residue this residue may or may not be subsequently cleaved from the expressed recombinant protein to provide a final product the human hematopoietic progenitor cells transduced in the presence of human mesenchymal stem cells thus may have stably integrated a recombinant transcriptional unit into chromosomal dna or carry the recombinant transcriptional unit as a component of a resident plasmid cells may be engineered with a polynucleotide dna or rna encoding a polypeptide ex vivo for example cells may be engineered by procedures known in the art by use of a retroviral particle containing rna encoding a polypeptide 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 generally regarding retroviral mediated gene transfer see mclachlin et al 1990 the nucleic acid sequence encoding the polypeptide is under the control of a suitable promoter suitable promoters which may be employed include but are not limited to adenoviral promoters such as the adenoviral major late promoter the cytomegalovirus cmv promoter the respiratory syncytial virus rsv promoter inducible promoters such as the mmt promoter the metallothionein promoter heat shock promoters the albumin promoter the apoai promoter human globin promoters viral thymidine kinase promoters such as the herpes simplex thymidine kinase promoter retroviral ltrs itrs the u03b2 actin promoter and human growth hormone promoters the promoter also may be the native promoter that controls the gene encoding the polypeptide these vectors also make it possible to regulate.