CAR T Cells Definition
CAR T-cells (chimeric antigen receptor T cells) are a kind of immune cell with modified receptors that allow them to react to different antigens. The T-cell membrane contains chimeric antigen receptors; chimaera DNA, also known as recombinant DNA, is a genetically modified sequence made from two distinct species. It’s possible that these species are fungi, viruses, plants, bacteria, or other animals. CART therapy is a novel immunological treatment option for individuals with cancer.
What are CAR T Cells?
CAR T cells are recombinant T cells that have been found to be beneficial in treating some types of cancer. They are cancer-fighting medications that are classified as immunotherapies because they alter the immune system’s response to cancer cells. T cells are modified ex vivo to express particular antigen receptor genes, either from the patient being treated or from a suitable donor. When these gene sequences are expressed, they generate antigen receptors in the T cell membrane. T cell receptors cause cells to activate in the presence of antigens, which are proteins found on the membranes of foreign or abnormal cells.
Chimeric antigen receptors (CARs) are fusion proteins that link T lymphocytes to the antigen for which they were engineered. They enhance natural immune responses by eliciting immune responses to antigens that the body would ordinarily ignore. At the centre of this method are TCRs (T cell receptors). When TCR-based recognition fails, as it often does in many types of malignancy, CAR-based identification takes over.
To comprehend what CAR T-cells are, you must first grasp the adaptive immune system. Invading pathogens are recognised, marked, and attacked by our immune cells, which safeguard us. They may also permanently eradicate non-infected, damaged cells.
MAMPs (microbe-associated molecular patterns) on the cell membranes of foreign species. Damage-associated molecular patterns (DAMPs) and lifestyle-associated molecular patterns (LAMPS) in the cytoplasm of wounded cells signal circulating antigen-presenting cells (APCs), which initiate the immunological response.
Natural Immune Response
Our native immune reaction is very intricate; in recent years, study has expanded, and our understanding – although far from full – has resulted in immunotherapy medications that were unheard of only five years ago.
The following phases occur during foreign antigen recognition:
- A foreign particle or a mutant cell with aberrant surface proteins enters the body and comes into contact with an antigen-presenting cell (APC). An antigen is a protein-based molecule that may trigger a reaction from the immune system. Pattern recognition receptors are found on the membranes of APCs as well as inside the cytoplasm (PRRs). PRRs are present in a variety of cell types, although APCs are the principal source of PRRs, as this page covers CAR T-cell processes.
- The PRR attaches the APC to the molecular pattern on the antigen when a certain DAMP (also termed PAMP with the P referring to pathogen), MAMP, or LAMP molecule is near by. The PRR also instructs the APC to produce cytokines, which attract additional immune cells to the area, modify infected cell gene expression to aid infection resistance, and raise or reduce the immune response. Interleukins and interferon are examples of cytokines.
- The aberrant cell is subsequently phagocytosed, pinocytosed, or endocytosed into the cytoplasm of the APC.
- The APC creates a flag molecule called the major histocompatibility complex (MHC) during this internalisation process (MHC).
- The APC moves to the lymph nodes, which contain immature T lymphocytes.
- Cell cell receptors (TCRs) on immature helper T cells (CD4+ TH) and cytotoxic T cells (CD8+ TC) attach to MHCs. When an MHC molecule comes into contact with a TCR, it activates its receptors. MHC class I (MHCI) molecules bind cytotoxic T cells, whereas MHC class II (MHCII) molecules attach to helper T cells. T cells also create co-receptors including CD16, CD19, CD20, and CD22 to help maintain the interaction between MHC and TCR. These are only a few of the co-receptors that are being studied and targeted in CAR T-cell therapies.
- The activated helper T cells are now split into two groups. The cytokines these cells produce define which category they belong to. Using cytokines from these categories, helper T cells either guide cytotoxic T cells to directly target foreign particles appearing with the detected antigen. Or they assist B cells in producing antibodies against that antigen using cytokines from these groups.
- B cells are activated through receptors as well, and this is often (but not always) facilitated by the activation of a helper T cell. Under the effect of TH, a protein (CD ligand) on the helper T cell membrane binds to the equivalent CD co-receptor on the B cell membrane. T-dependent antigens are any antigens that produce this interaction. B cells, once bound, create antibodies that bind to and kill particular antigens.
CAR T Cells and Cancer
Tests such as CA-125 (ovarian cancer cells), tyrosinase (malignant melanoma cells), and carcinoembryonic antigen (bowel cancer cells) are frequently used to detect the presence of cancer or to identify specific cells. Virus-caused cancers generate a variety of intracellular proteins. Normally, such indications would help the immune system recognise and destroy them.
Unfortunately, many malignancies suppress immunological responses and promote T-cell tolerance instead. Our immune system would rapidly become overloaded if it responded to every alien protein. Immune tolerance is disrupted in those who develop allergies to commonplace items.
Localized immune responses have been reported to be altered by solid tumours, blood and lymph malignancies, and cells found in the microenvironment of the tumour. They have an impact on the number of immune cells in the nearby region, how they react, communicate, and proliferate.
Researchers explored the possibility of altering immune cells to bypass tolerance mechanisms after this was discovered. Immune tolerance in cancer cells develops in three stages:
- Elimination:Immune cells identify and kill early cancer cells, resulting in their elimination.
