PECAM1 and neoplasm: As the multilayered fenestration described above may affect immune cell permeation of tumor parenchyma, a recent case in point [19], we analyzed T cell homing or infiltration in GBM 3DBx.T cell presence was detected by labeling CD3, and combined with endothelium marker CD31, GFAP to detect the tumor mass, and DAPI counterstaining to identify individual cells (Fig. 6a and b).