CAR-T Cells Immunotherapies for the Treatment of Acute Myeloid Leukemia-Recent Advances

Abstract

In order to increase the effectiveness of cancer therapies and extend the long-term survival of patients, more and more often, in addition to standard treatment, oncological patients receive also targeted therapy, i.e., CAR-T cells. These cells express a chimeric receptor (CAR) that specifically binds an antigen present on tumor cells, resulting in tumor cell lysis. The use of CAR-T cells in the therapy of relapsed and refractory B-type acute lymphoblastic leukemia (ALL) resulted in complete remission in many patients, which prompted researchers to conduct tests on the use of CAR-T cells in the treatment of other hematological malignancies, including acute myeloid leukemia (AML). AML is associated with a poorer prognosis compared to ALL due to a higher risk of relapse caused by the development of resistance to standard treatment. The 5-year relative survival rate in AML patients was estimated at 31.7%. The objective of the following review is to present the mechanism of action of CAR-T cells, and discuss the latest findings on the results of anti-CD33, -CD123, -FLT3 and -CLL-1 CAR-T cell therapy, the emerging challenges as well as the prospects for the future.

Keywords: AML; CAR-T; CD123; CD33; CLL-1; FLT3.

Figure 1

The structure of different CAR generations: The first generation contains only CD3ζ cytoplasmic domain with three immunoreceptor tyrosine-based activation motifs (ITAMs). The co-stimulatory domain is added in the second generation. The third generation contains two co-stimulatory domains. The fourth generation, apart from one co-stimulatory domain, additionally contains a transcription factor that brings about inflammatory cytokine production. The fifth generation, in addition to one co-stimulatory domain, contains IL-2Rβ, which triggers off JAK/STAT pathway activation. Image created with biorender.com (accessed on 22 April 2023). CAR—chimeric antigen receptor, scFv—single-chain variable fragment, V_H—heavy chain variable segment, V_L—light chain variable segment, CD3ζ—CD3ζ signaling domain, ITAM—immunoreceptor tyrosine-based activation motif, IL-12—interleukin 12, NFAT—nuclear factor of activated T cells, IL-2Rβ—interleukin 2 receptor subunit beta, JAK—janus kinase, STAT3/5—signal transducer and activator of transcription 3/5.

Figure 2

Effector mechanism of CAR-T cells: (a) Release of perforins and granzymes by active CAR-T cells leads to leukemic cell lysis. (b) Active CAR-T cells via the Fas and FasL pathway lead to leukemic cell apoptosis. (c) Active CAR-T cells secrete pro-inflammatory cytokines, enhancing the anti-cancer response of other cells of the immune system. Image created with biorender.com (accessed on 22 April 2023). CAR—chimeric antigen receptor, CAR-T—T cell with chimeric antigen receptors.

Figure 3

The construction of UniCAR, RevCAR and SUPRA CAR: (a) UniCAR consists of a universal effector module (EM) and a tumor-specific target module (TM). EM is composed of a signaling domain and a peptide epitope-binding domain. TM is composed of a peptide epitope (PE) and a tumor antigen-binding domain. The administration of TMs targets the UniCAR cell to the tumor cell, and enables the activation of cytotoxic mechanisms. (b) RevCAR consists of a universal EM and a tumor-specific target module (RevTM). EM is composed of a signaling domain and a peptide epitope (PE). TM is a bispecific target module composed of 2 scFvs: a peptide epitope-binding domain and a tumor antigen-binding domain. The administration of RevTM targets the RevCAR cell to the tumor cell, and enables the activation of cytotoxic mechanisms. (c) SUPRA CAR consists of a universal receptor with a leucine zipper adapter (zipCAR), and scFv with a leucine zipper adapter (zipFv) molecule, directed against the target antigen. A leucine zipper (AZip), linked to scFv, can link to the cognate a leucine zipper (BZip) present on the zipCAR. The zipFv binding to the target antigen and dimerizing with the zipCAR results in the activation of the SUPRA CAR cell. The administration of the zipFv targets the SUPRA CAR cell to the tumor cell, and enables the activation of cytotoxic mechanisms.

Figure 4

The structure and mechanism of activation of fms-like tyrosine kinase 3: FLT3 consists of five IG-like domains (extracellular part), the transmembrane domain and intracellular part, which includes the juxtamembrane domain (JM domain), two tyrosine kinase domains (TKD1 and TKD2) and an activating loop. The most common FLT3 mutations are internal tandem duplication in the JM domain and point mutations or deletion in the TKD. Physiologically, FLT3 becomes activated upon binding to the FLT3 ligand. Ligand binding causes the homodimerization of the receptor. This is followed by phosphorylation and the activation of RAS/RAF/MAPK/Erk, JAK/STAT5/PIM-1 and PI3K/AKT/mTOR intracellular signaling pathways, which regulate cell proliferation, differentiation and apoptosis. Image created with biorender.com (accessed on 22 April 2023). D1—domain one, D2—domain two, D3—domain three, D4—domain four, D5—domain five, JM domain—juxtamembrane domain, A-loop—an activating loop, ITD—internal tandem duplication, TKD—tyrosine kinase domain, FLT3L—FMS-like tyrosine kinase 3 ligand, P—phosphorus, RAS—from “Rat sarcoma virus”, RAF—rapidly accelerated fibrosarcoma kinases, MAPK—mitogen-activated protein kinase, Erk—extracellular-signal-regulated kinase, JAK—janus kinase, STAT5—signal transducer and activator of transcription 5, PIM-1—proto-oncogene serine/threonine-protein kinase, PI3K—phosphoinositide 3-kinase, AKT—protein kinase B, mTOR—mammalian target of rapamycin, BCL-2—B-cell lymphoma 2, MCL-1—induced myeloid leukemia cell differentiation protein.