Currently anti-fragment antigen binding (Fab) conjugates are most widely used to determine the
expression of CARs on gene-modified lymphocytes by flow cytometry. The limitations of these reagents are that
many of them are not commercially available, generally they are polyclonal antibodies and often the results are
inconsistent. In an effort to develop a simple universal flow cytometric method to detect the expression of CARs,
we employed protein L to determine the expression of CARs on transduced lymphocytes. Protein L is an
immunoglobulin (Ig)-binding protein that binds to the variable light chains (kappa chain) of Ig without interfering
with antigen binding site. Protein