May 2, 2012 — Gene transfer using a retroviral vector that directs a patient's T cells to recognize HIV appears to be safe and persistent, according to a study published May 2 in Science Translational Medicine.
"We have 43 patients and they are all healthy. Out of those, 41 patients show long-term persistence of the modified T cells in their bodies. T cells appear to be a safe haven for gene modification," said senior author Carl June, MD, from the Perelman School of Medicine at the University of Pennsylvania, Philadelphia.
The new report may put retroviruses back on the playing field for gene transfer after earlier trials raised concerns. In 2003, the retroviral vector used in a clinical trial for X-linked severe combined immunodeficiency (SCID-X1) inserted into an oncogene, causing leukemia. That study, in genetically modified hematopoietic stem cells, forced reconsideration of the use of retroviruses as vectors in gene transfer experiments.
In the current study, however, John Scholler, BS, also from the Perelman School of Medicine at the University of Pennsylvania, and colleagues detected modified T cells in 43 HIV-positive patients participating in 3 clinical trials, from 1998 to 2002, up to a decade later. In the trials, a retroviral vector introduced a chimeric antigen receptor (CAR) gene into autologous CD4+ and CD8+ T cells, enabling the cells to recognize the HIV envelope glycoprotein gp120, and triggering an immune response. (The chimeric antigen receptor that the transgene CD4ζ CAR encodes consists of the CD3ζ transmembrane region and endodomain and the CD4 cluster of differentiation antigen ectodomain that binds HIV.)
"T cells seem to be a much safer cell target than stem cells," Donald B. Kohn, MD, professor of microbiology, immunology, and molecular genetics and pediatrics at the University of California, Los Angeles, told Medscape Medical News. “Viruses tend to go into genes that are actively expressed in the cells they're hitting. In stem cells the early proliferation genes are being expressed, so these cells are more susceptible to insult than T cells, which are more mature even though they can divide." Dr. Kohn was not involved in the newly published study but has led several other gene transfer trials.
The leukemia problem in the earlier stem cell trial prompted the Food and Drug Administration to require follow-up of participants in gene transfer trials through at least 15 years. In the newly evaluated HIV trials, annual blood tests generated more than 500 years of combined patient safety data.
The researchers used quantitative polymerase chain reaction (PCR) to assess total genomic DNA from samples of peripheral blood mononuclear cells from the 43 patients, collected 1 to 11 years after infusion. Most patients had 0.01% to 0.1% CD4ζ CAR transgenes in their peripheral blood mononuclear cells, indicating a half-life greater than 16 years.
The investigators used reverse transcriptase PCR to show transgenes being actively transcribed up to 10 years after infusion, and they developed an assay using artificial antigen-presenting cells to demonstrate translation of the CD4ζ CAR transgenes. "It is amazing how long the cells are sticking around," said Dr. Kohn.
The modified cells and their descendants also passed safety tests. Additional experiments demonstrated that the transgene inserts in the same range of genome sites as nonaltered gamma retroviruses, which was not the case for SCID-X1. Nor were clonal expansions of T cell subsets, a precursor to leukemia, detected. And immunosuppression is not required for altered cells to proliferate.
Gene transfer to treat HIV could reduce reliance on antiretroviral agents, which have adverse effects. "It could cost what a year's drugs cost for a decades-long or permanent effect," Dr. Kohn said.
The work has wide implications because modified T cells can be used to treat other diseases, Dr. June said. The team published a report in 2011 demonstrating a similar strategy against chronic lymphocytic leukemia. However, the observed safety in the HIV trials applies only to the transgene and target cells tested.
"Their work represents an important milestone in developing genetically modified T cells for HIV therapy, clearly demonstrating the feasibility and safety of this novel strategy to fight HIV infection," Guangping Gao, PhD, director of the Gene Therapy Center and Vector Core at the University of Massachusetts Medical School, told Medscape Medical News. Dr. Gao was not involved in the study.
The study was supported by the National Institutes of Health, the University of Pennsylvania Center for AIDS Research, and the Infectious Diseases Clinical Research Program (a Department of Defense program funded in part with federal funds from the National Institute of Allergy and Infectious Diseases). One author is a Special Fellow of the Leukemia and Lymphoma Society. Another author is an advisor to Actimmune and is a clinical investigator for Sangamo Biosciences. The other authors have disclosed no relevant financial relationships.
Sci Transl Med. Published online May 2, 2012. Abstract
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Cite this: Gene Transfer Stable and Persistent in HIV-Infected Patients - Medscape - May 02, 2012.