Developing recombination-based genetic medicines
Recombination is the process of intentionally replacing endogenous genome segments with exogenous sequences, allowing targeted DNA insertion into the genome, and precise genetic modification in living cells.
Cells in the body are routinely exposed to DNA damage caused by environmental factors such as UV light, toxins, chemicals and more, which can create a double strand break (DSB) in the DNA and jeopardize genomic integrity and stability. When this happens, the damage is corrected through one of the cell’s two inherent repair mechanisms: Non-homologous End Joining, or Homology Directed Recombination.
- > Non-homologous End Joining (NHEJ) is the prominent repair mechanism of the cell. It is usually associated with the introduction of indel mutations at the cut site, which may cause genomic modifications.
- > Homology Directed Recombination (HDR) is the repair mechanism active during cell division, which mediates a strand-exchange process to repair DNA damage accurately, based on the availability of homologous DNA sequences.
Genome editing leverages the natural repair mechanisms to correct congenital genetic disorders. Using designer nucleases to make a cut at a particular sequence in the genome, followed by the deletion, repair or insertion of genetic material at the cut site. It is well established in gene editing to exploit the NHEJ mechanism to knock out specific target genes. However, the correction of a mutation in the locus remains a major challenge in the field.
Emendo is pursuing a range of recombination strategies. One is to enhance HDR to allow targeted DNA insertion into the genome, precisely modifying target genes.
To achieve this, we have modified CRISPR/Cas9 so that it is expressed only in HDR phases. So, we are able to achieve a significant increase in accurate insertion of a new DNA sequence, while eliminating the less-accurate NHEJ editing process and dramatically reducing unintended genomic modification.