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.