Targeting FLT3 in acute myeloid leukemia using ligand-based chimeric antigen receptor-engineered T cells

Abstract

BackgroundChimeric antigen receptor-engineered T (CAR-T) cells have extraordinary effect in treating lymphoblastic leukemia. However, treatment of acute myeloid leukemia (AML) using CAR-T cells remains limited to date. Leukemogenesis always relates with the abnormalities of cytogenetics, and nearly one third of AML patients have activating mutations in Fms-like tyrosine kinase 3 (FLT3) which reminded poor prognosis. Considering the FLT3 expressed in AML patients’ blast cells, it may be a new candidate target for CAR-T therapy to treat FLT3+ AML, especially patients harboring FLT3-ITD mutation.MethodsThe FLT3L CAR-T using FLT3 ligand as recognizing domain was constructed. The specific cytotoxicity against FLT3+ leukemia cell lines, primary AML cells, and normal hematopoietic progenitor stem cells (HPSCs) in vitro were evaluated. In addition, FLT3+ AML mouse model was used to assess the effect of FLT3L CAR-T therapy in vivo.ResultsFLT3L CAR-T cells could specifically kill FLT3+ leukemia cell lines and AML patients’ bone marrow mononuclear cells in vitro (with or without FLT3 mutation) and have more potent cytotoxicity to FLT3-ITD cells. In a human FLT3+ AML xenograft mouse model, FLT3L CAR-T cells could significantly prolong the survival of mice. Furthermore, it was found that FLT3L CAR-T cells could activate the FLT3/ERK signaling pathway of FLT3+ leukemia cells with wild-type FLT3; meanwhile, it had no inhibitory effects on the colony formation of CD34+ stem cells derived from normal human umbilical cord blood.ConclusionsThe ligand-based FLT3L CAR-T cells could be a promising strategy for FLT3+ AML treatment, especially those carried FLT3 mutation.Electronic supplementary materialThe online version of this article (10.1186/s13045-018-0603-7) contains supplementary material, which is available to authorized users.

Genetically engineered CAR NK cells display selective cytotoxicity against FLT3‐positive B‐ALL and inhibit in vivo leukemia growth

“…In a previous study parental antibody 4G8 on its own did not affect colony formation and was not cytotoxic toward CD34‐positive human bone marrow cells . Likewise, two prior studies with T cells carrying CARs based on FLT3‐specific scFv antibody or FLT3 ligand reported normal human hematopoiesis in NSG mice transplanted with HSCs after treatment with the FLT3‐specific CAR T cells, and undisturbed colony formation of cord blood derived HSCs in the presence of CAR T cells, respectively . In contrast, in another recent report, a marked reduction in colony formation and HSC viability was observed upon exposure of HSCs to FLT3‐targeted CAR T cells .…”

“…28 Likewise, two prior studies with T cells carrying CARs based on FLT3-specific scFv antibody or FLT3 ligand reported normal human hematopoiesis in NSG mice transplanted with HSCs after treatment with the FLT3-specific CAR T cells, and undisturbed colony formation of cord blood derived HSCs in the presence of CAR T cells, respectively. 53,54 In contrast, in another recent report, a marked reduction in colony formation and HSC viability was observed upon exposure of HSCs to FLT3-targeted CAR T cells. 55 Here we did not observe CAR-mediated killing of mobilized human CD34-positive HSCs by NK-92/4G8.…”

Target selection for CAR-T therapy

“…We believe that this was the main reason why the clinical response of CAR-T-22 is inferior to that of CAR-T-19. Recently, a report on the substitution of scFV with FMS-like tyrosine kinase-3 ligand [30] provided a novel strategy for overcoming the problem of targeted motif loss caused by gene mutation. In addition to the regulation mechanisms, another reason for the fixed expression of CD19 is that it plays an important role in the survival and proliferation of B cell malignancies.…”

A Bump in the Road: How the Hostile AML Microenvironment Affects CAR T Cell Therapy

“…Early clinical studies of CAR T cells for AML are ongoing, exploring several targets including CD123 (9, 10), CD33 (11), C-type lectin-like molecule 1 (CLL-1) (12,13), and Lewis-Y (14). Additional targets under preclinical investigation include CD135 (FLT-3 receptor) (15)(16)(17), Folate receptor β (18), CD44v6 (19), WT1 (20), B7-H3 (21-23), CD70 (24,25), and CD7 (26). While clinical experience thus far has shown feasibility and safety of CAR T cells for AML, efficacy has been limited in comparison to CD19-CAR T cell therapy for ALL (11,14).…”