Keiko Hatanaka

Mesenchymal stromal cells inhibit Th17 but not regulatory T-cell differentiation

BACKGROUND AIMS A previous study has demonstrated that mouse mesenchymal stromal cells (MSC) produce nitric oxide (NO), which suppresses signal transducer and activator of transcription (STAT) 5 phosphorylation and T-cell proliferation under neutral and T helper 1 cells (Th1) conditions. We aimed to determine the effects of MSC on T helper 17 cells (Th17) and regulatory T-cell (T-reg) differentiation. METHODS CD4 T cells obtained from mouse spleen were cultured in conditions for Th17 or Treg differentiation with or without mouse MSC. Th17 and Treg differentiation was assessed by flow cytometry using antibodies against interleukin (IL)-17 and forkhead box P3 (Foxp3), a master regulator of Treg cells. RESULTS MSC inhibited Th17 but not Treg differentiation. Under Th17 conditions, MSC did not produce NO, and inhibitors of indoleamine-2,3-dioxygenase (IDO) and prostaglandin E(2) (PGE2) both restored MSC suppression of differentiation, suggesting that MSC suppress Th17 differentiation at least in part through PGE2 and IDO. CONCLUSIONS Our results suggest that MSC regulate CD4 differentiation through different mechanisms depending on the culture conditions.

IL-21 is critical for GVHD in a mouse model

Immunological effects of IL-21 on T, B and natural killer (NK) cells have been reported, but the role of IL-21 in GVHD remains obscure. Here, we demonstrate that morbidity and mortality of GVHD was significantly reduced after BMT with splenocytes from IL-21R−/− mice compared with those from wild type mice. To further confirm our observation, we generated a decoy receptor for IL-21. GVHD was again less severe in mice receiving BM cells transduced with the IL-21 decoy receptor than control mice These results suggest that IL-21 critically regulates GVHD, and that blockade of the IL-21 signal may represent a novel strategy for the prophylaxis for GVHD.

Overexpression of interleukin 21 induces expansion of hematopoietic progenitor cells

The interleukin 21 (IL-21) receptor is expressed on T-cells, B-cells, and natural killer cells, and IL-21 is critical for regulating immunoglobulin production in vivo in cooperation with IL-4. So far, however, little is known about a role for IL-21 outside the immune system. We investigated the effect of IL-21 on hematopoiesis in vivo by using the hydrodynamics gene-delivery method. Overexpression of IL-21 increases Sca-1+ cells in the periphery and spleen. It also increases the numbers of c-Kit+, Sca-1+, and lineage-/low (KSL) cells and colony-forming units—granulocyte-macrophage (CFU-GM) in the spleen, indicating the expansion of hematopoietic progenitor cells. We found that even in RAG2-/- mice, which lack mature T-cells and B-cells, IL-21 induced an increase in KSL cells and CFU-GM in the spleen. These results demonstrate that IL-21 can induce the expansion of hematopoietic progenitor cells in vivo, even in the absence of mature T-cells and B-cells.

Altered effector CD4+ T cell function in IL-21R-/- CD4+ T cell-mediated graft-versus-host disease.

We previously showed that transplantation with IL-21R gene-deficient splenocytes resulted in less severe graft-versus-host disease (GVHD) than was observed with wild type splenocytes. In this study, we sought to find mechanism(s) explaining this observation. Recipients of donor CD4+ T cells lacking IL-21R exhibited diminished GVHD symptoms, with reduced inflammatory cell infiltration into the liver and intestine, leading to prolonged survival. After transplantation, CD4+ T cell numbers in the spleen were reduced, and MLR and cytokine production by CD4+ T cells were impaired. These results suggest that IL-21 might promote GVHD through enhanced production of effector CD4+ T cells. Moreover, we found that CD25 depletion altered neither the impaired MLR in vitro nor the ameliorated GVHD symptoms in vivo. Thus, the attenuated GVHD might be caused by an impairment of effector T cell differentiation itself, rather than by an increase in regulatory T cells and suppression of effector T cells.

Lack of IL-21 signal attenuates graft-versus-leukemia effect in the absence of CD8 T-cells.

Previously, we have shown that IL-21R−/− splenocytes ameliorate GVHD as compared with wild-type splenocytes. Here, we investigated whether or not IL-21R−/− splenocytes diminish the graft-versus-leukemia (GVL) effect. Surprisingly, IL-21R−/− splenocytes efficiently eliminate leukemic cells as well as wild-type splenocytes, suggesting the retention of GVL effects in the absence of IL-21 signaling. To compare the GVL effect between IL-21R−/− and wild-type cells, we titrated the number of splenocytes required for the elimination of leukemic cells and found that the threshold of GVL effect was obtained between 5 × 105 and 5 × 106 with both types of splenocytes. Cotransplantation with CD8-depleted splenocytes but not with purified CD8 T-cells resulted in a significant reduction in anti-leukemic effect of IL-21R−/− cells compared with wild-type cells, suggesting that the lack of IL-21 signaling primarily impairs CD4 T-cell rather than CD8 T-cell function and the comparable GVL effect with IL-21R−/− bulk splenocytes results from cooperative compensation by CD8 T-cells.