Arthritis & Rheumatism, Volume 62,
November 2010 Abstract Supplement

Abstracts of the American College of
Rheumatology/Association of Rheumatology Health Professionals
Annual Scientific Meeting
Atlanta, Georgia November 6-11, 2010.

The Effects of the Anti-CD22 Monoclonal Antibody Epratuzumab on B-Cell Surface Proteins.

Shock1,  Anthony, Brown2,  Derek, Crook2,  Kenneth, Bourne2,  Timothy

UCB, Slough, Berkshire, Slough, United Kingdom
UCB, Slough, Berkshire, UK


Epratuzumab is a humanized monoclonal antibody against CD22 that is currently being evaluated clinically in systemic lupus erythematosus (SLE). Epratuzumab treatment of SLE patients has been shown to reduce CD22 cell surface expression on B cells (Jacobi A, et al. Ann Rheum Dis 2008;67:450–457). The aim of the current study was to investigate the kinetics of internalization on B cells from healthy volunteers in vitro and to look at a range of other cell surface proteins.


In vitro studies used B cells that were purified by negative selection from human blood and incubated with a concentration range of epratuzumab or an isotype control antibody over time, washed and then stained with fluorescently-labeled antibodies specific to a range of B-cell surface proteins and analyzed by flow cytometry. In order to assess the expression of CD22 in the presence of epratuzumab, a non-competing anti-CD22 antibody (S-HCL-1-PE) was employed. CD22 internalization was also evaluated in a qualitative manner in confocal microscopy experiments employing Alexa488-labeled epratuzumab. Whole blood flow cytometry was used to assess CD22 levels on B cells from SLE patients dosed with epratuzumab.


Epratuzumab caused rapid internalization of B-cell surface CD22 in a range of in vitro experiments. Maximal internalization occurred in 30–60 min at concentrations above 1–2 mg/mL but the level of internalization typically did not exceed 50–70%, even at higher antibody concentrations, suggesting that some B-cell surface CD22 is resistant to epratuzumab-induced internalization. Internalization was prevented by prior cell fixation with paraformaldehyde and was reduced at a lower temperature. Internalization of CD22 on B cells in response to epratuzumab treatment was also confirmed using confocal microscopy. Although epratuzumab was capable of modulating the expression of CD22 in B-cell cultures, it had no consistent effect on several other B-cell markers including IgM, IgD, CD19, CD20, CD27, CD32, CD38, CD69, CD79b, CD95, and HLA-DR Class II measured at a variety of time points up to 6 days. Internalization of CD22 was observed on a number of B-cell subsets following treatment of SLE patients with epratuzumab.


Epratuzumab stimulated rapid internalization of its target, CD22, on human peri-pheral blood B cells in vitro and in vivo but had no consistent effect on a range of other B-cell markers. This could lead to modulation of B-cell functional responses that are regulated specifically by CD22, which may be relevant in the context of SLE.

To cite this abstract, please use the following information:
Shock, Anthony, Brown, Derek, Crook, Kenneth, Bourne, Timothy; The Effects of the Anti-CD22 Monoclonal Antibody Epratuzumab on B-Cell Surface Proteins. [abstract]. Arthritis Rheum 2010;62 Suppl 10 :751
DOI: 10.1002/art.28519

Abstract Supplement

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