Second opinion on CAR-T therapy

CAR-T therapy is a form of cellular immunotherapy in which a patient’s own T lymphocytes are genetically modified so that they can recognize and destroy target cells. To achieve this, a gene encoding a special chimeric antigen receptor (CAR) is introduced into the T lymphocytes. As a result, these cells acquire the ability to identify tumor cells by a specific surface protein and initiate their destruction. Today, CAR-T therapy is most widely used for certain types of leukemia, lymphoma, and multiple myeloma, while ongoing research continues to expand its potential applications.

How does CAR-T therapy work?

Under normal conditions, T lymphocytes are part of the immune system and are capable of identifying cells that carry foreign or altered molecules. However, tumors can evade the immune response: cancer cells may alter antigen expression or create an environment that suppresses T-cell activity.

The CAR provides the T lymphocyte with an additional recognition system. It is located on the cell surface and consists of several functional components. The extracellular component binds to a specific antigen on the target cell, while the intracellular component transmits signals that activate the T lymphocyte, stimulate its proliferation, and promote destruction of the target cell.

The target is selected depending on the disease. In B-cell malignancies, one of the most important targets is the transmembrane protein CD19, an antigen found on most B lymphocytes and many B-cell tumor cells. Another important target is B-cell maturation antigen (BCMA), which is expressed predominantly on plasma cells and is particularly relevant in multiple myeloma.

The choice of target is crucial. It should be present on tumor cells in sufficient quantities and, ideally, be absent from or expressed at significantly lower levels on vital healthy tissues. Otherwise, there is a risk of so-called “on-target, off-tumor” toxicity: CAR-T cells correctly recognize the selected antigen but destroy not only tumor cells, but also healthy cells that express the same antigen.

How are CAR-T cells manufactured?

Unlike conventional drug therapy, CAR-T is an individually manufactured cellular product. In its classical form, the therapy is autologous, meaning that the cellular material is obtained directly from the patient. The process begins with leukapheresis, a procedure in which white blood cells, including T lymphocytes, are separated from the blood. The remaining blood components are returned to the patient.

The collected cellular material is sent for manufacturing. T lymphocytes are activated and genetically modified. Lentiviral or retroviral vectors, for example, may be used to deliver the genetic construct. As a result, the cells begin to express the CAR on their surface.

The genetically modified T lymphocytes are then cultured under specialized conditions until the required number of cells has been obtained. The cellular product is subsequently purified and undergoes quality control, including assessment of its viability, composition, and other parameters, before being prepared for administration.

Before CAR-T cell infusion, lymphodepleting chemotherapy is usually administered. Its purpose is not to directly treat the tumor, but to create conditions that allow the infused CAR-T cells to proliferate effectively and persist in the body.

After lymphodepletion, the cellular product is administered intravenously. The patient then remains under medical observation because the most significant complications often occur during the first days and weeks after infusion.

Commercially manufactured and hospital-based CAR-T therapy

CAR-T products can be manufactured using different organizational models.

In commercial manufacturing, the patient’s cells are sent after leukapheresis to a specialized manufacturing facility operated by the product manufacturer. There, they undergo the entire manufacturing process, after which the finished product is delivered to the treating medical center. This model allows manufacturing to be standardized, quality control to be centralized, and products to be supplied to a large number of medical centers.

Another option is academic or hospital-based CAR-T therapy. In this model, manufacturing is performed directly at a university or specialized medical center, or at an affiliated laboratory with the necessary regulatory approvals and manufacturing capabilities. Such products may be developed for a specific disease, antigen, or group of patients.

Possible complications and risks

CAR-T therapy can produce a significant therapeutic effect, but it is a complex treatment associated with potentially severe complications.

Possible manifestations include high fever, chills, low blood pressure, rapid heart rate, and impaired function of the lungs and other organs. Severe cases may require treatment in an intensive care unit. CRS may be managed, among other approaches, with drugs that block the effects of interleukin-6, as well as corticosteroids.

Another serious complication is immune effector cell-associated neurotoxicity syndrome (ICANS). It may manifest as speech disturbances, confusion, drowsiness, impaired coordination, seizures, and, in severe cases, cerebral edema. Therefore, the patient’s neurological status must be regularly monitored after infusion.

CAR-T therapy may also be associated with prolonged reductions in blood cell counts, an increased risk of bacterial, viral, and fungal infections, reduced immunoglobulin levels, and, with some products, prolonged depletion of normal B cells. Tumor lysis syndrome, electrolyte abnormalities, and damage to various organs may also occur.

There are also late risks. Genetic modification of T lymphocytes, particularly when integrating viral vectors are used, has been associated both theoretically and in clinical practice with a risk of secondary T-cell malignancies. Regulatory authorities therefore require long-term monitoring of patients who have received such products.

Approved indications for CAR-T therapy

To date, the clinically approved use of CAR-T therapy is most extensively developed in hematologic oncology. Regulatory indications vary depending on the country, product, and specific line of therapy.

In particular, CAR-T products targeting CD19 and BCMA are approved in the United States.

CAR-T therapy for autoimmune diseases

CAR-T therapy is gradually expanding beyond oncology. In autoimmune diseases, the main concept is not to destroy a tumor but to profoundly reset a pathologically activated immune system.

