Scientists have successfully modified the white blood cells of 12 patients living with HIV, making their cells resistant to the retrovirus and improving the study participants' overall ability to fight off infection. The researchers achieved this result through a gene editing technique, described today in The New England Journal of Medicine.

In the study, scientists extracted white blood cells, called CD4 T cells, from the participants' blood. They then modified these cells by removing the gene responsible for the production of a protein called CCR5. The CCR5 protein is what allows HIV to enter white bloods cells in the first place, so its removal conveyed resistance. After verifying that nothing else had been altered within the cells, the researchers returned them — 10 billion of them — to the patients via blood transfusion. "The modified [white blood] cells survive longer in the presence of HIV, which we proved by stopping [antiretroviral] therapy in some patients," says Pablo Tebas, an infectious disease physician at the University of Pennsylvania and study co-author.

Unlike the child who went into HIV remission a year ago, the patients in this study continue to test positive for HIV. But the results of this Phase I clinical trial still represent a promising debut for HIV treatments involving tailored gene therapy, as the white blood cells persisted for nearly a year after transfusion. And the study's participants reacted well to the treatment, Tebas says, specifying that they "continue to be fine." One study participant, however, experienced an adverse reaction to the transfusion, causing the patient to experience chills, joint pains, and a fever. But these symptoms subsided after a few days.

The technique is "very elegant," says Kristina Allers, an HIV researcher at Charité-Universitätsmedizin Berlin who did not participate in the study. Allers cautions, however, that this advancement only represents a starting point. "The procedure does not achieve long-term effects in HIV-infected patients."

A second study will take place in April, Tebas says, in which participants will receive a higher dose of modified cells. Tebas' team of researchers will also continue to monitor the patients from this study for years to come. "We did not cure anybody with HIV," Tebas says, but we now know that we "can make the cells of each individual resistant to HIV."