Immunogenicity of human mesenchymal stem cells in HLA-class I-restricted T-cell responses against viral or tumor-associated antigens

Generation of mesenchymal stromal cells in the presence of platelet lysate: a phenotypic and functional comparison of umbilical cord blood- and bone marrow-derived progenitors

BACKGROUND

Mesenchymal stromal cells are employed in various different clinical settings in order to modulate immune response. However, relatively little is known about the mechanisms responsible for their immunomodulatory effects, which could be influenced by both the cell source and culture conditions.

DESIGN AND METHODS

We tested the ability of a 5% platelet lysate-supplemented medium to support isolation and ex vivo expansion of mesenchymal stromal cells from full-term umbilical-cord blood. We also investigated the biological/functional properties of umbilical cord blood mesenchymal stromal cells, in comparison with platelet lysate-expanded bone marrow mesenchymal stromal cells.

RESULTS

The success rate of isolation of mesenchymal stromal cells from umbilical cord blood was in the order of 20%. These cells exhibited typical morphology, immunophenotype and differentiation capacity. Although they have a low clonogenic efficiency, umbilical cord blood mesenchymal stromal cells may possess high proliferative potential. The genetic stability of these cells from umbilical cord blood was demonstrated by a normal molecular karyotype; in addition, these cells do not express hTERT and telomerase activity, do express p16(ink4a) protein and do not show anchorage-independent cell growth. Concerning alloantigen-specific immune responses, umbilical cord blood mesenchymal stromal cells were able to: (i) suppress T- and NK-lymphocyte proliferation, (ii) decrease cytotoxic activity and (iii) only slightly increase interleukin-10, while decreasing interferon-gamma secretion, in mixed lymphocyte culture supernatants. While an indoleamine 2,3-dioxygenase-specific inhibitor did not reverse mesenchymal stromal cell-induced suppressive effects, a prostaglandin E(2)-specific inhibitor hampered the suppressive effect of both umbilical cord blood- and bone marrow-mesenchymal stromal cells on alloantigen-induced cytotoxic activity. Mesenchymal stromal cells from both sources expressed HLA-G.

CONCLUSIONS

Umbilical cord blood- and bone marrow-mesenchymal stromal cells may differ in terms of clonogenic efficiency, proliferative capacity and immunomodulatory properties; these differences may be relevant for clinical applications.

Modulation of bone marrow stromal cell functions in infectious diseases by toll-like receptor ligands

Bone marrow-derived stromal cells (BMSCs, or as they are frequently referred to as mesenchymal stem cells) have been long known to support hematopoiesis and to regenerate bone, cartilage, and adipose tissue. In the last decade, however, a vast amount of data surfaced in the literature to suggest new roles for these cells including tissue regeneration and immunomodulation. A great number of review articles appeared that summarize these new data and focus on different aspects of the physiology of these cells. In this present short review, we will try to summarize the available data based on both mouse and human cells describing how the function of BMSCs might be affected by an infectious environment. These data strongly support the idea that different toll-like receptor ligands can lead to substantial changes in the function of BMSCs that affect their proliferation, apoptosis, migration, and their production and release of immunomodulatory factors.

Mesenchymal stromal cells cross-present soluble exogenous antigens as part of their antigen-presenting cell properties

Recent studies involving bone marrow mesenchymal stromal cells (MSCs) demonstrated that interferon (IFN)-gamma stimulation induces major histocompatibility complex (MHC) class II-mediated antigen presentation in MSCs both in vitro and in vivo. Concordantly, we investigated the ability of MSCs to present extracellular antigen through their MHC class I molecules, a process known as cross-presentation. Using an in vitro antigen presentation assay, we demonstrated that murine MSCs can cross-present soluble ovalbumin (OVA) to naive CD8(+) T cells from OT-I mice. Cross-presentation by MSC was proteasome dependent and partly dependent on transporter associated with antigen-processing molecules. Pretreatment of MSC with IFN-gamma increased cross-presentation by up-regulating antigen processing and presentation. However, although the transcription of the transporter associated with antigen processing-1 molecules and the immunoproteasome subunit LMP2 induced by IFN-gamma was inhibited by transforming growth factor-beta, the overall cross-presentation capacity of MSCs remained unchanged after transforming growth factor-beta treatment. These observations were validated in vivo by performing an immune reconstitution assay in beta(2)-microglobulin(-/-) mice and show that OVA cross-presentation by MSCs induces the proliferation of naive OVA-specific CD8(+) T cells. In conclusion, we demonstrate that MSCs can cross-present exogenous antigen and induce an effective CD8(+) T-cell immune response, a property that could be exploited as a therapeutic cell-based immune biopharmaceutic for the treatment of cancer or infectious diseases.

Mesenchymal stem cells in health and disease

Mesenchymal stem cells (MSCs) are a heterogeneous subset of stromal stem cells that can be isolated from many adult tissues. They can differentiate into cells of the mesodermal lineage, such as adipocytes, osteocytes and chondrocytes, as well as cells of other embryonic lineages. MSCs can interact with cells of both the innate and adaptive immune systems, leading to the modulation of several effector functions. After in vivo administration, MSCs induce peripheral tolerance and migrate to injured tissues, where they can inhibit the release of pro-inflammatory cytokines and promote the survival of damaged cells. This Review discusses the targets and mechanisms of MSC-mediated immunomodulation and the possible translation of MSCs to new therapeutic approaches.