"A significant number of subjects treated with SB-728-T have experienced a striking control of their viral load for a sustained period in the absence of ART," stated Dr. Sékaly. "This is particularly notable in cohorts treated with optimal doses of Cytoxan® in the SB-728-1101 study. Immunological and HIV reservoir analyses suggest that the best predictors for post-treatment viral control are higher levels of SB-728-T engraftment, specifically long-lived memory T-cells, evidence of polyfunctional antiviral CD8 responses during TI and lower HIV reservoir levels prior to TI. This may provide a model mechanism of action for SB-728-T and help identify HIV-infected individuals who will benefit most from this novel immune-based therapy."
"The evidence of sustained viral load control in subjects enrolled in the 1101 study is very encouraging," said
Of the nine subjects pre-conditioned with Cytoxan doses of 1.0 and 1.5 g/m2 (Cohorts 3, 3* and 5) six subjects demonstrated durable control of viremia (VL < 10,000) during an extended TI (14-26 months duration), with two subjects showing consistent ongoing VL measurements less than 1,000 (17 and 20 months at the time of analysis). Using a univariate linear regression model, the analysis demonstrated that greater levels of engrafted CCR5-modified cells before TI (p=0.03) and higher frequencies of long-lived CD4 memory T-cells (TSCM) during TI (p=0.01) correlated with lower VLs. The data suggest that an HIV resistant, long-lived CD4 TSCM compartment is likely to be critical in establishing VL control possibly by restoring immune homeostasis and providing help to HIV-specific CD8 T-cells. Multivariate analyses were used to determine parameters that further predict VL control during TI. Results indicate that higher CD4 TSCM levels, as well as a more robust polyfunctional anti-HIV gag CD8 response during TI (p=0.04) were associated with reduced VL. Furthermore, the analysis demonstrated that HIV reservoir size prior to TI showed a significant interaction with CD8 response in this model (p=0.03). These data suggest that a smaller HIV reservoir at the beginning of the TI coupled with a strong CD8 response resulted in better VL control.
In late 2015, Sangamo enrolled five additional subjects in Cohort 3* and expects to present that data at the end of 2016. Pending the data readout for SB-728-1101 Cohort 3*, the Company intends to partner the HIV program for pivotal studies and commercialization.
Sangamo's therapeutic candidate, SB-728-T, is generated by zinc finger nuclease (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.
About SB-728-1101 Cohorts 1-5 and Cohort 3*
SB-728-1101 is an open-label, dose escalation, multi-center study designed primarily to evaluate the safety and tolerability of escalating doses of cyclophosphamide (Cytoxan®) administered prior to SB-728-T infusion. By protocol, HIV-infected subjects on ART were enrolled into five dose-escalating cohorts (three subjects/cohort), and received intravenous Cytoxan (200 mg, 500 mg/m2, 1.0g/m2, 1.5g/m2 and 2.0g/m2). One to three days after receiving Cytoxan, subjects were infused with SB-728-T (8.2 to 36.2 billion cells). Six weeks after SB-728-T infusion, subjects with CD4 cell counts ≥500 cells/mm3 underwent a 16 week TI during which time their anti-retroviral therapy was discontinued. At the end of the TI, subjects with a sustained detectable viral load or reduced CD4 T-cell count were reinstituted on ART. In addition to safety, the study is designed to evaluate the effect of escalating doses of Cytoxan on SB-728-T engraftment, the effect of SB-728-T treatment on viral load following ART interruption, the change in CD4+ T-cell counts in peripheral blood and the long-term persistence of SB-728-T. SB-728-1101 was expanded in 2015 to include an additional cohort, Cohort 3*. Subjects in this cohort of the study are treated with an SB-728-T preparation of up to 40 billion ZFN-modified CD4 and CD8 T-cells. Up to eight subjects will be treated, all of whom have been accrued.
Cytoxan is a drug that is used to transiently reduce the numbers of T-cells in the body, which then rapidly repopulate once the drug is discontinued, and it is into this "growth" environment that SB-728-T is infused. Such lymphodepletive treatment has been used to enhance engraftment of adoptively transferred T-cells in the treatment of cancer, and as therapy for numerous autoimmune diseases. The drug has been previously used in HIV-infected individuals and studies demonstrate that while the drug was transiently lymphodepleting, it did not significantly reduce total CD4 T-cell counts over the long term and was adequately tolerated.
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 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, the projected timing of release of SB-728-T clinical data; and potential partnership for the HIV program. 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 and support the tolerability and efficacy of ZFNs, technological challenges, Sangamo's ability to develop
commercially viable products and technological developments by our competitors. For a more detailed discussion of these and other risks, please see Sangamo's public filings with the
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