The aim of the presented work was the design, production, and characterisation of a novel immunotoxin in the context of MS. Proteins were expressed in a prokaryotic and eukaryotic system, respectively. Stable producing 293T cell populations were established for the reference protein PLP that showed a good expression yield and a high purity after purification was obtained. This is the first time that a functional PLP fusion protein was expressed in 293T cells and purified from cell supernatant. The characterisation of the immunotoxin PLP-ETA comprised the verification of the functionality of the expressed protein in the context of the binding specifity and toxicity on a PLP- specific hybridoma cell line. This hybridoma cell line that served as a very feasible in vitro B cell model is the first step in the determination of the functionality of an immunotoxin. Documenting a high binding specifity and specific toxicity of this novel PLP based immunotoxin on a PLP- reactive hybridoma cell line, this work provides a contribution to the B cell specific therapies with immunotoxins in MS.