title: One step screening of retroviral producer clones by real time quantitative PCR.
abstract: BACKGROUND
  Recombinant retroviruses are obtained from either stably or transiently transfected retrovirus producer cells. In the case of stably producing lines, a large number of clones must be screened in order to select the one with the highest titre. The multi-step selection of high titre producing clones is time consuming and expensive.
  
  
  METHODS
  We have taken advantage of retroviral endogenous reverse transcription to develop a quantitative PCR assay on crude supernatant from producing clones. We used Taqman PCR technology, which, by using fluorescence measurement at each cycle of amplification, allows PCR product quantification. Fluorescence results from specific degradation of a probe oligonucleotide by the Taq polymerase 3'-5' exonuclease activity. Primers and probe sequences were chosen to anneal to the viral strong stop species, which is the first DNA molecule synthesised during reverse transcription. The protocol consists of a single real time PCR, using as template filtered viral supernatant without any other pre-treatment.
  
  
  RESULTS
  We show that the primers and probe described allow quantitation of serially diluted plasmid to as few as 15 plasmid molecules. We then test 200 GFP-expressing retroviral-producing clones either by FACS analysis of infected cells or by using the quantitative PCR. We confirm that the Taqman protocol allows the detection of virus in supernatant and selection of high titre clones. Furthermore, we can determine infectious titre by quantitative PCR on genomic DNA from infected cells, using an additional set of primers and probe to albumin to normalise for the genomic copy number.
  
  
  CONCLUSIONS
  We demonstrate that real time quantitative PCR can be used as a powerful and reliable single step, high throughput screen for high titre retroviral producer clones.
authors.affiliation: Genethon III, CNRS URA 1923, Evry, France.
authors.forename: G J
authors.initials: GJ
authors.lastname: Towers
authors.forename: D
authors.initials: D
authors.lastname: Stockholm
authors.forename: V
authors.initials: V
authors.lastname: Labrousse-Najburg
authors.forename: F
authors.initials: F
authors.lastname: Carlier
authors.forename: O
authors.initials: O
authors.lastname: Danos
authors.forename: J C
authors.initials: JC
authors.lastname: Pagès
mesh_terms: D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D017931:DNA Primers / Q000235:genetics; D015316:Genetic Therapy; D005822:Genetic Vectors; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction / Q000379:methods* / Q000592:standards / Q000706:statistics & numerical data; D012190:Retroviridae / Q000235:genetics*; D012680:Sensitivity and Specificity; D014162:Transfection
chemical_list: D017931:DNA Primers