Disclosed are compositions and methods for gene transfer in immune effector cells, e.g. to create chimeric antigen receptors (CARs). In particular, polypeptides are disclosed that comprising an antigen-binding region and a heparin binding domain, wherein the antigen-binding region is capable of specifically binding to an immune cell antigen located on an immune effector cell, and wherein the heparin binding domain is capable of binding a viral vector.