Dynamic tunnelling nanotube formation characterizes AML–Mesenchymal Stromal cell crosstalk in the Bone Marrow Microenvironment

Acute myeloid leukaemia (AML) is a rapidly progressing cancer that leads to the accumulation of immature blasts in the bone marrow (BM). The BM niche, in particular mesenchymal stromal cells (MSCs), supports and protects AML cells, leading to resistance to treatment and relapses. AML blasts actively interact with mesenchymal MSCs, reshaping the niche and engaging in direct cytoplasmic exchange through tunnelling nanotubes (TNTs). Using cocultures of MOLM-13 AML cells and MS-5 stromal cells labelled with distinct vital dyes, we observed the rapid formation of TNTs-like protrusions within the first hours of contact. Phalloidin staining confirmed their continuous F-actin structure, consistent with canonical TNT morphology. Notably, TNT frequency increased following treatment, indicating that therapeutic stress enhances AML–MSC crosstalk. These findings show that AML establishes fast, dynamic physical interactions with MSCs and that TNT formation is further stimulated by treatment, highlighting TNT-mediated crosstalk as a potential target to weaken stromal protection and improve therapeutic response.