Scientists from the University of Pennsylvania have engineered immune cells to seek out and attack a type of deadly brain cancer. In an important preclinical study, these souped-up immune cells were shown to be both safe and effective at controlling tumor growth in mice treated with these modified cells. This work is the result of collaboration between a team from the Perelman School of Medicine at the University of Pennsylvania and the Novartis Institutes for BioMedical Research. These results will hopefully be the impetus for a newly opened clinical trial for glioblastoma patients at Penn.
Marcela Maus, assistant professor of Hematology/Oncology at the Penn Abramson Cancer Center, said: “A series of trials that began in 2010 have found that engineered T cells have an effect in treating some blood cancers, but expanding this approach into solid tumors has posed challenges. A challenging aspect of applying engineered T cell technology is finding the best targets that are found on tumors but not normal tissues. This is the key to making this kind of T cell therapy both effective and safe.”
This new preclinical study, which was conducted with Hideho Okada and his colleagues at the University of Pittsburgh, makes use of T cells engineered to express a chimeric antigen receptor (CAR) that specifically binds to a mutant epidermal growth factor receptor protein called EGFRvIII. EGFRvIII is found on the cell surfaces of approximately 30 percent of glioblastoma tumors. Over 22,000 Americans are diagnosed with glioblastoma each year, and those patients whose glioblastomas express the EGFRvIII mutation tend to be more aggressive and are less likely to respond favorably to standard therapies and more likely to recur after treatment.
“Patients with this type of brain cancer have a very poor prognosis. Many survive less than 18 months following their diagnosis,” said M. Sean Grady, who is the Charles Harrison Frazier Professor and chair of the department of Neurosurgery. “We’ve brought together experts in an array of fields to develop an innovative personalized immunotherapy for certain brain cancers.”
This new trial is being led by Donald O’Rourke, associate professor of Neurosurgery, who heads an interdisciplinary collaboration of neurosurgeons, neuro-oncologists, neuropathologists, immunologists, and transfusion medicine experts.
In order to bring this experiment to fruition, Maus and her colleagues had to characterize the EGFRvIII CAR T cell. They had to develop and tested multiple antibodies that bind to cells expressing EGFRvIII on their surface. The single-chain variable fragments or scFvs that recognized the mutant EGFRvIII protein were then extensively tested in order to confirm that they do not also bind to those normal, EGFR proteins that are widely expressed on cells in the human body.
Maus and her group then generated a panel of humanized scFvs and tested their specificity and function in CAR modified T cells. The humanized scFvs have distinct amino acid sequences that more closely resemble human antibodies. From this huge panel of humanized scFvs, they selected one scFv to explore further based on its binding selectivity for EGFRvIII over normal non-mutated EGFR. They also evaluated the EGFRvIII CAR T cells by testing them against normal EGFR-expressing skin cells in mice grafted with human skin. This test showed that the engineered EGFRvIII CAR T cells did not attack cells with normal EGFR, at least under these conditions.
In order to test the selected scFv for its anti-cancer efficacy, Maus and others used human tumor cells that expressed EGFRvIII and showed that the EGFRvIII CAR T cells could multiply and secrete cytokines in response such to tumor cells. When used inside living animals, it was clear that the EGFRvIII CAR T cells ably controlled tumor growth in several mouse models of glioblastoma. The tumors were measured with magnetic resonance imaging (MRI) and the EGFRvIII CAR T cells caused tumor shrinkage, and were also effective with used in combination with the anticancer drug temozolomide, which is normally used to treat patients with glioblastoma.
On the strength of these preclinical successes, this team designed a phase 1 clinical study of CAR T cells transduced with humanized scFv directed to EGFRvIII for both newly diagnosed and recurrent glioblastoma patients who carry the EGFRvIII mutation. “There are unique aspects about the immune system that we’re now able to utilize to study a completely new type of therapy,” said O’Rourke.
For these glioblastoma patients, their T cells were removed by means of apheresis (a process similar to dialysis), and then the T cells were genetically engineered using a viral vector that programs them to find EGFRvIII-expressing cancer cells. The patient’s own engineered cells are infused back into their body, and when the T cells find the EGFRvIII-expressing cells, a signaling domain built into the CAR promotes proliferation of these “hunter” T-cells. This procedure is distinct from other T cell-based therapies that also target some healthy cells, since EGFRvIII seems to only be found on tumor tissue, which the study’s leaders hope will minimize side effects.
This new phase I clinical trial will enroll 12 adult patients whose tumors express EGFRvIII, in two groups: One arm of 6 patients whose cancers have returned after receiving other therapies, and one arm of 6 patients who are newly diagnosed with the disease and still have 1 cm or more of tumor tissue remaining after undergoing surgery to remove it.
The clinical trial is sponsored by the biotech company Novartis. In 2012, the University of Pennsylvania and Novartis announced an exclusive global research and licensing agreement to further study and commercialize novel cellular immunotherapies using CAR technologies. This STM study is the first pre-clinical paper developed within the Penn-Novartis alliance, with Penn and Novartis scientists working collaboratively. Ongoing clinical trials evaluating a different type of Penn-developed CAR therapy known as CTL019 have yielded promising results among some patients with certain blood cancers. In July 2014, the FDA granted CTL019 its Breakthrough Therapy designation for the treatment of relapsed and refractory acute lymphoblastic leukemia in both children and adults.