T cells armed with anti-CD3 x anti-CD20 bispecific antibody enhance killing of CD20+ malignant B cells and bypass complement-mediated rituximab resistance in vitro

Exp Hematol. 2005 Apr;33(4):452-9. doi: 10.1016/j.exphem.2005.01.007.


Objective: Resistance to rituximab, a chimeric monoclonal antibody that binds to CD20, is a major limitation for the successful treatment of patients with non-Hodgkin lymphoma and other CD20+ B-cell malignancies. To circumvent rituximab resistance in these patient populations, we have constructed a bispecific antibody (BiAb), anti-CD3 x anti-CD20 (CD20Bi), that combines rituximab targeting with non-major histocompatibility complex (non-MHC)-restricted cytotoxicity mediated by activated T cells (ATC).

Materials and methods: Activated T cells were obtained from anti-CD3 activated peripheral blood mononuclear cells (PBMC) of normal donors or the leukapheresis products of patients by culturing in the presence of interleukin-2 for 6-14 days. After ATC expansion, the cells were armed with CD20Bi. Killing activity was evaluated by 51Cr-release assay.

Results: Arming ATC with as little as 5 ng CD20Bi/10(6) cells significantly increased cytotoxicity above unarmed ATC. CD20Bi-armed ATC (50 ng/10(6) cells) efficiently lysed CD20+ cell lines at E:T of 6.25-50, but not the nonhematologic, CD20- SK-BR-3 cell line. High levels of cytotoxicity mediated by CD20Bi-armed ATC (p < 0.05) could not be blocked by an 8000-fold excess of soluble rituximab. CD20Bi-armed ATC in the presence of complement killed ARH-77 cells, a rituximab-complement pathway-resistant multiple myeloma, significantly (p < 0.05) better than rituximab or unarmed ATC, suggesting that CD20Bi-armed ATC may be clinically effective for treatment of rituximab-resistant CD20+ hematologic malignancies.

Conclusions: Our findings demonstrate that CD20Bi-armed ATC enhance cytotoxicity against CD20+ B-cell lines and circumvent complement-mediated rituximab resistance, providing a strong rationale for this immune-based strategy for the treatment of rituximab-refractory CD20+ B-cell malignancies.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Antibodies, Bispecific / pharmacology*
  • Antibodies, Monoclonal
  • Antibodies, Monoclonal, Murine-Derived
  • Antigens, CD20 / immunology*
  • Antineoplastic Agents / pharmacology
  • B-Lymphocytes / drug effects
  • B-Lymphocytes / pathology*
  • CD3 Complex / immunology*
  • Cell Death / drug effects
  • Cell Line, Transformed
  • Cell Line, Tumor
  • Complement System Proteins
  • Cytokines / metabolism
  • Cytotoxicity Tests, Immunologic
  • Drug Resistance, Neoplasm
  • Female
  • Humans
  • In Vitro Techniques
  • Rituximab
  • T-Lymphocytes / immunology*
  • T-Lymphocytes / metabolism


  • Antibodies, Bispecific
  • Antibodies, Monoclonal
  • Antibodies, Monoclonal, Murine-Derived
  • Antigens, CD20
  • Antineoplastic Agents
  • CD3 Complex
  • Cytokines
  • Rituximab
  • Complement System Proteins