A chimeric protein consisting of the Fv portion of a monoclonal antibody attached to a fragment of Pseudomonas exotoxin A without its cell-binding region. LMB-1 immunotoxin targets B3, a Lewis Y-related carbohydrate epitope found on some solid tumors. The antibody attaches to the tumor cell and the exotoxin stops protein synthesis by inactivating elongation factor 2. orA toxic substance linked to an antibody that attaches to tumor cells and kills them.