Penn researchers 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. This genetically-modified “serial killer” T-cell approach could provide a tumor-attack roadmap for the treatment of ovarian, lung, and pancreatic cancer, as well as myeloma and melanoma.
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 involves removing patients’ cells and modifying them in Penn’s vaccine production facility, followed by the infusion of the new cells back into the patient’s body following chemotherapy. This approach also represents a potential tumor-attack roadmap for the treatment of other cancers including those of the lung and ovaries and myeloma and melanoma. The findings, published simultaneously yesterday in the New England Journal of Medicine (NEJM) 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, M.D., Ph.D., 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 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, M.D., 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.”
Dr. 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 (Cluster of Differentiation 19).
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 of the target cells in the tumor are destroyed.
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“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 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, Ph.D., Michael Kalos, Ph.D., and Adam Bagg MB, BCh, all from Penn Medicine. Michael Kalos and Bruce Levine are co-first authors on the Science Translational Medicine paper. Other co-authors include Carl June, M.D., Ph.D., David Porter, M.D., Sharyn Katz, M.D., MTR, and Adam Bagg MB, BCh, from Penn Medicine, and Stephan Grupp, M.D., Ph.D., from 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.
Accompanying NEJM Editorial
In an accompanying NEJM editorial, Walter J. Urba, M.D., Ph.D. and Dan L. Longo, M.D. raise several important consideration in regard to the genetically-modified, serial killer T-cell therapy discussed above.
First, the editorial authors note that chimeric antigen receptors (or CARS) have theoretical advantages over other T-cell–based therapies, including: (i) use of the patient’s own cells, which avoids the risk of graft-versus-host disease; (ii) the ability to create CARs quickly; and (iii) use of the same CAR for multiple patients.
While noting the remarkable clinical outcome of the 64-year old male CLL patient described above, the editorial authors note that in addition to tumor lysis syndrome, the patient experienced B-cell depletion and hypogammaglobulinemia. Although these conditions may not create a major problem in patients with CLL, the authors state that the persistence of activated T-cells, memory T-cells, or both could pose substantial problems in other tumor types.
According to the editorial authors, both toxic effects to the target organ and also “on-target, but off-organ” toxic effects have been observed by other researchers in the past because of unanticipated cross-reactive target antigens.
While toxicity may become more of a problem as more potent second- and third-generation CARs are used in patients with different tumor types, the authors explain that additional safety measure may help offset that risk. The safety measures highlighted in the editorial include: (i) the infusion of a lower number of T-cells, (ii) the use of immunosuppressive agents, and (iii) the introduction of an inducible “suicide signal” to kill the cells when they are creating mischief.
In connection with the third safety measured provided above, the authors state that a novel, non-immunogenic, inducible caspase 9 “suicide gene” has already been developed. Nevertheless, the authors warn that the suicide gene strategy may not have time to work properly because the deaths from toxic effects reported in the past have been severe and occurred within hours after administration of the gene-transfected cells.
The editorial authors conclude that only with the more widespread clinical use of CAR T-cells will researchers learn whether the results reported by Porter et al. represent a true advancement toward a clinically applicable and effective therapy, or alternatively, another promising strategy that runs into an insurmountable barrier which is difficult to overcome.
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- Porter DL, et al. Chimeric Antigen Receptor–Modified T Cells in Chronic Lymphoid Leukemia. N Engl J Med. Published online August 10, 2011 (10.1056/NEJMoa1103849).
- Kalos M,et al. T Cells with Chimeric Antigen Receptors Have Potent Antitumor Effects and Can Establish Memory in Patients with Advanced Leukemia. Sci. Transl. Med. 3, 95ra73 (2011).
- Urba WJ & Longo DL. Redirecting T Cells. N Engl J Med Editorial. Published online August 10, 2011 (10.1056/NEJMe1106965).
- Genetically Modified “Serial Killer” T Cells Obliterate Tumors in Patients with Chronic Lymphocytic Leukemia, Penn Researchers Report, News Release, Penn Medicine, August 10, 2010.