By tinkering with a gene involved with the entry of HIV into cells, investigators have developed what they call a potential "functional cure" for HIV/AIDS.

The therapy is designed to keep HIV under control without additional antiretroviral drugs.

The technique involves collection of CD4 T cells from patients infected with HIV, genetically engineering the cells to disable the gene for the HIV coreceptor CCR5, and reinfusing the treated cells after the patients have been conditioned with the chemotherapy drug cyclophosphamide (Cytoxan), which stimulates engraftment of the modified cells, reported Dr. Gary Blick of Circle Care Center in Norwalk, Conn.

"We are seeing what we believe to be dose-dependent marked increases in both absolute CD4 cell counts as well as the engraftment of CCR5 modified T cells with the increasing doses of Cytoxan," he said at the Conference on Retroviruses and Opportunistic Infections 2014.

Results from a phase I proof-of-concept study with the same technology were reported in the March 6 New England Journal of Medicine (2014;370:901-10).

In the phase I/II dose-escalation study reported at CROI, a total of 12 HIV patients with chronic aviremic HIV infection while on highly active antiretroviral therapy (HAART) were enrolled into one of three cohorts. Each patient received one dose of the autologous CD4+ T-cell product in which the gene for CCR5, a coreceptor for HIV entry, is modified via zinc-finger nuclease (ZFN)–mediated genome editing.

Three patients received cyclophosphamide 200 mg as preconditioning, six received cyclophosphamide 500 mg/m², and three received the drug at a dose of 1 g/m².

Each patient then received a single infusion (8.2-36 billion cells) of his/her own CD4+ T cells, which had been genetically engineered using an adenoviral vector designed to carry a ZFN, an enzyme targeted at permanently disabling CCR5.

The therapy effectively mimics the CCR5 delta-32 mutation. Patients who are heterozygous for the allele have slower progression of HIV disease, and patients who are homozygous for the deletion are resistant to HIV infection.

The so-called Berlin patient was an HIV-infected man who is HIV free and off of antiretroviral therapy for more than 5 years after receiving a stem cell transplant from a donor who was homozygous for the delta-32 allele.

Dose-escalation study

The primary endpoint of the study was the safety and tolerability of cyclophosphamide. The drug was generally well tolerated, except for low-grade gastrointestinal side effects commonly seen with this agent. The side effects were treated with antiemetics.

The investigators saw a dose-related increase in total CD4 T-cell counts and engraftment of the modified cells at the highest cyclophosphamide dose. The cell counts approached levels found in patients with the CCR5 delta-32 deletion that confers natural resistance to HIV.

In addition, two patients at the 500-mg/m² dose had an approximate reduction of 0.8-1.1 log10 in viral load after a 16-week treatment interruption, and one patient on the 1-g/m² dose had a 1.9 log10 decrease after 16 weeks off HAART.

Two patients in the highest cyclophosphamide dose group had stable reduced viral loads and remain on treatment interruption.

The data suggest that cyclophosphamide conditioning may optimize the antiviral and engraftment effects of the adoptive T-cell strategy, and that the drug may play an important role as an immunomodulator in immunotherapy strategies for treating HIV, Dr. Blick said.

"The potential future of gene knockout by ZFNs and other techniques is not restricted to HIV infection. There are now methods that can be used not only to inactivate a gene but also to make specific nucleotide changes in a specific site in the genome and gene addition. These methods will be useful in fixing genes that contain harmful mutations and in supplying therapeutic proteins. Through repeated trips from bedside to bench and back again, it is likely that these approaches represent a basis for effective future therapeutic interventions," commented Dr. Mark A Kay of Stanford (Calif.) University and Dr. Bruce D. Walker of the Ragon Institute of MGH, MIT, and Harvard, in Cambridge, Mass., in an editorial accompanying the study published in the New England Journal of Medicine.

The study was supported by Sangamo Biosciences. Dr. Blick, Dr.Kay, and Dr. Walker reported having no relevant financial disclosures.

Commentary – ‘Elegant science’ with uncertain future

Dr. Anthony S. Fauci comments: The only way this is really going to be useful is if they in fact completely replace normal T cells ultimately, because as long as you have normal cells getting infected and spitting out virus, you’ve got a problem, and you’ve got a problem because normal cells making virus give you that immune activation that’s a very deleterious part of HIV disease – the aberrant activation associated with virus replication.

Is this elegant science? Yes. Is it an important step in the right direction? Yes. Will this turn out to be a successful approach? I can’t tell you that right now. It might not be.

Dr. Fauci is director of the National Institute of Allergy and Infectious Diseases in Bethesda, Md.

Early study: Potential ‘functional cure’ for AIDS?