Peripheral T-cell tolerance is thought to significantly contribute to the prevention of autoimmunity, and it has been shown that antigenpresenting steady-state dendritic cells efficiently induce peripheral tolerance. We previously showed that dendritic-cell-induced tolerance is a T-cell-intrinsic process that depends on coinhibitory molecules such as programmed death-1. Here we specifically analyze the involvement of FoxP3 + regulatory T cells, which are known to be important for maintenance of self-tolerance. We show that antigen presentation by steady-state dendritic cells failed to induce peripheral tolerance in the absence of FoxP3 + regulatory T cells but induced protective CD8 + T-cell-mediated immunity instead. Regulatory T-cell-depleted mice had massively increased numbers of dendritic cells in lymph nodes. Dendritic cells isolated from mice without regulatory T cells had upregulated costimulatory molecules and showed stronger T-cell stimulatory capacity ex vivo, suggesting that regulatory T cells contribute to peripheral tolerance by keeping the dendritic cells in an immature state. Using blocking antibodies, we demonstrate that CTLA-4 but not IL-10 is necessary for control of dendritic cells by regulatory T cells.M ost autoreactive T cells are deleted in the thymus by socalled "negative selection." Although this process is efficient, the presence of autoreactive T cells in every healthy individual demonstrates that it is not complete (1). Peripheral, mature autoreactive T cells are kept in check by peripheral tolerance, which acts through a variety of mechanisms that are not necessarily mutually exclusive and that include unresponsiveness/ anergy, regulation/suppression, and deletion.We and others have recently demonstrated that dendritic cells (DCs) play a central role in the induction of peripheral tolerance (2-4). Using transgenic mice that allow the inducible expression of viral cytotoxic T lymphocyte (CTL) epitopes selectively by DCs (DIETER mice), we showed that presentation of CTL epitopes by steady-state DCs induces robust tolerance in antigen-specific CD8 + T cells. We found that this tolerance depends on signaling via the inhibitory receptors programmed death-1 (PD-1) and cytotoxic T lymphocyte antigen 4 (CTLA-4) and follows a recessive mechanism such as induction of anergy in, or deletion of, CD8 + T cells specific for the antigens presented by the steady-state DCs. Using adoptive transfer of naive T cells into tolerant mice, we did not find any evidence for involvement of a dominant suppressive mechanism such as the induction of antigen-specific regulatory T cells (Treg cells) or the production of immunosuppressive cytokines. We did not, however, formally address the contribution of Treg cells to peripheral tolerance induced by steady-state DCs in DIETER mice (3, 4). CD4 + CD25 + FoxP3 + Treg cells, first characterized by their immunosuppressive properties (5, 6), comprise ≈10-15% of all peripheral CD4 + T cells in mice. The forkhead box transcription factor FoxP3 is the best marker for Tre...

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We studied in vitro the cytostatic/cytotoxic effects of the peptides dolastatin 10 and dolastatin 15 on various human leukemia cell lines, peripheral blood mononuclear cells (PBMNC), and tonsillar mononuclear cells (tonsillar MNC). On leukemia cell lines both drugs proved to be highly potent cvtostatic agents; however, the cells were not killed even at concentrations of maximum growth-inhibition. Growth-suppression was not paralleied by induced dift'erentiation as exposure to dolastatins did not significantly alter the immunophenotype, cytochemistry or morphology of HL-60 cells. Growth-inhibitory effects of dolastatins were reversed following the removal of the agents from the culture medium. The dolastatins inhibited proliferation of leukemia cell lines at lower concentrations than those which inhibited the growth of stimulated tonsillar MNC. The growth-inhibiting properties of the dolastatins regarding leukemia cell lines and their low toxicity towards normal MNC indicate that these agents might be promising new drugs for future experiments examining their effects on primary leukemic cells.

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We analyzed the acid phosphatase (AcP) isoenzyme profiles of normal and malignant hematopoietic cells using isoelectric focusing followed by diazo staining. Reproducibly defined bands and band complexes could be identified and were correlated with the cellular material analyzed. Different isoenzyme profiles were indeed associated with the various cell types and cell lineages. Lymphoid cells were characterized by the expression of one or two bands at pH 6.0, thus termed L1 or L2 pattern. Myeloid cells showed different isoenzyme profiles (consisting of 3-11 bands) designated M1 and M2. One particular isoenzyme near the cathodal end of the gel could not be inhibited by tarirate, the so-called tartrate-resistant AcP (TRAP). Expression of the TRAP isoenzyme was found in nearly all cases of hairy cell leukemia, but also in a significant number of other B-cell or monocyte derived malignancies. TRAP appears to be an enzymatic parameter for activated B-cells and monocytes. The monocytic cell lineage was clearly documented by the detection of a unique triplet of strongly stained isoenzymes. The AcP isoenzyme profiles represent biochemical cell markers indicating states of activation and lineage of differentiation.