Abstract W MP118: In Situ B-cell Clonal Expansion and Recombinant Antibody Construction in Human Cerebral Cavernous Malformation

Background: We had demonstrated immunocompetent cell infiltration and oligoclonal immune response in human cerebral cavernous malformation (CCM) lesions. However, T- and B- cell crosstalk, relationship between antibody and complement, and IgG repertoire in CCMs remain unknown. We hypothesize the synergetic role of T and B cells, antibody- and complement- mediated cytotoxicity, antigen-driven B cell clonal expansion, contributing to the CCM pathogenesis. Methods: This study enrolled a total of 10 patients with CCMs. B- and T- cells were immunostained in two excised human CCM lesion specimens. IgG and complement protein membrane attack complex (MAC) was co-localized in six other CCM lesions by immunofluorescence. Plasma cells in two CCM lesions were laser-microdissected, in which IgG heavy (H) and light (L) chain variable (V) region were amplified via nested PCR, cloned, sequenced, and aligned to a database IMGT®. The over-expressed IgGHV and IgGLV were used to construct the recombinant antibodies (r-abs). Results: In CCM lesions, T- and B- cells were clustered and co-localized, and plasma cells were clustered. IgG and MAC was co-localized in CCMs. IgG repertoire showed in situ B cell clonal expansion and ongoing somatic mutation. Four r-abs were constructed from clonally expanded plasma cells in CCM lesions. Conclusions: we showed the role of immunity in CCM pathogenesis via T- and B- cell crosstalk, antibody- and complement- mediated cytotoxicity, and clonal expansion. We gave the first demonstration that oligoclonal response is antigen-driven. The first synthesized r-abs will be used to identify disease relevant antigens. This would clarify the relationship of immune response to CCM lesion development, and may open novel therapeutic venues in CCMs.