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Gene Therapy Using Modified HIV Hailed as Potential Cancer Cure


Genetically engineered T-cells altered with a viral vector derived from HIV were able to destroy tumors and induce sustained remission in patients with leukemia -- a technique related to gene therapy currently being tested to protect T-cells from HIV infection.



As described in the August 10, 2011, issues of both Science Translational Medicine and the New England Journal of Medicine, Carl June from the University of Pennsylvania and colleagues removed a small number of T-cells from 3 patients with chronic lymphocytic leukemia (CLL) that did not respond to chemotherapy; their only remaining treatment option would have been a risky bone marrow transplant.

In the laboratory, the researchers used a lentivirus derived from HIV to insert a gene for a chimeric antigen receptor into the T-cells. When this receptor was expressed on the surface of these cells, they could recognize and destroy CLL tumor cells and B-cells carrying a specific marker (CD19).

The altered T-cells proliferated by 1000-fold and persisted at high levels for 6 months in the blood and bone marrow, continuing to express the chimeric antigen receptor, the researchers reported. The 3 patients experienced sustained, ongoing remission that started 3 weeks after infusion of the altered T-cells and had lasted 10 months at the time of the report.

Participants experienced tumor lysis syndrome -- a set of metabolic disturbances that occurs when a large number of tumor cells are killed and release toxic substances -- indicating that the treatment was working. The other main adverse event was that the treatment knocked out normal B-cells as well as CLL tumor cells, leading to B-cell aplasia and impaired antibody production.

June is also working with Jay Lalezari of Quest Clinical Research, Ronald Mitsuyasu of the University of California at Los Angeles, and others to test a gene therapy technique that uses zinc finger nucleases to alter CD4 T-cells in people with HIV.

While the newly reported leukemia treatment essentially adds a receptor to T-cells, the HIV treatment deletes a receptor. Zinc finger nucleases cut out the gene that encodes the CCR5 coreceptor used by many types of HIV to enter cells (along with the CD4 receptor). Because the altered CD4 cells no longer express CCR5, HIV is unable to infect them.

Interim results from an ongoing pilot study of participants who reached undetectable HIV viral load but had poor immunological recovery on antiretroviral therapy showed sustained CD4 cell gains out to 8 months so far.

The technique described in the present reports could possibly be used to target other types of cancer, including myeloma, lung cancer, and ovarian cancer. Gene therapy of this sort has the potential to be a mainstay of future medical treatment for a variety of diseases if it can be scaled up to allow for widespread, cost-effective use.


Below is an edited excerpt from a press release issued by the University of Pennsylvania Health system describing the research in more detail.

Genetically Modified "Serial Killer" T-Cells Obliterate Tumors in Patients with Chronic Lymphocytic Leukemia, Penn Researchers Report

Philadelphia -- August 10, 2011 -- In a cancer treatment breakthrough 20 years in the making, researchers from the University of Pennsylvania's Abramson Cancer Center and Perelman School of Medicine have shown sustained remissions of up to a year among a small group of advanced chronic lymphocytic leukemia (CLL) patients treated with genetically engineered versions of their own T-cells. The protocol, which involves removing patients' cells and modifying them in Penn's vaccine production facility, then infusing the new cells back into the patient's body following chemotherapy, provides a tumor-attack roadmap for the treatment of other cancers including those of the lung and ovaries and myeloma and melanoma. The findings, published simultaneously today in the New England Journal of Medicine and Science Translational Medicine, are the first demonstration of the use of gene transfer therapy to create "serial killer" T-cells aimed at cancerous tumors.

"Within three weeks, the tumors had been blown away, in a way that was much more violent than we ever expected," said senior author Carl June, MD, director of Translational Research and a professor of Pathology and Laboratory Medicine in the Abramson Cancer Center, who led the work. "It worked much better than we thought it would."

The results of the pilot trial of three patients are a stark contrast to existing therapies for CLL. The patients involved in the new study had few other treatment options. The only potential curative therapy would have involved a bone marrow transplant, a procedure which requires a lengthy hospitalization and carries at least a 20 percent mortality risk -- and even then offers only about a 50 percent chance of a cure, at best.

"Most of what I do is treat patients with no other options, with a very, very risky therapy with the intent to cure them," says co-principal investigator David Porter, MD, professor of Medicine and director of Blood and Marrow Transplantation. "This approach has the potential to do the same thing, but in a safer manner."

