and endothelial adhesion molecule expression contribute to capillary plugging. In vivo two-photon imaging revealed increased expression of ICAM-1 on brain capillaries, with spatially restricted VCAM-1 increases. TNF, IFN-γ, and IL-1β at concentrations equivalent to CAR T cell patient blood levels upregulated ICAM-1 and VCAM-1 in brain microendothelial cells. In mice, CAR T cells strongly upregulated VLA-4 (integrin α4β1) affinity to VCAM-1, but not affinity of LFA-1 (integrin αLβ2) to ICAM-1. Blocking integrin α4 but not integrin αL improved ICANS behavior in mice. In human CAR T cell patients, increased soluble ICAM-1 and VCAM-1 are associated with ICANS, and integrin α4 but not integrin αL is upregulated in CAR T cells after infusion. Our study highlights that cytokine-driven upregulation of endothelial-leukocyte adhesion may be sufficient to induce neurovascular dysfunction in CAR T cell patients.