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 (TNF alpha, IFN gamma, IL-1 alpha, IL-1 beta, 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 TNF alpha (96.8 +/- 4.8%) and IFN gamma (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.