Abstract T P231: B- Cell Depletion Decreases Lesion Burden in a Murine Model of Cerebral Cavernous Malformation Disease

Abstract

Introduction: The cerebral cavernous malformation (CCM), a common cerebrovascular anomaly, predisposes patients to a lifetime risk of seizures, hemorrhagic stroke, and other neurological sequelae. Previous studies revealed robust inflammatory cell infiltration and selective synthesis of IgG within the lesions. Recently, in situ antigen-driven B- cell clonal expansion and immune complex deposits were demonstrated in CCM lesions. However, we do not know whether B cells indeed could play a role in CCM genesis and maturation. Therefore we hypothesize B-cell depletion could inhibit CCM development in a murine model of CCMs. Methods: Based on the two-hit hypothesis, we crossed Ccm3 heterozygotes into a Trp53 background, a mouse model that demonstrated 100% penetrance with severe lesion burden. Three weeks after birth, 5 CCM3+/-Trp53-/- mice were assigned into treatment group, receiving anti-mouse BR3 (Genentech) to deplete B cells with IP injection once a week (5mg/kg/week) for a total of 12-15 weeks. At 4 months of age, the mouse brains were harvested and fixed. B cell depletion was demonstrated by FACS analysis of peripheral blood and spleen cell suspensions, further confirmed in the spleens via immunohistochemistry. CCM lesion burden was assessed using either poisson regression (number) or student t test (area). Results: CD19+, CD22+, and CD45R/B220+ B cells of peripheral blood and spleen cell suspensions was significantly decreased in all 5 CCM3+/-Trp53-/- mice treated with anti-mouse BR3, as compared with those in the control group. B cell depletion was further confirmed in spleen. Anti-mouse BR3-treated mice exhibited a significantly lower CCM burden, including the number of ballooned capillaries (stage 1) and multicavernous lesions (stage 2), and the areas of stage 2 lesions per animal, as compared to 15 placebo mice. Infiltrated B cells in CCM3+/-Trp53-/- CCM lesions were also depleted. Conclusions: This represented the first report of therapeutic benefit of B- cell depletion therapy in the development and progression of CCMs and provide proof of principle that B cells is a critical step in CCM lesion genesis and maturation.