Chimeric antigen receptor ( CAR , also known as chimeric immunoreceptors , synthetic T cell receptor or T cell receptors ) are engineered receptors that combine new specificity with immune cells to target cancer cells. Typically, these receptors transplant the specificity of monoclonal antibodies to T cells. Receptors are called chimeric because they coalesce part of different sources. CAR-T cells are a new type of treatment that uses altered living cells.
The basic principle of CAR-T cell design involves recombinant receptors that combine antigen-binding functions and T-cell activation functions. The general premise of CAR-T cells is to artificially produce T cells targeted at markers found in cancer cells. Scientists can remove T-cells from a person, genetically alter them, and return them to patients to attack cancer cells. After T cells have been engineered to become CAR-T cells, it acts as a "living medicine". The CAR-T cell makes the connection between the extracellular ligand recognition domain and the intracellular signal molecule which in turn activates T cells. The dominance of extracellular ligand recognition is usually a single-chain variable fragment (scFv). The question that often arises about the safety of this treatment is how do you ensure that only targeted cancer cells are cancerous and not normal cells? The specificity and safety of CAR-T cells is determined by the choice of targeted molecules.
CAR-Ts can be derived from the patient's own blood (autolog) or from any other healthy donor (allogenic). These T-cells are genetically engineered to express artificial T cell receptors, through which they are targeted for disease-related antigens. This process is independent MHC and thus the targeting efficiency is greatly improved. These CAR-T cells are programmed to target the antigen present in the tumor surface. When they come into contact with the antigen in the tumor, CAR-T cells are activated through the signal peptide, proliferating and becoming cytotoxic. They do all this independently of the major histocompatibility complex (MHC). CAR-T cells destroy cancer cells through mechanisms such as extensive cell stimulated proliferation, increasing the degree to which cells are toxic to other living cells cytotoxicity, and by causing increased production of secreted factors from cells in immunity. systems that affect other cells in the organism. These factors are called cytokines and include interleukins, interferons, and growth factors.
CAR-T cells were developed to be specific to the antigen expressed on tumors that are not expressed in healthy cells. CD19 is expressed on B-cells throughout its development and as a result, CD19 is also expressed in almost all B-cell malignancies. In addition, CD19 is expressed only in line B-cells and not in bloodlines or other tissues. This malignancy includes forms of cancer such as acute lymphoblastic leukemia (ALL), chronic lymphoblastic leukemia (CLL), and various forms of Hodgkin's lymphoma.
Video Chimeric antigen receptor
Use in cancer
An adoptive transfer of T cells that express chimeric antigen receptor is a promising anti-cancer therapy because MO modified T cells can be engineered to target virtually any tumor-related antigen. There is great potential for this approach to improve patient-specific cancer therapy in a profound way. After the collection of patient T cells, cells are genetically engineered to express CARs that are specifically directed to the antigen of the patient's tumor cells, then infused back into the patient.
Get started
The first step in the introduction of CAR-T cells into the patient's body is the removal of the active leukocytes from the blood in a process known as leukocyte aphesi. Leucocytes are removed using blood cell separators. The autologous peripheral blood mononuclear cells (PBMC) are then separated and collected from the buffy layer formed. The leukocyte apheresis products are then transferred to the cell-processing center. At the cell-processing center, certain T cells are activated in certain environments where they can actively proliferate. The cells are activated using a type of cytokine called interleukin, specifically Inter-Leukin 2 (IL-2) as well as anti-CD3 antibodies.
T-cells are then transfected with the CAR CD19 gene by integrating gammaretrovirus (RV) or with a lentivirus (LV) vector. This vector is very safe in modern times due to the removal of some U3 territory. The patient underwent lymphodepletion chemotherapy prior to the introduction of CD-T CDs that were engineered. The depletion of circulating leukocytes in patients increases the amount of cytokines produced that help increase the expansion of engineered CAR-T cells.
Security issues
The CAR-T cells are undoubtedly a major breakthrough in cancer treatment. However, there is still some expected toxicity as well as some unexpected toxicities that come along with CAR-T cells put into the body. These toxicities include cytokine release syndrome (CRS), neurological toxicity, On-target/Off-Tumor Introduction, insertional mutagenesis and anaphylaxis.
