Expression of genes transferred to haemopoietic stem cells by recombinant retroviruses.

We have compared several recombinant retroviruses carrying the selective marker NeoR for gene delivery to murine haemopoietic stem cells. Provirus content and expression was assessed in animals reconstituted with infected bone marrow cells. With viruses bearing only a NeoR gene, viral RNA was readily detectable both in spleen colonies and in the haemopoietic tissues of long-term reconstituted mice. Thus, the progeny of infected primitive multipotential cells are competent to express integrated proviruses. The level of expression was significantly greater for proviruses carrying a modified long terminal repeat in which the Moloney enhancer had been replaced with that from the myeloproliferative sarcoma virus. With viruses bearing the c-myc gene in addition to NeoR, however, no viral RNA could be detected in spleen colonies harbouring proviral inserts, even though these viruses are expressed in vitro within haemopoietic cells. The implications of these results for gene transfer to haemopoietic stem cells are discussed.