TGF-β Decreases NK Cell Mobility and Cytotoxic Efficacy in Complex in vitro Models of the Leukemia Microenvironment.

Background: Natural killer (NK) cell-based therapies represent a promising approach for acute myeloid leukemia (AML) relapse, yet their efficacy is hindered by immunosuppressive factors such as transforming growth factor beta (TGF-β) in the tumor microenvironment. This study investigated the effects of TGF-β on NK cell cytotoxicity and migration using 2D and 3D co-culture models that mimic the leukemic microenvironment.

Methods: TGF-β production was evaluated in AML-derived leukemic cell lines and mesenchymal stromal cells (hTERT-MSCs) using ELISA. Bulk RNA sequencing (RNA-seq) was performed to analyze global gene expression changes in TGF-β-treated primary human NK cells. NK cell cytotoxicity and migration were assessed in 2D monolayer and 3D spheroid co-cultures containing hTERT-MSCs and leukemic cells using flow cytometry and confocal microscopy.

Results: Both leukemic cells and MSCs produced TGF-β, with increased levels observed in MSCs after co-culture with primary AML blasts. RNA sequencing revealed that TGF-β altered key gene pathways associated with NK cell cytotoxicity, adhesion, and migration, supporting its immunosuppressive role. In functional assays, TGF-β exposure significantly reduced NK cell-mediated cytotoxicity in a time-dependent manner and impaired NK cell infiltration into 3D spheroids, particularly in models incorporating MSCs. Additionally, MSCs themselves provided a protective environment for leukemic cells, further reducing NK cell effectiveness in 2D co-cultures.

Conclusion: TGF-β suppresses both NK cell cytotoxicity and migration, limiting their ability to eliminate leukemic cells and infiltrate the bone marrow niche (BMN). These findings provide novel insights into TGF-β-mediated immune evasion mechanisms and provide important insights for the future design of NK-based immunotherapies and clinical trials.