Secret Ingredients

June thinks there were several "secret ingredients" that made the difference between the lackluster results that have been seen in previous trials with modified T-cells and the remarkable responses seen in the current trial. The details of the new cancer immunotherapy are detailed in Science Translational Medicine.

After removing the patients' cells, the team reprogrammed them to attack tumor cells by genetically modifying them using a lentivirus vector. The vector encodes an antibody-like protein, called a chimeric antigen receptor (CAR), which is expressed on the surface of the T-cells and designed to bind to a protein called CD19.

Once the T-cells start expressing the CAR, they focus all of their killing activity on cells that express CD19, which includes CLL tumor cells and normal B-cells. All of the other cells in the patient that do not express CD19 are ignored by the modified T-cells, which limits side effects typically experienced during standard therapies.

The team engineered a signaling molecule into the part of the CAR that resides inside the cell. When it binds to CD19, initiating the cancer-cell death, it also tells the cell to produce cytokines that trigger other T-cells to multiply -- building a bigger and bigger army until all the target cells in the tumor are destroyed.

Serial Killers

"We saw at least a 1000-fold increase in the number of modified T-cells in each of the patients. Drugs don't do that," June says. "In addition to an extensive capacity for self-replication, the infused T-cells are serial killers. On average, each infused T-cell led to the killing of thousands of tumor cells – and overall, destroyed at least two pounds of tumor in each patient."

The importance of the T-cell self-replication is illustrated in the New England Journal of Medicine paper, which describes the response of one patient, a 64-year old man. Prior to his T-cell treatment, his blood and marrow were replete with tumor cells. For the first two weeks after treatment, nothing seemed to change. Then on day 14, the patient began experiencing chills, nausea, and increasing fever, among other symptoms. Tests during that time showed an enormous increase in the number of T-cells in his blood that led to a tumor lysis syndrome, which occurs when a large number of cancer cells die all at once.

By day 28, the patient had recovered from the tumor lysis syndrome -- and his blood and marrow showed no evidence of leukemia.

"This massive killing of tumor is a direct proof of principle of the concept," Porter says.

The Penn team pioneered the use of the HIV-derived vector in a clinical trial in 2003 in which they treated HIV patients with an antisense version of the virus. That trial demonstrated the safety of the lentiviral vector used in the present work.

The cell culture methods used in this trial reawaken T-cells that have been suppressed by the leukemia and stimulate the generation of so-called "memory" T-cells, which the team hopes will provide ongoing protection against recurrence. Although long-term viability of the treatment is unknown, the doctors have found evidence that months after infusion, the new cells had multiplied and were capable of continuing their seek-and-destroy mission against cancerous cells throughout the patients’ bodies.

Moving forward, the team plans to test the same CD19 CAR construct in patients with other types of CD19-positive tumors, including non-Hodgkin's lymphoma and acute lymphocytic leukemia. They also plan to study the approach in pediatric leukemia patients who have failed standard therapy. Additionally, the team has engineered a CAR vector that binds to mesothelin, a protein expressed on the surface of mesothelioma cancer cells, as well as on ovarian and pancreatic cancer cells.

In addition to June and Porter, co-authors on the NEJM paper include Bruce Levine, Michael Kalos, and Adam Bagg, all from Penn Medicine. Michael Kalos and Bruce Levine are co-first authors on the Science Translational Medicine paper. Other co-authors include June, Porter, Sharyn Katz and Adam Bagg from Penn and Stephan Grupp the Children's Hospital of Philadelphia.

The work was supported by the Alliance for Cancer Gene Therapy, a foundation started by Penn graduates Barbara and Edward Netter, to promote gene therapy research to treat cancer, and the Leukemia & Lymphoma Society.



M Kalos, BL Levine, DL Porter, CH June, et al. T-Cells with Chimeric Antigen Receptors Have Potent Antitumor Effects and Can Establish Memory in Patients with Advanced Leukemia. Science Translational Medicine 3 (95): 95ra73 (full text). August 10, 2011.

DL Porter, BL Levine, M Kalos, CH June, et al. Chimeric Antigen Receptor–Modified T-Cells in Chronic Lymphoid Leukemia. New England Journal of Medicine (full text) August 10, 2011 (Epub ahead of print).

WJ Urba, Dan L. Longo. Redirecting T-Cells (Editorial). New England Journal of Medicine. August 10, 2011 (Epub ahead of print).

Other Source

Perelman School of Medicine, University of Pennsylvania Health System. Genetically Modified "Serial Killer" T Cells Obliterate Tumors in Patients with Chronic Lymphocytic Leukemia, Penn Researchers Report. Press release. August 10, 2011.