MYELOPROLIFERATIVE SARCOMA-VIRUS DIRECTED EXPRESSION OF BETA-GALACTOSIDASE FOLLOWING RETROVIRAL TRANSDUCTION OF MURINE HEMATOPOIETIC-CELLS

The introduction of genetic sequences into hematopoietic stem cells (H SC) has allowed study of HSC proliferation in vivo by proviral-sequenc e molecular analysis in the DNA of progeny. Analysis of HSC proliferat ion could be enhanced by development of a retroviral vector that encod es a reporter gene that allows sensitive detection of transduced cells . We developed a recombinant retrovirus vector encoding the reporter g ene IacZ under the transcriptional control of the myeloproliferative s arcoma virus long-terminal repeat (LTR). Bone marrow cells from C3H mi ce were co-cultured on retrovirus producer cell lines and cultured for growth of colony-forming unit granulocyte/macrophage (CFU-GM) and hig h proliferative potential colony-forming cells (HPP-CFC) in semisolid media or were transplanted into irradiated recipients. In other experi ments, recombinant retrovirus was injected in vivo into the liver of d eveloping fetal rat pups, and circulating hematopoietic cells of the p ostnatal rats were analyzed for evidence of proviral integration and e xpression of beta-galactosidase. Expression of lacZ was detected in bo th CFU-GM and HPP-CFC that were cultured immediately following in vitr o infection of mouse bone marrow. beta-galactosidase activity from the retrovirus was also detected in bone marrow cells isolated from recon stituted mice 22 weeks following transplantation as well as in blood c ells of postnatal rats transduced in utero with the recombinant retrov irus. This strategy may be especially useful for characterizing prolif eration of transduced populations of hematopoietic cells and in the de velopment of protocols for somatic gene therapy.