LGALS3BP and hemorrhage: As this assay provided a readout for CSF-CCM on human astrocyte proliferation, we probed the functional role of LGALS3BP by adding MDP1959, a humanized version of anti-LGALS3BP antibody (from MediaPharma)38 that also detects LGALS3BP in reactive astrocytes of the hemorrhage-affected human cerebral parenchyma (Extended Data Fig. 7a–e) and in hiAstros (Extended Data Fig. 7f,g).