Sangamo BioSciences Announces Nature Biotechnology Study Demonstrating the Use of Zinc Finger Nucleases to Generate HIV Resistant T Cells

Preclinical Animal Data Demonstrates Promising Therapeutic Strategy for HIV/AIDS

RICHMOND, Calif., June 30, 2008 /PRNewswire-FirstCall/ -- Sangamo BioSciences, Inc. announced today the publication of data demonstrating that human immune system cells (CD4 T-cells) can be made resistant to HIV infection by treatment with zinc finger DNA-binding protein nucleases (ZFN(TM)). The data suggest that the ZFN approach, which results in the permanent modification of the CCR5 gene encoding an important receptor for HIV infection, is a promising strategy for the treatment of HIV/AIDS.

The work, which was carried out in the laboratory of Carl June, M.D., Director of Translational Research at the Abramson Family Cancer Research Institute at the School of Medicine, in collaboration with Sangamo scientists, was published as an Advance Online Publication in Nature Biotechnology (http://www.nature.com/nbt/journal/vaop/ncurrent/abs/nbt1410.html).

"A ZFN approach represents the 'next generation' of HIV-entry blocking agents and a potentially promising class of anti-HIV compounds," said, Dr. June who is the senior author of the study. "These proof of principle data, together with experience from individuals that carry a natural mutation in their CCR5 gene suggest that permanent 'knock-out' of the of CCR5 gene is important and clinically relevant for long-term resistance to HIV infection and, we believe, may prove to be more effective than temporary 'knock down' approaches based on small molecule inhibitors, antibodies, antisense or RNAi."

Sangamo's ZFNs are designed to permanently modify the DNA sequence encoding CCR5, a co-receptor that enables HIV to enter and infect cells of the immune system. Individuals carrying a naturally occurring mutation of their CCR5 gene, a variant known as CCR5-delta32, have been shown to be resistant to HIV infection.

"The data described in this paper are an important demonstration of the potential therapeutic properties of our product," commented Dale Ando, M.D., Sangamo's vice president of therapeutic development and chief medical officer. "We have demonstrated that a single treatment with our CCR5-specific ZFNs generates a population of HIV-resistant human T-cells similar to the situation in individuals carrying the natural CCR5-delta32 mutation. ZFN-modification of these cells is permanent and makes them resistant to HIV. The modified cells preferentially survive and expand in an animal after HIV infection, providing a reservoir of healthy and uninfectable immune cells. Furthermore, we observed that animals given the ZFN-modified cells had increased numbers of CD4 cells and substantially lower levels of HIV in their blood compared to animals given non-modified cells demonstrating statistically significant protection from the virus. In an HIV-infected patient, such modified cells could be available as a protected reservoir within the immune system to fight both opportunistic infections and HIV itself."

Several major pharmaceutical companies have initiated programs to develop small molecule or monoclonal antibody approaches to block the binding of HIV to CCR5. However, a small molecule or antibody approach requires the constant presence of a sufficiently high concentration of these drugs or antibody to block therapeutically relevant numbers of the CCR5 protein, which is present in thousands of copies on the surface of each T-cell and other tissues in the body. One such drug has been approved by the US Food and Drug Administration with a "black box" warning, the strongest for prescription drugs, concerning the risk of liver toxicity and the possibility of heart attacks.

Sangamo's ZFN technology represents a means of potentially circumventing these limitations or risks by specifically modifying only CD4 T-cells, the principal target of HIV pathology, in a one-time exposure of the cells to ZFNs. This results in permanent modification of the CCR5 protein such that HIV cannot enter and infect the cells. This approach could potentially enable the generation of a reservoir of protected CD4 T-cells that are available to fight the opportunistic infections that are characteristic of AIDS as well as HIV itself. Sangamo expects to initiate a clinical trial to evaluate this approach by the end of the year.

