Predominant immature CD8?+dendritic cells prevent graft-vs.-host disease but do not increase the risk of leukemia recurrence

Tumor antigen-pulsed CD8α(+) dendritic cells induce T cell-mediated graft-versus-tumor effect in vitro

The graft-versus-tumor (GVT) effect of T cells induced by tumor antigen-pulsed CD8α(+) dendritic cells (DCs) in vitro was investigated in this study. Immature CD8α(+) DCs were prepared from C57BL/6 (H-2(b)) bone marrow cells by using a cytokine cocktail. On the 3rd day of culture, CD8α(+) DCs were pulsed by allogeneic (Balb/c, H-2(d)) EL9611 leukemia antigen, or RM-1 syngeneic prostate cancer antigen, with the concentration series of 0, 2.5, 5.0, 10.0, 20.0 μg/mL, respectively, then antigen-loaded immature CD8α(+) DCs were co-cultured with syngeneic T cells according to the DC/T ratio of 1:1, 2:1 and 4:1. T cell proliferation was measured by MTT assay. Cytokines including interferon gamma (IFN-γ) and interleukin-10 (IL-10) in CD8α(+) DCs and T co-culture supernatant were detected by using ELISA. Cytotoxic effect of antigen-specific T cells was tested by LDH release assay. Conventional mature DCs (mDCs) induced from C57BL/6 (H-2(b)) bone marrow cells by using granulocyte-macrophage colony stimulating factor (GM-CSF) and interleukin-4 (IL-4) served as a control. The results showed that the proliferative activity of T cells stimulated by CD8α(+) DCs loaded with allogeneic or syngeneic tumor antigen was augmented with the CD8α(+) DC/T ratio increased (P<0.05). When antigen concentration ≤ 5 μg/mL and CD8α(+) DC/T ratio ≤ 2:1, the ability of CD8α(+) DCs to stimulate T cell proliferation was higher than mDC control in allogeneic tumor antigen-pulsed groups (P<0.05), but not in syngeneic tumor antigen-pulsed groups (P>0.05). The level of IFN-γ and IL-10 in CD8α(+) DCs and T cell co-culture supernatant were increased in both allogeneic and syngeneic antigen-pulsed groups (P<0.05), and the cytokine level was higher in allogeneic antigen-pulsed groups than in syngeneic antigen groups when the CD8α(+) DC/T was 1:1 or 2:1 (P<0.05). There existed a negative correlation between the level of IL-10 and T cell proliferation. T cell cytotoxicity assay showed that when CD8α(+) DCs were pulsed with allogeneic tumor antigen, the maximal T cell killing efficiency could reach (100±7.7)%, whereas syngeneic tumor antigen-pulsed group had only (65.0±3.4)%. It was concluded that syngeneic and allogeneic tumor antigen-pulsed immature CD8α(+) DCs could stimulate T cells to exert the GVT effect in vitro, and the GVT effect was more obvious with allogeneic tumor antigen than with syngeneic tumor antigen. The optimal condition was low allogeneic tumor antigen pulsation (≤ 5 μg/mL) and low CD8α(+) DC/T ratio (1:1 and 2:1).

Mesenchymal stem cells: immunobiology and role in immunomodulation and tissue regeneration

Mesenchymal stem cells (MSC) are multipotent cells that differentiate into osteoblasts, myocytes, chondrocytes and adipocytes as well as insulin-producing cells. The mechanism underlying their in vivo differentiation is not clear and is thought to be caused by spontaneous cell fusion or factors present in the microenvironment. However, their ease of isolation, high 'ex-vivo' expansion potential and ability to differentiate into multiple lineages make them attractive tools for potential use in cell therapy. MSC have been isolated from several tissues, including bone/bone marrow, fat, Wharton's jelly, umbilical cord blood, placenta and pancreas. The 'immunosuppressive' property of human MSC makes them an important candidate for cellular therapy in allogeneic settings. Use of allogeneic MSC for repair of large defects may be an alternative to autologous and allogeneic tissue-grafting procedures. An allogeneic approach would enable MSC to be isolated from any donor, expanded and cryopreserved, providing a readily available source of progenitors for cell replacement therapy. Their immunomodulatory properties have raised the possibility of establishing allogeneic MSC banks for tissue regeneration. These facts are strongly reflected in the current exponential growth in stem cell research in the pharmaceutical and biotechnology communities. Current knowledge regarding the immunobiology and clinical application of MSC needs to be strengthened further to establish MSC as a safe and effective therapeutic tool in regenerative medicine. This paper discusses human MSC with particular reference to the expression of their surface markers, their role as immunomodulators and their multilineage differentiation potential and possible use in tissue regeneration and repair.