Human leukemia cell binding and killing by anti-CD5 radioimmunotoxins

Donald J. Buchsbaum, Lezlie A. Nelson, David E. Hanna, Daniel A. Vallera

Research output: Contribution to journalArticlepeer-review

2 Scopus citations


We have synthesized a reagent for antibody directed cell targeting composed of the monoclonal antibody (MoAb) T101 linked to the potent toxin ricin. The immunotoxin (IT) was subsequently radiolabeled by a cyclic anhydride procedure with 90Yttrium (90Y) to construct a radioimmunotoxin (RIT) that may have potential for cancer therapy. We evaluated the reagent for selectivity in binding and protein synthesis inhibition (PSI) assays. The RIT selectively bound antigen positive leukemia T-cell lines, with minimal binding to antigen negative control lines. The IT inhibited 87% or greater protein synthesis activity at 1 μg ml and exhibited an IC50 (the dose inhibiting 50% activity) of 0.18 ± 0.08 μg ml in the presence of lactose. RIT and nonlabeled IT showed comparable degrees of PSI at 1 μg ml and 10 μg ml, suggesting that labeling had little overall effect on the activity of the immunoconjugate. However, indirect evidence showed that the galactose binding site of ricin was inhibited 10-fold by its exposure to 90Y. Control RIT were minimally inhibitory. IT labeled with 131Iodine (131I) by an iodine monochloride technique also retained its capability to selectively inhibit protein synthesis. When RIT were tested for potency in a clonogenic assay against human leukemia T-cell lines, they inhibited 3.61 logs of tumor cell growth at μg mlml. This did not represent an improvement over the log elimination with radiolabeled antibody alone, which showed 4.19 log elimination of tumor cells. Our observation that the 90Y-labeled RIT and labeled antibody can selectively eliminate about four logs of tumor cells in an in vitro clonogenic assay is unique. The ability of RIT to kill several logs of tumor cells in vitro renders RIT interesting anti-tumor reagents.

Original languageEnglish (US)
Pages (from-to)1701-1712
Number of pages12
JournalInternational Journal of Radiation Oncology, Biology, Physics
Issue number11
StatePublished - Nov 1987

Bibliographical note

Funding Information:
This work was supported in part by National Cancer Institute grants CA-43368, CA-3 16 18, CA-36725, and grants from the Minnesota Medical Foundation and the Medical Research Foundation, Inc., Atlanta, GA. Dr. Vallera is a Scholar of the Leukemia Society of America. Center for Experimental Transplantation and Cancer Research manuscript no 32. Presented at the Proceedings of the American Society for Therapeutic Radiology and Oncology 28th Annual Meeting, November 7, 1986, Los Angeles, CA. Reprint requests to: Donald J. Buchsbaum, Ph.D., The University of Michigan Medical Center, Department of Radiation


  • Antibodies
  • Cancer therapy
  • Immunoconjugates
  • Immunotoxins
  • Iodine monoclonal antibodies
  • Isotopes
  • Leukemia
  • Monoclonal antibodies
  • Protein labeling
  • Radioimmunotherapy
  • Radioimmunotoxin
  • Radioisotope
  • Radiolabeled antibodies
  • Ricin
  • Therapy
  • Yttrium monoclonal antibodies


Dive into the research topics of 'Human leukemia cell binding and killing by anti-CD5 radioimmunotoxins'. Together they form a unique fingerprint.

Cite this