IL‑2–Armored FLT3 CAR‑γδT Cells: Preclinical Efficacy and Translational Signals

Investigators report a preclinical evaluation of FLT3-targeted CAR-γδT cells “armored” to co-express IL-2 or IL-7 in acute myeloid leukemia (AML) models. The study describes three engineered products—FLT3-CAR, FLT3-IL2-CAR, and FLT3-IL7-CAR—generated in γδT cells and compared head-to-head across in vitro and in vivo assays. Across the reported experiments, the IL-2–coexpressing construct is described as showing stronger cytotoxicity and persistence readouts than the IL-7–coexpressing and non-cytokine constructs. The results are presented as a sequence: construct confirmation followed by cytotoxic function, persistence under repeated antigen exposure, and activity in a xenograft setting.

For construct generation, the authors describe designing a FLT3-CAR incorporating an anti-FLT3 VHH nanobody extracellular domain with CD28 and CD3ζ signaling elements, then adding IL-2 or IL-7 sequences to create the armored variants. Lentiviral transduction was performed in activated γδT cells, and CAR positivity was assessed by flow cytometry using an antibody recognizing the FLT3-VHH component, with serial measurements during in vitro culture used to support stable expression. To verify the “armoring” feature, cytokine concentrations were measured in culture supernatants; the investigators report autocrine secretion of IL-2 by FLT3-IL2-CAR-γδT cells and IL-7 by FLT3-IL7-CAR-γδT cells over the assessed culture window. These steps were used to indicate that the three products were comparably generated and suitable for downstream functional comparisons.

In vitro function was assessed using flow-cytometry–based killing assays after 24-hour co-culture with multiple FLT3-expressing AML cell lines (OCI-AML3, MOLM-13, THP-1, and MV4-11) across several effector-to-target ratios. The authors report that the FLT3-IL2-CAR-γδT group showed the most pronounced tumor cell lysis across tested conditions, with the other constructs showing lower activity by comparison. In parallel, cytokine and effector-molecule release in co-culture supernatants was quantified, and the study reports higher levels of granzyme B, IFN-γ, and TNF-α associated with FLT3-IL2-CAR-γδT cells. The investigators also evaluated primary AML samples from seven patients and describe cytotoxicity in a subset of specimens, with numerically higher killing by the IL-2–armored construct that was not statistically significant in their analysis. Overall, the in vitro dataset is presented by the authors as supporting enhanced effector function for the IL-2–coexpressing CAR-γδT product.

Durability in vitro was examined using an antigen-repetitive stimulation assay intended to model ongoing tumor antigen exposure, with OCI-AML3 cells repeatedly added over sequential stimulations. Reported endpoints included maintained killing performance, effector-cell viability assessed by Annexin V/7-AAD staining, and sustained release of functional mediators measured in stimulation supernatants. Phenotyping by flow cytometry tracked differentiation states using CD45RO and CD62L, and the authors report that FLT3-IL2-CAR-γδT cells preserved a CD45RO−CD62L+ stem cell-like memory (TSCM) subset during serial stimulation when other groups showed declines in that compartment. The study also reports immune-checkpoint marker patterns during repeated stimulation: LAG-3 and TIM-3 levels decreased after the first stimulation and then rose with additional rounds in several groups, while the IL-2–armored cells maintained higher LAG-3 and TIM-3 expression and had the highest proportion of cells co-expressing multiple checkpoint molecules, which the authors frame as a marker profile in γδT cells rather than a definitive exhaustion readout. These repeated-exposure experiments were used to examine functional durability alongside phenotype maintenance under sustained antigen challenge.

In vivo activity was evaluated in an AML xenograft model using luciferase-labeled OCI-AML3 cells, with tumor burden followed by bioluminescence imaging and survival tracked over time. The authors report that FLT3-IL2-CAR-γδT treatment was associated with reduced tumor signal and that survival extended beyond 68 days in that group, compared with the other conditions. As an additional persistence readout, γδT cells were measured in peripheral blood after infusion, and the investigators report detectable γδT cells at Day 19 only in the FLT3-IL2-CAR-γδT group. In discussion, the authors describe γδT cells as a potential allogeneic “off-the-shelf” platform, citing non-MHC-restricted targeting and stable phenotypes, while also noting a safety caveat that FLT3 can be expressed on some hematopoietic stem and myeloid progenitor cells and that further safety assessment is needed before clinical application. The in vivo findings are presented as supportive preclinical signals alongside the authors’ stated translational aims and safety considerations.

Key Takeaways:

• The authors report that IL-2 coexpression in FLT3-CAR-γδT cells aligned with the most prominent in vitro killing and higher granzyme B, IFN-γ, and TNF-α release across AML cell-line assays.
• During antigen-repetitive stimulation, the study describes maintained viability and mediator release with preservation of a CD45RO−CD62L+ TSCM subset in the FLT3-IL2-CAR-γδT group, alongside distinct checkpoint-marker expression patterns observed over serial challenges.
• In vivo, the authors report reduced bioluminescence tumor burden with survival beyond 68 days and peripheral-blood detectability at Day 19 uniquely in the FLT3-IL2-CAR-γδT group, while the authors highlight that further safety evaluation is warranted given FLT3 expression on some hematopoietic progenitors.