INTRODUCTION:

Therapy with chimeric antigen receptor (CAR)-T cells has been revolutionary since it has led to surprisingly positive and long-lasting therapeutic outcomes. CARs are created synthetic receptors that drive lymphocytes—most often T cells—to identify and destroy cells that are overexpressing a particular target antigen. Strong T cell activation and potent anti-tumor responses are brought about by CAR binding to target antigens produced on the surface of cells, which occurs independently of the MHC receptor. There are significant drawbacks to CAR-T cell therapy, though, that still need to be resolved. These drawbacks include potentially fatal side effects linked to CAR-T cells, a lack of effectiveness against solid tumours, inhibition and resistance in B cell malignancies, antigen emigration, poor persistence, poor trafficking and tumour infiltration, and the immunosuppressive microenvironment.^1,2,3

Car structure:

CARs are modular synthetic receptors that consist of Four main components:

(1) Binding domain:

The part of the CAR that imparts target antigen specificity is the antigen binding domain. the variable heavy (VH) and light (VL) chains of monoclonal anti-bodies were used to create the antigen-binding domains. These chains were then joined by a flexible linker to create a single chain variable fragment⁴.

(2) A hinge region:

The extracellular structural area known as the "hinge" or "spacer region" is what extends the binding units from the transmembrane domain. The antigen binding domain needs access to the targeted epitope, therefore the hinge contributes to length and serves to offer flexibility to overcome steric hindrance. The chosen hinge is significant because variations in the length and makeup of the hinge region can impact flexibility, CAR expression, signalling, epitope recognition, strength of activation outputs, and epitope recognition.^5,6

(3) A transmembrane Domain:

The transmembrane domain of CARs is presumably the region with the least amount of characterization. The transmembrane domain's primary job is to hold the CAR to the T cell membrane, but there is evidence that it may also be important for CAR-T cell activity.^7,8

(4) Intracellular signaling:

Understanding the effects of CAR co-stimulation in order to produce CAR constructs with the best endodomain has arguably received the greatest attention in CAR engineering. Second generation CARs were created with one co-stimulatory domain in sequence with the CD3 intracellular signalling domain. The first generation CARs were created in the late 1990s. Third generation CARs did not outperform second generation CARs in models for leukaemia or pancreatic cancer and did not provide any benefits for in vivo treatment.^9,10,11

Process of car t cell therapy:

A molecule called an antigen, which is present on the surface of particular cancer cells, is what CAR T-cell therapy instructs T cells to concentrate their attention toward. To help the T cells acquire this focus during CAR T cell production, a protein is introduced to their surface. Chimeric antigen receptors, also known as CARs, are the name of this protein. Actually, there are 3 additional proteins in this CAR protein. Two proteins are involved in signaling the T cell to become activated when the first protein binds to an antigen on the cancer cell, which is recognised by one protein on the cancer cell. Adding a CAR to a T cell makes it a "CAR T cell," as the name suggests." CAR T cells search for cells that carry the antigen encoded into the CAR protein, such as specific cancer cells, as they float around the body. A CAR T cell becomes activated when it comes into touch with an antigen on a cancer cell. CAR T cells that have been activated proliferate and alert other immune system components to travel to the cancer cell's location. Cytokines are the name given to these signaling proteins. Following considerable inflammation concentrated on the cancer cell brought on by all of these cytokines and activated T cells, the cancer cell eventually perishes. The cancer may go into remission, which indicates that it has either temporarily or permanently disappeared, if all of the cancer cells are eliminated.

Figure 01: Process of CAR-T cell therapy

Car t cell therapy for cancer treatment:

1. Ovarian cancer:

The surprising rate of recurrence of ovarian cancer (OC) following surgery and multiagent chemotherapy necessitates the prompt development of novel therapeutic approaches. CAR-Tcell treatment has been used to target tumor associated glycoprotein 72 (TAG72), which is expressed at a high level on the surface of ovarian cancer.¹²

2. Breast Cancer:

According to studies, HRG1based CART cells effectively stop the growth of breast cancer cells through the HER family of receptors and can provide a tempting therapeutic strategy to overcome cancer resistance to HER2-based targeted therapy^13.

3. prostate cancer:

Targeting chimeric antigen receptors to achieve the desired treatment effects in prostate cancer generally involves using prostate stem cell antigen and prostate-specific membrane antigen^[14].

4. Renal cancer:

Various forms of renal malignancies express carboxyanhydrase IX, which has been identified as a novel target for CAR T cell treatment. Normally, the metalloprotease catalyses hydration of carbon dioxide, however it also functions as a key antigen in renal cell cancer. And it is mildly expressed in the duodenum, small intestine, stomach mucosa, and biliary tree, among other normal tissues^15,16,17

5. Gastric cancer:

Recent research demonstrated that the use of CAR T cells, either alone or in conjunction with the chemotherapy drug Paclitaxel or CAR T cells modified INTERLEUKIN-12 release, is a promising strategy that significantly improves the quality of life for patients with ICAM-1high-advanced gastric cancer^18.

