Last year, chimeric antigen receptor (CAR) T cell therapy was recognized as the Advance of the Year in the American Society of Clinical Oncology (ASCO) Annual Report for its demonstrated benefits in certain blood cancers and its potential in many other tumor types. At this year’s ASCO annual meeting, the interest in CAR T cell therapy remains strong with the availability of more data for approved and investigational therapies.
“So far, the oncology community has greeted CAR T cell therapy with extraordinary enthusiasm,” said Dr. Jeremy Abramson, clinical director for the Center for Lymphoma at Massachusetts General Hospital. “We’ve had few effective treatment options for difficult-to-treat blood cancers like diffuse large B-cell lymphoma [DLBCL]. The newest data from ASCO continues to suggest that CAR T cell therapy may represent an important advance for some patients.”
A Long Time in the Making
The first investigational CAR T cells were developed over 30 years ago, using genetic engineering advances with the goal to reprogram a patient’s immune system to recognize and attack cancer cells. Early attempts were lackluster; the engineered T cells were slow to reproduce, died quickly and produced weak immune responses that weren’t effective at killing tumor cells.
Advances in genetic engineering tools and techniques, as well as a far better understanding of the human genome, have advanced this type of technology. Over the past five years, the number of clinical trials involving CAR T cell therapies has skyrocketed from just a handful to more than 180.
In 2017, the U.S. Food and Drug Administration approved the first two CAR T cell therapies — one for children with relapsed or refractory acute lymphoblastic leukemia and another for non-Hodgkin lymphoma in adults who have failed at least two other kinds of treatment.
These are just two examples of diseases for which CAR T cell therapy represents a radically different therapeutic approach.
“CAR T cells are specifically engineered to recognize, go after and attack the cancer cells,” Abramson said.
CAR T CELL THERAPY BEGINS BY REMOVING A PATIENT’S T CELLS, WHICH FIGHT INFECTIONS IN THE BODY, THROUGH A BLOOD DRAW. THOSE CELLS ARE THEN SENT TO A MANUFACTURING SITE WHERE THEY ARE GENETICALLY ENGINEERED TO RECOGNIZE AND ATTACH TO ANTIGENS EXPRESSED ON CANCER CELLS AND SOME NORMAL CELLS. PATIENTS THEN RECEIVE CHEMOTHERAPY BEFORE THESE PROGRAMMED CELLS ARE RETURNED TO THEIR BODIES TO SEEK AND ATTACK CANCER CELLS. PATIENTS ARE MONITORED FOR SIDE EFFECTS AFTER CAR T CELL THERAPY.
Exploring Questions in Blood Cancers
While the first two CAR T therapies have been approved, Abramson notes that many questions remain, including CAR T cell therapy production, safety and longevity.
Scientists are still fine-tuning the process of creating CAR T cell therapies. For instance, studies continue around different ratios of two subtypes of T cells—CD4+ and CD8+ T cells— that may behave differently. That’s because CD8+ T cells have a cancer-killing effect, while CD4+ T cells produce chemical messages that boost T cell production. Finding the right ratio of CAR T cells created from these subtypes may impact the efficacy and safety of these treatments, according to Abramson. But the clinical significance of CD4:CD8 ratio remains unknown.
“Even the most effective therapies can only be administered if the toxicities can be identified and successfully treated and reversed,” Abramson explained. “We’re continuing to learn about potential toxicities with the different approved and investigational CAR T cell therapies, and how to optimally manage and prevent them.”
We are studying ways to make these therapies work better, designing more effective CAR T cells that may target different or multiple cancer proteins and combining them with other medications.
Adverse events that have been noted in trials of CAR T cell therapy include cytokine release syndrome (CRS) and neurotoxicity. CRS symptoms include fever, nausea, or headaches, and neurotoxicity symptoms include delirium, headaches and problems speaking. ASCO attendees will get a better understanding of the severity and timing of these and other potential safety issues as well as insight into paths for their prevention and treatment.
As for the durability of CAR T cell therapies, Abramson believes there’s work to be done.
“Less than half of patients with DLBCL who receive CAR T cell therapy are still in remission a year later,” he said. “We are studying ways to design more effective CAR T cells that may target different or multiple cancer proteins and learn how to combine them with other medications like checkpoint inhibitors or immunomodulators to see if we can enhance CAR T cell activity.”
Beyond the Blood
So far, CAR T cell therapies have only been approved for the treatment of blood cancers. The major challenge in solid tumors, such as lung and breast cancers, has been identifying a target that’s restricted to the tumor, so the CAR T cells don’t also attack the patient’s healthy cells.
CAR T cells kill healthy immune cells called B lymphocytes, for instance, as well as lymphoma cells, but patients can often do without those particular cells. But a treatment that attacked an entire organ — or organs — would have catastrophic effects.
According to Abramson, one potential way to get around the problem may be to create CAR T cells that attack only when they encounter a specific combination of targets. While a single protein might be shared by cancer and healthy cells, researchers are searching for patterns of multiple targets only found on cancer cells. Whether or not this tactic succeeds, Abramson is optimistic that scientists can find a way.
To learn more about the advances that will be discussed at ASCO 2018, read “ASCO 2018 Preview: Precision Medicine, CAR T Cells and Immunomodulators.”
Dr. Abramson is a lead principal investigator for Juno and has consultant/advisory roles with Celgene.