CRS is a condition in which the immune system is activated and releases an increase in the number of inflammatory cytokines. Clinical manifestations of this syndrome include: high fever, fatigue, myalgia, nausea, tachycardia, capillary leak, cardiac dysfunction, liver failure and renal impairment.
Neurologic toxicity associated with CAR-T cells has clinical manifestations including delirium, loss of some speech-language ability while still possessing the ability to interpret language (expressive aphasia), obtundation and seizures. During some clinical trials, deaths caused by neurotoxicity have occurred. The main cause of death due to neurotoxicity is cerebral edema. In a study conducted by Juno Therapeutics, Inc., five patients enrolled in the trial died as a result of cerebral edema. Two patients were treated with cyclophosphamide alone and the remaining three were treated with a combination of cyclophosphamide and fludarabin. In another clinical trial sponsored by the Fred Hutchinson Cancer Research Center, there was one reported case of irreversible and fatal neurologic toxicity 122 days after the administration of CAR-T cells.
The on-target/Off-tumor recognition occurs when CAR-T cells recognize the correct antigen, but the antigen is expressed on a non-pathogenic tissue. These adverse effects can vary in the severity of B-Cell Aplasia to severe toxicity that causes death.
Anaphylaxis is the expected side effect because CAR is made with foreign monoclonal antibodies and as a result, demands an immune response. There is also potential for inserti- tional mutagenesis that can occur when inserting DNA vectors into the host cell. The lentiviral (LV) vector carries a lower risk than the retroviral (RV) vector. However, both have the potential to be oncogenic.
There has not been much long-term research done on the effects of CAR-T cells because they are relatively new drugs still in the experimental phase so there is still concern for long-term survival and pregnancy complications in female patients treated with CAR-T cells.
FDA initial approval
The first two FDA-approved CAR-T therapies are targeted at CD19 (found in many types of lymphoma cells, especially B-cell lymphoma). They are approved for diffuse relapse/refractory B cell lymphoma (DLBCL) for axicabtagene ciloleucel and relaps/refractory B cell precursor acute lymphoblastic leukemia (ALL) for tisagenlecleucel.
Maps Chimeric antigen receptor
Structure
CAR consists of three areas: ectodomain, transmembrane domain and endodomain.
Ectodomain
Ektodomain is a receptor region that is exposed to extracellular fluid and consists of 3 components: signal peptide, antigen recognition region and spacer.
Signal peptides direct the newborn protein into the endoplasmic reticulum. The signal proteins in the CAR are called single-chain variable fragments (scFv), a type of protein known as the fusion protein or the chimeric protein. Fusion proteins are proteins that are formed by combining two or more genes that code initially for different proteins but when they are translated in cells, the translation produces one or more polypeptides with functional properties derived for each of the original genes.
ScFv is a chimeric protein consisting of light and heavy immunoglobin chains that are linked to short linker peptides. The linker consists of a hydrophilic residue with glycine and serine stretches in it for flexibility as well as stretching glutamate and lysine for added solubility.
transmembrane domain
The transmembrane domain is a hydrophobic alpha helix that extends the membrane. The transmembrane domain is essential for overall receptor stability. Currently, the CD28 transmembrane domain is the most stable domain.
In general, transmembrane domains of the most membranous proximal components of endodomain are used. Interestingly, using the CD3-zeta transmembrane domain can result in the incorporation of artificial TCR into the original TCR, a factor that depends on the original transmitted CD3-zeta aspartic acid transmembrane. Different transmembrane domains produce different receptor stability. The CD28 transmembrane domain produces a stable receptor which is otherwise high.
Endodomain
This is the functional end of the receptor. After the introduction of the antigen, the receptors clump and the signals are transmitted to the cell. The most common endodomain component used is CD3-zeta which contains 3 ITAMs. This transmits the activation signal to the T cell after the antigen is bound. CD3-zeta may not provide a fully competent activation signal and co-stimulation signaling is required. For example, CD28 chimeric and OX40 can be used with CD3-Zeta to transmit proliferative/survival signals or all three can be used together.
