Engineering chimeric antigen receptor (CAR) T cells to lower their affinity for the protein epithelial growth factor receptor (EGFR) made the cells preferentially recognize and eliminate tumor cells that have high amounts of EGFR while sparing normal cells that have lower amounts of the protein, according to a preclinical study.
CAR T cells that are currently being tested to treat B-cell malignancies target a specific protein present on leukemia and lymphoma, but these immune cells cannot distinguish cancer cells from normal cells, explained Cooper. Even though such CAR T cells attack cancer cells and normal B cells alike, the side effects are manageable, which may not be the case with solid tumors. "Many proteins that are present on solid tumors may also be present on normal cells that are vital to the body. So, while recipients of CAR T cells can tolerate the loss of normal B cells, they cannot endure damage to vital structures if the engineered T cells inappropriately damage essential tissues. Because of this, CAR T-cell-based immunotherapy may not yet be entirely safe for patients with solid tumors," added Cooper.
To make CAR T-cell therapy applicable to solid tumors, Cooper and his colleagues developed CAR molecules with reduced affinity for a target on solid tumors. The target they chose in this study was wild-type EGFR, a protein that is present at high levels in certain brain cancers, but is also found at low levels on some normal cells. These experiments were performed by Hillary Caruso, PhD, while a graduate student with Cooper.
The researchers used two monoclonal antibodies, cetuximab, which has higher affinity for EGFR, and nimotuzumab, which has lower affinity for EGFR, and from these, they engineered high-affinity cetux-CAR T cells and low-affinity nimo-CAR T cells.
The researchers tested the different CAR T cells on cancer cells with high levels of EGFR and normal cells with low levels of EGFR and found that while the cetux-CAR T cells killed both cancer and normal cells, the nimo-CAR T cells were selectively activated only in response to cancer cells, but not normal cells.
The researchers then tested the CAR T cells in mice bearing human brain cancer cells expressing high levels of EGFR and found that both cetux- and nimo-CAR T cells were equally effective in inhibiting tumor growth. However, the cetux-CAR T cells caused significant toxicity to the mice, leading to death in some, whereas the infused nimo-CAR T cells were safe. The researchers further tested the new CAR T cells in mice bearing cells that had low levels of EGFR (to mimic normal human cells), and found that unlike cetux-CAR T cells, the nimo-CAR T cells did not impact the growth of these cells.
In an interview, Cooper said, "The goal of the study was to make CAR-expressing T cells differentiate friend from foe. We wanted to provide CAR T cells an improved opportunity of targeting a protein that is overexpressed on a cancer cell and spare normal cells that may also have the same protein, but at lower levels.
"We think this provides an advance in the field of CAR T-cell therapy because until now the focus in terms of T-cell activation was on the intracellular portion of the CAR design, which led to the development of second- and third-generation CARs with different abilities to signal T cells. Our study has shown that another possibility is to tweak the extracellular portion of the CAR that docks with the tumor by adjusting its affinity for the target protein," said Cooper. This technology can be used to develop CAR T cells that can be fine-tuned to target other overexpressed cancer proteins besides EGFR, Cooper explained. "An important derivative of this study is that scientists can now tweak, or modulate, the affinity of a CAR T cell to meet the needs of a given tumor."
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Journal in Which the Study was Published: Cancer Research, a journal of the American Association for Cancer Research
Author: Laurence Cooper, MD, PhD, CEO of ZIOPHARM Oncology in Boston, and formerly, professor of pediatrics at The University of Texas MD Anderson Cancer Center, while conducting this study.
Funding & Disclosures: This study was funded by multiple groups including the National Institutes of Health and private foundations.
In January 2015, the technology was licensed for commercial application to ZIOPHARM Oncology and Intrexon Corporation in exchange for equity interests in each of these companies and, as a result, Cooper and some of the authors of this study have a financial interest in ZIOPHARM Oncology Inc. and Intrexon Corporation.
For further reading:
CAR T-cell Therapy: Engineering Patients' Immune Cells to Treat Their Cancers
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About the American Association for Cancer Research
Founded in 1907, the American Association for Cancer Research (AACR) is the world's oldest and largest professional organization dedicated to advancing cancer research and its mission to prevent and cure cancer. AACR membership includes more than 35,000 laboratory, translational, and clinical researchers; population scientists; other health care professionals; and cancer advocates residing in 101 countries. The AACR marshals the full spectrum of expertise of the cancer community to accelerate progress in the prevention, biology, diagnosis, and treatment of cancer by annually convening more than 25 conferences and educational workshops, the largest of which is the AACR Annual Meeting with almost 19,300 attendees. In addition, the AACR publishes eight prestigious, peer-reviewed scientific journals and a magazine for cancer survivors, patients, and their caregivers. The AACR funds meritorious research directly as well as in cooperation with numerous cancer organizations. As the Scientific Partner of Stand Up To Cancer, the AACR provides expert peer review, grants administration, and scientific oversight of team science and individual investigator grants in cancer research that have the potential for near-term patient benefit. The AACR actively communicates with legislators and other policymakers about the value of cancer research and related biomedical science in saving lives from cancer. For more information about the AACR, visit http://www.AACR.org.
To interview Laurence Cooper, contact Julia Gunther at julia.gunther@aacr.org or 215-446-6896.
Journal
Cancer Research