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Thymic regulatory T cells (tTregs) and induced regulatory T cells (iTregs) suppress murine acute graft‐versus‐host disease (GVHD). Previously, we demonstrated that the plasmacytoid dendritic cell indoleamine 2,3‐dioxygenase (IDO) fosters the in vitrodevelopment of human iTregs via tryptophan depletion and kynurenine (Kyn) metabolites. We now show that stimulation of naïve CD4+T cells in low tryptophan (low Trp) plus Kyn supports human iTreg generation. In vitro, low Trp + Kyn iTregs and tTregs potently suppress T effector cell proliferation equivalently but are phenotypically distinct. Compared with tTregs or T effector cells, bioenergetics profiling reveals that low Trp + Kyn iTregs have increased basal glycolysis and oxidative phosphorylation and use glutaminolysis as an energy source. Low Trp + Kyn iTreg viability was reliant on interleukin (IL)‐2 in vitro. Although in vivo IL‐2 administration increased low Trp + Kyn iTreg persistence on adoptive transfer into immunodeficient mice given peripheral blood mononuclear cells to induce GVHD,IL‐2–supported iTregs did not improve recipient survival. We conclude that low Trp + Kyn create suppressive iTregs that have high metabolic needs that will need to be addressed before clinical translation. This work defines the clinical‐scale production of Tregs induced via in vitroexpansion of effector T cells under conditions of low tryptophan plus kynurenines that are as suppressive in vitroas thymic Tregs, but have high metabolic demands that hinder in vivoefficacy.

The human MHC class Ib antigen HLA-G is thought to regulate maternal immune responses during pregnancy. Here we show that expression of HLA-G in transgenic mice diminished cellular immunity by inhibiting maturation of myelomonocytic cells into functional antigen-presenting cells (APC). Skin allografts applied to HLA-G transgenic mice survived longer and resultant T cell responses were less potent compared to control mice. T cells from HLA-G mice responded normally to allogeneic APC and immunohistological analyses of spleen revealed no marked abnormalities. However, spontaneous outgrowths of myeloid cells were observed when bone marrow or splenocytes from HLA-G mice were cultured in vitro, but functionally competent APC did not develop spontaneously in bone marrow cultures supplemented with granulocyte macrophage colony stimulating factor (GM-CSF). Addition of lipopolysaccharide (LPS) to GM-CSF-derived bone marrow cultures rescued APC maturation. Studies using HLA-G tetrameric reagents revealed that HLA-G-specific binding activity was associated with CD11c(+) myelomonocytic cells, while binding to lymphoid and NK cell subsets was undetectable. These data show that spontaneous maturation of functionally competent dendritic cells (DC) is compromised in HLA-G mice. We hypothesize that HLA-G inhibits maturation of DC via receptor-mediated interactions with myelomonocytic precursors, which render immature DC precursors unable to receive signals from activated T cells.

Nitrogen uptake by rooted cuttings of sweet potato [Ipomoea batatas(L.) Lam.] has not been studied extensively although “slips” (rooted sprouts) are the normal plant part used in commercial propagation. Experiments with rooted cuttings of sweet potato, cultivar ‘Jewell’, were conducted in solution culture to investigate the effects of ambient acidity and the presence and concentration effects of ammonium and nitrate on rates of nitrate and ammonium uptake. Plant stem cuttings were rooted in Hoagland's solution (plus or minus nitrate) then transferred to 980 ml containers of experimental solutions. In experiment I rates of N uptake from 0.1 mMNH4NO3were measured at pH of 4.5, 5.5, and 6.5. In experiment II rates of N uptake were measured from 0.1 mMsolutions with and without the presence of the ammonium in the case of nitrate uptake and vice versa. In experiment III nitrate uptake was measured from 0.1 mMnitrate without ammonium and in the presence of 0.1 mMand 1 mMammonium. Solutions were sampled periodically and analyzed for nitrate, ammonium, and K. Nitrate uptake rate was decreased by increasing ambient pH while ammonium uptake rate was increased. Presence of ambient ammonium at equimolar concentration decreased rate of nitrate uptake ,∼30% at pH 5.5. However, a tenfold increase in ammonium concentration did not further reduce rate of nitrate uptake although rate of ammonium uptake was doubled. Presence of equimolar nitrate had no effect on rate of ammonium uptake at 0.1 mMammonium. Efflux of K to initially K‐free solutions was increased by ambient ammonium, but a transition from K efflux to influx occurred without a consistent change in rates of ammonium or nitrate uptake. A suggestion is made that two components of nitrate uptake by sweet potato roots exist, one of which is assumed to be associated with nitrate reductase and inhibited by ammonium.

Four Ohio soils of wide range in K release capability were initially K‐treated (0, 100, 200, 800 ppm) and successively cropped three times with corn in a growth chamber. Aliquots of the soils with and without K added and before and after cropping were assayed by extraction, equilibration, and plant uptake techniques for the effects of cropping and K‐treatment. Uptake of K by the corn was closely related to the K release capabilities of the soils. Exchangeable K increased as rate of K increased. Initial cropping decreased the exchangeable K in all soils eliminating the effect of K treatments on exchangeable K. However, after initial cropping where no K was added, exchangeable K varied sixfold from the lowest to the highest. Nonexchangeable K removed with H2SO4initially reflected K additions, but after the first crop, the values decreased progressively as K release capabilities of the soils increased. Parameters from Q/Iisotherms of the soils gave correlations with percentage and total K contents of assay crops less satisfactory than for exchangeable and H2SO4extractable K. There was a tendency for prior cropping to increase the fixation and reduce the plant recovery of subsequently applied K in the two soils high in clay and total K.

Macrophage colony-stimulating factor (M-CSF) is known to stimulate proliferation of monocyte/macrophage progenitors and enhance in vitro antitumor cytotoxicity by murine macrophages. In this paper we have shown that recombinant human M-CSF causes human peripheral blood monocytes to differentiate in culture into metabolically active macrophage-like cells. These cells mediate very efficient antibody-dependent cellular cytotoxicity (ADCC) against human melanoma and neuroblastoma cell lines in the presence of two murine IgG3 mAbs (3F8 and R24). They also mediate antibody-independent cytotoxicity (or cytostasis) to a lesser extent. Human serum had an inconsistent effect on ADCC, but often induced similar high levels of ADCC. Cytotoxicity was measured using a novel ELISA to detect surviving tumor cells after ADCC. Two conventional isotope-release assays (51Cr and [3H]TdR) underestimated or entirely failed to detect ADCC by M-CSF-activated monocytes. Optimal activation occurred with 100-300 U/ml of M-CSF, and required 9-11 d for completion. Most of the M-CSF cultured monocytes expressed the low-affinity Fc receptor (CD16). ADCC by cells of the monocyte/macrophage lineage using murine IgG3 mAbs may have significance for the immunotherapy of human malignancies.