CAR T Cells as “Living Drugs”

“Incredibly exciting” is how experts are describing the new development with chimeric antigen receptor (CAR) T cells, as the first of these novel therapies approaches the market.

“Living Drugs”

The treatment product is made individually for each patient. After blood is taken from the patient, it undergoes a process that involves extracting immune system T cells, subjecting the cells to CAR cell engineering, and then infusing the engineered T cells back into the patient. The engineering changes the T cell in two ways. First, it adds a receptor that targets the CD19 antigen that is found on most leukemia cells. When the cells are returned to the patient’s body, they home in on this antigen, latch on, and destroy the leukemia cell. Second, the process inserts a viral vector mechanism into the cells that, once the cells have latched onto the leukemia cell, triggers these T cells to expand and proliferate, so that they seek out and destroy all the remaining leukemia cells.

Because they grow and expand in the body and then lie dormant, CAR T cells have been described as “living drugs.” It is not clear whether CAR T cells will also last a lifetime or whether will they gradually disappear over decades. It is also not clear how long immunosurveillance may be needed, he said. While policing the blood, these cells wipe out any leukemia B cells that may reappear, but there can be a downside. In some patients, this has also led to depletion of healthy B cells, a condition known as known as B cell aplasia. “This is not a major problem, at least not so far,” commented one expert, because this deficiency can be corrected by giving immunoglobulin supplements, in some cases long-term.

The worst of the side effects occur within a week or two of infusion, when the cells are expanding and attacking the leukemia. Some of the side effects can be very severe, even life-threatening. The two most concerning side effects are cytokine release syndrome, which was severe in about half of the patients in the pivotal trial, and neurologic toxicity, which developed in nearly half of the patients (44%). Because there can be severe side effects, patient care needs to be overseen by clinicians with experience in this field, and suitable facilities are required. Patients may need to be treated in the intensive care unit, for example, and some patients may need to undergo intubation.

Having industry involvement has streamlined a complicated production process and has shortened the manufacturing time. Whereas patients at the beginning of the clinical trial needed to wait 44 days between giving blood and undergoing CAR T-cell infusion, the process now takes only 22 days from “vein to vein,” the drug company Novartis reports. For the future, there is hope that it may be possible to make “off the shelf” products that would require no waiting time. There is also work underway to incorporate a “genetic switch” into the CAR T cell, which would make it possible to “turn off” the therapy by taking another drug. This could be useful when side effects become very severe, he suggested.

There is a tremendous amount of work ongoing involving other blood cancers, all of which appear suitable to this approach. There is also hope that the therapy could be made to work against solid tumors. This first product that is heading to market is just the tip of the iceberg. I’m Dr. Michael Hunter. Medscape did a great job reporting it, and I thought I’d share this news with you.



New app for Android: My Breast Cancer by Dr. Michael Hunter


Immunotherapy for Cancer

The latest approval of a cancer drug by the US Food and Drug Administration (FDA) changes the paradigm of cancer treatment — the new indication specifies a genetic defect without any mention of tumor types. It allows the drug to be used in any cancer that harbors the specified genetic defect, wherever the tumor appears in the body.

What: Historically, the US Food and Drug Administration (FDA) has approved cancer treatments based on where in the body the cancer started — for example, prostate or breast cancers. For the first time, the FDA approved a drug based on a tumor’s biomarker without regard to the tumor’s original location.

Details: The new approval is for the immunotherapy pembrolizumab (Keytruda, Merck & Co), which is already approved for use in several different tumor types, including melanoma and lung cancer. But this latest approval covers the use of pembrolizumab in tumors that have microsatellite instability-high (MSI-H) or are mismatch repair deficient (dMMR). These defects are found most commonly in colorectal, endometrial, and gastrointestinal cancers but also less commonly appear in cancers arising in the breast, prostate, bladder, thyroid gland, and other places, the agency notes.

Microsatellite instability & immunotherapy: It’s not just colorectal cancer: The results from that trial showed that patients with colorectal cancer with normal DNA repair (microsatellite stable) had zero response to pembrolizumab, whereas those with MSI and deficient DNA repair had a 50% response rate, she said. In addition, about 20% had stable disease. This is much higher than has been seen with immunotherapy in other tumor types, where fewer than 20% patients respond. But the trial also included patients with any solid tumor and MSI, and these patients also showed the 50% response rate and 20% stable disease results.

Downsides: Common side effects of pembrolizumab include fatigue, itchiness, diarrhea, decreased appetite, rash, fever, cough, dyspnea, musculoskeletal pain, constipation, and nausea. The drugs can also cause serious immune-mediated side effects, including lung, liver, kidney, or colon inflammation, endocrine problems.

Action point: All patients with advanced cancer who have had at least one standard therapy should be tested to see if their tumor harbors these genetic defects.

I’m Dr. Michael Hunter.