Modular Chimeric Antigen Receptor Systems for Universal CAR T Cell Retargeting

Abstract

The engineering of T cells through expression of chimeric antigen receptors (CARs) against tumor-associated antigens (TAAs) has shown significant potential for use as an anti-cancer therapeutic. The development of strategies for flexible and modular CAR T systems is accelerating, allowing for multiple antigen targeting, precise programming, and adaptable solutions in the field of cellular immunotherapy. Moving beyond the fixed antigen specificity of traditional CAR T systems, the modular CAR T technology splits the T cell signaling domains and the targeting elements through use of a switch molecule. The activity of CAR T cells depends on the presence of the switch, offering dose-titratable response and precise control over CAR T cells. In this review, we summarize developments in universal or modular CAR T strategies that expand on current CAR T systems and open the door for more customizable T cell activity.

Keywords: CAR adaptor; adoptive immunotherapy; antibody; chimeric antigen receptor (CAR T); modular CAR T; split CAR; universal CAR T; universal immune receptor.

Figure 1

Schematic representation of a conventional CAR T cell and a universal or modular CAR T cell (A) Conventional CAR T cells have a single-chain antibody fragment (scFv) targeting element, expressed in tandem with signaling domains derived from the T cell receptor and costimulatory domains such as 4-1BB and CD28 connected through a transmembrane (TM) domain and a flexible spacer or hinge region; (B) a universal CAR T cell has a split design containing a tumor-associated antigen (TAA) targeting element, usually derived from a monoclonal antibody, a switch element and the signaling module, consisting of the T cell signaling domains and an extracellular region which interacts with the switch element.

Figure 2

A schematic of strategies used in universal CAR T design: (A) biotin-binding immune receptor; (B) anti-FITC CAR T; (C) the SpyTag/SpyCatcher CAR T system; (D) leucine zipper or SUPRA CAR T; (E) convertibleCAR or modified NKG2D CAR T; (F) SNAP CAR T enzymatic CAR labeling system; (G) the co-localization-dependent protein switch (Co-LOCKR) CAR T system; (H) UniCAR or anti-5B9 peptide CAR platform; (I) anti-peptide neo-epitope (PNE) CAR T.