Kinetic analyses of stability of simple and complex retroviral vectors

Simple and complex retroviral vectors derived from Moloney murine leukemia virus (MLV) and human immunodeficiency virus type 1 (HIV-1), respectively, are useful tools for gene transfer studies. However, factors affecting the stability of these vectors have not been carefully investigated. Here we st udied the stability factors on vesicular stomatitis viral envelope glycopro tein (VSV-G)-pseudotyped MLV- and HIV-1-derived vectors. Analysis of the ra tio of defective particles Versus infectious units using electron microscop y and a functional transduction assay revealed that both vectors consisted of high numbers of defective particles (similar to 100-350:1), which could be reduced (similar to 10-20:1) by centrifugation. Frequent freeze-and-thaw rapidly decreased vector titer in the first three to five cycles and stabi lized thereafter. Both viral vectors were sensitive to temperatures above 3 7 degreesC but more stable at temperatures below 37 degreesC, exhibiting a two-phase inactivation kinetic starting with a steep inactivation phase, fo llowed by a more leveled phase. Interestingly, HIV-l-derived vectors were s ignificantly more stable than MLV-derived vectors at higher temperatures (> 37 degreesC). Both vectors were rapidly destabilized at pH either below or above 7.0. Incubation with human or mouse serum significantly inhibited VSV -G-pseudotyped vector activities. Preheated human serum still reduced vecto r half-lives to similar to 50% (150 min), suggesting that certain inactivat ion factors are not heat-labile. Analyses of these stability factors may im prove future production and applications of retroviral and lentiviral vecto rs. (C) 2001 Academic Press.