Provided is a chimeric antigen receptor (CAR) or a T cell receptor (TCR) comprising one or more of the antigen binding motifs disclosed herein. Aspects of the disclosure relate to a polynucleotide encoding a chimeric antigen receptor (CAR) or a T cell receptor (TCR) comprising one or more of the antigen binding motifs. Provided are antibodies and antigen binding systems that comprise a binding motif that binds CD20 and optionally a binding motif that binds CD19, and methods of producing and using the same. Antibodies and antigen binding systems of the present disclosure comprise CARs that comprise an anti-CD20 binding motif and an anti-CD19 binding motif. Provided are compositions, such as antibodies and CARs that are or comprise an anti-CD20/anti-CD19 antigen binding system of the present disclosure, and cell therapies comprising the same, are useful, e.g., in the treatment of cancer.