Mesenchymal cells inhibit expansion but not cytotoxicity exerted by gamma–delta T cells

Background Multipotent mesenchymal stromal cells (MSCs) exert a relevant immunosuppressive activity by inhibiting T‐ and B‐lymphocytes, natural killer (NK) cells and dendritic cell expansion. Nevertheless, a possible activity on gamma/delta T cells has still not been evaluated. Gamma–delta T lymphocytes play an important role in the control of cancer and they have been shown to be implicated in graft‐vs.‐host disease. Thus, modulation of activation and proliferation of these cells could be relevant for therapeutic purposes. Materials and methods Peripheral blood mononuclear cells from 21 healthy donors were used as source for gamma–delta T cells, expanded in presence of 10 IU mL^?1 interleukin‐2 (IL‐2) and 1 μM zoledronate. MSCs were recovered from patients undergoing routine total hip replacement surgery, and characterised by flow cytometry. Cytotoxicity on multiple myeloma and melanoma cell lines was assessed by measuring dilution of the carboxyfluorescein diacetate succinimydylester dye (CFSE). Gamma–delta T cells were then incubated with MSCs in contact cultures, and with addition of MSC‐conditioned medium. Results In this article we confirmed that (1) in vitro expanded gamma–delta T cells play a significant anti‐proliferative effect on multiple myeloma and melanoma cells and (2) multipotent mesenchymal stromal cells effectively suppress the ex vivo expansion of T cells carrying a specific T‐cell receptor gene (TCR) rearrangement, Vgamma9/Vdelta2, induced by the combination of IL‐2 and zoledronate, without interfering with their cytotoxic activity. Discussion These findings contribute to explain the activity of ex vivo expanded mesenchymal cells, suggesting that MSCs would interact with gamma–delta T lymphocytes. Conclusion This effect could be relevant in separating graft‐vs.‐host from the graft‐vs.‐tumour effect, especially considering the possibility of modulating T‐lymphocytes activity by the immunomodulating drugs now available.