CAR T Cells:
Costimulatory signaling domains have been added to a new generation of CAR T cells to increase their ability to produce more T cells after infusion and to survive longer in the circulation.
For many years, cancer treatment has been based on surgery, chemotherapy, and radiation therapy. In the past two decades, targeted therapies such as imatinib (Gleevec) and trastuzumab (Herceptin®) have been targeted by looking for specific molecular changes seen primarily in these cells. Drugs for cancer cells – have also consolidated their standard treatments for many cancers.
But in the past few years, immunotherapy has emerged, just as many people in the cancer community call it the “fifth pillar” of cancer treatment, which can enhance the patient’s immune system’s ability to attack tumors.
A Turning Point In Clinical Development:
A rapidly emerging immunotherapeutic method is called adoptive cell transfer (ACT): collecting and using the patient’s immune cells to treat cancer. There are several types of ACT (see box below, titled “ACT: TILs, TCRs, and CARs”), but by far the fastest-growing in clinical development is called CAR T cell therapy.
Until recently, the use of CAR T cell therapy was limited to small clinical trials, mainly in patients with advanced blood cancer. However, these treatments have caught the attention of researchers and the public because they have produced significant responses in some patients – including children and adults – and all other treatments have stopped working.
In 2017, the US Food and Drug Administration (FDA) approved two CAR T cell therapies, one for children with acute lymphoblastic leukemia (ALL) and the other for adults with advanced lymphoma. Despite this, the researchers warn that in many ways, CAR T cells and other forms of ACT are still in their early stages, including whether they are effective against solid tumors such as breast cancer and colorectal cancer.
Different forms of ACT are “still under development,” said Steven Rosenberg, MD, director of the surgical division of the NCI Cancer Research Center (CCR), a pioneer in immunotherapy, and his laboratory is the first laboratory to report successful cancer.
But after decades of hard research, the field has reached a tipping point, Dr. Rosenberg continues. In the past few years, advances in CAR T cells and other ACT methods have accelerated, and researchers have a better understanding of how these therapies work in patients and translate this knowledge into improved how to develop and test.
“In the next few years,” he said, “I think we will see tremendous progress and drive the belief that many people believe that adopting adoptive cell transfer therapy.”
A “Living Drug”:
CAR T cells are equivalent to “giving patients a living drug,” explains Dr. Renier J. Brentjens of the Memorial Sloan Kettering Cancer Center in New York, who is another early leader in the field of CAR T cells.
As the name suggests, the backbone of CAR T cell therapy is T cells, which are often referred to as the mainstay of the immune system because they play a key role in coordinating immune responses and killing cells infected by pathogens. The therapy requires drawing blood from the patient and isolating the T cells. Next, T cells are genetically engineered using a disarmed virus to produce a receptor called a chimeric antigen receptor or CAR on its surface.
These receptors are “synthetic molecules that are not naturally occurring,” Carl June, M.D., of the Abramson Cancer Center at the University of Pennsylvania. In a recent report on the National Institutes of Health campus CAR T cells, it was explained. Dr. June led a series of clinical trials of CAR T cells, mainly for leukemia patients.
These specific receptors allow T cells to recognize and attach to specific proteins or antigens on tumor cells. The farthest CAR T cell therapy in development targets antigens found on B cells called CD19 (see box below, entitled “Creating CAR T cells”).
Once the collected T cells are engineered to express antigen-specific CARs, they “expand” to hundreds of millions in the laboratory.
The final step is to infuse CAR T cells into the patient (previously the “lymphatic regression” chemotherapy regimen). If everything goes as planned, the engineered cells will multiply in the patient’s body and, under the guidance of their engineered receptors, identify and kill cancer cells whose surface contains antigen.
Production of CAR-T Cells:
More and more CAR T cell therapies are being developed and tested in clinical research.
Despite the important differences between these therapies, they all have similar components. The CAR on the cell surface consists of a fragment or domain of the synthetic antibody. The domain used can affect the extent to which the receptor recognizes or binds to antigens on tumor cells.
Receptors rely on stimuli from inside the cell to do their job. Thus, each CAR T cell has a signaling and “costimulatory” domain within the cell that signals cells from surface receptors. The different domains used can affect the overall function of the cell.
