Analysis of ALV-based packaging cell lines for production of contaminant defective viruses

Abstract

We have previously described avian leukosis virus based packaging cell lines that express gag, pol, and env proteins from two transcomplementing genomes and produce helper-free stocks of retroviral vectors with different host ranges. In this report, we demonstrated that (i) despite 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 transferred along with the vector to target cells as these genomes were also bearing 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. © 1995 Academic Press, Inc.