One of the most extensively studied approaches targets CD19-positive B cells. These cells contribute to autoimmune responses and the production of pathogenic antibodies. Following CD19 CAR-T therapy, B cells are extensively depleted, and when they subsequently recover, the immune system may be reconstituted with a lower level of pathological autoimmune activity.

CAR-T therapy is being actively investigated, particularly for systemic lupus erythematosus, systemic sclerosis, and certain inflammatory muscle diseases. Myasthenia gravis and other B-cell-mediated autoimmune diseases are also being studied. Clinical data have emerged not only for CD19-directed but also for BCMA-directed cells, as long-lived plasma cells may contribute to the persistence of autoantibody production.

CAR-T therapy for solid tumors

Translating the success of CAR-T therapy from hematologic malignancies to solid tumors is one of the major challenges in modern cellular therapy. Targets currently being investigated include CLDN18.2, GPC3, HER2, EGFR, MSLN, CEA, MUC1, GD2, and others.

However, solid tumors present considerably more obstacles for CAR-T cells. In the bloodstream, CAR-T cells can relatively freely encounter tumor cells. In a dense solid tumor, they must first penetrate abnormal blood vessels and the extracellular matrix and then locate tumor cells among large numbers of normal cells.

In addition, solid tumors are often highly heterogeneous. One part of a tumor may contain large amounts of a particular antigen, while another may contain much less. If CAR-T cells recognize only one antigen, tumor cells that have lost that antigen may evade destruction.

For this reason, researchers are developing bispecific and multispecific CARs, local administration of cells directly into the tumor or a body cavity, combinations of CAR-T therapy with other forms of immunotherapy, and constructs designed to enable CAR-T cells to function more effectively in an immunosuppressive environment.

Thus, CAR-T therapy for solid tumors is an actively developing clinical field, but in most cases it remains experimental or investigational.

Leading countries in CAR-T therapy

The main centers of CAR-T development today are the United States, China, and European countries.

The United States was the first country where CAR-T therapy received broad regulatory recognition. The first commercial CAR-T products were approved there in 2017, and U.S. universities and biotechnology companies continue to play an important role in developing new CAR constructs, manufacturing technologies, and clinical protocols.

Over the past several years, China has established one of the world’s largest CAR-T ecosystems. The country has approved both international and domestically developed products, primarily targeting CD19 and BCMA. Chinese centers are actively investigating CAR-T therapy for hematologic malignancies, autoimmune diseases, and solid tumors, while also developing nanobody-based, multispecific, and universal cell-based constructs.

Europe also has major cellular therapy centers. Germany, Spain, France, the United Kingdom, Italy, and other countries have made significant contributions to CAR-T development. A distinctive feature of the European system is the combination of large pharmaceutical manufacturers with academic and hospital-based programs.

How is CAR-T therapy being improved?

Current research is focused simultaneously on increasing efficacy, shortening manufacturing time, and reducing toxicity.

One area of development is the use of nanobodies, or VHH domains. These are small single-domain antibody fragments that can serve as the antigen-recognition component of a CAR. Their compact size makes it possible to develop new receptor designs, including constructs capable of recognizing multiple targets. Such technologies are being actively investigated, particularly for diseases in which conventional CAR designs face limitations related to antigen accessibility.

Another approach is U-CAR-T, or universal CAR-T cells. In conventional therapy, the cells belong to the patient and therefore have to be individually collected and manufactured. U-CAR-T approaches use donor-derived cells that are genetically modified to reduce the risk of immune rejection and other complications. In theory, such a product could be manufactured in advance and stored until needed. This is the concept of an “off-the-shelf” cellular product.

Allogeneic CAR-T cells could potentially reduce waiting times and simplify logistics, particularly for patients with rapidly progressing disease. However, important challenges remain, including immune rejection of donor cells, the risk of graft-versus-host disease, limited persistence of the cells in the body, and the need for reliable control of their genetic characteristics.

Another trend is moving CAR-T therapy into earlier lines of treatment. Initially, CAR-T was primarily used in patients with relapsed or refractory disease after several previous lines of therapy. Clinical trials and subsequent regulatory changes are now exploring earlier use of CAR-T, when the patient’s body has not yet been exposed to multiple courses of chemotherapy and T lymphocytes may retain better functional characteristics.

Manufacturing technology is also evolving. Researchers are investigating accelerated manufacturing protocols, automated closed systems, local manufacturing, and methods for preserving younger and more functionally active T cells. The shorter the interval between leukapheresis and infusion, the lower the likelihood that rapidly progressive disease will significantly worsen while the patient is waiting for the cellular product.

Another important area is improving safety. CAR constructs with multiple activation requirements, logical “AND” and “OR” antigen-recognition systems, cellular suicide switches, and other mechanisms are being developed to limit CAR-T activity if severe toxicity occurs. Researchers are also investigating constructs that can better resist T-cell exhaustion and the immunosuppressive tumor microenvironment.

Finally, the concept of generating CAR-T cells directly inside the body is emerging. Instead of extracting T lymphocytes, genetically modifying them in the laboratory, and returning them to the patient, researchers are attempting to deliver genetic instructions directly to the body’s T cells. This approach is still at an early stage of development but could potentially transform the manufacturing of cellular therapies.