Human bone marrow mesenchymal stem cells and chondrocytes promote and/or suppress the in vitro proliferation of lymphocytes stimulated by interleukins 2, 7 and 15.

OBJECTIVES: To investigate whether human bone marrow-derived mesenchymal stem cells (BM-MSCs) and articular chondrocytes (ACs) affect the in vitro proliferation of T lymphocytes and peripheral blood mononuclear cells (PBMCs) driven by the homeostatic interleukin (IL)2, IL7 and IL15 cytokines binding to the common cytokine receptor gamma-chain (gamma(c)) in the absence of T cell receptor (TCR) triggering. METHODS: PBMCs, total T cells and T cell subsets (CD4+ and CD8+) were stimulated with IL2, IL7 or IL15 and exposed to cultured BM-MSCs and ACs at varying cell:cell ratio either in contact or in transwell conditions. Lymphocyte proliferation was measured by (3)H-thymidine uptake or by flow cytometry of carboxyfluorescein succinimidyl ester (CFSE)-labelled lymphocytes. RESULTS: MSCs and ACs enhanced and inhibited lymphocyte proliferation depending on the extent of lymphocyte baseline proliferation and on the MSC/AC to lymphocyte ratio. Enhancement was significant on poorly proliferating lymphocytes and mostly at lower MSC/AC to lymphocyte ratio. Suppression occurred only on actively proliferating lymphocytes and at high MSC/AC to lymphocyte ratio. Neither enhancement nor inhibition required cell-cell contact. CONCLUSIONS: There is a dichotomous effect of MSCs/ACs on lymphocytes proliferating in response to the homeostatic IL2, IL7 and IL15 cytokines likely to be encountered in homeostatic and autoimmune inflammatory conditions. The effect is determined by baseline lymphocyte proliferation, cell:cell ratio and is dependent on soluble factor(s). This should be taken into account when planning cellular therapy for autoimmune disease (AD) using stromal-derived cells such as MSCs.

Multiple mechanisms underlie defective recognition of melanoma cells cultured in three-dimensional architectures by antigen-specific cytotoxic T lymphocytes.

Cancer cells' growth in three-dimensional (3D) architectures promotes resistance to drugs, cytokines, or irradiation. We investigated effects of 3D culture as compared to monolayers (2D) on melanoma cells' recognition by tumour-associated antigen (TAA)-specific HLA-A(*)0201-restricted cytotoxic T-lymphocytes (CTL). Culture of HBL, D10 (both HLA-A(*)0201+, TAA+) and NA8 (HLA-A(*)0201+, TAA-) melanoma cells on polyHEMA-coated plates, resulted in generation of 3D multicellular tumour spheroids (MCTS). Interferon-gamma (IFN-gamma) production by HLA-A(*)0201-restricted Melan-A/MART-1(27-35) or gp 100(280-288)-specific CTL clones served as immunorecognition marker. Co-culture with melanoma MCTS, resulted in defective TAA recognition by CTL as compared to 2D as witnessed by decreased IFN-gamma production and decreased Fas Ligand, perforin and granzyme B gene expression. A multiplicity of mechanisms were potentially involved. First, MCTS per se limit CTL capacity of recognising HLA class I restricted antigens by reducing exposed cell surfaces. Second, expression of melanoma differentiation antigens is downregulated in MCTS. Third, expression of HLA class I molecules can be downregulated in melanoma MCTS, possibly due to decreased interferon-regulating factor-1 gene expression. Fourth, lactic acid production is increased in MCTS, as compared to 2D. These data suggest that melanoma cells growing in 3D, even in the absence of immune selection, feature characteristics capable of dramatically inhibiting TAA recognition by specific CTL.