C5 and B-cell non-Hodgkin lymphoma: Thus, in the present study, we aimed to generate a new class of therapeutics based on a recombinant single-domain antibody (sdAb) immunotoxin derived from the PE38 Pseudomonas aeruginosa exotoxin A. For this purpose, we fused the PE38 toxin with the specific C5 sdAb antibody, previously developed by our group for canine B-cell lymphoma.