Shedding of the soluble form of CD30 from the Hodgkin-analogous cell line L540 is strongly inhibited by a new CD30-specific antibody (Ki-4).

The CD30-activation marker was detected as the Hodgkin-associated Ki-I antigen and is regarded as a target for the treatment of Hodgkin patients with immunotoxins. The CD30 is released from tumor cells and this soluble CD30 (sCD30) is an indicator of the disease activity. Since the shedding of sCD30 may be influenced by antibodies, we produced 6 new CD30-specific antibodies (Ki-2 to Ki-7) for the purpose of finding antibodies that might inhibit the formation of sCD30. Ki-2 to Ki-7 and the other anti-CD30 antibodies Ki-I, Ber-H2, HeFi-I, M44, M67, HRS-I, HRS-4 and C10 were employed for epitope mapping. The binding of a particular radio-labeled anti-CD30 antibody to Hodgkin's-disease-derived L540 cells was completed by addition of the various non-labeled anti-CD30 antibodies. Three non-overlapping regions, expressing different antigen-specific determinants, could be defined on the extracellular part of the CD30 molecule. Cluster A of determinants was recognized by Ki-2, Ki-4, Ki-6 and Ki-7, Ber-H2, HRS-I and HRS-4, while cluster B was detected by Ki-I, Ki-5 and M67. Cluster C, which probably contains the binding site for the CD30 ligand, was defined by Ki-3, M44, HeFi-I and C10. Co-culture experiments of L540 cells with the various antibodies followed by the isolation of sCD30 from culture supernatant fluids revealed that the release of sCD30 was most strongly increased by Ki-I and weakly enhanced by Ki-2, Ki-3, Ki-5 and HeFi-I, whereas it was almost completely inhibited by Ki-4 and to a slightly lesser extent by Ber-H2.