A novel anti-prion protein monoclonal antibody and its single-chain fragment variable derivative with ability to inhibit abnormal prion protein accumulation in cultured cells.

mAbs T1 and T2 were established by immunizing PrP gene ablated mice with recombinant MoPrP of residues 121-231. Both mAbs were cross-reactive with PrP from hamster, sheep, cattle and deer. A linear epitope of mAb T1 was identified at residues 137-143 of MoPrP and buried in PrP(C) expressed on the cell surface. mAb T1 showed no inhibitory effect on accumulation of PrP(Sc) in cultured scrapie-infected neuroblastoma (ScN2a) cells. In contrast, mAb T2 recognized a discontinuous epitope ranged on, or structured by, residues 132-217 and this epitope was exposed on the cell surface PrP(C). mAb T2 showed an excellent inhibitory effect on PrP(Sc) accumulation in vitro at a 50% inhibitory concentration of 0.02 microg/ml (0.14 nM). The scFv form of mAb T2 (scFv T2) was secreted in neuroblastoma (N2a58) cell cultures by transfection through eukaryotic secretion vector. Coculturing of ScN2a cells with scFv T2-producing N2a58 cells induced a clear inhibitory effect on PrP(Sc) accumulation, suggesting that scFv T2 could potentially be an immunotherapeutic tool for prion diseases by inhibition of PrP(Sc) accumulation.