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Background and purpose Mechanical thrombectomy (MT) is the standard of care for emergent large vessel occlusion (ELVO), one of the most severe subtypes of ischemic stroke, which accounts for 30–40% of all cases. Through MT, we can isolate distal blood within the artery immediately downstream from the clot and compare it to systemic arterial blood to provide insight into local intraluminal changes during ischemia. CXCL9 is in interferon gamma-inducible chemokine that binds CXCR3, degrading endothelial tight junctions, attracting T cells, and facilitating immune cell extravasation into brain parenchyma. We aimed to study local CXCL9 expression distal to the intracranial thrombus during large vessel occlusion in human patients. Methods Tissue samples of distal and proximal blood were collected as part of the BACTRAC tissue bank (www.clinicaltrials.gov NCT03153683). Adult subjects with ELVO were prospectively enrolled, and arterial blood distal (intracranial) and proximal (cervical) were collected and processed to optimize RNA quality. RNA were isolated and used to evaluate gene expression in both samples for each subject; proximal systemic blood was used as an internal control for each subject. Results 22 subjects were included in this preliminary analysis. 15 (68.2%) were female. 54.5% of subjects had a CTA collateral score of 1 (18.2% had a score of 0). 4.5% (1 subject) did not attain TICI 2B or 3 recanalization. Infarct time (last known normal to thrombectomy recanalization) was 491 ± 243 minutes. Mean change in NIHSS from admission to discharge was -8 ± 8. CXCL9 expression in distal blood was upregulated an average of 106-fold with a maximum upregulation of 805-fold in one subject. In plotting CXCL9 expression against infarct time, there was a clear negative correlation (Spearman coefficient -0.43, p=0.05). Conclusion For the first time, we evaluate chemokine alterations in human stroke patients in distal stagnant blood during ELVO. There is a significant variance in CXCL9 expression in distal blood in relationship to infarct time, which mirrors the known timing of blood-brain barrier disruption. Disclosures J. Fraser: None. S. Martha: None. L. Collier: None. S. Davis: None. A. Alhajeri: None. S. Grupke: None. K. Pennypacker: None.

Background Mechanical thrombectomy offers a unique opportunity to examine neurophysiological changes occurring during stroke. We developed a tissue banking protocol to capture intracranial thrombi as well as the blood immediately proximal and distal. These tissues provide a rare resource to correlate changes occurring at the time of stroke to patient outcomes. The purpose of this study is to develop a tissue banking protocol in order to provide high-quality yields of RNA for gene expression analysis and protein for proteomics. Methods We instituted an IRB-approved protocol for tissue processing during mechanical thrombectomy (www.clinicaltrials.gov NCT03153683). The protocol is a joint clinical/basic science effort among multiple laboratories and the NeuroInterventional Radiology service line. We developed a step-by-step process for specimen retrieval, initial processing, and storage, which begins in a designated workspace constructed for the study in the angiography suite. Further processing and analysis is performed in our basic science laboratories, and includes extraction of RNA from thrombi with distal and proximal blood samples to assess RNA integrity number (RIN) values. To demonstrate viability of the collected plasma, proteomics of distal and proximal blood was evaluated through an outside vendor (Olink Proteomics). Results We have enrolled 34 subjects (age=66±13.3, 14 males) in the BACTRAC registry thusfar. In our preliminary dataset, the process yielded adequate RNA for gene expression analysis and protein for proteomics. RNA integrity analysis reveal mean RIN values (±SD) for distal arterial blood (n=8) were 8.89±0.41 (range from 8.30 to 9.60) and mean RIN values (±SD) for proximal arterial blood (n=8) were 6.98±0.29 (range from 6.60 to 7.50), indicating moderate to high quality RNA with minimal degradation. Mean RIN values for the thrombi (n=7) were undetectable. The first subject samples of distal and proximal blood were analyzed for proteomics. Duplicates of these samples passed quality control, and were run on all 11 of their proteomic panels (92 proteins/panel) for a total of 1012 proteins. 100% of proteins were detected on cardiovascular 3 and neurology panels. The organ damage panel detected the fewest, with 61% of this panel. The cardiometabolic and cardiovascular 3 panels each showed the most proteins with the greatest differences in expression. Conclusion We have developed a novel tissue banking protocol utilizing mechanical thrombectomy to capture thrombus along with arterial blood distal and proximal to it. The protocol provides high-quality specimens facilitating analysis of the initial molecular response to ischemic stroke in the human condition for the first time. In addition, preliminary integrity analyses demonstrated high-quality yields for RNA and protein in distal and proximal blood samples. Disclosures S. Martha: None. L. Collier: None. A. Gorman: None. K. Salmeron: None. A. Trout: None. D. Edwards: None. S. Davis: None. A. Alhajeri: None. S. Grupke: None. J. Roberts: None. G. Bix: None. K. Pennypacker: None. J. Fraser: None.