Advances in CAR T cell therapy: antigen selection, modifications, and current trials for solid tumors

Abstract

Chimeric antigen receptor (CAR) T cell therapy has revolutionized the treatment of hematologic malignancies, achieving remarkable clinical success with FDA-approved therapies targeting CD19 and BCMA. However, the extension of these successes to solid tumors remains limited due to several intrinsic challenges, including antigen heterogeneity and immunosuppressive tumor microenvironments. In this review, we provide a comprehensive overview of recent advances in CAR T cell therapy aimed at overcoming these obstacles. We discuss the importance of antigen identification by emphasizing the identification of tumor-specific and tumor-associated antigens and the development of CAR T therapies targeting these antigens. Furthermore, we highlight key structural innovations, including cytokine-armored CARs, protease-regulated CARs, and CARs engineered with chemokine receptors, to enhance tumor infiltration and activity within the immunosuppressive microenvironment. Additionally, novel manufacturing approaches, such as the Sleeping Beauty transposon system, mRNA-based CAR transfection, and in vivo CAR T cell production, are discussed as scalable solution to improve the accessibility of CAR T cell therapies. Finally, we address critical therapeutic limitations, including cytokine release syndrome (CRS), immune effector cell-associated neurotoxicity syndrome (ICANS), and suboptimal persistence of CAR T cells. An examination of emerging strategies for countering these limitations reveals that CRISPR-Cas9-mediated genetic modifications and combination therapies utilizing checkpoint inhibitors can improve CAR T cell functionality and durability. By integrating insights from preclinical models, clinical trials, and innovative engineering approaches, this review addresses advances in CAR T cell therapies and their performance in solid tumors.

Keywords: CAR T cell; cancer; immunotherapy; solid tumors; structure; targets.

Figure 1

CAR Structure and Function in Killing Cancer Cells (A) The CAR’s antigen binding domain is typically derived from a single-chain variable fragment (scFv). The antigen binding domain is present on the ectodomain of the T cell and is connected to hinge, transmembrane, and intracellular signaling domains that allow for CAR stability and binding induced attack of cancer cells by T cells. (B) CAR T cell binding to target antigens on cancer cells allows for T cell activation and T cell mediated killing of cancer cells.

Figure 2

CAR T Generation Classification by Intracellular Structure. CARs are commonly grouped into generations based on the various structures present in their intracytoplasmic domains. Multiple costimulatory domains and combinations of costimulatory domains have been analyzed. Parentheses under costimulatory domains 1 and 2 represent specific domains that have been tested at that position throughout CAR generations.

Figure 3

Selected Modifications of CAR T Cells. (A) Construction of a dual-signaling CAR utilizing a second-generation CAR. (B) Construction of a tandem CAR utilizing two scFvs in a second-generation CAR. (C) Construction of a CAR with Combinatorial Antigen Sensing Circuits in the form of an “AND” logic gate CAR. (D) Derivation of nanobodies for construction of nanoCARs. (E) T cell receptor fusion constructs (TRuCs) that contain an ScFv linked to various subunits of an endogenous TCR.

Figure 4

Utilization of Allogeneic T Cells to Produce CAR T Cells. Isolated T cells collected from healthy donor leukocytes allow engineering of the T cells so that they can be used universally. This process includes the introduction of a recombinant lentivirus to add the desired CAR to the T cell and includes the CRISPR/Cas9 mediated disruption of the HLA-A, HLA-B, class II major histocompatibility complex transactivator (CIITA), T-cell receptor alpha constant (TRAC), and Programmed Cell Death Protein 1 (PD-1) on transduced T cells. Further amplification and purification of these allogeneic T cells produces universal CAR T cells that can be infused to multiple patients.