Lentivector constructs for expression of recombinant proteins, polypeptides or fragments thereof and methods of making the same are described. The lentivectors typically have a self-processing cleavage sequence between a first and second protein or polypeptide coding sequence allowing for expression of a functional protein or polypeptide under operative control of a single promoter and may further include an additional proteolytic cleavage sequence which provides a means to remove the self-processing cleavage sequence from the expressed protein or polypeptide. The vector constructs find utility in methods relating to enhanced production of biologically active proteins, such as immunoglobulins or fragments thereof in vitro and in vivo.