High CD21 expression inhibits internalization of anti-CD19 antibodies and cytotoxicity of an anti-CD19-drug conjugate

Br J Haematol. 2008 Jan;140(1):46-58. doi: 10.1111/j.1365-2141.2007.06883.x. Epub 2007 Nov 7.


CD19 and CD21 (CR2) are co-receptors found on B-cells and various B-cell lymphomas, including non-Hodgkin lymphoma. To evaluate their suitability as targets for therapy of such lymphomas using internalization-dependent antibody-drug conjugates [such as antibody-4-(N-maleimidomethyl)cyclohexane-1-carboxylate, (N2'-deacetyl-N2'-(3-mercapto-1-oxopropyl)-maytansine) (MCC-DM1) conjugates, which require lysosomal degradation of the antibody moiety for efficacy], we examined uptake of antibodies to CD19 and CD21 in a panel of B-cell lines. Anti-CD21 antibodies were not sufficiently internalized even in the highest CD21-expressing Raji cells, resulting in lack of efficacy with anti-CD21-MCC-DM1 conjugates. Anti-CD19 antibody uptake was variable, and was unexpectedly negatively correlated with CD21 expression. Thus, high CD21-expressing Raji, ARH77 and primary B-cells only very slowly internalized anti-CD19 antibodies, while CD21-negative or low expressing cells, including Ramos and Daudi, rapidly internalized these antibodies in clathrin-coated vesicles followed by lysosomal delivery. Anti-CD19-MCC-DM1 caused greater cytotoxicity in the faster anti-CD19-internalizing cell lines, implying that the rate of lysosomal delivery and subsequent drug release is important. Furthermore, transfection of Ramos cells with CD21 impeded anti-CD19 uptake and decreased anti-CD19-MCC-DM1 efficacy, suggesting that CD21-negative tumours should respond better to such anti-CD19 conjugates. This may have possible clinical implications, as anti-CD21 immunohistochemistry revealed only approximately 30% of 54 diffuse large B-cell lymphoma patients lack CD21 expression.

MeSH terms

  • Antibodies, Neoplasm / immunology*
  • Antigens, CD19 / immunology*
  • Apoptosis / immunology
  • Cell Line, Tumor
  • Clathrin / pharmacology
  • Cytotoxicity, Immunologic / immunology
  • Flow Cytometry
  • Humans
  • Immunoconjugates / therapeutic use*
  • Immunohistochemistry
  • Lymphoma, B-Cell / immunology
  • Lymphoma, B-Cell / therapy*
  • Receptors, Complement 3d / metabolism*


  • Antibodies, Neoplasm
  • Antigens, CD19
  • Clathrin
  • Immunoconjugates
  • Receptors, Complement 3d