CAR-T-Derived Extracellular Vesicles: A Promising Development of CAR-T Anti-Tumor Therapy

Abstract

Extracellular vesicles (EVs) are a heterogenous population of plasma membrane-surrounded particles that are released in the extracellular milieu by almost all types of living cells. EVs are key players in intercellular crosstalk, both locally and systemically, given that they deliver their cargoes (consisting of proteins, lipids, mRNAs, miRNAs, and DNA fragments) to target cells, crossing biological barriers. Those mechanisms further trigger a wide range of biological responses. Interestingly, EV phenotypes and cargoes and, therefore, their functions, stem from their specific parental cells. For these reasons, EVs have been proposed as promising candidates for EV-based, cell-free therapies. One of the new frontiers of cell-based immunotherapy for the fight against refractory neoplastic diseases is represented by genetically engineered chimeric antigen receptor T (CAR-T) lymphocytes, which in recent years have demonstrated their effectiveness by reaching commercialization and clinical application for some neoplastic diseases. CAR-T-derived EVs represent a recent promising development of CAR-T immunotherapy approaches. This crosscutting innovative strategy is designed to exploit the advantages of genetically engineered cell-based immunotherapy together with those of cell-free EVs, which in principle might be safer and more efficient in crossing biological and tumor-associated barriers. In this review, we underlined the potential of CAR-T-derived EVs as therapeutic agents in tumors.

Keywords: CAR-T cells; anti-tumor agents; extracellular vesicles; tumors.

Figure 1

Structure and evolution of CAR-T cells. (A) The CAR contains an extracellular binding domain (usually in the form of scFv), a hinge region, a transmembrane domain, and an intracellular signaling domain. (B) The first generation of CARs has only a single transduction intracellular domain such as the CD3ζ-chain, while the second generation includes the addition of one co-stimulatory molecule such as CD28, OX-40 (CD134), and 4-1BB (CD137). The third CAR generation, instead, is equipped with two different co-stimulatory molecules; while the fourth generation contains usually one costimulatory molecule and a transcription factor that is capable of inducing the production of specific cytokines (e.g., IL-12). Lastly, the fifth CAR generation has been developed based on the second CAR generation with the addition of an extra intracellular domain of cytokine receptors with a binding site for transcription factors, such as STAT-3/5. (C) Different intracellular domains of CAR-T cells.

Figure 2

Schematic representation of the targets used to produce CAR-T cells to treat solid tumors.

Figure 3

Schematic representation of extracellular vesicle subtypes. Large extracellular vesicles include EV subtypes with diameters larger than 100–200 nm, such as apoptotic bodies, migrasomes, and microvescicles. Small extracellular vesicles include exosomes, exomeres, and supermeres (supernatant of exomeres), all characterized by diameters smaller than 200 nm. In some cases, large and small EV size overlap.

Figure 4

T-lymphocyte-derived extracellular vesicle involvement in immune responses.