DEVELOPMENT OF NEW RICIN A-CHAIN IMMUNOTOXINS WITH POTENT ANTITUMOR EFFECTS AGAINST HUMAN HODGKIN CELLS IN-VITRO AND DISSEMINATED HODGKIN TUMORS IN SCID MICE USING HIGH-AFFINITY MONOCLONAL-ANTIBODIES DIRECTED AGAINST THE CD30 ANTIGEN

The lymphocyte activation marker CD30 has been shown to be an excellen t target for the immunotherapy of human Hodgkin's lymphoma. In order t o develop new potent immunotoxins (ITs) against CD30, we chemically li nked 6 recently described monoclonal antibodies (MAbs) via SMPT to deg lycosylated ricin A-chain (dgA). Cross-blocking experiments demonstrat ed that these MAbs, termed Ki-2 to Ki-7, recognize 3 different cluster s on the CD30 antigen: Ki-2, Ki-4, Ki-5 and Ki-7 recognize cluster A; Ki-6 recognizes cluster B; Ki-3 binds to cluster C. Staining of 29 sec tions of normal human organs revealed no major cross-reactivity of any MAbs tested. Binding to the CD30 antigen on L540Cy Hodgkin cells was assessed by how cytometry, and demonstrated high affinities for Ki-2, Ki-3 and Ki-4. The concentration giving 50% of the mean fluorescence i ntensity (MFI(50)) was 0.58 mu g/ml to 0.78 mu g/ml. MAbs Ki-5, Ki-6, and Ki-7 bound much more weakly. The staining intensity of the MAbs co rrelated with the cytotoxicity of the corresponding ITs. Ki-2.dgA, Ki- 3.dgA and Ki-4.dgA inhibited the protein synthesis of L540Cy cells by 50% at concentrations (IC50) of 3.5 x 10(-10) M to 4.0 x 10(-11) M. Th e most effective IT, Ki-4.dgA, is 5-fold more potent than previously r eported CD30 ricin A-chain ITs. Ki-4.dgA was subsequently used for the treatment of disseminated human Hodgkin's lymphoma in a SCID mouse mo del. The mean survival time (MST) of lymphoma-bearing SCID mice was ex tended from 42 days in untreated controls to more than 132 days when K i-4.dgA was applied one day after tumor challenge. Ki-4.dgA is a new p otent IT suitable for further evaluation against Hodgkin's lymphoma in man. (C) 1995 Wiley-Liss, Inc.