The present invention provides compositions comprising a protein expression blocker or PEBL comprising a target-binding molecule and localizing domain, and methods of using such compositions in cancer therapy. PEBLs are useful as a blockade of expression of target surface receptors (peptides or antigens) in immune cells. Also provided herein are CD3/TCRaß- deficient T cells and CD3/TCRaß-deficient chimeric antigen receptor T cells that express such PEBLs.