Improved helper virus-free packaging system for HSV amplicon vectors using an ICP27-deleted, oversized HSV-1 DNA in a bacterial artificial chromosome

Yoshinaga Saeki, Cornel Fraefel, Tomotsugu Ichikawa, Xandra O. Breakefield, E. Antonio Chiocca

Research output: Contribution to journalArticle

181 Citations (Scopus)


Herpes simplex virus type 1 (HSV-1) amplicons are prokaryotic plasmids containing one or more transcriptional units and two cis-acting HSV-1 sequences: a viral origin of DNA replication and a viral DNA cleavage/packaging signal. In the presence of HSV-1 "helper" functions, amplicons are replicated and packaged into HSV-1 virions. Despite recent improvements in packaging methods, stocks of amplicon vectors are still contaminated with replication-competent helper virus at a frequency of 10-4-10-6. To overcome this problem, we report that: (i) genetic modifications of HSV-1 genomes can be routinely achieved in Escherichia coli, either by homologous or site-specific recombination, (ii) a novel HSV-1 bacterial artificial chromosome (fHSVΔpacΔ27 0+), which has a deletion in the essential gene encoding ICP27 and an addition of ICP0 "stuffer" sequences to increase its size to 178 kb, supports the replication and packaging of cotransfected amplicon DNA without generating replication-competent helper virus (< 1 helper virus per 108 TU amplicon vectors), and (iii) the resulting amplicon stocks have titers of up to 3-10 × 108 TU/ml after concentration. Elimination of replication-competent helper virus from HSV-1 amplicon vector stocks further improves safety in gene transfer applications.

Original languageEnglish
Pages (from-to)591-601
Number of pages11
JournalMolecular Therapy
Issue number4
Publication statusPublished - Jan 1 2001



  • Amplicon
  • BAC
  • Cre/loxP
  • Gene therapy
  • Helper virus-free
  • Herpes virus
  • Homologous recombination
  • RecA
  • Site-specific recombination

ASJC Scopus subject areas

  • Molecular Medicine
  • Molecular Biology
  • Genetics
  • Pharmacology
  • Drug Discovery

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