What is CAR T-Cell therapy ?
CAR T-Cell therapy, the full name is Chimeric Antigen Receptor T-Cell Immunotherapy. This is a new type of cell therapy that has been used for many years, but has only been improved and used clinically in recent years. Similar to other immunotherapy, its basic principle is to use the patient’s own immune cells to clear cancer cells, but the difference is that this is a cell therapy, not a drug.
Process of CAR T-Cell therapy
1: Isolate immune T cells from cancer patients.
2: Using genetic engineering technology to add a chimeric antibody that recognizes tumor cells and activates T cells to kill tumor cells at the same time, T cells instantly turn into tall CAR-T cells. It is no longer an ordinary T cell, it is a “terrorist” T cell with GPS navigation, ready to find cancer cells and launch suicide attacks at the same time!
3: In vitro culture, a large number of CAR-T cells are expanded. Generally, a patient needs billions or even tens of billions of CAR-T cells (the larger the body size, the more cells are required).
4: The expanded CAR-T cells are returned to the patient.
5: Closely monitor the patients, especially the violent reactions of the body a few days ago (the reason will be described later), and get the job done.
Improve cell production process
How to produce universal CAR-T cells to reduce production costs is a great challenge. One possible method is to obtain T cells from donors, knock out the HLA gene of the cells, and express non-classical HLA molecules to prevent natural killer cell-mediated cell recognition and cell lysis, thereby producing a universal T cell product . In addition, it may not be necessary to integrate the CAR gene into the chromosomes of T cells, as transient expression of CAR transfected with RNA also works in animal models. For added safety, serum-free media is recommended.
The FDA recently developed and published draft guidelines for cell and gene therapy products, one of which requires manufacturers to determine the activity indicators of these cells or gene therapy products. For genetically modified T cells, there are many factors that may be related to activity, including gene carrier, culture conditions, CAR structure, cell type, and the proportion of the cell type. At present, the simplest indicator of activity is the number of CAR + cells. However, the exact type of cell may be equally important for activity. For example, the long-term survival of central memory cells, CD8 + cells, may be an indicator of activity. Most researchers currently focus on T cells derived from peripheral blood. Some researchers have used second-generation CAR to transduce natural killer cells.
CAR T-Cell therapy advantages for treatment of hematological malignancies
In the past five years, CAR-T’s excellent efficacy has continuously become the headlines of some research institutions. Because there are many known antigen expressions on blood cell membranes, and it is relatively easy to obtain leukocytes and T cells naturally home to blood organs (such as blood, bone marrow, and lymph nodes), CAR-T cells are first used to treat malignant leukemia. Astonished.
CAR-T cells are also the most used clinical trials for hematological malignancies. The results of these clinical trials indicate several key factors that may affect the efficacy of CAR-T cell therapy. For example, although all diseases can express CD19, acute lymphoblastic leukemia appears to have a higher response rate than chronic lymphocytic leukemia or indolent lymphoma. The reasons may include patients with lymphoma have T cell defects, tumor microenvironment inhibition, previous treatment, the patient’s age and T cell activity and components (such as the ratio of CD4: CD8, the content of regulatory T cells). The tumor microenvironment may also affect the function of CAR-T cells to dissolve tumor cells. By analyzing CAR-T cells isolated from tumor tissue, they found that they express PD-1, so the therapeutic effect may be affected by PD-L1. Checkpoint blocking technology can increase T cell viability. Application of lymphatic attrition and injection of lymphokines can support the in vivo expansion and survival of imported T cells.
It is important to understand the key characteristics of CAR-T cell activity. The expression of CAR on the cell surface is undoubtedly important. Second, sufficient CAR-T cells must be detectable in the blood after transplantation. CAR-T cells can be detected by polymerase chain reaction and flow cytometry. It is unclear what the minimum dose of CAR-T cells is required to be effective. If CAR-T cells can be effectively expanded in vivo, then a small amount of CAR-T cells can still produce good effects. In view of the complexity of producing CAR-T cells, it is very attractive to be able to achieve therapeutic effects at a low dose of cells. There is no doubt that the imported cells must survive enough time. Based on the kinetics of tumor cell clearance that has been observed, transplanted cells need to survive in vivo for at least several months. On the other hand, if CAR-T cells are only used as a transitional therapy for bone marrow transplantation, then they may only need to last for a few weeks. There is no random clinical study to prove that CAR-T cells can replace bone marrow transplantation. But at least patients who are not suitable for bone marrow transplantation can receive CAR-T cell transplantation.
Toxicity and adverse reactions mainly include cytokine release syndrome, macrophage activation syndrome, hemophilic lymphoma and B cell hypoplasia. Cytokine release syndrome is often accompanied by high levels of IL-6 secretion and leads to macrophage activation syndrome. Although it can be clearly assumed that CAR-T cells can directly kill tumor cells, it is not completely clear which cells produce a large number of cytokines, especially IL-6 (a key factor for toxic response). It is also unclear whether general immunosuppression of anti-cytokine antibodies or steroid hormones can affect anti-tumor responses. IL-6 may be produced by dead B cells, dead tumor cells, or macrophages recruited to lyse tumor cells. It is still unclear whether the severity of cytokine release syndrome or macrophage activation syndrome is related to the anti-tumor effect. The relatively rare adverse reactions include slow response, epilepsy, aphasia, changes in mental state, etc. These are reversible. Macrophage activation syndrome is often associated with neurological toxicity. B cell hypoplasia is the expected result of CD-19 targeted therapy and can be used as an indicator of the survival and effectiveness of CD-19 targeted CAR-T cells in vivo. B cell hypoplasia can be injected with glycinin as a supplementary treatment. Persistent B-cell hypoplasia, even with replacement therapies, can lead to an increased risk of infection. B cells can recover after CAR-T cells disappear in the body, so patients can receive CAR-T cells again. As more patients receive CAR-T cell therapy, clinical research should focus on the study of toxic reactions and their management methods, including cytokine blockade, steroids, and the optimal timing and dose of immune protein supplementation.
Due to the significant toxicity of CAR-T cells, researchers have also tried strategies to integrate suicide genes in cells or turn off gene expression. However, it is still difficult to integrate the suicide gene system into all CAR-T cells, because many suicide gene systems are immunogenic (for example, herpes simplex virus expressing thymus kinase) or prodrugs that induce suicide should be administered intravenously . In addition, the T-cell homing can be altered by the transient expression of chemokine receptors or the pharmacological blockade of chemokine receptors can be used as a strategy to enhance efficacy and reduce toxicity.
Exciting prospects of CAR T-Cell therapy
There are two main obstacles in expanding the application of CAR-T cells beyond B-cell malignancies: finding new targets and mass production. Potentially promising targets include CD30 (for the treatment of Hodgkin’s disease and mycosis fungoides), immunoglobulin Gκ light chain (for the treatment of B-cell leukocytes), CD33 and Lewis-Y (acute myeloid leukemia), CD123 and CD44v6 (Acute myeloid leukemia and myeloma), CD19 (B cells), CD23, and ROR1 (chronic lymphocytic leukemia). New targets under study include BCMA, CD70, CD74, CD138 and CS1 (see table below). Currently, pharmaceutical companies, biotechnology companies, universities, and cooperative organizations are conducting CAR-T cell research. This is an exciting period for the treatment of all hematological malignancies; ten years ago, few people expected that the hope of modifying gene therapy would be realized by CAR-T cells for the treatment of hematological malignancies.