The biotech company was reacting to an article published in the Washington Post on Monday which alleged that the way the recruitment of the patient, who died on 24 July, was conducted was in serious breach of clinical trial regulation standards.
According to the Washington Post report, "two fundamental rules of clinical research were violated that day [the day the patient was enrolled], experts said."
"First, consent forms are to be taken home and considered, not signed on first sight. Second, when a patient's own doctor is a principal investigator in a study, someone else is supposed to make the proposal."
The reporter quoted a scientist from Stanford University as well as an expert in the ethics of medical experiments at the University of Pennsylvania.
However, Targeted Genetics maintains that it stuck to the rules and that its drug is safe.
"We shared a very detailed chronology of our analyses and reporting activities regarding this particular study patient with the reporter from the Washington Post, which demonstrated how we acted in strictest compliance with today's best clinical trial practices, and which was not included in the article," H. Stewart Parker, president and chief executive officer of Targeted Genetics, said in a statement released on Monday.
Seattle-based Targeted Genetics announced last month it had halted the PhaseI/II study of its investigational gene therapy for the treatment of inflammatory arthritis after one of the trial subjects died.
"Even though the cause of the illness wasn't known, and is still uncertain, the agency immediately placed the trial on clinical hold - meaning no further product can be administered and no new patients can be enrolled," the US Food and Drug Administration (FDA) said in a statement at the time.
The drug tested uses an adeno-associated virus (AAV) vector to deliver the gene encoding for tumor-necrosis factor receptor (TNF-R) - a key mediator of inflammation in arthritis - directly into the joints.
More than 100 subjects have been enrolled in the trial, according to Targeted Genetics, and since it started in October 2005 no similar serious events have appeared.
Overall, 55 subjects have received two doses of active drug, which is what could have triggered the deceased patient's serious adverse event (SAE), as she became sick after a second gene-therapy injection into an arthritic joint.
However, the biopharma company stressed that a link between the death of the patient and the injection of the second dose of the therapy cannot be made until there is further research conducted.
FDA spokesperson Paul Richards told BioPharma-Reporter.com that the agency is currently conducting an "intensive and continuing investigation to determine, if possible, the cause of this patient's illness".
In addition, "as a precaution we are re-reviewing ongoing studies using AAV in any way. If we find evidence that raises safety questions about other products or uses of AAV, we will take any action needed," he said.
However, he stressed that at this point, the FDA does not have sufficient information to determine what caused the patient's illness or death and added that Targeted Genetics is "cooperating to obtain and provide needed information as it becomes available".
There are approximately 300 active gene therapy investigational new drug applications (INDs) in the US and over 20 active AVV trials, said Richards.
"It is important to note that there are more trials going on outside the US," he added.
At this time, the FDA has not received any reports of adverse events similar to those observed in the Targeted Genetics trial in other ongoing clinical trials studying AAV vectors.
It is not the first casualty this area of research has recorded. In 1999, Jesse Gelsinger, an 18-year-old with a rare metabolic disease who was participating in an experimental gene therapy at the University of Pennsylvania died of a strong immune reaction to the treatment.
Whatever the outcome of the investigation, the whole event may have already put a cloud on the future of the gene therapy field, an area once hailed as having the potential to revolutionise the drug industry.