Browsing by Author "Johnson, Terry"

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    Certification assays for HIV-1-based vectors: frequent passage of gag sequences without evidence of replication-competent viruses
    (Elsevier, 2003-11-01) Sastry, Lakshmi; Xu, Yi; Johnson, Terry; Desai, Kunal; Rissing, David; Marsh, Jonathan; Cornetta, Kenneth; Microbiology and Immunology, School of Medicine
    A principal concern regarding the safety of HIV-1-based vectors is replication-competent lentivirus (RCL). We have developed two PCR assays for detecting RCL; the first detects recombination between gag regions in the transfer vector and the packaging construct (sensitivity of detection ∼10–100 copies of target sequence). The second assay uses real-time PCR to detect vesicular stomatitis virus glycoprotein (VSVG) envelope DNA (sensitivity ∼5–50 VSVG sequences). In an attempt to amplify any RCL, test vectors were used to transduce C8166 and 293 cells, which were then screened weekly for 3 weeks. Psi–gag recombinants were routinely detected (20 of 21 analyses) in four transductions using the RRL-CMV-GFP vector. In contrast, VSVG sequences were detected only once in 21 analyses. Interestingly, p24 levels (as measured by ELISA) were occasionally detectable after 3 weeks of culture. To determine if a true RCL was present, 21-day cell-free medium was used to transduce naïve cells. No evidence of psi–gag or VSVG transfer was detected, indicating that the recombination events were insufficient to reconstitute a true RCL. These findings have important implications for the design and safety of HIV-1-based vectors intended for clinical applications.
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    Testing for Replication Competent Lentivirus Associated with HIV1 Lentiviral Vectors
    (Elsevier, 2003-05-01) Sastry, Lakshmi; Xu, Yi; Johnson, Terry; Cornetta, Ken; Medical and Molecular Genetics, School of Medicine