Over time, advances in intracellular engineering of CAR T cells have improved the ability of engineered T cells to produce more T cells after infusion into a patient (amplification) and survive longer in the circulation (lasting Sex).
Progress has also been made in the time required to produce a batch of CAR T cells. Although it took several weeks to start, many laboratories have now reduced the time to less than 7 days.
No Possible Choice:
The initial development of CAR T cell therapy was focused on ALL, the most common cancer in children.
More than 80% of children with ALL diagnosed with B cells – the main type of pediatric ALL – will be cured by intensive chemotherapy. But for patients with cancer that relapse after chemotherapy or stem cell transplantation, there are “nearly” treatment options, says Dr. Stephen Grup of the Children’s Hospital of Philadelphia (CHOP).
Relapsed ALL is the leading cause of cancer death in children.
Dr. Grupp has conducted several CAR T cell trials in children and young adults, with ALL having relapsed or not responding to existing therapies. In one of the early trials using CD19 to target CAR T cells, 27 of the 30 patients treated in the study had all signs of cancer disappearing (complete remission), many of which continued to show no signs of recurrence after treatment.
These early successes gave up a disclaimer based on CD19-targeted CAR T cell therapy for larger trials called tissuelecleucel (KymriahTM) for children and adolescents with ALL. Many of the patients who participated in the trial, funded by Novartis, had complete and lasting relief. Based on the test results, the FDA approved the research
Similar results were observed in the CD19-targeted CAR T cell test led by researchers at the CCR Pediatric Oncology (POB).
The progress of CAR T cells in the treatment of ALL children is “very good,” said Terry Fry, principal investigator of the CAR T cell POB trial at Colorado Children’s Hospital. CD19-targeted CAR T cells were initially tested in adults. But Dr. Frye continues, the fact that the first approval for the treatment of children and adolescents with ALL is a watershed moment.
He said the agency approved new treatments for children before adults “almost unheard of in cancer.”
However, CAR T cells used to treat adult patients with blood cancer do not lack promising data. Targeting CAR T cells with CD19 produces strong results not only in patients with ALL but also in patients with lymphoma. For example, in a small NCI-dominant CAR T cell trial that targets primarily patients with advanced diffuse large B-cell lymphoma, more than half of the patients have a complete response to treatment.
“Our data for the first time truly demonstrates the potential of this approach in patients with invasive lymphoma, which was almost incurable until now,” said the main investigator of the trial, the NCI Experimental Transplant, and Immunology Division. Medical doctor James Kochenderfer said.
Since then, the results of larger trials funded by Kite Pharmaceuticals (a research agreement with NCI to develop ACT-based therapies) confirm these early results and lay the groundwork for FDA approval of Kite’s CAR T cell product axicabgene ciloleucel. (YescartaTM), for some lymphoma patients.
So far, the results of lymphoma “have achieved incredible success,” Dr. Kochenderfer said. “CAR T cells are almost certainly a common treatment for several types of lymphoma.”
The rapid advancement and development of CAR T cell therapy have exceeded the expectations of those who believe in their potential early on.
“Do I think it works? Yes,” Dr. Brentjens said. But he initially thought it would be a “boutique therapy” limited to a very small, well-defined patient population. The experience of the past five years, including the entry of the biopharmaceutical industry into the field, has changed his prospects.
“We have a group of patients who are considered to be terminal and now have lasting and meaningful relief, with a quality of life of up to five years,” he continued. “So the enthusiasm for this technology is now very high.”
Understand, Manage Side Effects:
Like all cancer therapies, CAR T cell therapy can cause several worrying, sometimes fatal, side effects. The most common of these is cytokine release syndrome (CRS).
As part of its immune-related responsibilities, T cells release cytokines, chemical messengers, that help stimulate and guide the immune response. In the case of CRS, cytokines are rapidly and massively released into the bloodstream, which can lead to dangerous high fever and a sharp drop in blood pressure.
