First Step to Creating HIV-Resistant T Cells in Patients

Ricki Lewis, PhD

March 05, 2014

Using gene editing to mimic a mutation that prevents HIV from entering CD4 T cells appears to be safe in a small group of patients, according to a study published online March 5 in the New England Journal of Medicine.

CCR5 (chemokine [C-C motif] receptor 5) is the major transmembrane protein that serves as coreceptor, with CD4, for HIV. Individuals who are homozygous for a 32-base deletion in the CCR5 gene are naturally resistant to infection by the virus.

The "Berlin patient," Timothy Brown, made the CCR5 effect famous when he was apparently cured of HIV infection after receiving bone marrow from a homozygous mutant donor to treat leukemia. Experiments using humanized mice confirm that CCR5-modifed T cells deflect HIV.

In an open-label, nonrandomized, uncontrolled study of targeted gene disruption, Pablo Tebas, MD, from the Perelman School of Medicine, University of Pennsylvania, Philadelphia, and director of the Adult AIDS Clinical Trials Unit, and colleagues disabled ex vivo the CCR5 gene in CD4 T cells from 12 patients and then infused each participant's cells in a single dose.

The investigators used zinc finger nuclease introduced with an adenoviral vector to cut at a specific site within the targeted gene, creating a functional knockout. The team then expanded the cells in vitro and reinfused them back into the patient in a single dose. The modified cells included a 5-nucleotide duplication that enabled the researchers to track engraftment.

Each patient received 10 billion autologous CD4 T cells, 11% to 28% of which were altered. All patients were aviremic while receiving highly active antiretroviral therapy (HAART). Six patients stopped HAART for a 12-week period beginning at week 4 after receiving the modified T cells. The primary outcome for the trial was safety, and secondary outcomes assessed immune reconstitution and HIV resistance.

The CCR5-modified CD4 T cells quickly became established in the circulation. Median CD4 T-cell count jumped from 448/mm3 to 1517/mm3 within a week 1 (P < .001) of infusion. Median concentration of modified cells at 1 week was 250 cells/mm3, equaling 13.9% of circulating CD4 T cells. Mean half-life was 48 weeks. Modified cells also infiltrated the rectal mucosa.

In 4 of the 6 patients who temporarily stopped HAART, viremia returned and CD4 T-cell count predictably plummeted, but unmodified cells declined much faster (−7.25 cells per day; 95% confidence interval [CI], −12.14 to −2.94 cells) than modified cells (−1.81 cells per day; 95% CI, −3.08 to −0.46 cells; P = 0.02), suggesting a survival advantage for the modified cells.

HIV DNA in peripheral blood mononuclear cells dropped in the patients who stopped treatment, and copy numbers of the HIV gene gag dropped in peripheral blood of the other patients. One participant had fever, chills, joint pain, and back pain attributed to a transfusion reaction.

The researchers conclude that inducing acquired genetic resistance to HIV infection in this small group is safe and call for attempts to increase engraftment. Limitations of the study include the small and variable patient pool and the focus on modified cells in the vascular compartment.

In an editorial, Mark A. Kay, MD, PhD, from Stanford University School of Medicine in California, and Bruce D. Walker, MD, from the Ragon Institute, MIT, Harvard, and Massachusetts General Hospital, Boston, call the work an "important step forward" in the "bedside-to-bench-to-bedside" saga of the protective CCR5 mutation, as well as validation of genome editing in a broader sense.

"The firm conclusion of this study is that genome editing of human cells was safe and associated with an acceptable adverse-event profile and that the cells persisted in vivo," they write. "The tantalizing question raised by the transient treatment interruption is whether it might actually have been partially effective."

The study was supported by Sangamo BioSciences, the Penn Center for AIDS Research, and the National Institutes of Health/National Institute of Allergy and Infectious Diseases. Eight coauthors own stock in and are employees of Sangamo BioSciences. One coauthor consults for Gilead Sciences, Abbott, and Janssen and receives funding from GlaxoSmithKline. One coauthor holds a patent on cell culture technology and has licensed an invention to Life Technology. One coauthor is on the board of Adaptive Biotechnologies. Dr. Tebas consults for Merck and GlaxoSmithKline and has received payment for a book chapter on HIV and transplants. Dr. Kay and Dr. Walker have disclosed no relevant financial relationships.

N Engl J Med. 2014;370:901-910.

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