In their study MCP-1 evaluation was superior to CRP testing, serum Willebrand factor VWF and the serum angiopoietin Ang-2:Ang-1 ratio were higher before starting CAR T-cell immunotherapy in patients who subsequently developed more severe CRS, suggesting that preexisting endothelial activation might be a previously unrecognized risk factor for severe CRS. Here, VWF is linked to congenital rubella syndrome.