On Thursday, another gene therapy startup announced its launch. Dimension Therapeutics hopes to develop virus-delivered gene treatments for rare diseases and its first target is the blood-clotting disorder hemophilia.

The announcement comes just a week after the launch of another gene therapy startup, Spark Therapeutics (see “New Gene Therapy Company Launches”). One reason that the dashed hopes of gene therapy seem to be mending is that researchers have improved the technologies for delivering genetic fixes. Functional copies of genes are carried by modified viruses, or vectors, into the cells of patients who have missing or dysfunctional copies of those genes. Many groups use vectors based on adeno-associated viruses, or AAVs, which live in most of our bodies already to no ill effect.

Dimension has licensed AAV technology from Washington, D.C.,-based Regenx Biosciences, a company founded by gene therapy pioneer James Wilson. Wilson headed the University of Pennsylvania institute that oversaw a gene therapy trial in 1999 that ended with the death of Jesse Gelsinger, an 18-year-old trial volunteer (see “The Glimmering Promise of Gene Therapy”). Gelsinger’s death was blamed on an immune reaction to the experimental therapy’s viral vector.

That trial used a different kind of virus and since its tragic end, Wilson had searched for better vectors, which he found in AAVs. According to Wired, Wilson’s original AAV, AAV1, was the basis for the first gene therapy to be approved in a Western market (see “Gene Therapy on the Mend as Treatment Gets Western Approval”). Spark Therapeutics is also using a type of AAV to deliver its treatments.

Wilson and his team have since discovered and developed hundreds of modified AAVs, which can target different organs in the body but have been stripped of their ability to replicate. Regenx licensed several vectors to Dimension. A release announcing Dimension’s launch suggests that it was Regenx technology that inspired confidence from venture capital firm Fidelity Biosciences to fund the new company:  

“A core challenge for gene therapy has been the development of safe, efficient vectors to enable delivery of the replacement gene to the correct cells and tissues of the patient to yield benefit,” said Fidelity partner and interim CEO of Dimension Thomas Beck.  “We believe Regenex [vectors] are the most promising approach for in vivo gene therapy.”

An early-stage trial of a Regenx vector carrying the gene missing from certain hemophilia patients showed it could correct the disorder (four of the six trial participants were able to quit taking their prophylactic clotting medication) with few side-effects, reported researchers in 2011. The modified virus vectors can still attract the attention of the immune system, but the medical researchers were able to control the immune reaction with immunosuppressive drugs.

While many gene therapy researchers and companies use AAV technology, there are some exceptions. Bluebird Bio, for instance, uses an attenuated version of an HIV viruses that cannot replicate. Bluebird is recruiting patients for a late-stage trial of a gene therapy for a hereditary form of childhood neurodegeneration.