306 Endothelial Infiltrating Regulatory B Cells and NK T Cells Precipitate Inflammatory Cascade That Leads to Aneurysmal Rupture

INTRODUCTION: Current literature examining the mechanisms delineating intracranial aneurysm development and subsequent rupture is sparse. Studies from decades prior defined the aneurysm model as being one largely driven by flow changes. However, the scope of these models is limited and does not fully explain why only a subset of patients with existing intracranial aneurysms subsequently go on to rupture. METHODS: We obtained aneurysm endothelial lining from 20 patients with ruptured, unruptured, sentinel hemorrhage, and recurrent aneurysms during endovascular coil embolization, which were processed and analyzed using mass spectrometry. RESULTS: Compared to unruptured aneurysms, ruptured aneurysms had significantly increased infiltrating populations of NK cells (5.5% vs 1.4%, p < 0.01), regulatory B cells (27.6% vs 16.0%, p < 0.05), and cytotoxic CD8 T cells (23.7% vs 13.5%, p < 0.05). To understand whether these cells were recruited at the time of rupture or whether they were present prior to the ictus event, we examined aneurysms that were treated after presenting with sentinel hemorrhages – again these patients had that same population of early-NK cells (7.5%, p = 0.2), suggesting that these cells were present at the nexus point immediately prior to rupture. Further, the regulatory B cells were even more prominent in the sentinel population, (45.6%, p < 0.01). CONCLUSIONS: These findings all point to a complex, coordinated immune response that is driving the remodeling of the aneurysm vessel wall. We interpret the results to suggest that regulatory B cell driven destabilization of the aneurysmal wall leads to a series of events; namely the recruitment of NK cells, subsequent inflammatory cascade, and ultimate rupture. While there remains much to be understood about this multi-faceted picture, these findings provide the basis for further studies looking at targets for adjunctive immune therapies in both our unruptured and ruptured patient populations.