ANALYSIS OF ALV-BASED PACKAGING CELL-LINES FOR PRODUCTION OF CONTAMINANT DEFECTIVE VIRUSES

We have previously described avian leukosis virus-based packaging cell lines that express gag, pol, and env proteins from two transcomplemen ting genomes and produce helper-free stocks of retroviral vectors with different host ranges. In this report, we demonstrated that (i) despi te the deletion of the psi packaging sequence, the packaging-defective transcomplementing retroviral transcripts were packaged into virions at a level that could reach 2.3% of a wild-type virus packaging level and (ii) despite deletion of the 3' LTR, these genomes were transferre d along with the vector to target cells. As these genomes were also be aring a selectable gene, titers of the resulting contaminant particles could be estimated, depending on the cell line to be between 0 and 6 infectious particles/ml of supernatant. (C) 1995 Academic Press, Inc.