- Equilibrium:If not all cancer cells are eliminated, they enter a state of equilibrium and go dormant. During this time, they develop a variety of strategies for evading the immune system’s natural defences.
- Escape:Cancer cells that have developed may trigger immune tolerance and proliferate.
Due to advancements in genetic engineering, altering the DNA of immune cells is now feasible. It is theoretically feasible to induce immune cells to target certain antigens by having a gene produce a specific receptor. There is no escape phase and no tolerance if the equilibrium phase is skipped.
In actuality, our understanding of the many cell connections makes this treatment a hit-or-miss proposition. Because not all B cells express the requisite number of CD co-receptor proteins, for example, not all B cells can interact with CARs; even when T cells react to cancer cells, antibodies are not generated in adequate quantities.
Even modified T cells are unable to act in the tumour microenvironment, which surrounds a mass of cancer cells; CAR-T cells do not seem to be successful in the therapy of solid tumours. CAR-T treatments have the greatest results in the treatment of lymphomas and leukemias, two forms of B-cell malignancies.
Cytokine release syndrome is another issue with CAR T cell therapy. The immune system’s quick activation results in a flood of cytokines, which are hazardous at high doses. Fever, hypotension, and low tissue oxygen levels are some of the symptoms. CAR-T cell treatment may cause cytokine release syndrome (CRS), which can be severe or even deadly. Despite this, studies demonstrate that CRS is connected to a better CAR-T therapy response.
Immune effector cell-associated neurotoxicity syndrome is another unfavourable side effect (ICANS). This is generally associated with CRS. Low levels of awareness, convulsions, motor nerve injury, and cerebral edoema are all symptoms.
What is CAR-T Cell Therapy?
Adoptive cell transfer (ACT) is a technique used in CAR-T cell therapy. T cells are collected by leukapheresis from a patient’s blood and genetically modified to make CARs, then amplified. Engineered T cells are returned to the body after sufficient quantities have been created.
The kind of chimeric antigen receptor generated is determined by the type of malignancy. CAR T cells used in cancer treatment are primarily used to stimulate B cells to generate antibodies. Cellular lymphomas, acute lymphoblastic leukaemia (ALL), and chronic lymphocytic leukaemia may all be treated by creating receptors for the CD19 antigen on certain B cells (CART-19 or CAR T cell CD19 treatment).
It is not necessary for CAR-T cells to have interacted with an antigen-presenting cell. They can develop into cytotoxic T cells (which may kill antigen-marked cancer cells right away) and helper T cells (to stimulate B cells to produce antibodies for the specific cancer cell antigen). They are not presently used to treat non-blood malignancies because they are not totally resistant to the effects of the tumour microenvironment.
The majority of CAR-T cell therapies are done using the patient’s own blood (autologous treatment). Sometimes blood from a donor is used (allogeneic treatment). An intravenous catheter delivers venous blood to a leukapheresis machine. Apheresis machine technology has progressed to the point where only helper or cytotoxic T cells may be extracted from the blood before the remainder is returned to the patient. Immune stem cells are used in certain therapies. T cells may be isolated and frozen for later use.
The T cells are then reintroduced into the patient’s venous circulation after being altered. This therapy works endlessly because memory T cells are also created; memory cells survive in the body years after the cancer cells that were targeted are eradicated.
CAR T Cells Manufacturing Process
Manufacturing CAR T cells takes around two weeks. It will take time to develop sufficient numbers of modified T cells.
T cells that have been harvested must first be activated in the lab. T cells are activated in response to a particular cancer-associated antigen using artificial antigen-presenting cells, T cell activation reagents, or monoclonal antibody-coated beads.
A T cell’s CAR gene must be expressed in order for it to make chimeric antigen receptors. This gene may be turned on using inactivated viral vectors. The viral vector may be put through the activation process in an incubator and then washed away with the activation chemicals. The viral vector injects RNA sequences into activated T cells, which code for the chimeric antigen receptor in CAR T-cell therapies.
The CAR gene will be expressed in any cell formed by the proliferation of these modified T cells. The proteins that assemble and construct antigen-specific membrane receptors are synthesised after CAR expression starts.
The modified T cells are then housed in a bioreactor culture system under ideal cell division conditions. In ten to twelve days, a cell culture may yield up to five litres of culture. After a sufficient number of CAR T cells have been generated, they are washed and any extra fluids are eliminated. This concentrates the solution into a frozen product that may be taken to a treatment facility in a bag. The engineered CAR-expressing T cells may be given intravenously after being frozen and warmed. They trigger a long-term immunological response against the antigen they were designed to eliminate.
- Janeway CA Jr, Travers P, Walport M, et al. Immunobiology: The Immune System in Health and Disease. 5th edition. New York: Garland Science; 2001. T cell-mediated cytotoxicity. Available from: https://www.ncbi.nlm.nih.gov/books/NBK27101/
- Posey Jr, AD, Maher J, Maus MV (Eds). (2018). E-book. CAR-T Cell Therapies for Non-Hematopoietic Malignancies: Taking Off the Training Wheels. Frontiers in Immunology. doi: 10.3389/fimmu.2018.01740.