Introduction of a Selectable Gene into Different Animal Tissue by a Retrovirus Recombinant Vector

The potential use of retrovirus vectors to transduce foreign genetic information into cells of different tissues of an animal was explored by introducing a recombinant genome carrying the Eco gpt gene into postimplantation mouse embryos. To obviate the need for preparing concentrated virus stocks, ψ 2-2-5 cells producing the replication-defective murine sarcoma virus (MSV)-gpt virus were microinjected directly into embryos. The ψ 2-2-5 cells were mixed with cells producing replication-competent Moloney murine leukemia virus (Mo-MuLV) to facilitate spread of the vector. A high percentage of the manipulated embryos continued to develop without disturbance and were analyzed either prior to birth or as adults for expression of both helper and Eco gpt virus. Microinjection of as few as 10 Mo-MuLV-producing cells resulted in viremia of >50% of the embryos or adults, 25%-30% of which produced MSV-gpt recombinant virus in a variety of organs including thymus, spleen, lung, kidney, and brain. The fraction of vector-producing cells, however, was 3 to 5 orders of magnitude lower than that of helper-virus-producing cells. Our results demonstrate that a selectable gene can be introduced by retroviral vectors into animals and can be expressed in a wide variety of different somatic tissues.