Donor-derived mesenchymal stem cells are immunogenic in an allogeneic host and stimulate donor graft rejection in a nonmyeloablative setting

Immune regulation of T lymphocyte by a newly characterized human umbilical cord blood stem cell

Previous work identified a novel type of stem cell from human umbilical cord blood, designated cord blood-stem cells (CB-SC). To further evaluate their immune characteristics, we cocultured CB-SC with allogeneic peripheral blood lymphocytes in the presence of phytohaemagglutinin (PHA) or interleukin-2 (IL-2). Results showed that CB-SC could significantly inhibit lymphocyte proliferation and reduce tyrosine phosphorylation of STAT5 in both PHA- and IL-2-stimulated lymphocytes, along with the regulation on the phenotypes of CD4+ and CD8+ T cells. Additionally, CB-SC also suppressed the proliferation of IL-2-stimulated CD4+CD25+ regulatory T cells. Mechanism studies revealed that programmed death receptor-1 ligand 1 (PD-L1) expressed on CB-SC membrane, together with a soluble factor nitric oxide (NO) released by PHA-stimulated CB-SC, not prostaglandin E2 (PGE2) and transforming growth factor-beta1 (TGF-beta1), mainly contributed to the T cell suppression induced by CB-SC, as demonstrated by blocking experiments with a nitric oxide synthase inhibitor (Nomega-nitro-l-arginine, l-NNA) and a neutralizing antibody to PD-L1. Our findings may advance our understanding of the immunobiology of stem cells and facilitate the therapeutic application of cord blood stem cells.

Immune properties of mesenchymal stem cells

Mesenchymal stem cells (MSCs) are multipotent progenitor cells isolated by various relatively easily accessible tissues, such as bone marrow and cord blood. MSCs gained attention because of their ease for in vitro expansion together with their multilineage potential. More recently, in vitro and in vivo immunosuppressive properties have been ascribed to them, as they are able to modulate the function of all major immune cell populations, thus impeding immune responses. The underlying mechanisms of their differentiation and function are not thoroughly understood, but still they represent important candidates for tissue regeneration and manipulation of the immune response in graft rejection, graft versus host disease, and autoimmune disorders. Characteristics and immunogenic profile of MSCs, their interface with immune system and their potential use as immunosuppressive elements in cellular therapeutic protocols are reviewed in this chapter.

Cell therapy for autoimmune diseases

Cell therapy, pioneered for the treatment of malignancies in the form of bone marrow transplantation, has subsequently been tested and successfully employed in autoimmune diseases. Autologous haemopoietic stem cell transplantation (HSCT) has become a curative option for conditions with very poor prognosis such as severe forms of scleroderma, multiple sclerosis, and lupus, in which targeted therapies have little or no effect. The refinement of the conditioning regimens has virtually eliminated transplant-related mortality, thus making HSCT a relatively safe choice. Although HSCT remains a nonspecific approach, the knowledge gained in this field has led to the identification of new avenues. In fact, it has become evident that the therapeutic efficacy of HSCT cannot merely be the consequence of a high-dose immuno-suppression, but rather the result of a resetting of the abnormal immune regulation underlying autoimmune conditions. The identification of professional and nonprofessional immunosuppressive cells and their biological properties is generating a huge interest for their clinical exploitation. Regulatory T cells, found abnormal in several autoimmune diseases, have been proposed as central to achieve long-term remissions. Mesenchymal stem cells of bone marrow origin have more recently been shown not only to be able to differentiate into multiple tissues, but also to exert a potent antiproliferative effect that results in the inhibition of immune responses and prolonged survival of haemopoietic stem cells. All of these potential resources clearly need to be investigated at the preclinical level but support a great deal of enthusiasm for cell therapy of autoimmune diseases.

The immunobiological development of human bone marrow mesenchymal stem cells in the course of neuronal differentiation

The central nervous system (CNS) has been referred to as the "immunological privileged site". However, it is now clear that the privileged status of the CNS is a result of a balance between immune privilege and effective response. In vitro, human bone marrow mesenchymal stem cells (MSCs) have the ability to differentiate into neurons. Based on this biological attribute we gain the possibility by means of using MSCs as the donors to develop a future cell therapy in clinical application. But using MSCs as donor cells inevitably raises the question as to whether these donor cells would be immunogenic, and if so, would they be rejected after transplantation. To investigate this, human MSCs were cultured in vitro and induced to differentiate along neuronal lineage. The expression of human leukocyte antigen (HLA) class I and class II molecules and the co-stimulatory protein CD80 were increased on the surface of MSCs in the course of neuronal differentiation. But neither of the co-stimulatory proteins, CD40 or CD86, was expressed. After IFN-gamma exposure, the expression of the HLA molecules was further enhanced, but the co-stimulatory proteins were unaffected. MSCs that had been differentiated along neuronal lineage were not capable of inducing the proliferation of peripheral blood lymphocytes (PBLs). Even after IFN-gamma exposure, PBLs remained unresponsive. Furthermore, MSCs differentiated along neuronal lineage suppressed the proliferation of PBLs induced by allogeneic PBLs and mitogens. The mechanisms involved in the immunosuppression may be related to the effect of soluble factors and cell-cell interactions of neuronal differentiated MSCs and PBLs. From the above data we suggested that the low immunogenicity and immunomodulatory function of MSCs in the course of neuronal differentiation in vitro, which will be helpful to further investigation in order to establish the new way for future medical application.