CAR-T CELL THERAPY (part1)
1. INTRODUCTION
All organs in our body are made up of cells. Cells are the smallest building blocks of our body and can only be seen with the aid of a microscope. Healthy cells in our body have the ability to divide. However, this feature is not found in muscle and nerve cells. With this division, it is aimed to renew the cells that die and to repair the injured tissues. But their ability to divide is limited. They cannot be divided forever. Throughout its life, every cell has a certain number of divisibility. On the other hand, cancer cells lose this consciousness and begin to divide uncontrollably. Cancer cells accumulate and form tumors (masses), tumors can compress, infiltrate or destroy normal tissues. If cancer cells leave the tumor where they formed, they can travel to other parts of the body via the blood or lymph circulation. They form tumor colonies where they go and continue to grow. The spread of cancer to other parts of the body in this way is called metastasis [1]. Inside the nucleus, located in the center of the cells, there are microscopic strands called DNA, in which the genetic information of the cell and the organism is stored. DNA is necessary for the cell to function normally. The main factor in the formation of cancer is the deterioration of the genetic structure. DNA can be damaged by chemicals, viruses, tobacco products or excessive sunlight, etc. Even if there is DNA damage in the normal life cycle of the cell, the cell either repairs it or dies. In cancer cells, damaged DNA cannot be repaired and uncontrolled proliferation begins [2].
Cancers are classified according to the organ in which they begin to form and their appearance under the microscope. Different types of cancers grow at different rates, show different ways of spreading, and respond to different treatments. For this reason, different treatments are applied in the treatment of cancer patients according to the type of cancer present [1].
The immune system is divided into two branches, the innate and the adaptive immune system. Thanks to the surveillance of the immune system, non-self molecules are eliminated. pathogens (viral, bacterial, etc.) are eliminated in cells that have undergone antigenic transformation by proteins and tumors. However, cancer cells have evolved various mutations to evade or suppress the immune system. Therefore, tumors live and cause harm in the human body by regulating the expression of their antigens and changing environmental factors. Today, at the point reached in understanding the molecular structure and behavior of the immune system; Numerous innovative treatments are being developed through the direct use of one's own cells or indirectly through genetic modifications that optimize the target response [3].
For many years, cancer treatment has been done with chemotherapy, radiotherapy and surgery, but in the last 20 years, targeted agents have replaced most standard cancer treatments. Recently, immunotherapy has come to the fore. Immunotherapy is to fight cancer cells by activating the person's immune system. The latest development in immunotherapy is chimeric antigen receptor (CAR; chimeric antigen receptor)-t cell therapy. this cell therapy has shown very good results in clinical trials [4]. CAR-T cell therapy, which was applied for the first time in a phase I study in a chronic lymphocytic leukemia (CLL) patient with 17p deletion in 2011, was evaluated and approved by the American Food and Drug Administration (FDA) as a "breakthrough therapy" [5]. In August 2017, Kymriah (Tisagenlecleucel) received FDA approval for the treatment of B-cell precursor acute lymphoblastic leukemia (ALL) under 25 years of age, and Yescarta (Axicabtagene Cioleucel) in October 2017 for the treatment of relapsed or refractory large cell lymphoma after two or more series of treatments(Tablo 1). [4]
CAR-T cell therapy uses T cells engineered with CARs for cancer treatment. The goal of CAR-T immunotherapy is to target and destroy T cells more effectively to cancer cells. Scientists harvest T cells from humans, genetically modify them, and then inject the resulting CAR-T cells into patients to attack tumors. [6]
CAR-T cells can be derived from T cells from a patient's own blood (autologous) or from T cells (allogeneic) from another healthy donor. T cells isolated from an individual are then genetically engineered to target an antigen found on the surface of tumors. Once infused into a patient, CAR-T cells act as a "live drug" against cancer cells. Upon contact with the targeted antigen on a cell, CAR-T cells bind to it and become activated, then continue to proliferate and become cytotoxic. [7,8]
1. GENERAL INFORMATIONS
2.1 The role of T cells in cancer and T cell recipient gene therapy
In 1909, Paul Ehrlich first proposed that the immune defense system identifies and destroys tumor cells. However, recent studies have shown that the immune response may be ineffective against tumor development due to immunological tolerance and anergy. Cancer immunoregulation consists of three phases: Elimination, Equilibrium, and Escape. In the elimination phase, cancer is eliminated intact by innate and adaptive immunity, whereas in the equilibrium phase, variant tumor cells that develop genetic instability survive despite immune attack. In the escape phase, uncontrolled proliferation of variant tumor cells occurs. [9]
In 1890, William B. Coley observed that patients with malignant tumors responded to intratumoral inoculations in which live bacterial organisms or bacterial toxins caused the tumors to express unique proteins that could elicit an immune response. Since the early 20th century, research has shown that most cancer cells carry overexpressed tumor-associated or tumor-specific antigens that are not found on healthy cells; this property has led to the successful implementation of the hypothesized T-cell transfer. The discovery of the role of T-cell growth factor, in vitro T-cell culture, and lymphodepletion led to studies on T-cell-based therapy. The first successful trial of T-cell transfer immunotherapy using autologous TILs was performed in 1990 for advanced melanoma. Since tumor-infiltrating lymphocytes were attempted to be isolated for the first time, in vitro expansion and reinfusion was shown to be time-consuming and produce transient anti-tumor effects, and genetic engineering methods were used to generate specific T cell-derived TCRs. [10]
The TCR is a heterodimer that carries information for identified tumor antigens and consists of alpha and beta chains associated with a CD3 complex (Figure 2.1.1). TCR technology has advantages for targeted T cell therapy. Ideal effector T cells are aligned with tumor target antigens selected by HLA recognition. The natural mechanism of T-cell immunity is associated with a lower risk of cytokine release syndrome. The major challenges to overcome are the low surface expression of TCRs, HLA dependency, and short-term persistence of transferred T cells in vivo. In thymic selection during T cell development, a few mutant proteins are encoded by cancer-causing genetic mutations (driver mutations), the majority of tumor antigens are self-antigens, and T cells have low affinity for self-antigens. To generate higher avidity, TCRs selected from immunized human HLA transgenic mice with the desired epitopes are used, with targeted mutations in the variable regions of the TCR alpha/beta chains added with targeted mutations in the complementary determinant region 2 or 3 (CDR2 or 3). . These modified TCRs interact with the HLA/epitope complex . However, TCRs can form unwanted alpha/beta heterodimers between new and endogenous TCR alpha/beta chains, which is referred to as mismatching and results in low avidity. TCR-modified T cells adapted for solid tumors have been unsuccessful in most studies (Figure 2) [10,11].
leukapheresis: T cells of the patient are separated and collected by apheresis device [12].
T - cell activation: T cells differentiated using antibody coated beads are activated [12].
Transduction: The gene encoding the CAR construct is reprogrammed ex vivo by transferring it to the genome of the T cell via a gene transfer vector such as a retrovirus, lentivirus or transposon [12].
Expansion: Genetically reprogrammed activated T cells are further expanded ex vivo [12].
Chemotherapy: Before the T-cell infusion, the patient is given a priming regimen that causes lymphocyte depletion. By increasing the serum level of cytokines such as interleukin ( IL ) -7 , IL - 15 and decreasing the number of regulatory T cells, the activity of the transferred T cells in the recipient is increased. The conditioning regimen that provides the best therapeutic response is the fludarabine cyclophosphamide combination [12].
CAR-T cell infusion: Genetically modified T cells are infused into the patient. The ideal cell dose is 1-5 x 10% / kg. Infused CAR-T cells remain in the circulation for a median of 30-300 days [12].
