Cytotoxicity Acquired by Conjugation of an Anti‐Thy1.1 Monoclonal Antibody and the Ribosome‐Inactivating Protein, Gelonin

Abstract

Gelonin, a plant protein which can powerfully reduce the protein-synthetic capacity of ribosome preparations, was covalently coupled to anti-Thy_1.1 antibody. The conjugate was prepared using N-succinimidyl-3-(2-pyridyldithio)propionate which generates a disulphide linkage between the component molecules. Two conjugate fractions were obtained with M_r of 180000 and > 200000. After its linkage to the antibody, gelonin suppressed those Thy_1.1-bearing T lymphocytes from AKR mice which will respond to phytohaemagglutinin and concanavalin A in tissue culture. The [³H]leucine incorporation with the T-cell mitogens was inhibited by 50% with the 180000-M_r fraction at a concentration of 0.4 nM and with the > 200000-M_r fraction of pM. Unconjugated gelonin induced comparable reductions in T-cell responsiveness but at concentrations of 30 nM. The conjugates exerted little or no effect upon B lymphocytes or T lymphocytes from CBA mice (Thy_1.2+ve). Two Thy_1.1-expressing AKR lymphoma cell lines, AKR-A and BW5147, were found to be sensitive to the conjugates, albeit much less so than the normal T lymphocytes. The conjugates injected in vivo significantly prolonged the life of CBA mice bearing an AKR-A lymphoma allograft. It is concluded that gelonin can, by its linkage to an antibody, be rendered cytotoxic with a potency to match or exceed those of the toxins abrin and ricin.