Previous reports suggested that culture as 3D aggregates or as spheroids can increase the therapeutic potential of the adult stem/progenitor cells referred to as mesenchymal stem cells or multipotent mesenchymal stromal cells (MSCs). Here we used a hanging drop protocol to prepare human MSCs (hMSCs) as spheroids that maximally expressed TNFα stimulated gene/protein 6 (TSG-6), the antiinflammatory protein that was expressed at high levels by hMSCs trapped in the lung after i.v. infusion and that largely explained the beneficial effects of hMSCs in mice with myocardial infarcts. The properties of spheroid hMSCs were found to depend critically on the culture conditions. Under optimal conditions for expression of TSG-6, the hMSCs also expressed high levels of stanniocalcin-1, a protein with both antiinflammatory and antiapoptotic properties. In addition, they expressed high levels of three anticancer proteins: IL-24, TNFα-related apoptosis inducing ligand, and CD82. The spheroid hMSCs were more effective than hMSCs from adherent monolayer cultures in suppressing inflammatory responses in a coculture system with LPS-activated macrophages and in a mouse model for peritonitis. In addition, the spheroid hMSCs were about one-fourth the volume of hMSCs from adherent cultures. Apparently as a result, larger numbers of the cells trafficked through the lung after i.v. infusion and were recovered in spleen, liver, kidney, and heart. The data suggest that spheroid hMSCs may be more effective than hMSCs from adherent cultures in therapies for diseases characterized by sterile tissue injury and unresolved inflammation and for some cancers that are sensitive to antiinflammatory agents.

To investigate stem cell differentiation in response to tissue injury, human mesenchymal stem cells (hMSCs) were cocultured with heat-shocked small airway epithelial cells. A subset of the hMSCs rapidly differentiated into epithelium-like cells, and they restored the epithelial monolayer. Immunocytochemistry and microarray analyses demonstrated that the cells expressed many genes characteristic of normal small airway epithelial cells. Some hMSCs differentiated directly after incorporation into the epithelial monolayer but other hMSCs fused with epithelial cells. Surprisingly, cell fusion was a frequent rather than rare event, in that up to 1% of the hMSCs added to the coculture system were recovered as binucleated cells expressing an epithelial surface epitope. Some of the fused cells also underwent nuclear fusion.

Culturing cells in three dimension (3D) provides an insight into their characteristics in vivo. We previously reported that human mesenchymal stem/stromal cells (hMSCs) cultured as 3D spheroids acquire enhanced anti‐inflammatory properties. Here, we explored the effects of hMSC spheroids on macrophages that are critical cells in the regulation of inflammation. Conditioned medium (CM) from hMSC spheroids inhibited lipopolysaccharide‐stimulated macrophages from secreting proinflammatory cytokines TNFα, CXCL2, IL6, IL12p40, and IL23. CM also increased the secretion of anti‐inflammatory cytokines IL10 and IL1ra by the stimulated macrophages, and augmented expression of CD206, a marker of alternatively activated M2 macrophages. The principal anti‐inflammatory activity in CM had a small molecular weight, and microarray data suggested that it was prostaglandin E2 (PGE2). This was confirmed by the observations that PGE2 levels were markedly elevated in hMSC spheroid‐CM, and that the anti‐inflammatory activity was abolished by an inhibitor of cyclooxygenase‐2 (COX‐2), a silencing RNA for COX‐2, and an antibody to PGE2. The anti‐inflammatory effects of the PGE2 on stimulated macrophages were mediated by the EP4 receptor. Spheroids formed by human adult dermal fibroblasts produced low levels of PGE2 and displayed negligible anti‐inflammatory effects on stimulated macrophages, suggesting the features as unique to hMSCs. Moreover, production of PGE2 by hMSC spheroids was dependent on the activity of caspases and NFκB activation in the hMSCs. The results indicated that hMSCs in 3D‐spheroid cultures are self‐activated, in part by intracellular stress responses, to produce PGE2 that can change stimulated macrophages from a primarily proinflammatory M1 phenotype to a more anti‐inflammatory M2 phenotype. STEM Cells2012;30:2283–2296

Human mesenchymal stromal cells (hMSCs) were injected into the hippocampus of adult mice 1 day after transient global ischemia. The hMSCs both improved neurologic function and markedly decreased neuronal cell death of the hippocampus. Microarray assays indicated that ischemia up-regulated 586 mouse genes. The hMSCs persisted for 10% of the ischemia-induced genes, most of which were involved in inflammatory and immune responses. The hMSCs also up-regulated three mouse genes, including the neuroprotective gene Ym1 that is expressed by activated microglia/macrophages. In addition, the transcriptomes of the hMSC changed with up-regulation of 170 human genes and down-regulation of 54 human genes. Protein assays of the hippocampus demonstrated increased expression in microglia/macrophages of Ym1, the cell survival factor insulin-like growth factor 1, galectin-3, cytokines reflective of a type 2 T cell immune bias, and the major histocompatibility complex II. The observed beneficial effects of hMSCs were largely explained by their modulation of inflammatory and immune responses, apparently by alternative activation of microglia and/or macrophages.

Previous reports demonstrated that the deleterious effects of chemical injury to the cornea were ameliorated by local or systemic administration of adult stem/progenitor cells from bone marrow referred to as mesenchymal stem or stromal cells (MSCs). However, the mechanisms for the beneficial effects of MSCs on the injured cornea were not clarified. Herein, we demonstrated that human MSCs (hMSCs) were effective in reducing corneal opacity and inflammation without engraftment after either intraperitoneal (i.p.) or intravenous (i.v.) administration following chemical injury to the rat cornea. A quantitative assay for human mRNA for glyceraldehyde 3-phosphate dehydrogenase (GAPDH) demonstrated that less than 10 hMSCs were present in the corneas of rats 1-day and 3 days after i.v. or i.p. administration of 1 × 107 hMSCs. In vitro experiments using a transwell coculture system demonstrated that chemical injury to corneal epithelial cells activated hMSCs to secrete the multipotent anti-inflammatory protein TNF-α stimulated gene/protein 6 (TSG-6). In vivo, the effects of i.v. injection of hMSCs were largely abrogated by knockdown of TSG-6. Also, the effects of hMSCs were essentially duplicated by either i.v. or topical administration of TSG-6. Therefore, the results demonstrated that systemically administered hMSCs reduce inflammatory damage to the cornea without engraftment and primarily by secretion of the anti-inflammatory protein TSG-6 in response to injury signals from the cornea.