To establish a more appropriate animal recipient for xenotransplantation, NOD/ SCID/␥ c null mice double homozygous for the severe combined immunodeficiency (SCID) mutation and interleukin-2R␥ (IL-2R␥) allelic mutation (␥ c null ) were generated by 8 backcross matings of C57BL/6J-␥ c null mice and NOD/Shi-scid mice. When human CD34 ؉ cells from umbilical cord blood were transplanted into this strain, the engraftment rate in the peripheral circulation, spleen, and bone marrow were significantly higher than that in NOD/Shiscid mice treated with anti-asialo GM1 antibody or in the ␤2-microglobulindeficient NOD/LtSz-scid (NOD/SCID/ ␤2m null ) mice, which were as completely defective in NK cell activity as NOD/SCID/ ␥ c null mice. The same high engraftment rate of human mature cells was observed in ascites when peripheral blood mononuclear cells were intraperitoneally transferred. In addition to the high engraftment rate, multilineage cell differentiation was also observed.

IntroductionMultipotential mesenchymal stem/progenitor cells (MSCs) can be induced to differentiate into bone, adipose, cartilage, muscle, and endothelium if these cells are cultured under specific permissive conditions [1,2]. In rodents, a specific type of MSC (termed multipotent adult progenitor cell) can be isolated from bone marrow (BM) and contributes to most somatic cell types when injected into early blastocysts at the single-cell level [3] , kidney, lung, and liver). These cells are also present in the fetal environment (e.g., blood, liver, BM, and kidney). However, MSCs are a rare population in these tissues. Here we tried to identify cells with MSC-like potency in human placenta. We isolated adherent cells from trypsin-digested term placentas and established two clones by limiting dilution. We examined these cells for morphology, surface markers, gene expression patterns, and differentiation potential and found that they expressed several stem cell markers, hematopoietic/ endothelial cell-related genes, and organ-specific genes, as determined by reverse transcription-polymerase chain reaction and fluorescence-activated cell sorter analysis. They also showed osteogenic and adipogenic differentiation potentials under appropriate conditions. We suggest that placenta-derived cells have multilineage differentiation potential similar to MSCs in terms of morphology, cell-surface antigen expression, and gene expression patterns. The placenta may prove to be a useful source of MSCs.

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Various cytokines utilize Janus kinase (JAK) and the STAT (signal transducers and activators of transcription) family of transcription factors to carry out their biological functions. Among STATs, two highly related proteins, STAT5a and STAT5b, are activated by various cytokines, including prolactin, growth hormone, erythropoietin, interleukin 2 (IL-2), and IL-3. We have cloned a STAT5-dependent immediate-early cytokine-responsive gene, CIS1 (encoding cytokine-inducible SH2-containing protein 1). In this study, we created CIS1 transgenic mice under the control of a beta-actin promoter. The transgenic mice developed normally; however, their body weight was lower than that of the wild-type mice, suggesting a defect in growth hormone signaling. Female transgenic mice failed to lactate after parturition because of a failure in terminal differentiation of the mammary glands, suggesting a defect in prolactin signaling. The IL-2-dependent upregulation of the IL-2 receptor alpha chain and proliferation were partially suppressed in the T cells of transgenic mice. These phenotypes remarkably resembled those found in STAT5a and/or STAT5b knockout mice. Indeed, STAT5 tyrosine phosphorylation was suppressed in mammary glands and the liver. Furthermore, the IL-2-induced activation of STAT5 was markedly inhibited in T cells in transgenic mice, while leukemia inhibitory factor-induced STAT3 phosphorylation was not affected. We also found that the numbers of gamma delta T cells, as well as those of natural killer (NK) cells and NKT cells, were dramatically decreased and that Th1/Th2 differentiation was altered in transgenic mice. These data suggest that CIS1 functions as a specific negative regulator of STAT5 in vivo and plays an important regulatory role in the liver, mammary glands, and T cells.

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