Crosstalk between Immune Cells and Mesenchymal Stromal Cells in a 3D Bioreactor System

Introduction Mesenchymal stromal cells (MSC), known for their high immune modulatory capacity are promising tools for several cell-based therapies. To better mimic the in vivo situation of MSC interactions with immune cells, we applied an artificial lymph node (ALN)-bioreactor culture system combining a miniaturized perfusion bioreactor with a 3D matrix-based cell culture of immune competent cells forming micro-organoids. Methods Rat lymph node cells and allogeneic bone marrow-derived MSCs were seeded in a 20:1 ratio within the agarose matrix of the ALN-reactor. Lymphocytes were pre-incubated with Concanavalin A (ConA) and then co-cultured with MSC in the matrix with additional ConA in the perfusing medium. Live/dead staining showed survival of the co-cultures during the 8-day ALN-reactor run. Paraffin sections of bioreactor matrices were analyzed by proliferating cell nuclear antigen (PCNA)-specific staining to determine MSC proliferation. Immune modulatory capacity was defined by daily analysis of cytokine secretion profiles (TNFα, IFNγ, IL-1α, IL-1β, IL-2, IL-4, IL-6, IL-10, IL-12p40/p70, GM-CSF). Results Cytokine peak secretion at day 2 was significantly inhibited by MSCs for TNFα (96.8 ± 4.8%) and IFNγ (88.7 ± 12.0%) in 3D co-cultures. In contrast, other cytokines (IL-1, IL-6, IL-12) were induced. Furthermore, we detected a significantly higher (58.8%) fraction of proliferating MSCs in the presence of immune cells compared to control bioreactors loaded with MSCs only. Conclusions In the future, this system might be an excellent tool to investigate the mechanisms of MSC-mediated immune modulation during simulated in vivo conditions.