Selective Killing of Normal and Neoplastic Human B Cells with Anti-CD 19- and Anti-CD22-Ricin A Chain Immunotoxins

Monoclonal antibodies directed against two human B cell-restricted antigens, CD19 and CD22, were conjugated to highly purified ricin A chain. These A chain immunotoxins (A-IT) were specifically cytotoxic to Daudi cells and normal human peripheral blood B cells in vitro. The concentration required for 50% inhibition of protein synthesis (IC₅₀) in these cells ranged from 7.5 x 10^-10 M to 4.2 x 10^-9 M. The specific toxicities of these A-ITs for Daudi cells were augmented 2-to 6-fold in the presence of 20mM NH₄Cl. These studies demonstrate that A-ITs specific for CD19 and CD22 may be useful in the clinical treatment of B cell malignancies.