Although the cells may not have been successful in targeting and killing HIV-infected cells, which they were designed to do, the results are promising as they bolster the safety credentials of gene therapy for clinical use.
Patients enrolled in three clinical trials were monitored for up to 16 years. Each patient received injections of their own T cells, a type of immune cell, modified to identify and kill HIV-infected cells in the body.
Over a decade after the treatment, called adoptive T cell transfer, the modified T cells were still circulating in the blood stream.
'We have 43 patients and they are all healthy', confirmed senior author Professor Carl June of the University of Pennsylvania. 'And out of those, 41 patients show long term persistence of the modified T cells in their bodies'.
The study highlights the potential of gene therapy as a long-lasting alternative to the costly lifetime course of anti-retroviral drug therapy currently used in HIV.
'Just think about what an HIV patient has to do: take drugs every day for the rest of their life, and the minute a person stops taking them, the virus starts coming back', said Dr John Rossi of the Beckman Research Institute in California, who was not involved with the study.
Most importantly, there was no evidence that the modified T cells caused cancer. Previous trials of adoptive T cell transfer had resulted in the genes being inserted in the wrong place and causing out-of-control, cancerous cell growth.
However, the study, published in Science Translational Medicine, did not indicate that the therapy was active against HIV. 'It may not have worked at all', summarised co-author Dr Frederic Bushman.
Using a baseball analogy, Dr Pablo Tebas, director of the AIDS Clinical Trials Unit at the University of Pennsylvania, told NPR: 'We're not hitting a home run. This is a single'.
In further encouraging news, a potential stem cell therapy against HIV was safe and effective in animal studies. Researchers at the University of California tested a technique which involves replacing the immune system with stem cells genetically engineered with a triple combination of HIV-resistant genes.
The team is currently seeking funding and regulatory approval to test the technique in clinical trials.