In Situ Programming of CAR-T Cells: A Pressing Need in Modern Immunotherapy

Abstract

Chimeric antigen receptor-T (CAR-T) cell-based therapy has become a successful option for treatment of numerous hematological malignancies, but also raises hope in a range of non-malignant diseases. However, in a traditional approach, generation of CAR-T cells is associated with the separation of patient's lymphocytes, their in vitro modification, and expansion and infusion back into patient's bloodstream. This classical protocol is complex, time-consuming, and expensive. Those problems could be solved by successful protocols to produce CAR-T cells, but also CAR-natural killer cells or CAR macrophages, in situ, using viral platforms or non-viral delivery systems. Moreover, it was demonstrated that in situ CAR-T induction may be associated with reduced risk of the most common toxicities associated with CAR-T therapy, such as cytokine release syndrome, immune effector cell-associated neurotoxicity syndrome, and "on-target, off-tumor" toxicity. This review aims to summarize the current state-of-the-art and future perspectives for the in situ-produced CAR-T cells. Indeed, preclinical work in this area, including animal studies, raises hope for prospective translational development and validation in practical medicine of strategies for in situ generation of CAR-bearing immune effector cells.

Keywords: Adoptive cellular therapy; CAR-T cells; Gene-editing tools; In-situ generation.

Fig. 1

Evolution of CAR structure throughout different generations. First generation of CARs contains only antigen recognition domains and CD3ζ activation domain. Second generation of CARs additionally comprises a co-stimulatory domain (such as 4-1BB or CD28). In the third generation, two co-stimulatory domains are included. T cells expressing fourth generation CAR (sometimes called TRUCKs) contain an additional cDNA cassette, e.g., encoding an immunomodulator. Fifth generation of CARs is a group of next gen receptors, such as ON-switch CARs (on the figure above), the universal CAR-T cells, etc., all aiming at improving safety and efficiency of immunotherapies

Fig. 2

Most prominent advantages of the in situ CAR-T generation