P2-212: Suppression of PrP Sc replication in follicular dendritic cells in vitro and in vivo by therapeutic 6D11 monoclonal antibody

Abstract

Prionoses are invariably fatal, transmissible neurodegenerative diseases associated with a conformational transformation of cellular prion protein PrPC into a toxic, infectious, and self-replicating PrPSc conformer. Following peripheral exposure, PrPSc replicates within the lymphatic system for months to years before invading the CNS and producing neurological symptoms. The persistence of PrPSc in the lymphatic system is critically dependent on follicular dendritic cells (FDCs). Therefore, FDCs constitute a primary target for therapeutically effective anti-PrP monoclonal antibodies (Mabs), which could be administered to subjects exposed to prions to effectively delay or prevent neuroinvasion. The main objective of this study was to create a model of peripheral PrPSc replication by infecting FDCs and to investigate the therapeutic effect of anti-PrP Mabs on infected FDCs in vitro and in vivo. The murine FDC-P1 line was infected with 22L mouse adapted scrapie. The effect of 6D11 Mab on PrPSc accumulation in infected FDCs-P1 cells was analyzed by proteinase K (PK) digestion of the cell lysate, SDS-PAGE and Western-blotting. CD-1 mice were intraperitoneally inoculated with 22L strain, and then passively immunized with 6D11 Mab, murine IgG, or vehicle for four or eight weeks. Onset of neurological symptoms in mice was determined by repeated locomotor testing. The content of PrPSc in the spleen and the brain was analyzed by PK digestion and Western-blot in asymptomatic and early symptomatic mice. Mab 6D11 cleared PrPSc from infected FDCs-P1 cells at the concentration of 0.1μg/ml and was also shown to prevent infection when the infection procedure was carried out in the presence of 6D11 Mab. Passive immunization with 6D11 Mab effectively suppressed replication of PrPSc in the spleen and resulted in a 40% extension of the incubation period (p<0.0001). Furthermore, 6D11 treated mice showed a 79% (p<0.0001) reduction of PrPSc content in the brain and a 48.4% (p<0.0001) reduction of spongiform lesions density. Anti-PrP Mab can effectively suppress PrPSc replication in the FDCs cells in vitro and in vivo. Passive immunization with therapeutic anti-PrP Mabs effectively delays neuroinvasion and makes it less effective, resulting in an amelioration of the brain pathology.