The molecular mechanisms by which mesenchymal stem cells (MSCs) suppress T-cell proliferation are poorly understood, and whether a soluble factor plays a major role remains controversial. Here we demonstrate that the T-cell-receptor complex is not a target for the suppression, suggesting that downstream signals mediate the suppression. We found that Stat5 phosphorylation in T cells is suppressed in the presence of MSCs and that nitric oxide (NO) is involved in the suppression of Stat5 phosphorylation and T-cell proliferation. The induction of inducible NO synthase (NOS) was readily detected in MSCs but not T cells, and a specific inhibitor of NOS reversed the suppression of Stat5 phosphorylation and T-cell proliferation. This production of NO in the presence of MSCs was mediated by CD4 or CD8 T cells but not by CD19 B cells. Furthermore, inhibitors of prostaglandin synthase or NOS restored the proliferation of T cells, whereas an inhibitor of indoleamine 2,3-dioxygenase and a transforming growth factor-␤-neutralizing antibody had no effect. Finally, MSCs from inducible NOS ؊/؊ mice had a reduced ability to suppress T-cell proliferation. Taken IntroductionBecause mesenchymal stem cells (MSCs) differentiate into osteocytes, chondrocytes, myotubes, and adipocytes, 1-3 they are expected to become a source of cells for regenerative therapy. Also, MSCs support hematopoietic stem cell engraftment 4-9 and modulate immunologic responses by unknown mechanisms. [9][10][11][12][13][14] Here, we investigated the molecular mechanisms by which MSCs suppress T-cell proliferation.Transforming growth factor-␤ (TGF-␤), hepatocyte growth factor, indoleamine 2,3-dioxygenase (IDO), and prostaglandin E2 (PGE 2 ) have been reported to mediate T-cell suppression by MSCs. [13][14][15] Specifically, neutralizing antibodies against TGF-␤ or hepatocyte growth factor, 13 an inhibitor of IDO,14 or an inhibitor of prostaglandin production reverse the inhibition of T-cell proliferation by MSCs. 15 In addition, some reports have shown that a soluble factor is the major mediator of suppression, [13][14][15][16][17] whereas some reports have demonstrated that T-cell-MSC contact is required for this suppression. [12][13][14]16,17 In the current study, we sought to resolve these conflicting results by using a mouse bone marrow-derived MSC system.One candidate soluble factor for T-cell suppression is nitric oxide (NO) because it is known to inhibit T-cell proliferation. [18][19][20][21][22][23][24][25] NO is produced by NO synthases (NOSs), of which there are 3 subtypes: inducible NOS (iNOS), endothelial NOS, and neuronal NOS. Like MSCs, it has been known that macrophages suppress T-cell proliferation. This suppression was reported to be mediated by NO inhibition of Stat5 phosphorylation. 18,19 Also, MSCs were reported to produce NO when they differentiate into chondrocytes. 26 We therefore investigated whether MSCs can produce NO and whether NO is involved in their ability to suppress T-cell proliferation. Materials and methods MaterialsN-nitro-L-a...

We conducted a multi-institutional randomized study to determine whether highdose daunorubicin would be as effective as standard-dose idarubicin in remissioninduction therapy for newly diagnosed adult patients younger than 65 years of age with acute myeloid leukemia. Of 1064 patients registered, 1057 were evaluable. They were randomly assigned to receive either daunorubicin (

We conducted a prospective randomized study to assess the optimal postremission therapy for adult acute myeloid leukemia in patients younger than 65 years in the first complete remission. A total of 781 patients in complete remission were randomly assigned to receive consolidation chemotherapy of either 3 courses of high-dose cytarabine (HiDAC, 2 g/m 2 twice daily for 5 days) alone or 4 courses of conventional standard-dose multiagent chemotherapy (CT) established in the previous JALSG AML97 study. Five-year disease-free survival was 43% for the HiDAC group and 39% for the multiagent CT group (P ‫؍‬ .724), and 5-year overall survival was 58% and 56%, respectively (P ‫؍‬ .954). Among the favorable cytogenetic risk group (n ‫؍‬ 218), 5-year diseasefree survival was 57% for HiDAC and 39% for multiagent CT (P ‫؍‬ .050), and 5-year overall survival was 75% and 66%, respectively (P ‫؍‬ .174). In the HiDAC group, the nadir of leukocyte counts was lower, and the duration of leukocyte less than 1.0 ؋ 10 9 /L longer, and the frequency of documented infections higher. The present study demonstrated that the multiagent CT regimen is as effective as our HiDAC regimen for consolidation. Our HiDAC regimen resulted in a beneficial effect on disease-free survival only in the favorable cytogenetic leukemia group. This trial was registered at www.umin.ac.jp/ ctr/ as #C000000157. IntroductionApproximately 70% to 80% of the newly diagnosed younger adult patients with acute myeloid leukemia (AML) achieve complete remission (CR) when treated with an anthracycline, usually daunorubicin (DNR) or idarubicin (IDR), and cytarabine (Ara-C); however, only approximately one-third of these patients remain free of disease for more than 5 years. [1][2][3][4][5] If CR patients are left untreated, almost all of them will relapse and die. 6 Therefore, postremission therapy is indispensable. Postremission therapy is divided into consolidation and maintenance therapy. In the previous studies of Japan Adult Leukemia Study Group (JALSG) for adult AML (AML87, 89, 92, and 95), 1-3,5 we administered 3 courses of consolidation therapy and 6 courses of intensified maintenance therapy. In the AML97 study, 7 we conducted a randomized study to compare the conventional 3-course consolidation and 6-course maintenance therapies with 4 courses of intensive consolidation therapy without maintenance and demonstrated no difference in overall survival (OS) and disease-free survival (DFS). Therefore, the 4 courses of conventional standard-dose multiagent chemotherapy (CT) became the standard regimen in Japan. On the other hand, multiple cycles of high-dose cytarabine (HiDAC) have been commonly used as consolidation therapy in the United States and other countries. However, our national medical insurance system did not allow us to use HiDAC until 2001, and thus we could not use HiDAC in the previous treatment regimens for leukemia. We therefore conducted this prospective, multicenter cooperative An Inside Blood analysis of this article appears at the front of this issu...

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