Among the highly expressed proteins screened in Figure S4E, CD44 was positively correlated with ER stress and UPR activation (Fig. S4G), and the expression of XBP1 was positively correlated with CD44 expression in glioma data from TCGA (Fig. S4H), indicating that glioma exosomal CD44 might be responsible for ER stress and XBP1s upregulation in MSCs. Here, CD44 is linked to central nervous system cancer.