CAR Constructs and the Impact of CAR T Cancer Therapy

Updated on Mar 1, 2024 By Jason Ellis, PhD Share

Cancer continues to pose significant health challenges worldwide, affecting millions of patients each year. Its diverse forms and complexity often require a multifaceted treatment approach.

Over the years, various therapeutic strategies have emerged, each bringing its own set of benefits and challenges. Among these strategies, adoptive cell therapy stands out as a promising approach. It involves the direct infusion of immune cells—primed and empowered to combat malignancies—back into the patient. This method takes advantage of the body’s defense mechanisms, amplifying their effectiveness against cancer.

As a specific and highly innovative subset of adoptive cell therapy, CAR T cell therapy offers a precision-guided solution. Central to this treatment is the chimeric antigen receptor (CAR) construct, an engineered immunotherapy tool designed to target and combat cancer cells with unparalleled specificity.

What Is a CAR Construct?

The CAR construct is a genetic blueprint for a custom-designed protein receptor. Through various synthetic biology techniques, the construct is encoded into the genes of T cells isolated from a cancer patient. As the enhanced cells grow and divide, transcribing their genetic instructions into proteins, they will also express CAR receptors.

CAR constructs are designed to equip T cells with the specificity to target cancer cells directly. Unlike natural T cell receptors (TCRs) that rely on interactions with antigen-presenting cells, the CAR construct merges the specificity of antibodies with the functionality of T cell responses, offering a potent mechanism against malignancies.

Components of CAR Constructs

Chimeric antigen constructs contain three major sections that translate to functional domains on the membrane receptor it codes for. Scientists fine-tune each domain during the design process to ensure that the T cell is specific to the type of cancer in the patient and that the T cell will be properly activated once the cancer antigen is encountered.

Extracellular Domain

This domain resides on the outside of the cell’s surface and provides the T cell with its specificity. Often derived from monoclonal antibodies linked together as a single-chain variable fragment (scFv), the extracellular domain allows for the recognition of specific antigens on target cells. This ensures that CAR T cells can differentiate between healthy and malignant cells.

This domain also includes the hinge region, often referred to as the spacer. The spacer is the structure that links the antigen recognition component of the CAR receptor to the transmembrane domain that is anchored through the cell surface. Well-designed hinge regions increase the spatial flexibility of the antigen-recognition portion of the CAR receptor to bind to its corresponding cancer antigen, increasing the likelihood of successful T cell activation.

Transmembrane Domain

This stabilizing element anchors the CAR within the T cell’s membrane, ensuring the CAR’s consistent presence and functionality. This hydrophobic section protein connects the intracellular and extracellular domains of the CAR. The construct for this piece is often copied from the natural CD28 receptor that helps increase protein expression and stability.

Intracellular Signaling Domain

This is the interior portion of the CAR receptor that initiates internal cell signaling cascades. When the extracellular domain binds to its target, it triggers the intracellular domain and activates the T cell. These components often originate from the intracellular portions of TCRs (CD3-zeta) and co-stimulatory molecules. This helps ensure that the CAR T cell not only binds to the antigen but also follows through with activation, proliferation, and execution of its cytotoxic, cancer-killing activities.

The synergy of these components transforms a T cell into an effective tool against cancer, underlining the importance of the CAR construct in the broader context of cancer treatment.

Design Considerations of CAR Constructs

In developing effective CAR T therapy, the design of the CAR construct is paramount. This is not a one-size-fits-all mechanism; it requires strategic considerations to achieve optimal therapeutic results.

Selecting Target Antigens on Cancer Cells

The choice of target antigens is crucial. The objective is to identify antigens predominantly expressed on malignant cells but minimally on healthy tissues. This distinction ensures specificity in the CAR T cell’s attack, minimizing collateral damage to healthy cells.

Importance of the Signaling Domain

The signaling domain is more than just a switch; it’s the command center. It is responsible for the cascade of events that lead to T cell activation, expansion, and, ultimately, the destruction of target cells. The co-stimulatory functions of the signaling domain are vital for the sustained activity and longevity of engineered cells. By enhancing their activation and proliferation, these molecules contribute to a robust and lasting immunotherapy response.

Proliferation and Lifespan of CAR T Cells

A balance between T cell quantity and patient safety is critical. Over-expansion could lead to cytokine release syndrome (CRS), necessitating a design that ensures vigorous yet controlled CAR T cell expansion. Cytokines are key modulators of T cell function. Their presence can enhance proliferation, persistence, and effector functions, emphasizing the need for a comprehensive understanding of their role in CAR T cell dynamics.

The Pivotal Role of CAR Constructs in Activating CAR T Cells

By leveraging the specificity of the antibody-derived domain, CAR constructs provide T cells with the precision to target distinct antigens. This specificity ensures that healthy cells remain largely untouched, focusing the therapeutic assault on malignant cells.

Unlike traditional lymphocyte TCR activation, which requires antigen presentation, CAR constructs bypass this step. Upon antigen recognition by the extracellular domain, the intracellular signaling domains initiate a series of events that culminate in T cell activation, expansion, and effector functions.

