The main objective of this work was to compare the general toxicity and immunogenicity of the targeted toxin DARPin-LoPE with the previously created analogous targeted toxin DARPin-PE40, which showed high activity against HER2-positive tumor cells both in vitro and in vivo [12], but contained an immunogenic fragment of PE (aa 252–612, denoted by “PE40”). Here, ERBB2 is linked to neoplasm.