The journey of CAR-T therapy in hematological malignancies

Abstract

Chimeric antigen receptor T (CAR-T) cells therapy has revolutionized the treatment paradigms for hematological malignancies, with multi-line therapy-refractory patients achieving durable complete remissions (CR) and relatively high objective response rate (ORR). So far, many CAR-T products, such as Kymriah, Yescarta and Tecartus, have been developed and got the unprecedented results. However, some patients may relapse afterwards, driving intense investigations into promoting the development of novel strategies to overcome resistance and mechanisms of relapse. Notable technical progress, such as nanobodies and CRISPR-Case9, has also taken place to ensure CAR-T cell therapy fully satisfies its medical potential. In this review, we outline the basic principles for the development and manufacturing processes of CAR-T cell therapy, summarize the similarities and differences in efficacy of different products as well as their corresponding clinical results, and discuss CAR-T immunotherapy combined with other clinical effects of drug therapy.

Keywords: CAR-T cell therapy; Combinatorial therapy; Drug product; Hematological malignancies; Targeted therapy.

Fig. 1

The development processes of five generations of CARs The first generation only had the intracellular CD3-ζ signal molecule, which are phosphorylated via SRC tyrosine kinase family. In the second generation, CD28 or 4-1BB co-stimulatory region was integrated with the CD3-ζ molecule. Various proteins containing SH2 domain (PI3K, GRB2 and GADs) are recruited while IL-2 is induced. Based on the second generation, the third generation (such as CAR 22–19) added two different co-stimulatory domains (CD28–4-1BB/ICOS-4-1BB). The fourth generation (TRUCKs or armoured CARs) paired with a constitutively expressed chemokine (IL-12). The fifth generation, also based on the second generation, added intracellular domains of cytokine receptor (IL-2Rβ). The activation of JAK-STAT, deriving from IL-2Rβ and incorporated between CD28/4-1BB and CD3-ζ, stimulates cell proliferation. (By Figdraw)

Fig. 2

Mechanisms of CAR-T therapy A monoclonal antibody is usually used to generate the extracellular portion of the CARs. The scFv, able to recognize TAAs, is composed of the VL and VH region. In addition to scFv, the targeting domain also use VHH, also known as nanobodies, which are derived from the variable domain of HcAbs. The hinge region connects the transmembrane region and extracellular region. The intracellular activation region can be divided into co-stimulatory region and signaling region. Signals generated by co-stimulatory mechanisms depend on the co-stimulation domain (CD28 depends on PI3K, while 4-1BB employs NF-κB and TRAFs). CD3-ζ is usually a signal region with three ITAMs. Once the scFv recognizes and binds TAAs, Phosphorylation of the ITAMs initiates signal transduction through ZAP70, and then sends out signals to release T cell response (granzyme and perforin/BID or FADD). (By Figdraw)

Fig. 3

Application of immune checkpoint blocking technology in CAR-T cells. (I) Combination therapy, treated with pembrolizumab (anti-PD-1); (II) CAR-T cells self-secrete immune checkpoint molecules (III) Genetic perturbation of CAR-T cell autoimmune checkpoint genes. (By Figdraw)