A group led by the Sanger Institute and the University of Cambridge, working with the Sangamo Biosciences, has shown that it's possible to fix mutations in reprogrammed cells. This work, which was published in Nature, takes two previous advances and combines them into one proof-of-concept.
Since 2007 stem cell scientists have been able to reprogram adult cells such as skin back into an embryonic-like state. These so-called iPS cells can then mature into any cell type in the body, much like embryonic stem cells.
Other groups have shown that it's possible to take adult stem cells such as those from the bone marrow, correct mutations, and create mutation-free cells that, at least in animal models, can fix diseases. That's the idea behind CIRM's two HIV/AIDS disease team awards (described here and here) and a sickle cell disease team. In fact, one of the HIV/AIDS disease teams is also working with technology developed by Sangamo to fix the mutations.
In the work reported in Nature, the team created iPS cells from a person with a genetic liver disease, fixed the mutation, then matured the iPS cells into functional liver cells. A Reuters story quotes Allan Bradley, director of the Sanger Institute:
"These are early steps, but if this technology can be taken into treatment, it will offer great possible benefits for patients," he added.
Reuters quoted David Lomas, who was part of the team from Cambridge, saying that the liver cells survived when transplanted into mice.
The researchers said it could be another five to 10 years before full clinical trials of the technique could be run using patients with liver disease. But if they succeed, liver transplants -- costly and complicated procedures where patients need a lifetime of drugs to ensure the new organ is not rejected -- could become a thing of the past.
"If we can use a patient's own skins cells to produce liver cells that we can put back into the patient, we may prevent the future need for transplantation," said Lomas.
Last week the company Sangamo Biosciences announced good results from their HIV/AIDS trial in which they genetically altered patients' own T-cells. CIRM is following this trial closely, since it's the precursor to one being developed by a team of CIRM-funded researchers led by John Zaia at City of Hope that includes Sangamo.
The goal was to see if receiving these altered cells would let patients go off their anti-retroviral drugs. The results, reported at a recent conference in Chicago, were mixed—the cells didn’t always survive long in the fifteen people enrolled. But two patients saw their HIV levels drop 10-fold, and one patient who stopped his anti-retrovirals first saw a spike in virus levels but then had them decline to undetectable levels.
The work funded by CIRM is a next generation version of this trial. In both cases, Sangamo's technology is used to snip the DNA of cells taken from a patient's bone marrow. Those snips introduce a mutation in a gene called CCR5, which makes the protein that the HIV virus uses to enter a cell. No CCR5 gene means HIV can't infect the cells.
Doctors then reintroduce those cells into the patient. The idea is that the patient will then be resistant to the HIV in their bloodstream and eventually can go off drugs. In the recently reported study, the team altered the adult T-cells, which would supply a finite number of resistant T cells. The CIRM study will be altering the blood-forming stem cells, which give rise to T-cells, in hopes of creating a more permanent supply of HIV-resistant T-cells.
This video gives more information about the goal of the CIRM-funded team:
Sangamo's so-called zinc finger technology can recognize a specific location in the DNA, snip it out, and replace it with a different sequence. In the case of HIV, the molecular zinc scissors are being used to create a mutation in a small region of DNA in blood-forming stem cells.
Those cells altered in the lab lack a working copy of the protein CCR5, which the HIV virus uses to enter and destroy immune cells. The team then plans to transplant those altered stem cells into a person, where they create a new immune system that is resistant to HIV infection. Early results from this work in animals look promising and the team is hoping to be able to enter human clinical trials with the technique in the next few years.
This is one of two CIRM disease teams attempting to generate a stem cell-based therapy for HIV/AIDS. The other award, to Irvin Chen at UCLA, is using a different type of molecule to mutate the CCR5.
Ron Leuty of the San Francisco Business Journal had a story yesterday about Sangamo's prospects, which include a trial to treat pain associated with diabetes, called diabetic neuropathy. The technique is also being used in research to treat the blood-clotting disease hemophilia B and to create disease-in-a-dish models of heart disease. Reuty wrote about the heart disease work, being carried out by Sangamo and researchers at the Scripps Translational Science Institute:
Using induced pluripotent stem cells — adult stem cells manipulated to give them embryonic-like qualities — researchers will recreate cells that line the arteries. ...
"Genome editing allows us to do an experiment no one has ever tried — that is, if you change someone's genetics, can you make their cells revert away from acquiring a disease?" Samuel Levy, director of genomic sciences at the Scripps Translational Science Institute, said in a press release.
This video describes how the City of Hope team hopes to use the zinc finger technology in their proposed therapy for HIV.
You can also watch talks by City of Hope research John Zaia, CIRM board member and HIV patient advocate Jeff Sheehy, and HIV advocate Loren Leeds when they spoke to the CIRM governing board about the work.
At the 18th Conference on Retroviruses and Opportunistic Infections (CROI) in Boston, two members of CIRM’s HIV/AIDS Disease Team led by John Zaia at City of Hope presented new research showing the team’s progress toward the clinic.
The team’s overall goal is to use technology developed by Sangamo Biosciences to modify the blood-forming stem cells of people infected with HIV. The modifications would effectively remove the doorway protein—called CCR5—the HIV virus uses to enter immune cells. The less than one percent of the population who lack CCR5 are naturally resistant to HIV infection and one HIV patient in Berlin who received a complete bone marrow transplant from someone born lacking the CCR5 receptor has been functionally “cured” of HIV.
In a presentation on Monday, Sangamo Biosciences released preliminary data from 6 HIV patients in its gene therapy clinical trial targeting T-cells, which are the primary immune cells invaded by the HIV virus. The study uses Sangamo’s zinc finger gene modification technique to remove the CCR5 receptor from T-cells taken from the patients with HIV. Those modified T cells were then returned to the patients’ blood system. The patients saw both survival and expansion of the modified T-cells—a critical finding since this implies some competitive advantage for cells protected by CCR5 deletion over cells that are not protected.
This finding is not itself a cure, since T-cells are just one type of immune cell that HIV attacks. However, it is encouraging for the CIRM funded Disease Team project, which seeks to use the same gene modification technique on a HIV patient’s blood-forming stem cells in the bone marrow. These tissue-specific stem cells give rise to all of the blood cells in the body and modifying them successfully could lead to protection for all of the immune cells that HIV attacks – not just the T cells. A full bone marrow transplant replacing the entire blood-forming stem cell compartment with modified cells carries significant risk, with mortality close to twenty percent. However, partial replacement of the stem cell compartment with CCR5 deleted cells and successful survival and expansion might be a safer and more accessible avenue for replicating the functional cure achieved in the single Berlin patient.
In a presentation Wednesday at CROI supporting this approach, Paula Cannon from USC and a member of the same Disease Team, will expand on her research on the use of hematopoietic stem cells genetically modified with the Sangamo zinc finer technology to remove CCR5 in mice with humanized immune systems. In her previously published study (here's a link to the Nature paper), the partial replacement of the bone marrow stem cell compartment with a minority of gene-modified cells led to competition between modified and unmodified cells with the CCR5 deleted modified cells (here's our blog entry on the work). In the humanized mice, the modified cells were eventually selected to the point where the humanized immune systems of the mice were able to control HIV successfully to a level where HIV is undetectable and without the use of antiretroviral therapies.
Together these two studies suggest that the Sangamo technology is able to effectively remove the CCR5 protein from modified cells, and that those cells are able to resist HIV infection.