History
The first generation CAR was developed in 1989 by Gideon Gross and Zelig Eshhar at the Weizmann Institute, Israel. The first generation of CARs consists of extracellular binder domains, hinge regions, transmembrane domains, and one or more intracellular signal domains. Extracellular binding domains contain single-chain variable fragments (scFvs) derived from tumor antigen-reactive antibodies and usually have high specificity against tumor antigens. All CAR save CD3? the domain chain as an intracellular signal domain, which is the main transmitter of the signal. Second-generation CARs also contain co-stimulation domains, such as CD28 and/or 4-1BB. The involvement of these intracellular signaling domains increases the proliferation of T cells, cytokine secretion, resistance to apoptosis, and persistence in vivo. In addition to the co-stimulation domains, third-generation CARs combine multiple domain signaling, such as CD3z-CD28-41BB or CD3z-CD28-OX40, to increase T cell activity. Preclinical data suggest that third-generation CARs show improved effector function and persistence in vivo compared to second generation CAR. Recently, a fourth-generation CAR (also known as armored TRUCK or CAR), combines second-generation CAR expression with factors that increase anti-tumoral activity (eg, cytokines, co-stimulatory ligands).
The evolution of CAR therapy is an excellent example of basic research applications to clinics. The PI3K binding site used is identified in CD28 co-receptor, whereas the ITAM motif is identified as the target of CD4 and CD8-p56lck complexes.
The introduction of the Strep-tag II sequence (a sequence of at least eight residual peptides (Trp-Ser-His-Pro-Gln-Phe-Glu-Lys) that exhibit intrinsic affinity to streptavidin) into certain sites in synthetic CAR or T- T cells are engineered with identification markers for quick purification, a method for adjusting the length of the chimeric receptor spacer for optimal function and functional elements for selectively coated antibodies, microbeads, large-scale expansions. Strep-tags can be used to stimulate engineered cells, causing them to grow rapidly. Using Strep-tag-binding antibodies, the engineered cells can be expanded up to 200-fold. Unlike existing methods, this technology only stimulates specific cancer T cells.
Smart T cell
Combined with exogenous molecules, some synthetic control devices have been implemented on CAR-T cells and alter cell activity. Smart T cells are engineered with suicidal genes or other synthetic control panels to precisely control therapeutic function over time and dosage, there by reducing cytotoxicity. Some strategies to improve the safety and efficacy of CAR-T cells are:
Suicide gene engineering: engineered T cells coupled with a suicidal gene, which can be activated by extracellular molecules and then induce T cell apoptosis. Herpes simplex thymidine kinase (HSV-TK) and caspase 9 induced virus iCas9) are two types of suicide genes that have been integrated into CAR-T cells. In the iCas9 system, the suicide gene consists of a sequence of FK506 binding proteins that are mutations with high specificity in small molecules, AP1903 and genes that encode a human caspase 9 switch. When cytokine release by CAR-T cells becomes more apparent than baseline, iCas9 can be dimerized and cause rapid T-cell apoptosis. Although both suicidal genes exhibit a tangible function as safety switches in clinical trials for cellular therapy, some inhibitory disabilities limit the application of this strategy. HSV-TK comes from a virus and may be immunogenic to humans. The suicide gene strategy may not act fast enough to remove off-tumor cytotoxicity as well.
Double-antigen receptor: T cells are engineered to express two tumor-related antigen receptors at the same time. Dual-antigen receptors from engineered T cell modules have been reported to have less intense side effects. Activation of CAR-T cells via TCR-CD3? the signal transduction path is the transient and complementary signal path provided by the co-stimulating molecule on the antigen presenter cells improves the survival of modified T cells that are capable of controlling the tumor. An in vivo study in mice showed double receptor T cells effectively eradicate prostate cancer and achieve complete long-term survival.
ON-switch: The TT's TT-celled synthetic receptor off-switch becomes two parts: the first part contains mainly the antigen binding domains and the other shows two different downstream signaling elements (eg CD3 and 4-1BB ). In the presence of exogenous molecules (eg rapamycin analogues), two physically separated signaling elements join together and CAR-T cells perform therapeutic functions. In this mechanism, engineered T cells exhibit therapeutic function only in the presence of tumor antigens and benign exogenous molecules.
