High-titer MSCV-based retrovirus generated in the pCL acute virus packaging system confers sustained gene expression in vivo

Retroviral gene transfer using vectors encoding tumor suppressor genes has been tested repeatedly as a potential anti-tumor therapy. However, most att empts have been hindered by the inability to deliver genes efficiently and to obtain sustained expression in cells growing in vivo. In this paper we d escribe a method for producing high-titer MSCV virus using the pCL acute re troviral packaging system. This method facilitates the generation of MSCV v irus encoding genes that convey the cytostatic or cytocidal phenotypes of b enefit in the treatment of cancer. Amphotropic MSCV virus with an average t iter of 6 x 10(6) CFU/ml has been routinely produced in this system. We dem onstrate that, unlike the pCL retroviral vectors, the MSCV vector is capabl e of directing sustained in vivo expression of the green fluorescent protei n in infected glioma cells following implantation and tumor growth in nude mice. (C) 1998 Elsevier Science B.V. All rights reserved.