Data from the late-breaking presentation demonstrate that viral load (VL) became undetectable during a treatment interruption (TI) from antiretroviral therapy (ART) in three of seven evaluable CCR5 delta-32 heterozygote HIV-infected subjects, including two of six subjects that had completed TI in the ongoing SB-728-902 Cohort 5 study and an additional subject from an earlier Phase 1 clinical trial of SB-728-T. In one SB-728-902 Cohort 5 subject, VL has remained undetectable (at or below the limits of quantification (LOQ) of the current ultra-sensitive assays for HIV) for seven weeks (to last measurement taken) and the TI is ongoing. Reduction in VL from peak during TI showed a statistically significant correlation (p=0.015) with estimated numbers of engrafted ZFN modified cells (SB-728-T) in which both copies of the CCR5 gene had been disrupted (biallelic modification), in line with previously presented data from this program.
"The data presented today demonstrate that a single infusion of SB-728-T can lead to profound suppression of viral load in the blood and sustained functional control of the virus," stated
In a presentation on
"These data are extremely important and suggest that an immunological approach to control of HIV infection is obtainable," commented
Central and transitional memory T-cells remember previously encountered foreign invaders, such as viruses or bacteria. These cells can survive in the body for the individual's lifetime and reactivate when they re-encounter the same antigen. On reactivation they produce a faster and stronger immune response than the previous encounter. SB-728-T seems to both expand the total memory pool and, by CCR5 modification, protect a proportion of that pool from HIV entry, suggesting that SB-728-T treatment has the potential to durably reconstitute and protect an effective immune system in HIV-infected individuals.
"We are amassing a body of data suggesting that SB-728-T treatment can potentially enable attacks on HIV infection from several angles," said
Dr. Nichol added, "In addition to our SB-728-902 Cohort 5 study, we have a second ongoing trial (SB-1101) designed to maximize the engraftment of SB-728-T in subjects who are not CCR5 delta-32 heterozygotes and who represent the vast majority of HIV-infected individuals. Maximizing circulating SB-728-T is important, as viral control appears related to the extent of engraftment. This trial is evaluating escalating doses of a preconditioning drug, cyclophosphamide (Cytoxan®), which is used to transiently reduce the numbers of T-cells in the body. The cells rapidly repopulate once the drug is discontinued, an effect that can enhance engraftment of concurrently administered exogenous T-cells such as SB-728-T. We intend to present data from all dose-escalation cohorts in these studies before the end of 2013."
Sangamo's drug, SB-728-T, is generated by ZFN-mediated modification of the gene encoding the CCR5 receptor in a patient's own T-cells. ZFN modification disrupts the expression of this key co-receptor for HIV entry and renders cells resistant to HIV infection. The approach is based on the observation that a naturally occurring mutation in the CCR5 gene, CCR5 delta-32, provides protection from HIV infection. Individuals in whom both copies of the CCR5 gene carry the delta-32 mutation are generally not susceptible to the most common strain of HIV.
Summary of Clinical Trial Design
About SB-728-902 Cohorts 1-3
The study is an open-label Phase 1 clinical trial to evaluate the safety and tolerability of single infusions of an escalating dose of an autologous (a patient's own) CD4+ T-cell product genetically modified at the CCR5 gene by CCR5-specific ZFNs (SB-728-T). The trial enrolled nine HIV-infected subjects (three cohorts of three subjects each) who have sub-optimal T-cell levels and no detectable viral load on long-term ART. Subjects remained on their existing antiviral therapy while receiving treatment with SB-728-T.
About SB-728-902 Cohort 5
Up to 20 HIV-infected subjects heterozygous for the CCR5 delta-32 mutation (i.e. with one CCR5 gene that is naturally modified) who are currently on ART are being enrolled and will receive a single intravenous infusion of SB-728-T (5 to 30 billion modified cells). Two months after SB-728-T treatment, subjects undergo a 16 week TI during which time their ART is discontinued. ART will be reinstituted in subjects whose CD4 T-cell counts drop to < 350 cells/ mm3 and/or whose HIV-RNA increases to > 100,000 /mL for three consecutive weekly measurements. At the end of the TI, subjects with a sustained detectable HIV viral load are reinstituted on ART. Subjects with an undetectable viral load can remain off ART until HIV RNA levels are detectable or their CD4 T-cell count drops below 350 cell/mm3 for three consecutive weekly measurements.
A total of ten subjects have been treated in this cohort.
Of the six evaluable subjects, we observed two subjects in which their VL became undetectable during TI from ART:
A third subject completed the TI with 1-log decrease in VL from peak.
In three subjects, there was no reduction in VL during the TI, one completed the TI and in two the TI was terminated early due to their viral loads exceeding the upper limit allowed in the protocol.
A seventh subject has not completed TI and is still being evaluated.
The non-employee authors of these abstracts have no financial relationship with Sangamo.
ZFP Therapeutic® is a registered trademark of
This press release may contain forward-looking statements based on Sangamo's current expectations. These forward-looking statements include, without limitation, references relating to research and development of novel ZFP TFs and ZFNs and therapeutic applications of Sangamo's ZFP technology platform for the treatment of HIV/AIDS, including a potential functional cure for HIV/AIDS, the ability of a ZFP Therapeutic to control HIV infection, projected timing of release of SB-728-T clinical data, the expansion of clinical studies for HIV-infected individuals and the initiation of additional preclinical studies of ZFN-gene modification. Actual results may differ materially from these forward-looking statements due to a number of factors, including uncertainties relating to the initiation and completion of stages of our clinical trials, whether the clinical trials will validate
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