cells may be engineered by the use of a retroviral plasmid vector containing rna encoding a polypeptide of the present invention similarly cells may be engineered in vivo for expression of a polypeptide in vivo by for example procedures known in the art for example a packaging cell is transduced with a retroviral plasmid vector containing rna encoding a polypeptide of the present invention such that the packaging cell now produces infectious viral particles containing the gene of interest these producer cells may be administered to a patient for engineering cells in vivo and expression of the polypeptide in vivo these and other methods for administering a polypeptide of the present invention by such method should be apparent to those skilled in the art from the teachings of the present invention retroviruses from which the retroviral plasmid vectors hereinabove mentioned may be derived include but are not limited to moloney murine leukemia virus spleen necrosis virus retroviruses such as rous sarcoma virus harvey sarcoma virus avian leukosis virus gibbon ape leukemia virus human immunodeficiency virus adenovirus myeloproliferative sarcoma virus and mammary tumor virus in one embodiment the retroviral plasmid vector is derived from moloney murine leukemia virus the vector includes one or more promoters suitable promoters which may be employed include but are not limited to the retroviral ltr the sv40 promoter and the human cytomegalovirus cmv promoter described in miller et al biotechniques vol 7 no 9 980 990 1989 or any other promoter e g cellular promoters such as eukaryotic cellular promoters including but not limited to the histone pol iii and u03b2 actin.