Ki-4(scFv)-ETA ', a new recombinant anti-CD30 immunotoxin with highly specific cytotoxic activity against disseminated Hodgkin tumors in SCID mice

The human lymphocyte activation marker CD30 is highly overexpressed on Hodg kin/Reed-Sternberg cells and represents an ideal target for selective immun otherapy. We used the murine anti CD30 hybridoma Ki-4 to construct a new re combinant immunotoxin (rlT) for possible clinical use in patients with CD30 (+) lymphoma. Hybridoma V genes were polymerase chain reaction-amplified, a ssembled, cloned, and expressed as a mini-library for display on filamentou s phage, Functional Ki-4 scFv obtained by selection of binding phage on the CD30-expressing Hodgkin lymphoma cell line L540cy was inserted into the ba cterial expression vector pBM1.1 and fused to a deletion mutant of Pseudomo nas exotoxin A (ETA'), Periplasmically expressed Ki-4(scFv)-ETA' demonstrat ed specific activity against a variety of CD30(+) lymphoma cells as assesse d by different in vitro assays. To evaluate in vivo antitumor activity, sev ere combined immunodeficient mice challenged with human lymphoma cell lines were treated with the immunotoxin. The blood distribution time t(1/4)alpha of Ki-4(scFv)-ETA' was 19 minutes, and its serum elimination time t(1/2)al pha was 193 minutes. A single intravenous injection of 40 mu g rlT 1 day af ter tumor inoculation rendered 90% of the mice tumor free, extending the me an survival time to more than 200 days compared with 38.1 days in the phosp hate-buffered saline control group (P < .001), This new rlT is a promising candidate for further clinical evaluation in patients with Hodgkin lymphoma or other CD3(+) malignancies. (C) 2000 by The American Society of Hematolo gy.