Identification of Autoantibody Producing Plasma Cells in the CSF of Autoimmune Encephalitis (AIE) Patients (P6.132)

OBJECTIVE: To characterize the intrathecal plasma cell repertoire of patients with autoimmune encephalitis (AIE) syndromes, identify autoantibody producing plasma cell clones and produce their antibody signatures in recombinant form. BACKGROUND: AIE syndromes are characterized by autoantibody signatures specific for antigens at pre- or post-synaptic sites of the neuronal membrane. Passive transfer experiments of pooled cerebrospinal fluid (CSF) imply their pathogenic relevance. Yet, patients9 CSF is heterogeneous, impairing a conclusive characterization. DESIGN/METHODS: RT-PCR of expressed immunoglobulin (Ig) gene transcripts of single FACS sorted CSF plasma cells; sequence analysis and identification of expanded plasma cell clones (cePc); expression of paired Ig-genes of cePc as recombinant antibodies; analysis of the antigen specificity of the resulting human monoclonal antibodies. RESULTS: We analyzed the intrathecal plasma cell repertoire of AIE patients with a variety of antibody signatures. After FACS sorting of individual CD138+ CSF plasma cells, single cell RT-PCR of expressed Ig genes revealed a skewed VH usage. In all patients, clonally expanded plasma cells (cePc) were identified, many of which contained strongly hypermutated Ig genes. Sofar, we cloned and expressed matched Ig heavy and light chain genes from cePc of AIE patients with antibody signatures specific for GAD, NMDA-R, Lgi1 and CASPR2 as recombinant human monoclonal antibodies (rhuMAb). Specificities of rhuMAb were identified by Euroimmun and confirmed by IHC and / or immunoprecipitation. The characterization of their functional properties is ongoing. CONCLUSIONS: Single cell RT-PCR analysis of the intrathecal plasma cell repertoire of AIE patients indicates an ongoing antigen driven humoral immune response in the CSF compartment. We have cloned autoantibodies from AIE patients9 CSF plasma cells and expressed them as recombinant human mAbs, which may facilitate the further characterization of their epitope specificity and pathogenic role. Study Supported by: BMFT, Walter-and-Ilse-Rose Stiftung, Forschungskommission of the Heinrich-Heine-University Duesseldorf, Germany. Disclosure: Dr. Goebels has received personal compensation for activities with Biogen Idec, Genzyme, and Novartis. Dr. Malviya has nothing to disclose. Dr. Barman has nothing to disclose. Dr. Melzer has nothing to disclose. Dr. Elger has received personal compensation from UCB, Novartis, Desitin, and Eisai. Dr. Wiendl has received research support from Bayer HealthCare, Biogen Idec, the German Ministry for Education and Research, Deutsche Forschungsgesellschaft, and the Else Kroner Fresenius Foundation. Dr. Hartung has received personal compensation for activities with from Bayer, Biogen, GeNeuro, Genzyme as speaker, committee member, consultant.