letolizumab letolizumab letolizumab (inn; development code bms-986004) is a humanized monoclonal antibody designed for the treatment of inflammatory diseases. letolizumabmonoclonal antibodytypesingle-chain variable fragmentsourcehumanized (from mouse)targettumor necrosis factor-related activation proteinclinical dataother namesbms-986004atc codenoneidentifierscas number1450981-87-9chemspidernoneunii449mie2sd6keggd11122chemical and physical dataformulac1734h2688n466o538s10molar mass38991.90 g·mol−1 this drug was developed by bristol-myers squibb.