Development of an avian leukosis-sarcoma virus subgroup A pseudotyped lentiviral vector

We are using avian leukosis-sarcoma virus (ALSV) vectors to generate mouse tumor models in transgenic mice expressing TVA, the receptor for subgroup A ALSV. Like other classical retroviruses, ALSV requires cell division to es tablish a provirus after infection of host cells. In contrast, lentiviral v ectors are capable of integrating their viral DNA into the genomes of nondi viding cells. With the intention of initiating tumorigenesis in resting, TV A-positive cells, we have developed a system for the preparation of a human immunodeficiency virus type 1 (HIV-1)-based lentiviral vector, pseudotyped with the envelope protein of ALSV subgroup A (EnvA). The HIV(ALSV-A) vecto r retains the requirement for TVA on the surface of target cells and can be produced at titers of 5 x 10(3) infectious units (IU)/ml. By inserting the central polypurine tract (cPPT) from the HIV-1 pol gene and removing the c ytoplasmic tail of EnvA, the pseudotype can be produced at titers approachi ng 10(5) IU/ml and can be concentrated by ultracentrifugation to titers of 10(7) IU/ml. HIV(ALSV-A) also infects embryonic fibroblasts derived from tr ansgenic mice in which TVA expression is driven by the beta -actin promoter . In addition, this lentivirus pseudotype efficiently infects these fibrobl asts after cell cycle arrest, when they are resistant to infection by ALSV vectors. This system may be useful for introducing genes into somatic cells in adult TVA transgenic animals and allows evaluation of the effects of al tered gene expression in differentiated cell types in vivo.