Scientists have created a new and more advanced form of immune-based cancer therapy using engineered cells known as CAR-NK (natural killer) cells. Like CAR-T cells, these modified immune cells can be programmed to recognize and attack cancer, but they rely on a different type of immune cell that naturally targets abnormal or infected cells.
A team from MIT and Harvard Medical School has now developed a more effective way to engineer CAR-NK cells that dramatically reduces the chance of the body’s immune system rejecting them. Immune rejection has been one of the biggest limitations of cell-based therapies, often weakening their effectiveness.
This innovation could also make it possible to produce “off-the-shelf” CAR-NK treatments that are available immediately after diagnosis, rather than waiting weeks for custom-engineered cells. Traditional CAR-NK and CAR-T manufacturing methods typically require several weeks to complete before patients can begin treatment.
“This enables us to do one-step engineering of CAR-NK cells that can avoid rejection by host T cells and other immune cells. And, they kill cancer cells better and they’re safer,” says Jianzhu Chen, an MIT professor of biology, a member of the Koch Institute for Integrative Cancer Research, and one of the senior authors of the study.
In tests using mice with humanized immune systems, the newly engineered cells successfully destroyed most cancer cells while avoiding attack from the host’s own immune defenses.
Rizwan Romee, an associate professor of medicine at Harvard Medical School and Dana-Farber Cancer Institute, is also a senior author of the paper, which was published in Nature Communications. The study’s lead author is Fuguo Liu, a postdoctoral researcher at the Koch Institute and a research fellow at Dana-Farber.
Evading the immune system
Natural killer (NK) cells are a vital part of the body’s built-in immune defense, responsible for identifying and destroying cancerous and virus-infected cells. They eliminate these threats through a process called degranulation, which releases a protein known as perforin. This protein punctures the membrane of target cells, leading to their death.
To produce CAR-NK cells for treatment, doctors typically collect a blood sample from the patient. NK cells are then extracted and engineered to express a specialized protein called a chimeric antigen receptor (CAR), which is designed to target specific markers found on cancer cells.
Once modified, the cells must multiply in the lab for several weeks before there are enough to be infused back into the patient. The same general process is used for CAR-T cell therapies, some of which have already been approved to treat blood cancers like lymphoma and leukemia. CAR-NK therapies, however, are still being tested in clinical trials.
Because growing enough personalized CAR-NK cells takes time and the patient’s cells may not always be healthy enough for reliable use, scientists have been exploring an alternative: creating NK cells from healthy donors. These donor-derived cells could be mass-produced and stored for rapid use. The challenge, however, is that the recipient’s immune system often identifies donor cells as foreign and destroys them before they can attack the cancer.
In their latest research, the MIT team aimed to solve this problem by helping NK cells “hide” from immune detection. Their experiments showed that removing surface proteins known as HLA class 1 molecules allowed NK cells to avoid attack from T cells in the host’s immune system. These proteins normally act as identity markers that tell the immune system whether a cell belongs to the body.
To make use of this insight, the researchers added a sequence of siRNA (short interfering RNA) that silences the genes responsible for producing HLA class 1 proteins. Along with this genetic tweak, they introduced the CAR gene itself and another gene that encodes either PD-L1 or single-chain HLA-E (SCE), both of which help strengthen the NK cells’ cancer-fighting abilities.
All of these genetic components were combined into a single DNA construct, which allowed the team to efficiently convert donor NK cells into immune-evasive CAR-NK cells. Using this method, they engineered cells that target CD-19, a protein commonly found on malignant B cells in lymphoma patients.
NK cells unleashed
The researchers tested these CAR-NK cells in mice with a human-like immune system. These mice were also injected with lymphoma cells.
Mice that received CAR-NK cells with the new construct maintained the NK cell population for at least three weeks, and the NK cells were able to nearly eliminate cancer in those mice. In mice that received either NK cells with no genetic modifications or NK cells with only the CAR gene, the host immune cells attacked the donor NK cells. In these mice, the NK cells died out within two weeks, and the cancer spread unchecked.
The researchers also found that these engineered CAR-NK cells were much less likely to induce cytokine release syndrome — a common side effect of immunotherapy treatments, which can cause life-threatening complications.
Because of CAR-NK cells’ potentially better safety profile, Chen anticipates that they could eventually be used in place of CAR-T cells. For any CAR-NK cells that are now in development to target lymphoma or other types of cancer, it should be possible to adapt them by adding the construct developed in this study, he says.
The researchers now hope to run a clinical trial of this approach, working with colleagues at Dana-Farber. They are also working with a local biotech company to test CAR-NK cells to treat lupus, an autoimmune disorder that causes the immune system to attack healthy tissues and organs.
The research was funded, in part, by Skyline Therapeutics, the Koch Institute Frontier Research Program through the Kathy and Curt Marble Cancer Research Fund and the Elisa Rah Memorial Fund, the Claudia Adams Barr Foundation, and the Koch Institute Support (core) Grant from the National Cancer Institute.