Early infiltration of ischemia-conditioned Tregs attenuates BBB damage via suppressing neutrophil extracellular traps in ischemic stroke.

Regulatory T cells (Tregs) modulate myeloid cells but are absent early after ischemic stroke when neutrophil infiltration peaks. Whether promoting their early infiltration into the brain as an introduced niche could modulate the cerebral immune micromilieu remains unknown. Here, we show that splenic Tregs at day 5 post-MCAO (ischemia-conditioned Tregs, ICTregs) exhibit enhanced adhesion. Transferred ICTregs infiltrate the infarcted area early, alter brain cellular composition, reduce neutrophil extracellular traps (NETs) and preserve blood-brain barrier (BBB) integrity during the acute phase. Mechanistically, integrin α4 anchors ICTregs to cerebral venous endothelium, and ICTreg Annexin A1 interacts with neutrophil Dectin-1 to suppress NETs. The transcription factor Ikzf2 is critical for ICTreg induction, and modulating Ikzf2 enables Sham Tregs to acquire early brain-homing capacity. These findings offer valuable insights into the neuroprotective function of ICTregs in the early stage of ischemic stroke and identify engineered-Tregs target for optimizing the brain-immune ecosystem for neural protection.