A. Illustration showing the binding sites (arrows) of Protein A, Protein G, and Protein L to the heavy and light chain regions of the antibody. Protein L binding is restricted to those antibodies that contain kappa light chains. B. Schema showing Protein L binding to the kappa light chain of a single chain variable fragment (scFv) portion of a chimeric antigen receptor (CAR). TM, transmembrane region of CAR; vH, variable heavy chain; vL, variable light chain.