Pediatric acute myelogenous leukemia cells express IL-6 receptors and are sensitive to a recombinant IL6-Pseudomonas exotoxin.
We have studied IL-6 receptor (IL-6R) expression on AML cells from 15 pediatric patients by immunocytochemistry/flow cytometry, reverse-transcription polymerase chain reaction, and Scatchard analysis. High-affinity IL-6R were detected on leukemic cells from 12 (80%) patients. Binding sites per cell ranged from 140 to 3580 (median 920; mean 1240), with dissociation constants of 0.26 to 0.71 nM. We therefore assessed the in vitro sensitivity of IL-6R+ AML cells to treatment with a recombinant IL6-Pseudomonas exotoxin fusion protein (IL6-PE4E), using the XTT cytotoxicity assay. Leukemic cells from eight patients had ID50 values (concentration of IL6-PE4E producing a 50% decrease in cell viability) of <1000 ng/ml (median, 87 ng/ml; mean, 262 ng/ml). Sensitivity to IL6-PE4E correlated significantly with receptor number. Normal bone marrow mononuclear cells had undetectable IL6-R expression (<20 receptors/cell) and were relatively resistant to IL6-PE4E. To test the efficacy of IL6-PE4E for ex vivo purging in an autologous stem cell transplantation setting, we incubated primary IL-6R+ AML cells with 10(3) ng/ml IL6-PE4E for 24 h, followed by inoculation into SCID mice. Mice receiving treated cells showed no leukemic engraftment, while all mice receiving untreated or control-treated cells developed leukemia with a median presymptomatic interval of 55 days. In recipients of IL6-PE4E treated cells, no evidence of occult leukemia was detected by PCR analysis of blood and bone marrow cells at 185 days postinoculation. These data suggest that IL-6R are expressed on leukemic cells from a substantial percentage of pediatric AML patients. Furthermore, leukemic cells expressing high numbers of IL6-R may be sensitive to IL6-PE4E in an ex vivo purging protocol.
Boayue
K B
KB
Department of Pediatrics, Emory University School of Medicine, Atlanta, GA 30322, USA.
Gu
L
L
Yeager
A M
AM
Kreitman
R J
RJ
Findley
H W
HW
D036002:ADP Ribose Transferases; D000293:Adolescent; D000818:Animals; D001427:Bacterial Toxins; D016465:Bone Marrow Purging; D002648:Child; D002675:Child, Preschool; D005098:Exotoxins / Q000494:pharmacology*; D005260:Female; D005434:Flow Cytometry; D006085:Graft Survival / Q000187:drug effects; D006801:Humans; D007150:Immunohistochemistry; D007223:Infant; D015850:Interleukin-6 / Q000494:pharmacology*; D007700:Kinetics; D015470:Leukemia, Myeloid, Acute / Q000188:drug therapy* / Q000473:pathology*; D008297:Male; D051379:Mice; D016513:Mice, SCID; D009368:Neoplasm Transplantation; D019947:Receptors, Interleukin-6 / Q000096:biosynthesis* / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000494:pharmacology*; D012680:Sensitivity and Specificity; D037521:Virulence Factors; D000097668:Pseudomonas aeruginosa Exotoxin A
D036002:ADP Ribose Transferases; D001427:Bacterial Toxins; D005098:Exotoxins; D015850:Interleukin-6; D019947:Receptors, Interleukin-6; D011993:Recombinant Fusion Proteins; D037521:Virulence Factors; D000097668:Pseudomonas aeruginosa Exotoxin A; C064195:IL-6-PE40 protein, chimeric