Evaluation of four CD22 antibodies as ricin A chain-containing immunotoxins for the in vivo therapy of human B-cell leukemias and lymphomas.
Ricin A chain-containing immunotoxins (IT-As) specific for the human B-cell antigen, CD22, were prepared from 4 monoclonal antibodies (MAbs) or their Fab' fragments: RFB4, HD6, UV22-I and UV22-2. The ITs were tested for their ability to kill cells from the Burkitt lymphoma line, Daudi, the pre-B-cell leukemia line, NALM-6, and the myeloma cell line, ARH-77. Daudi expresses high levels of CD22, whereas NALM-6 and ARH-77 express low levels of CD22. The IgG-RFB4-A was highly toxic to all 3 cell lines; it killed 50% of the Daudi cells at a concentration of 1.2 x 10(-12) M and 50% of NALM-6 and ARH-77 cells at concentrations of 1.5 to 2.1 x 10(-11) M. IgG-RFB4-A was 10-30 times more toxic to Daudi cells than were the IgG-As constructed from the other 3 CD22 MAbs and 10 times more toxic than ricin itself. IT-As constructed from the Fab' fragments of the 4 CD22 antibodies were 2 to 5 times less toxic to Daudi cells than their IgG-A counterparts. Fab'-RFB4-A was twice as toxic to Daudi cells as ricin, whereas the other Fab'-As were about 7 times less toxic than ricin. Scatchard analyses of the binding of the radio-iodinated antibodies to Daudi cells showed that the intact RFB4 antibody bound 3-10 times more strongly than the other antibodies, whereas the Fab'-RFB4 bound 1.2 to 3.5 times more strongly than the Fab' fragments prepared from the other antibodies. Thus, the potent cytotoxic activity of the RFB4-As appears to derive, in part, from their superior binding affinity. Prior studies have shown that UV22-I and HD6 cross-react with certain normal human tissues lacking cells of B-cell lineage, whereas UV22-2 and RFB4 are B-cell-specific. This fact, together with its superior potency as an IT-A, suggests that RFB4 is the antibody of choice for preparing Fab'-As or IgG-As for in vivo therapy of human B-cell leukemias and lymphomas.
Shen
G L
GL
Department of Microbiology, University of Texas Southwestern Medical Center, Dallas 75235.
Li
J L
JL
Ghetie
M A
MA
Ghetie
V
V
May
R D
RD
Till
M
M
Brown
A N
AN
Relf
M
M
Knowles
P
P
Uhr
J W
JW
D000818:Animals; D000906:Antibodies; D015703:Antigens, CD; D000944:Antigens, Differentiation, B-Lymphocyte / Q000276:immunology*; D015815:Cell Adhesion Molecules; D002460:Cell Line; D006801:Humans; D007140:Immunoglobulin Fab Fragments / Q000378:metabolism; D000922:Immunotoxins / Q000627:therapeutic use*; D037102:Lectins; D015448:Leukemia, B-Cell / Q000628:therapy*; D008223:Lymphoma / Q000628:therapy*; D051379:Mice; D012276:Ricin / Q000276:immunology*; D051918:Sialic Acid Binding Ig-like Lectin 2
D000906:Antibodies; D015703:Antigens, CD; D000944:Antigens, Differentiation, B-Lymphocyte; C497867:CD22 protein, human; C497868:Cd22 protein, mouse; D015815:Cell Adhesion Molecules; D007140:Immunoglobulin Fab Fragments; D000922:Immunotoxins; D037102:Lectins; D051918:Sialic Acid Binding Ig-like Lectin 2; D012276:Ricin