Production of anti-CD3 and anti-CD7 ricin A-immunotoxins for a clinical pilot study

This report describes the preparation of an immunotoxin-combination, consis ting of an anti-CD3 and anti-CD7 monoclonal antibody (MoAb) both conjugated to the A-chain of plant toxin ricin, for the experimental treatment of gra ft-versus-host disease. MoAbs and toxin were conjugated by conventional bio chemical and chromatographic techniques. Raw materials, intermediate and fi nal products were evaluated in accordance with the relevant 'points to cons ider' of the FDA. Yields, purity and sterility of the two final products we re all satisfactory. Preservation of MoAb-affinity and toxin-activity were confirmed in biological assays. The LD50, 25-45 mg immunotoxin-combination/ kg mouse, equalled that of similar immunotoxins already in clinical use. Be cause in vitro cross-reactivity screening revealed an unexpected binding of the CD3-MoAb to the esophagus epithelium, human doses of immunotoxin-combi nation were administered to two cynomolgus monkeys. Clinically relevant ser um concentrations were obtained without irreversible toxicities occurring. The T-1/2 varied between similar to6 and 9 h and the C-max ranged from 1.8 to 3.9 mug/ml. The main side effect was a transient rise of serum creatine kinase. Importantly, neither damage nor binding of the CD3-immunotoxin to t he monkey esophagus epithelium could be demonstrated. It was concluded that sufficient material of proper quality and with an acceptable toxicity prof ile was produced, warranting the evaluation in a clinical pilot-study. (C) 2001 Elsevier Science B.V. All rights reserved.