Three new monoclonal antibodies that define a unique antigen associated with prolymphocytic leukemia/non-Hodgkin's lymphoma and are effectively internalized after binding to the cell surface antigen.
Prolymphocytic leukemia (PLL) is closely related to chronic lymphocytic leukemia (CLL), but present with distinctive clinical/laboratory features and associated with much worse prognosis. In this study, we generated three new IgG1-kappa monoclonal antibodies (MoAbs), termed SN8, SN8a and SN8b, by use of an unconventional approach, ie, by using an isolated B PLL antigen preparation to immunize mice. These MoAbs, particularly SN8, showed a highly selective reactivity to B PLL and B non-Hodgkin's lymphoma (NHL) among various human leukemia-lymphoma specimens tested; eg, SN8 was capable of effectively distinguishing B PLL from B CLL as well as from hairy cell leukemia (HCL) cell specimens. The cell surface antigen defined by the three MoAbs was determined to be a covalently linked heterodimeric glycoprotein complex (gp49/40) consisting of a 49,000 dalton (alpha-chain) and a 40,000-dalton component (beta-chain). Epitope comparison showed that the epitope defined by SN8 (SN8 epitope) is in close proximity to SN8a epitope but in a distant position from SN8b epitope. Western blot analysis showed that both SN8 and SN8a epitopes are on the beta-chain, but SN8b epitope was not detected on either the alpha- or the beta-chain of the reduced antigen in the same analysis. Binding of either SN8 or SN8b to the cell surface gp49/40 did not cause significant downregulation of the antigen expression whereas binding of SN8a to the antigen caused small (approximately 20%) decrease in the antigen expression. Among the various normal peripheral blood cells, only a subpopulation (6.0% to 24.2% among different specimens derived from different donors) of B cells reacted with the SN8 series MoAbs; these MoAbs showed no significant reactivity against T cells, granulocytes, monocytes, erythrocytes, and platelets. Minimal or no significant reactivity (0 to 2.6% among different specimens) was detected against normal bone marrow cells. Ricin A-chain conjugates of the three MoAbs are all strongly effective for specific killing of SN8 antigen-expressing leukemia cells in the absence of any potentiators; furthermore, the addition of 10 mmol/L NH4Cl, a potentiator, enhanced strongly the cytotoxic activities of the SN8, SN8a, and SN8b conjugates. Thus, each of the three MoAbs was effectively internalized after binding to the cell surface antigen.
Okazaki
M
M
Department of Molecular Immunology, Roswell Park Cancer Institute, Buffalo, NY 14263.
Luo
Y
Y
Han
T
T
Yoshida
M
M
Seon
B K
BK
D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology / Q000378:metabolism*; D000915:Antibody Affinity; D000918:Antibody Specificity; D000951:Antigens, Neoplasm / Q000032:analysis* / Q000276:immunology; D001402:B-Lymphocytes / Q000276:immunology; D001667:Binding, Competitive; D015153:Blotting, Western; D003937:Diagnosis, Differential; D006801:Humans; D006825:Hybridomas / Q000276:immunology; D007163:Immunosorbent Techniques; D007938:Leukemia / Q000276:immunology; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000276:immunology; D015463:Leukemia, Prolymphocytic / Q000175:diagnosis / Q000276:immunology*; D008223:Lymphoma / Q000276:immunology; D008228:Lymphoma, Non-Hodgkin / Q000175:diagnosis / Q000276:immunology*; D051379:Mice; D014407:Tumor Cells, Cultured
D000911:Antibodies, Monoclonal; D000951:Antigens, Neoplasm