CD20, expressed on greater than 90% of B-
lymphocytic lymphomas, is an attractive target for antibody
therapy.
Rituximab is a chimeric murine/human-engineered
monoclonal antibody which can selectively deplete CD20-expressing cells in peripheral blood and lymphoid tissues. The immobilization of B-lymphoblast-like
Burkitt's lymphoma Raji cells on the
quartz crystal microbalance (QCM)
gold electrode surface using
arginine-glycine-aspartic acid (
RGD) tripeptide was electrochemically confirmed. The real-time processes of attachment of Raji cells on the
gold electrode and the subsequent binding of
Rituximab to the cells were studied using a QCM biosensor. The interaction between
Rituximab and Raji cells led to the increased resonant frequency shifts (Δf0) in the studied antibody concentration range from 5 to 250 μg mL(-1) following the Langmuir adsorption model. From these observations, the apparent binding constant between a single-layer of
Rituximab and Raji cells was calculated to be 1.6 × 10(6) M(-1). Control experiments using other therapeutic
antibodies (i.e.,
Trastuzumab and
Bevacizumab) and different cells (i.e., T cells and endothelial cells) proved the specific interaction between
Rituximab and B cells. The effects of Ca(2+) and Mn(2+)
ions on the
Rituximab-Raji cell interaction were also studied providing the enhanced QCM signals, in particular with Ca(2+), further indicating that CD20 is a
calcium ion channel that can transport these
metal ions into the cells and accelerate the cell lysis induced by
Rituximab. Thus, the real time capability of QCM and its simplicity of operation are shown to be highly suitable for multipurpose studies on living cells including cell-immobilization, cytotoxicity of drugs, and the cell action mechanisms.