title: Inhibition of human B-cell lymphoma by an anti-CD20 antibody and its chimeric F(ab')2 fragment via induction of apoptosis.
abstract: Monoclonal antibodies (mAb) directed against CD20, either unmodified or in radiolabeled forms, have been successfully used in clinic as effective therapeutic agents in the management of non-Hodgkin's B-cell lymphoma. Despite all clinical success the exact mechanisms of action of various anti-CD20 antibodies remains mostly unclear. Several mechanisms have been proposed to be responsible for the therapeutic activity of anti-CD20 antibodies, including antibody-dependent cell-mediated cytotoxicity, complement-mediated cytotoxicity, and direct inhibition of tumor growth via induction of apoptosis. We previously produced an anti-CD20 mAb, HI47, and showed that the antibody effectively blocked human B-cell proliferation in vitro and inhibited xenografted B-cell lymphoma in nude mice. In this study, we engineered the chimeric versions of both the Fab and F(ab)'2 fragments of HI47 and produced the fragments in E. coli. Both fragments competed efficiently with HI47 for binding to CD20+ B cells, and inhibited proliferation of B-lymphoma cells in a dose-dependent manner. Mechanistic studies revealed that both antibody fragments induced significant degree of B-cell apoptosis that is independent of any cross-linking agents. Further, both the F(ab)'2 and Fab fragments when administered in vivo significantly inhibited the growth of human B-cell lymphoma xenografts in nude mice. The bivalent F(ab)'2 fragment showed consistently better efficacy compared to its monovalent Fab counterpart in inducing apoptosis and inhibiting B-cell lymphoma growth both in vitro and in vivo. Taken together, these observations suggest that HI47 and its fragments most likely exert their antitumor activity through induction of cell apoptosis, and cross-linking/dimerization of CD20 molecules on B- cell surface is an important, but not essential, process for therapeutic efficacy of HI47 and its fragments.
authors.affiliation: State Key Laboratory of Experimental Hematology, Institute of Hematology, Chinese Academy of Medical Sciences, 288 Nanjing Road, Tianjin 300020, China.
authors.forename: Yinxing
authors.initials: Y
authors.lastname: Liu
authors.forename: Mengjie
authors.initials: M
authors.lastname: Zheng
authors.forename: Zengzu
authors.initials: Z
authors.lastname: Lai
authors.forename: Dongsheng
authors.initials: D
authors.lastname: Xiong
authors.forename: Dongmei
authors.initials: D
authors.lastname: Fan
authors.forename: Yuanfu
authors.initials: Y
authors.lastname: Xu
authors.forename: Hui
authors.initials: H
authors.lastname: Peng
authors.forename: Xiaofeng
authors.initials: X
authors.lastname: Shao
authors.forename: Yuansheng
authors.initials: Y
authors.lastname: Xu
authors.forename: Ming
authors.initials: M
authors.lastname: Yang
authors.forename: Jinhong
authors.initials: J
authors.lastname: Wang
authors.forename: Hanzhi
authors.initials: H
authors.lastname: Liu
authors.forename: Yong
authors.initials: Y
authors.lastname: Xie
authors.forename: Chunzheng
authors.initials: C
authors.lastname: Yang
authors.forename: Zhenping
authors.initials: Z
authors.lastname: Zhu
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000627:therapeutic use*; D018951:Antigens, CD20 / Q000276:immunology / Q000502:physiology*; D017209:Apoptosis; D002455:Cell Division; D005260:Female; D006801:Humans; D007140:Immunoglobulin Fab Fragments / Q000627:therapeutic use*; D016393:Lymphoma, B-Cell / Q000517:prevention & control*; D051379:Mice; D008807:Mice, Inbred BALB C; D009368:Neoplasm Transplantation; D011993:Recombinant Fusion Proteins / Q000627:therapeutic use*; D014183:Transplantation, Heterologous
chemical_list: D000911:Antibodies, Monoclonal; D018951:Antigens, CD20; D007140:Immunoglobulin Fab Fragments; D011993:Recombinant Fusion Proteins