R&D pipeline

When a DNA fragment is introduced in the nucleus of a cell it can integrate randomly into the genome. If the introduced DNA is identical (homologous) to a DNA sequence (locus A) present in the genome, then the integration can occur in the locus A. Based on that property it is then possible to target a mutation in a specific location of the genome.
This technology is called homologous recombination.

A foreign sequence (e.g., a Neo cassette) can be introduced by homologous recombination in a mouse gene A. The insertion of the foreign sequence is designed to prevent the transcription of the mouse gene A. The mouse gene A is no longer expressed; the gene A is "knocked-out". If the experiment is performed with mouse Embryonic Stem cells (ES cell), injection of the recombinant Embryonic Stem cells (ES cell) into blastocysts give rise to chimeras, heterozygous and homozygous animals, also called knock out mouse.

A transgene B (e.g., a sequence coding for a fluorescent protein) can be introduced by homologous recombination in a mouse gene A in such a way that the transgene B transcription is driven by the promoter of the mouse gene A. The transgene B is expressed with the same pattern of expression as the mouse gene A; this strategy is called "knock-in". If the transgene B is the human counterpart of the mouse gene A, then this strategy is called humanization and the mouse a humanized mouse.