Sangamo BioSciences, Inc., based in Richmond, California, is reporting positive news showing that CD4 T-cells can be made HIV resistant with the help of the company’s proprietary zinc finger DNA-binding protein nucleases (ZFN), specially developed transcription factors.
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.
Press release: Sangamo BioSciences Announces Nature Biotechnology Study Demonstrating the Use of Zinc Finger Nucleases to Generate HIV Resistant T Cells …
Sangamo ZFP technology page…
Abstract in Nature: Establishment of HIV-1 resistance in CD4+ T cells by genome editing using zinc-finger nucleases