Cytotoxicity of anti-CD64-ricin a chain immunotoxin against human acute myeloid leukemia cells in vitro and in SCID mice.
Blast cells from patients with acute myeloid leukemia (AML) commonly express CD64, the high-affinity receptor for immunoglobulin G (FcgammaRI). An immunotoxin (MDX-44) was constructed by coupling humanized anti-CD64 monoclonal antibody (mAb) H22 via a bivalent linker to deglycosylated ricin A-chain (RA). Human leukemia cell lines were incubated with MDX-44 or H22/free RA. The effect of MDX-44 on the proliferation of leukemia cells was assessed by [(3)H]thymidine incorporation. In the presence of interferon-gamma (IFN-gamma), MDX-44 significantly inhibited the proliferation of CD64(+) HL-60, NB4, and U937 cells in 72-h cultures in a dose-dependent manner. The mechanism of action appeared to be the induction of apoptosis, as measured by propidium iodide staining and flow cytometry analysis. However, CD64(-) KG-1a and Daudi cells were not affected by MDX-44/IFN-gamma. Incubating HL-60 cells with MDX-44/IFN-gamma resulted in a 99% decrease in colony-forming units, whereas colony-forming cells in normal bone marrow were not significantly suppressed by such treatment. Cells from 60% of AML patients (6/10) were inhibited by MDX-44/IFN-gamma, and the inhibition was correlated with CD64 expression on these cells (r = 0.65). In a human AML model in NOD/SCID mice, MDX-44/IFN-gamma inhibited 95-98% of peritoneal exudate AML cell proliferation and 85-90% of solid leukemia masses. The effect of MDX-44 on AML cells was dependent on activation of cells by IFN-gamma. MDX-44/IFN-gamma may have value in the therapy of AML cells expressing cell-surface CD64.
Department of Medicine, and the Cancer Center, University of California, San Diego, La Jolla, CA 92093, USA.
R K
RK
Zhong
J G
JG
van de Winkel
T
T
Thepen
L D
LD
Schultz
E D
ED
Ball
D000208:Acute Disease; D000328:Adult; D000818:Animals; D000911:Antibodies, Monoclonal / Q000627:therapeutic use; D016022:Case-Control Studies; D002470:Cell Survival / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D005260:Female; D018922:HL-60 Cells / Q000637:transplantation; D006801:Humans; D000922:Immunotoxins / Q000627:therapeutic use*; D007371:Interferon-gamma / Q000494:pharmacology; D007951:Leukemia, Myeloid / Q000188:drug therapy* / Q000473:pathology; D008297:Male; D051379:Mice; D016513:Mice, SCID; D017452:Receptors, IgG / Q000276:immunology*; D012276:Ricin / Q000627:therapeutic use*; D013234:Stem Cells / Q000187:drug effects; D014407:Tumor Cells, Cultured / Q000187:drug effects
D000911:Antibodies, Monoclonal; D000922:Immunotoxins; D017452:Receptors, IgG; D007371:Interferon-gamma; D012276:Ricin