A single-chain TNF receptor antagonist is an effective inhibitor of TNF mediated cytotoxicity.

Tumour necrosis factor (TNF) is an important mediator of immune and inflammatory responses and has been recognized as a major pathogenic factor in several autoimmune and inflammatory diseases. TNF receptor TR60 plays a critical role in signalling the pathogenic activities of TNF. We here describe molecular cloning and bacterial production of a single-chain antibody (scFv H398) directed against TR60 which possesses antagonistic activity. VH and VL encoding sequences were isolated by PCR from the murine hybridoma cell line H398, cloned into a scFv expression vector and expressed in Escherichia coli. The recombinant antibody (Ab) fragment was found as an active soluble protein in the periplasm but also formed inclusion bodies. Re-folded scFv H398 purified from inclusion bodies was shown to be functional and stable at 37 degrees C with a half-life of 50 h. Comparison of the antigen binding characteristics of scFv with the parental enzymatically produced Fab H398 revealed that both Ab fragments have the same epitope specificity and an identical antigen binding affinity of 1.5 nM. In an in vitro assay it was demonstrated that scFv H398 is an efficient inhibitor of TNF mediated cytotoxicity with an IC50 of 22 nM, which is comparable to the antagonistic activity of natural Fab H398 with an IC50 of 12 nM. As scFv H398 possesses the high affinity TR60 binding and receptor antagonistic activity of the parental Ab H398 but is expected to be less antigenic in man, it provides a valuable tool for the development of novel therapeutic reagents against TNF mediated diseases.