CAR-T Cell Challenges and Existing Solutions; Special Look at Solid Tumors
CAR-T Cell Challenges and Existing Solutions; Special Look at Solid Tumors
Ahmad Noei,1Shafieeh Mansoori,2Zahra Sharifzadeh,3,*
1. Immunology Department, Pasteur Institute of Iran, Tehran, Iran 2. Immunology Department, Pasteur Institute of Iran, Tehran, Iran 3. Immunology Department, Pasteur Institute of Iran, Tehran, Iran
Introduction: T cell engineering with the ability to express chimeric antigen receptor (CAR) is a dramatic breakthrough in the treatment of some malignancies, especially B-cell-related malignancies. Despite the brilliant results, there are limitations to the widespread use of this approach in relation to different clinical conditions and in general. Systemic complications associated with inflammatory cytokines that lead to pervasive inflammation, as well as on-target, off-tumor toxicity, are among many barriers to the performance of the CAR system. These problems include low persistence and tumor antigen escape of CAR-T cells. In addition, the optimal function of CARs in solid tumors is still an active area of research. Here we intend to briefly review the solutions from the perspective of synthetic biology, while pointing out the existing barriers.
Methods: In the present review, the data were extracted from google scholar papers between 2010 to 2021.
Results: The best results of CAR-T cell therapy have been associated with blood malignancies, specifically CD19 + ALL. However, antigen escape and cell survival of tumors in vivo reduce the effectiveness of treatment. Many engineering strategies have been developed to solve these problems. CAR design with the ability to identify multiple tumor associated antigens (TAAs) in the form of Tandem CAR or dual CAR is one of the solutions known to overcome the escape of antigen or heterogeneity of the tumors. These approaches, not only have the benefits of detection efficiency, but also can reduce off-target complications. In the split CAR approach, one receptor is designed against one TAA with CD3 signaling domain and another receptor against another TAA is designed with co-stimulatory domain (CD28 or 4-1BB). With a change in the second receptor against one TAA, an iCAR approach has been developed that detects activity-inhibitory signals if a non-tumor antigen is detected. The use of logic gating and / or conditional expression systems is another approach in which CAR-T activity depends on the expression of a target antigen and a specific transcription factor. In the Tandem CAR approach, two targeting domain (scFv) are placed in a single structure. In another design, cells that have the ability to secrete bispecific antibodies can be engineered, which are engineered molecules that have the ability to target two antigens simultaneously. Universal CARs are another category that uses the modular structure to divide the classic CAR function into two separate parts. One part is to identify a switchable molecule or tag and the second part is the switching molecule itself. These modular CARs provide the ability to detect different antigens without the need for cell re-engineering. To increase the T cell persistence in vivo, less differentiated T cell subsets can be used that have a higher proliferation potential. Bystander cells, such as dendritic cells, can be engineered to secrete factors such as IL-12 and alter tumor microenvironment (TME) to help them survive longer in the body.
The most important challenge in solid tumors is their trafficking. There are many physical and biochemical barriers to CAR-T-cells. Direct injection into the tumor site is known as a general solution. According to Synthetic biology, T-cells can be designed to secrete different chemokines. Stroma retargeting of T-cells including the designed CARs against FAP, or heparinase expressing CAR-T cells are another solution to enhance the CAR-T-cell infiltration. Suppressor TME is another major challenge in this area. The change in TME has been achieved by the Armored CAR approach, known as fourth-generation CARs. These cells are able to secrete or superficially express factors that alter TME in favor of optimal CAR function. This approach can also promote the microenvironment of the tumor in favor of the anti-inflammatory status and prevent systemic toxicity.
Conclusion: Exciting approaches are being developed to increase the effectiveness and scope of CAR-T Cell therapy. These approaches aim to promote the safety and efficacy of CAR-T-Cells. The effective solutions that synthetic biology has presented to us have raised hopes for the widespread use of these agents in the treatment of cancer.