Ironically, CRS is considered to be the “targeting” effect of CAR T cell therapy – that is, its presence suggests that active T cells function in vivo. Dr. Kochenderfer explained that, in general, patients with the most extensive disease before receiving CAR T cells are more likely to develop severe CRS.
In many children and adults, CRS can be managed through standard supportive therapies, including steroids. As researchers gain more experience with CAR T cell therapy, they have learned how to better manage more severe CRS cases.
For example, a few years ago, CHOP’s team noted that patients with severe CRS have a particularly high level of IL-6, a cytokine secreted by T cells and macrophages to fight inflammation. As a result, they turned to treatments approved for the treatment of inflammatory conditions, such as juvenile arthritis, including the drug tocilizumab (Actemra®), which blocks IL-6 activity.
This method is very effective and can quickly solve the problems of most patients. Since then, tocilizumab has become the standard of care for the treatment of severe CRS.
“We have learned how to score [CRS] and we have learned how to treat it,” Dr. Grupp said at the Novartis FDA Advisory Committee meeting on CD19 targeted therapy. “The IL-6 blockade is the key.”
Another potential side effect of CAR T cell therapy – off-target effects – is the massive death of B cells, known as B cell dysplasia. CD19 is also expressed on normal B cells, which are responsible for the production of antibodies that kill pathogens. These normal B cells are also often killed by infused CAR T cells. To compensate, many patients must receive immunoglobulin therapy, which provides them with the necessary antibodies to fight infection.
Recently, another serious and potentially fatal side effect – brain swelling or cerebral edema – has been discovered in some of the larger trials to support FDA-approved CAR T cells in patients with advanced leukemia. One company decided to stop further development of its leading CAR T cell therapy because several clinical trial patients died of cerebral edema caused by treatment.
However, this problem seems to be limited, and other leaders of the CAR T cell therapy trial did not report brain edema.
Other so-called neurotoxicities – such as confusion or epileptic activity – have been discovered in most CAR T cell therapy trials. But Dr. Brentjens said that the problems of almost all patients are short-lived and reversible.
It has been speculated in the early days that these neurotoxicities may be related to CRS. But while researchers are still trying to understand these mechanisms, he adds, “I think most investigators (in this area) will agree that they are different from CRS.”
New target antigen for CAR T cells
Research on CAR T cells is rapidly progressing, mainly in patients with blood cancer, as well as in solid tumor patients. For example, as the biopharmaceutical industry is increasingly involved in the field, the number of clinical trials testing CAR T cells has increased dramatically, from a few years ago to more than 180.
Most of the experiments performed to date have used CD19-targeted CAR T cells. But this change is very fast, partly because it is necessary.
For example, some ALL patients do not respond to CD19 targeted therapy. Dr. Frye said that even among those who have experienced a complete response, as many as one in three will see their disease relapse within a year. Many of these disease recurrences are associated with the fact that ALL cells no longer express CD19, a phenomenon known as antigen loss.
Therefore, in children with advanced ALL and young adults, researchers at NCI POB are testing CAR T cells that target CD22 proteins, which are also frequently overexpressed by ALL cells. In the first trial of CD22-targeted CAR T cells, most of the treated patients achieved complete remission, including patients who initially progressed to cancer after complete response to CD19-targeted therapy.
Similar to the case of CD19 targeting CAR T cells, however, recurrence, after CD22 targeted therapy, is not uncommon, Dr. Fry explained.
“From the perspective of easing persistence, there is room for improvement,” he said.
One possible way to increase durability and possibly at least prevent antigen loss is to attack multiple antigens simultaneously if not completely. For example, some research groups are testing T cells for CD19 and CD22 in early clinical trials.
CHOP researchers are also testing CAR T cells, which target both CD19 and CD123, another antigen commonly found in leukemia cells. Early studies in animal models have shown that this dual targeting prevents antigen loss.
Antigen targets for CAR T cell therapy, including multiple myeloma, have been identified in other blood cancers.
As part of a collaboration with Kite, Dr. Kochenderfer and his colleagues at NCI developed CAR T cells that target the BCMA protein, which is present in almost all myeloma cells.