While robust activation is desired, unchecked T cell activity can be detrimental. The design of the CAR construct must ensure potent activation while incorporating safety mechanisms, such as inducible kill switches, to control CAR T cell activity when necessary.

The Broader Promise of CAR T Cell Therapy

Beyond individual stories, CAR T therapy offers tangible hope to countless patients. With increasing clinical trials and research, the outlook is promising. The therapy’s adaptability, backed by the versatile CAR construct design, has the potential to tackle a wide range of malignancies.

As transformative as current CAR T cell therapy is, the field is still evolving, with numerous innovations on the horizon. The next generation of CAR constructs features multi-specific targeting, improved signaling domains, and integrated safety mechanisms. These advancements aim to increase the therapy’s efficacy towards tumor cells while ensuring patient safety.

Stem cells, with their ability to self-renew and differentiate, offer exciting possibilities. By integrating stem cells into CAR T therapy, there’s potential for longer-lasting responses, reduced side effects, and the possibility of targeting an even broader range of cancers.

Current Challenges in CAR T Therapy

Despite its successes, CAR T cell therapy faces challenges, from managing side effects like cytokine release syndrome to addressing relapses.

• Antigen escape: Some cancers can mutate and downregulate the targeted antigen, making them invisible to CAR T cells. This phenomenon, known as antigen escape, can lead to relapse in patients.
• On-target, off-tumor effects: While CAR T cell receptors specifically target cancer cells, they might occasionally bind to healthy tissues expressing low levels of the targeted antigen, leading to unintended cell damage.
• Managing side effects: Apart from cytokine release syndrome, patients can also experience neurotoxicity, a poorly understood side effect of CAR T therapy. Managing and understanding these side effects is crucial for patient safety.
• Limited efficacy in solid tumors: While CAR T therapy has shown remarkable results in hematologic malignancies like leukemia, its efficacy in solid tumors is still under investigation. The tumor microenvironment, which often suppresses immune responses, and the challenge of getting CAR T cells to infiltrate these tumors are notable hurdles.
• Persistence and longevity: For some patients, the introduced CAR T cells do not persist long enough in the body to elicit a prolonged therapeutic response.
• Manufacturing and cost: Producing patient-specific CAR T constructs and cells is time-consuming and costly. Streamlining this process and making it more affordable will be essential for broader access.

Ongoing research aims to overcome these hurdles, making the therapy safer and more effective by optimizing CAR construct design.

The Role of Clinical Trials in Advancing CAR T Cell Therapy

Clinical trials remain the backbone of progress in this field. As more trials are conducted with diverse patient groups and cancer types, the data will further refine CAR T therapy, ensuring it realizes its full potential.

• Providing novel oncology treatments: Traditional oncology treatments, including chemotherapy and radiation, target both healthy and cancerous tumor cells, often resulting in severe side effects. CAR T cell therapy, backed by meticulously designed CAR constructs, focuses its assault primarily on cancer cells, drastically reducing collateral damage and improving patients’ quality of life.
• Offering hope to previously untreatable cases: For patients with refractory or relapsed malignancies, CAR T therapy has opened new therapeutic doors. Cases once deemed untreatable or terminal are now going into remission, showcasing this treatment’s immense potential.
• Setting the stage for personalized medicine: CAR T therapy could become the epitome of personalized medicine. By engineering a patient’s T cells, the therapy can conceivably be tailored to each individual’s unique cancer profile. This customization promises higher efficacy rates and lays the groundwork for further advancements in individualized treatments in the future.

Real-Life Impact of CAR T Therapy

Behind the complex science and intricate construct designs are real patients whose lives have been profoundly impacted by CAR T cell therapy. As of a 2019 HemaSphere study survey, over 1,000 patients have undergone adoptive CAR T therapy in the United States.

This includes one patient whose story was shared by the Herbert Irving Comprehensive Cancer Center. The patient was previously diagnosed with lymphoma and faced several recurring cancer challenges. Traditional treatments, including chemotherapy and stem cell transplants, provided only temporary remission. However, after the patient underwent CAR T immunotherapy, their engineered T cells successfully targeted and destroyed their cancer cells. Post-treatment, the patient has celebrated two years cancer-free and counting, a testament to the potential of CAR T cell therapy and the expertise of dedicated medical professionals.

Embracing the Future of CAR T Cancer Therapy With Akadeum

As the field of CAR T cell therapy continues to evolve, Akadeum Life Sciences is dedicated to staying at the forefront of innovation. With our specialized buoyancy-activated cell sorting (BACSTM) microbubble T cell isolation kits, Akadeum’s innovative technology provides cell therapy developers with powerful tools to create improved manufacturing workflows for use in cancer immunotherapy, including CAR T therapy. Our technology ensures a higher purity of isolated cells, contributing to the overall success of treatments.

We invite scientists, researchers, and other professionals working in the field of cell and gene therapies to collaborate and engage with Akadeum. Together, we can push the boundaries of what’s possible in CAR T therapy and beyond.

Dive deeper into the world of CAR T cell therapy with Akadeum. Explore our advanced solutions, and let’s embark on a journey to revolutionize cancer treatments together.

Reach out to Akadeum to learn how our microbubble technology can make it possible.