Cytotoxicity of the anti-CD22 immunotoxin HA22 (CAT-8015) against paediatric acute lymphoblastic leukaemia.
Acute lymphoblastic leukaemia (ALL) remains the most frequent cause of cancer-related mortality in paediatrics and outcome is poor for patients who have high-risk ALL or relapse. HA22 (CAT-8015) is an immunotoxin composed of an anti-CD22 variable fragment linked to a 38 kDa truncated protein derived from Pseudomonas exotoxin A. Using a bone marrow mesenchymal cell culture assay to support ALL cell viability, we investigated the in vitro cytotoxicity of HA22 against ALL blasts from newly diagnosed (n = 13) and relapsed patients (n = 22). There was interpatient variability in sensitivity to HA22. Twenty-four of 35 patient samples tested were sensitive (median 50% lethal concentration 3 ng/ml, range 1-80 ng/ml). Blasts from the other 11 patients were not killed by 500 ng/ml HA22. The median 50% lethal concentration was 20 ng/ml for all patients. There was no significant difference in HA22 sensitivity between diagnosis and relapse samples but peripheral blood ALL blasts were more sensitive to HA22 than those from bone marrow (P = 0.008). Thus, HA22, at concentrations achievable in patients, is highly cytotoxic to B-lineage ALL cells. These results provide a strong rationale for clinical testing of this agent in children with drug-resistant ALL and offers the potential to reduce morbidities of treatment while improving outcome.
Laboratory of Molecular Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892-4264, USA.
Francis
F
Mussai
Dario
D
Campana
Deepa
D
Bhojwani
Maryalice
M
Stetler-Stevenson
Seth M
SM
Steinberg
Alan S
AS
Wayne
Ira
I
Pastan
D000293:Adolescent; D000970:Antineoplastic Agents / Q000494:pharmacology*; D018931:Antineoplastic Agents, Hormonal / Q000494:pharmacology; D001427:Bacterial Toxins / Q000494:pharmacology*; D016923:Cell Death / Q000187:drug effects; D002648:Child; D002675:Child, Preschool; D003907:Dexamethasone / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004353:Drug Evaluation, Preclinical; D005098:Exotoxins / Q000494:pharmacology*; D005260:Female; D006801:Humans; D007223:Infant; D007928:Lethal Dose 50; D008297:Male; D054198:Precursor Cell Lymphoblastic Leukemia-Lymphoma / Q000473:pathology*; D051918:Sialic Acid Binding Ig-like Lectin 2 / Q000276:immunology*; D014407:Tumor Cells, Cultured; D055815:Young Adult
D000970:Antineoplastic Agents; D018931:Antineoplastic Agents, Hormonal; D001427:Bacterial Toxins; D005098:Exotoxins; D051918:Sialic Acid Binding Ig-like Lectin 2; C541974:immunotoxin HA22; D003907:Dexamethasone