Bifunctional molecules as switches: Bispecive antibodies are developed as efficacious bridges to target cytotoxic T cells to cancer cells and cause localized T cell activation. In this strategy, bispecific antibodies target CD3 T cell molecules and tumor-related antigens presented on the surface of cancer cells. The bispecific anti-CD20/CD3 molecule exhibits high specificity for both B cells and malignant cancer cells in mice. FITC is another bifunctional molecule used in this strategy. FITC can direct and regulate the activity of FITC-specific T-T cells against tumor cells with folate receptors.
SMDC adapter technology
SMDCs (small molecule conjugate drugs) platform in immuno-oncology is an experimental (currently experimental) approach that allows the engineering of a single universal MO T cell, which binds with unusually high affinity to a benign molecule designated as FITC. These cells are then used to treat different types of cancer when administered together with SMDC bispecific adapter molecules. This unique bispecific adapter is built with FITC molecules and tumor-homing molecules to precisely bridge the universal CAR cells with cancer cells, leading to the activation of local T cells. Anti-tumor activity in rats was only induced when both universal T-MO cells plus precise antigen-specific adapter molecules were present. Anti-tumor activity and toxicity can be controlled by adjusting the dose of the adapter molecule provided. Treatment of a heterogeneous antigenic tumor can be achieved by administering a mixture of the desired antigen-specific adapter. Thus, some of the challenges of T-cell T-cell therapy today, such as:
- inability to control the rate of cytokine release and lysis of tumors
- the absence of a "switch" that can stop cytotoxic activity when tumor eradication is completed
- requirements for generating different CAR cells for each unique tumor antigen
can be solved or reduced using this approach.
Clinical studies
The first CAR-T therapy approved by the FDA is tisagenlecleucel Novartis, also known as Kymriah. Kymriah's first launch was conducted in August 2016. The results of clinical trials show a remission rate of 83% of all types of acute B cell lymphoblastic leukemia after three months post-treatment. However, 49% of patients also suffered severe side effects, such as neurotoxicity and cytokine release syndrome. These side effects have been reported to be responsible for multiple deaths in late-stage clinical trials with CAR-T therapy. Until August 2017, there are about 200 globally occurring clinical trials involving CAR-T cells. Of these trials, about 65% were experiments in which haematological malignancies were explored, and 80% of them involved CD19 CAR-T cells targeting B cell cancer. Studies have begun in 2016 to explore the viability of other antigens such as CD20.
Initial example
Armored T-MOV Cell
CAR-T cells are more effective in liquid tumors and have not shown much hope in treating solid tumors. Ovarian cancer is one of the main killers of women because most cases of ovarian cancer (about 70%) are diagnosed at an advanced stage. Of those diagnosed, about 30% are expected to survive for five years. Ovarian cancer is difficult to treat because it is a solid tumor with a microenvironment that selectively selects T-cells transferred. The unfriendly microenvironment of solid tumors also comprises myeloid-derived supressor cells (MDSC) and tumor-associated macrophages (TAMs). TAM and MDSC promote growth and tumor development aspects. Environmental microenvironmental tumors also consist of vascular leukocytes (VLC) that promote the development of solid tumors. All components of the microenvironment of the tumor act to suppress T-Cells.
The armored CAR-T cells are designed to secrete strong cytokines such as interleukin 12 (I L-12) and express ligand-tied or dissolved membranes to enhance CAR-T cell effectiveness. IL-12 secretion is promising because it is a proinflammatory cytokine that is known for its ability to increase the cytotoxic ability of CD8 cells, involves and recruiting macrophages to prevent the release of antigen-loss tumor cells. Cells CD19 CAR-T secrete IL-12 can eradicate the established lymphoma in mice without the need for pre-conditioning through host immune induction. Phase II clinical trials were recently performed on ovarian cancer patients in whom they were given IL-12. This treatment causes stable disease in 50% of the cohort.
See also
- Gene therapy
References
External links
- CAR T Cells: Immune Cells Patient Techniques to Treat Their Cancer
Source of the article : Wikipedia
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