Data Reported in the Nature Biotechnology Paper

The reported results demonstrate that a one-time exposure to CCR5-specific ZFNs resulted in the generation of an HIV-resistant population of human primary T-cells by the permanent genetic modification of the CCR5 gene. These ZFN-modified CD4 T-cells expanded stably in HIV-infected cultures for several weeks and appeared to behave identically to untreated T-cells except that they were resistant to infection by HIV. ZFN treated primary CD4 T-cells and transformed CD4 cell lines resisted infection with R5-tropic HIV (virus that uses the CCR5 co-receptor to enter cells), resulting in enrichment of ZFN- generated CCR5-disrupted cells in the population upon long-term exposure to virus (>50 days). Importantly, in the presence of HIV, ZFN-modified CD4 T- cells also preferentially expanded in a mouse model. The modified cells were infused into mice that lack a normal immune system and thus do not reject human cells. After 33 days, the mice were sacrificed and analyzed for the presence of ZFN-modified cells. Researchers determined that ZFN-modified cells engrafted normally in the mouse and that the proportion of modified cells present at the end of the experiment was greater than two to three fold higher in mice in the presence of HIV infection (p=0.008). In a second experiment it was determined that 50 days after infection, mice given the ZFN- modified cells had increased numbers of CD4 cells and a statistically significant reduction in viral load in their peripheral blood (P<0.001) compared to mice given control cells. These data suggest that, in the presence of HIV, the ZFN-modified cells have a selective advantage allowing them to evade infection and destruction leaving them able fight opportunistic infections and HIV itself.

About HIV/AIDS and CCR5

HIV stands for Human Immunodeficiency Virus. HIV infection kills or impairs cells of the immune system, progressively destroying the body's ability to fight infections and certain cancers resulting in AIDS (Acquired Immune Deficiency Syndrome). Individuals diagnosed with AIDS are susceptible to life-threatening diseases called opportunistic infections, which are caused by microbes that usually do not cause illness in healthy people. According to Worldaidsday.org, over 3 million people were infected with HIV in 2005. There are now over 40 million people living with HIV and AIDS worldwide.

CCR5 is the chemokine receptor that HIV uses as a co-receptor to gain entry into immune cells. CCR5 is perhaps the most important of the known co- receptors for HIV, since the most commonly transmitted strains of HIV are strains that bind to CCR5 -- so-called "R5" strains. A small fraction of the population carries a mutation in their CCR5 gene, called the delta32 mutation. This mutated version of the gene results in a truncated CCR5 protein which cannot be used by HIV as a co-receptor. Individuals that have mutant delta 32 versions of both of their CCR5 genes are resistant to infection by R5 HIV strains.

About Sangamo

Sangamo BioSciences, Inc. is focused on the research and development of novel DNA-binding proteins for therapeutic gene regulation and modification. The most advanced ZFP Therapeutic(TM) development program is currently in Phase 2 clinical trials for evaluation of safety and clinical effect in patients with diabetic neuropathy. Phase 1 clinical trials are ongoing to evaluate a ZFP Therapeutic for peripheral artery disease. Other therapeutic development programs are focused on ALS, cancer, HIV/AIDS, neuropathic pain, nerve regeneration, Parkinson's disease and monogenic diseases. Sangamo's core competencies enable the engineering of a class of DNA-binding proteins known as zinc finger DNA-binding proteins (ZFPs). By engineering ZFPs that recognize a specific DNA sequence Sangamo has created ZFP transcription factors (ZFP TF(TM)) that can control gene expression and, consequently, cell function. Sangamo is also developing sequence-specific ZFP Nucleases (ZFN(TM)) for gene modification. Sangamo has established strategic partnerships with companies outside of the human therapeutic space including Dow AgroSciences, Sigma-Aldrich Corporation and several companies applying its ZFP Technology to enhance the production of protein pharmaceuticals. For more information about Sangamo, visit the company's web site at http://www.sangamo.com.

This press release may contain forward-looking statements based on Sangamo's current expectations. These forward-looking statements include, without limitation, references to the research and development of novel ZFP TFs and ZFNs as ZFP Therapeutics, applications of Sangamo's ZFP technology platform, the therapeutic potential of ZFNs for the treatment of HIV/AIDS, strategic partnerships with collaborators and clinical trials of ZFP Therapeutics. Actual results may differ materially from these forward-looking statements due to a number of factors, including technological challenges, uncertainties relating to the initiation and completion of stages of ZFP Therapeutic clinical trials, Sangamo's ability to develop commercially viable products and technological developments by our competitors. See the company's SEC filings, and in particular, the risk factors described in the company's Annual Report on Form 10-K and its most recent Quarterly Report on Form 10-Q. Sangamo BioSciences, Inc. assumes no obligation to update the forward-looking information contained in this press release.

CONTACT: Elizabeth Wolffe, Ph.D. of Sangamo BioSciences, Inc.,+1-510-970-6000, ext. 271, ewolffe@sangamo.com

Web site: http://www.sangamo.com/

Ticker Symbol: (NASDAQ-NMS:SGMO)

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Posted: June 2008

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