Limitations of car-t cell therapy:

1. Antigen escape:

Tumor resistance to single antigen targeting CAR constructions is one of the most difficult limitations of CAR-T cell therapy. The malignant cells of a sizable fraction of patients treated with these CAR-T cells show either partial or complete loss of target antigen expression, despite the fact that single antigen targeting CAR cells initially have the potential to produce high response rates. Antigen escape is this phenomenon's scientific name. Many approaches currently rely on targeting numerous antigens to decrease the relapse rate in CAR T cell treatment of both haematological malignancies and solid tumours^19,20,21.

2. On-target off-tumor effects:

The fact that solid tumour antigens are frequently and at varied degrees expressed on normal tissues makes it difficult to target solid tumour antigens. Antigen selection is therefore essential in CAR design to prevent "on-target off-tumor" harm and to guarantee therapeutic efficacy. The targeting of tumor-specific post translational changes represents a potential strategy to circumvent the targeting of solid tumour antigens that are also present on normal tissues. There have been studies on four primary CAR-T cell targets, including (TAG7228, B7- H3 ,MUC1 16 and MUC16) In order to increase the clinical usage of CAR-T cell therapies, additional creative ways to stop antigen escape and choose antigens capable of producing a significant antitumor activity while minimising safety issues would be required^22,23]

3. Immunosuppressive microenvironment:

Numerous immune-suppressive cell types, such as myeloid-derived suppressor cells, tumor-associated macrophages, and regulatory T cells, can infiltrate solid tumours in the tumour microenvironment. Growth factors, cytokines, and chemokines that promote tumour growth are produced as a result of these infiltrates and tumour cells. Poor T cell multiplication T cell persistence are two of the key reasons for no response or a subpar response to CART cell treatment. It has been proposed that coinhibitory mechanisms are what start the development of this T cell fatigue. Due to the fact that it offers the two components required for potent immune responses, combination immunotherapy using CAR-T cells and checkpoint blockade is considered to be the next step in immunotherapy^24,25,26.

4. CAR-T cell trafficking and tumor infiltration:

Solid tumour CAR-T cell therapy is more limited than CAR-T cell therapy for haematological malignancies because CAR-T cells can only travel to and enter solid tumours through physical tumour barriers such the tumour stroma and an immunosuppressive tumour microenvironment. Utilizing delivery methods other than systemic delivery is one way to address these drawbacks since local administration (1) decreases the requirement for CAR-T cells to travel to disease areas and (2) reduces toxicities that occur when CAR-T cells treat tumours but do not directly target normal tissues. The expression of chemokine receptors that are compatible with and responsive to tumor-derived chemokines on CAR-T cells is one recently discovered method that looks to dramatically improve CAR-T cell trafficking^27,28.

Advantages of car - t cell therapy:

The sudden early impact and single CAR T cell injection are CAR T cell therapy's most prominent advantages over other cancer therapies. Furthermore, the patient only needs good care and surveillance for two to three weeks. CAR T cell therapy is referred to as a "medicine of the present day" and its effectiveness may last for decades due to the cells' long-term survival in the host body and ongoing capacity to identify and eradicate cancer cells upon recurrence. For individuals for whom transplantation has not been curative and who relapse after transplant, CAR T cell treatment is currently approved for usage.

It is anticipated that CAR T cell treatment would replace various transplants. Clinical trials on blood cancer have demonstrated that CAR T cell therapy was effective in totally curing the disease, even in individuals with a refractory condition in which cancer relapsed after multiple transplants (118). Patients can also live a normal life free from the threat of relapse and gain access to curative treatments like stem cell transplants thanks to CAR T cells. As a result, CAR T cell treatment is sometimes called a "living medication."^29-33

Future perspectives:

Blood malignancies that express CD19 seem to respond best to CAR-T cell therapy for a number of well-explained reasons. The distinctive characteristics of CD19 as a target include its high levels of tumour antigen expression, ease of physical access to tumour cells via the blood and lymphatics, and the tolerance of the on-target off-tumor effect of B cell aplasia. The technical design of CAR-T cells has undergone a number of advancements, though, in an effort to boost effectiveness and lessen toxicity in haematological malignancies and address the problems associated with solid tumours. Multiple antigen targeting is one strategy gaining attention with the goal of increasing specificity, catching different tumour clones, and lowering antigen-negative relapse. The best documented example of this secretes IL-12 upon encountering the target antigen, altering the tumour microenvironment in favour of immune activation and tumour cell death. Cytokine release by T cells guided for universal cytokine killing .With the addition of chemokine receptors to facilitate trafficking or components to detect and activate in the presence of hypoxia, further advancements have made it possible to use the hostile tumour microenvironment to guide and activate CAR-T cells^34-3].

DISCUSSION:

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Received on 24.11.2022 Accepted on 08.08.2023

Int. J. Tech. 2023; 13(1):68-72.

DOI: 10.52711/2231-3915.2023.00008