A CD19-specific single-chain immunotoxin mediates potent apoptosis of B-lineage leukemic cells.
CD19 is a B-lineage-specific transmembrane signaling protein participating in the control of proliferation and differentiation. It is present at high surface density on chronic B-lymphocytic leukemia (B-CLL) cells and cells of other B-cell malignancies, and is a prime target for therapy with antibody-derived agents. Many attempts have been made to target malignant cells via CD19, but to date none of these agents have received drug approval. Here we report the design of a monovalent immunotoxin consisting of a CD19-specific single-chain Fv antibody fragment fused to a derivative of Pseudomonas Exotoxin A. This fusion protein induced efficient antigen-restricted apoptosis of several human leukemia- and lymphoma-derived cell lines including Nalm-6, which it eliminated at an effective concentration (EC(50)) of 2.5 nM. The agent displayed synergistic toxicity when used in combination with valproic acid and cyclosporin A in cell-culture assays. It induced apoptosis of primary malignant cells in 12/12 samples from B-CLL patients, including patients responding poorly to fludarabine, and of cells from one pediatric acute lymphoblastic leukemia patient. In NOD/SCID mice transplanted with Nalm-6 cells, the toxin prevented engraftment and significantly prolonged survival of treated mice. Owing to its efficient antigen-restricted antileukemic activity, the agent deserves further development towards clinical testing.
Schwemmlein
M
M
Genetics, University of Erlangen-Nuremberg, Erwin-Rommel-Strasse 3, Erlangen, Germany.
Stieglmaier
J
J
Kellner
C
C
Peipp
M
M
Saul
D
D
Oduncu
F
F
Emmerich
B
B
Stockmeyer
B
B
Lang
P
P
Beck
J D
JD
Fey
G H
GH
D000818:Animals; D018941:Antigens, CD19 / Q000187:drug effects* / Q000276:immunology; D017209:Apoptosis / Q000187:drug effects*; D004353:Drug Evaluation, Preclinical; D004357:Drug Synergism; D005098:Exotoxins; D006801:Humans; D007128:Immunoglobulin Fragments; D000922:Immunotoxins / Q000494:pharmacology* / Q000627:therapeutic use; D015448:Leukemia, B-Cell / Q000188:drug therapy* / Q000473:pathology; D051379:Mice; D016513:Mice, SCID; D009368:Neoplasm Transplantation; D009374:Neoplasms, Experimental / Q000188:drug therapy; D054198:Precursor Cell Lymphoblastic Leukemia-Lymphoma / Q000188:drug therapy* / Q000473:pathology; D011549:Pseudomonas; D011993:Recombinant Fusion Proteins / Q000494:pharmacology / Q000627:therapeutic use; D015996:Survival Rate; D047368:Tumor Burden / Q000187:drug effects; D014407:Tumor Cells, Cultured
D018941:Antigens, CD19; D005098:Exotoxins; D007128:Immunoglobulin Fragments; D000922:Immunotoxins; D011993:Recombinant Fusion Proteins