Four ricin chain A-based immunotoxins directed against the common chronic
lymphocytic leukemia antigen: in vitro characterization
GB Faguet and JF Agee
Cancer Immunology Research Laboratory, Veterans Administration Medical
Center, Augusta, GA 30910.
The common B-chronic lymphocytic leukemia (B-CLL) antigen (cCLLa) appears
to be ideal for targeted immunotherapy in that it is the most prevalent and
disease-restricted marker in B-CLL. To assess this potential, we developed
four immunotoxins (ITs) of anti-cCLLa monoclonal antibody CLL2m (an IgG2a
kappa), using ricin chain A (RTA) or its deglycosylated derivative (dgA),
each conjugated to either the whole IgG molecule or its Fab' fragment. Each
IT was tested in vitro for specificity and cytotoxic activity (assessed by
protein synthesis inhibition [PSI] and by cell kill [CK] in the clonogenic
assay) against B-CLL cells. RTA-based anti-CD5 ITs and enriched normal B
and T lymphocytes were used as controls. Each IT exhibited
antigen-specific, dose-dependent activity. Thus, whereas B-CLL cells
exhibited dose- dependent PSI and CK (whether the B-CLL clone was CD5+ or
CD5-), normal B (cCLLa-/CD5-) and T lymphocytes (cCLLa-/CD5+) remained
unaffected. IT potency was independent of toxin glycosylation, but was
slightly influenced by antibody valence; divalent ITs were twice as potent
as monovalent ITs (IC50, 2.3 v 7.1 x 10(-11) mol/L; CK, 2.6- v 2.0-log
reached with 524 v 1,072 IT molecules bound/cell, respectively). In the
presence of ammonium chloride or Verapamil, IT-induced CK was enhanced 10-
to 80-fold. These data suggest that the cCLLa is a promising target for
IT-based immunotherapy of B-CLL in vivo and ex vivo.
Volume 82,
Issue 2,
pp. 536-543,
07/15/1993
Copyright © 1993 by The American Society of Hematology
