The recombinant immunotoxin anti-Tac(Fv)-Pseudomonas exotoxin 40 is cytotoxic toward peripheral blood malignant cells from patients with adult T-cell leukemia.
Anti-Tac(Fv)-PE40 is a recombinant single-chain immunotoxin containing the heavy and light variable regions of the anti-Tac monoclonal antibody fused to a mutant form of Pseudomonas exotoxin (PE). Anti-Tac binds to the p55 subunit of the human interleukin 2 (IL-2) receptor, and anti-Tac(Fv)-PE40 kills human or monkey cell lines that contain either the intact IL-2 receptor or its p55 subunit alone. To assess the usefulness of anti-Tac(Fv)-PE40 in treatment of IL-2 receptor-positive leukemia, we tested peripheral blood mononuclear cells from six patients with adult T-cell leukemia. In each of the six patients, anti-Tac(Fv)-PE40 was extremely cytotoxic to the malignant cells. Metabolic activity and sensitivity of the fresh cells improved when a small amount of IL-2 (10 units per ml) was present during incubation. The toxin concentration necessary to inhibit protein synthesis by 50% after 16-hr incubation of cells with immunotoxin varied from 1.6 to 16 ng/ml (2.5-25 x 10(-11) M). In every case, binding was by means of the Tac antigen because anti-Tac(Fv)-PE40 cytotoxicity was prevented by adding excess anti-Tac antibody. Moreover, anti-Tac alone or an inactive mutant of anti-Tac(Fv)-PE40 without ADP-ribosylation activity had very little cytotoxic activity. Peripheral blood mononuclear cells from normal controls, from a patient with Tac-negative leukemia, and from adult T-cell leukemia patients without significant peripheral blood involvement were not sensitive to anti-Tac(Fv)-PE40. These results indicate that anti-Tac(Fv)-PE40 is a potent cytotoxin against adult T-cell leukemia cells in vitro and warrants clinical testing.
Kreitman
R J
RJ
Laboratory of Molecular Biology, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892.
Chaudhary
V K
VK
Waldmann
T
T
Willingham
M C
MC
FitzGerald
D J
DJ
Pastan
I
I
D036002:ADP Ribose Transferases; D000911:Antibodies, Monoclonal; D015703:Antigens, CD / Q000032:analysis; D001427:Bacterial Toxins; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects*; D005098:Exotoxins / Q000494:pharmacology*; D005260:Female; D006801:Humans; D007135:Immunoglobulin Variable Region; D000922:Immunotoxins / Q000494:pharmacology*; D015458:Leukemia, T-Cell / Q000097:blood* / Q000276:immunology; D015459:Leukemia-Lymphoma, Adult T-Cell / Q000097:blood* / Q000276:immunology; D007963:Leukocytes, Mononuclear / Q000187:drug effects* / Q000473:pathology; D008297:Male; D011549:Pseudomonas; D014407:Tumor Cells, Cultured / Q000166:cytology* / Q000187:drug effects; D037521:Virulence Factors; D000097668:Pseudomonas aeruginosa Exotoxin A
D036002:ADP Ribose Transferases; D000911:Antibodies, Monoclonal; D015703:Antigens, CD; D001427:Bacterial Toxins; D005098:Exotoxins; D007135:Immunoglobulin Variable Region; D000922:Immunotoxins; D037521:Virulence Factors; D000097668:Pseudomonas aeruginosa Exotoxin A