Leukocyte dynamics after intracerebral hemorrhage in a living patient reveal rapid adaptations to tissue milieu. Leukocyte dynamics after intracerebral hemorrhage in a living patient reveal rapid adaptations to tissue milieu

Intracerebral hemorrhage (ICH) is a devastating form of stroke with a high mortality rate and few treatment options. Discovery of therapeutic interventions has been slow given the challenges associated with studying acute injury, particularly over time, in the human brain. Inflammation induced by exposure of brain tissue to blood appears to be a major part of brain tissue injury. Here we longitudinally profiled blood and cerebral hematoma effluent from a patient enrolled in the Minimally Invasive Surgery with Thrombolysis in Intracerebral Haemorrhage Evacuation (MISTIEIII) trial, offering a rare window into the local and systemic immune responses to acute brain injury. Using single-cell RNA-sequencing, we characterized the local cellular response during ICH in the brain of a living patient at single-cell resolution for the first time. Our analysis revealed rapid shifts in the activation states of myeloid and T cells in the brain over time, suggesting that leukocyte responses are dynamically reshaped by the hematoma microenvironment. Interestingly, the patient had an asymptomatic re-bleed (second local exposure to blood) that our transcriptional data indicated occurred more than 30 hours prior to detection by CT scan. This case highlights the rapid immune dynamics in the brain after ICH and suggests that sensitive methods like scRNA-seq can inform our understanding of complex intracerebral events. Overall design: We generated single cell RNA-sequencing data on cells isolated longitudinally from patient blood and hematoma drainage. We additionally performed scRNA-seq on patient followup blood 2.5 years after stroke, and on the blood of four age-matched control donors.

脑出血（Intracerebral hemorrhage, ICH）是一类致死率高、治疗手段匮乏的毁灭性卒中亚型。由于人类脑部急性损伤的研究（尤其是时序纵向研究）存在诸多挑战，相关治疗干预手段的研发进展始终缓慢。脑组织暴露于血液后引发的炎症反应，被认为是脑组织损伤的核心机制之一。

本研究对一名参与脑出血溶栓微创手术清除术试验（Minimally Invasive Surgery with Thrombolysis in Intracerebral Haemorrhage Evacuation, MISTIEIII）的患者的血液及脑部血肿引流液进行了纵向组学分析，为探究急性脑损伤后的局部与全身免疫应答提供了难得的研究窗口。本研究首次以单细胞分辨率，采用单细胞RNA测序（single-cell RNA-sequencing, scRNA-seq）技术，对活体患者脑出血过程中的脑部局部细胞应答进行了精准表征。分析结果显示，脑部髓系细胞与T细胞的激活状态随时间发生快速动态变化，提示血肿微环境可动态重塑白细胞的应答模式。

值得注意的是，该患者出现了无症状性再出血（即第二次局部血液暴露），转录组数据分析显示，此次再出血发生于CT扫描检出前超过30小时。本案例凸显了脑出血后脑部免疫应答的快速动态变化，同时表明单细胞RNA测序（scRNA-seq）这类高灵敏度技术，可助力我们深入理解复杂的颅内病理事件。

研究设计：我们对从该患者血液及血肿引流液中纵向分离得到的细胞进行了单细胞RNA测序。此外，我们还对该患者卒中后2.5年的随访血液样本，以及4名年龄匹配的健康对照者的血液样本开展了scRNA-seq检测。