In early clinical trials of BCMA-targeted CAR T cells in patients with advanced multiple myeloma, more than half of the patients had a complete response to treatment. Kite has now conducted a trial to test BCMA-targeted T cells in a larger group of patients.
Amplification of CAR T cells into solid tumors?
Some people suspect that CAR T cells will achieve the same success in solid tumors. Dr. Rosenberg believes that in most cases, finding the right antigen to target solid tumors – which has always been a major challenge – may prove too difficult.
“Efforts to identify unique antigens on the surface of solid tumors have been largely unsuccessful,” he said.
The researchers estimate that the vast majority of tumor antigens are present in tumor cells, beyond the scope of CAR, and CAR can only bind to antigens on the cell surface.
Therefore, as already shown in melanoma, Dr. Rosenberg said he believes that other forms of ACT may be more suitable for solid tumors.
But that doesn’t mean researchers won’t try to use CAR T cells.
For example, the researchers are conducting experiments on CAR T cells against protein mesothelin, which is found in some of the most deadly cancers (including pancreatic cancer and lung cancer), and on the tumor cells of the protein, EGFRvIII found in almost all tumor cells. Overexpression. A patient with invasive brain cancer glioblastoma.
However, early reports of these trials did not report the same success as blood cancer.
Dr. Brentjens admits: “As for the targeting of antigens in solid tumors in the same way as CD19, I don’t think it will work in most cases.”
He explained that another major obstacle to solid tumors is that they weaken the immune response around their microenvironmental components.
Therefore, the success of solid tumors may require “super T cells,” he said, and the cells have been designed to overcome the immunosuppressive environment of many advanced solid tumors. He said that at the Memorial Sloan Kettering, CAR T cells with these properties – an “armored” CAR T cell – are being studied.
ACT: TIL, TCR, and CAR:
CAR T cells have received the greatest attention when it comes to cell therapy under the ACT umbrella. But other forms of ACT have also shown promise in small clinical trials, including in patients with solid tumors.
One method uses immune cells that have penetrated into and around the tumor, called tumor-infiltrating lymphocytes (TIL). NCI researchers pioneered the use of TIL to successfully treat patients with advanced cancer – initially melanoma and later several other cancers, including cervical cancer. Recently, NCI researchers have developed a technique for identifying TIL that recognizes cancer cells with this cancer-specific mutation. In some cases, this approach results in advanced colorectal immune immunization and tumor regression in patients with liver cancer.
Another major approach to ACT involves engineering patient T cells to express specific T cell receptors (TCRs). CAR uses a synthetic antibody portion that only recognizes cell surface-specific antigens. On the other hand, TCR uses naturally occurring receptors, which also recognize antigens within tumor cells. Small pieces of these antigens are shuttled to the cell surface and “presented” to the immune system as part of a collection of proteins called MHC complexes.
To date, TCR T cells have been tested in patients with various solid tumors, showing promise for melanoma and sarcoma.
Evolution of CAR T Cell Therapy:
Other improvements or reconfigurations of CAR T cells are being tested. One approach is to develop CAR T cell therapy using immune cells that are not collected from patients but collected from healthy donors. Our idea is to create so-called off-the-shelf CAR T cell therapies that can be used immediately without having to be made for every patient.
The French company Cellectis has launched a phase I trial of its ready-made CD19-targeted CAR T cell product in patients with advanced acute myeloid leukemia in the United States. The company’s products – made using genetic editing technology called TALEN – have been tested in Europe, including two babies who have exhausted all other treatment options. In both cases, the treatment is effective.
Many other methods are under investigation. For example, researchers are using nanotechnology to create CAR T cells in vivo, developing CAR T cells with “off switches” as a means of preventing or limiting side effects such as CRS, and using genetic editing technology CRISPR / Cas9 for more precise design of T cells.
But Dr. Free said there is still a lot of work to do with existing CAR T cell therapy.
He is particularly keen on the early use of CAR T cells in the treatment of children with ALL, especially those who return to the disease at a high risk (based on specific clinical factors) after initial treatment, which is usually given for about 2 and a half years.
In this case, he explained that if early indicators indicate that these high-risk patients do not respond optimally to chemotherapy, they can stop and the patient can be treated with CAR T cells.