Finger Nuclease that Disables CCR5 Gene May Offer Potential New HIV Treatment
are small DNA-binding proteins that mediate DNA-protein interactions within
cells, playing an important role in regulation of DNA expression.|
may be possible to create CD4 cells that are resistant to HIV infection by using
zinc finger protein nucleases to disable the gene that encodes the CCR5 co-receptor,
according to research presented at the 48th International
Conference on Antimicrobial Agents and Chemotherapy (ICAAC 2008) last month
in Washington, DC.
CCR5 is one of 2 co-receptors HIV uses to enter cells
(the other is CXCR4). CCR5 antagonist drugs such as maraviroc
(Selzentry) work by preventing the virus from using this co-receptor. The
new results indicate that HIV entry may also be prevented by disrupting expression
of CCR5 on cell surfaces.
Holmes of Sangamo BioSciences and colleagues developed zinc finger protein nucleases
(ZFNs) that target the CCR5 gene and cause double strand breaks at a predetermined
sites in the DNA. Natural DNA repair mechanisms can then be usurped to imperfectly
mend these breaks, resulting in the permanent disruption of the gene.
were introduced into human cells using an adenovirus vector. Cell-based assays
revealed that the CCR5 ZFNs produced the expected DNA breaks, leading to efficient
gene disruption (> 50%) in human CD4 cells.
ZFN-treated primary CD4
cells and transformed CD4 cell lines were specifically resistant to infection
with CCR5-tropic HIV, but otherwise behaved normally.
data demonstrate that ZFN-treated cells can be permanently modified to prevent
[CCR5]-dependent HIV infection," the researchers concluded.
laboratory cultures and in immunodeficient mice, the modified CD4 cells survived
and replicated well in the presence of HIV. Mice that received ZFN-modified cells
had increased numbers of CD4 cells and a statistically significant 7-fold reduction
in peripheral blood HIV viral load, compared to mice given non-modified cells.
Furthermore, the ZFN-altered cells appeared to have a selective advantage relative
to unmodified cells.
results led the investigators to suggest that "these cells may be able to
reconstitute immune function in patients with HIV/AIDS via maintenance of an HIV-resistant
using this method would involve removing some CD4 cells from a patient, modifying
them in the laboratory, and returning them to the body, where they would hopefully
replicate to create a reservoir of protected, HIV-resistant cells, thereby preserving
permanently modifying cells so they cannot express CCR5, the zinc finger approach
has a potential advantage over small molecule CCR5 antagonists or antibodies such
140 that must be continually administered to block the co-receptor and prevent
HIV entry. The zinc finger method would only alter CCR5 expression on CD4 cells
-- not other cell types -- but it is not yet clear whether disrupting CCR5 expression
could have unknown detrimental effects on immune function.
are very excited about these data and our collaboration with Sangamo to develop
an HIV/AIDS therapeutic," said Carl June, MD, of the University of Pennsylvania
School of Medicine in a press release issued by the company. "The ability
to prevent immune cells from becoming infected by HIV has the potential to provide
long term control of both the opportunistic infections characteristic of AIDS
as well as the virus itself. We look forward to bringing this program into the
Sangamo plans to test this strategy in human clinical trials
and intends to file an Investigational New Drug application by the end of 2008.
Univ. of Pennsylvania, Philadelphia, PA; Sangamo BioSci., Richmond,
EE Perez, J Wang, JC Miller,
and others. Establishment of HIV Resistant CD4 T Cells using Engineered Zinc Finger
Protein Nucleases. 48th International Conference on Antimicrobial Agents and Chemotherapy
(ICAAC 2008). Washington, DC. October 25-28, 2008. Abstract H-4044.
Sangamo BioSciences, Inc. Sangamo BioSciences Presents Data at ICAAC
Demonstrating 'In Vivo' Protection Against HIV Infection by CCR5-ZFN Therapeutic
Preclinical Animal Data Demonstrates Selective Survival Advantage of ZFN-Treated
Immune Cells after HIV Infection and Reduced Viral Loads. Press release.
October 28, 2008.