Biomedical subjects

L Gammaitoni

Publications and source records attributed to L Gammaitoni.

At least 19 recordsLinked to original sources

PubMed2003

Signal detection via residence-time asymmetry in noisy bistable devices.

We introduce a dynamical readout description for a wide class of nonlinear dynamic sensors operating in a noisy environment. The presence of weak unknown signals is assessed via the monitoring of the residence time in the metastable attractors of the system, in the presence of a known, usually time-periodic, bias signal. This operational scenario can mitigate the effects of sensor noise, providing a greatly simplified readout scheme, as well as significantly reduced processing procedures. Such devices can also show a wide variety of interesting dynamical features. This scheme for quantifying the response of a nonlinear dynamic device has been implemented in experiments involving a simple laboratory version of a fluxgate magnetometer. We present the results of the experiments and demonstrate that they match the theoretical predictions reasonably well.

Journal Article↗

PubMed2002

Noise activated nonlinear dynamic sensors.

We introduce a novel dynamical description for a wide class of nonlinear physical sensors operating in a noisy environment. The presence of unknown physical signals is assessed via the monitoring of the residence times in the metastable attractors of the system. We show that the presence of ambient noise, far from degrading the sensor operation, can actually improve its sensitivity and provide a greatly simplified readout scheme, as well as significantly reduce processing procedures for this new class of devices that we propose to call noise activated nonlinear dynamic sensors. Such devices can also show interesting dynamical features such as the resonant trapping effect.

Journal Article↗

PubMed2002

Role of different medium and growth factors on placental blood stem cell expansion: an in vitro and in vivo study.

Expansion of haemopoietic stem cells from placental blood has been obtained with a combination of flt3 ligand (FL), thrombopoietin (TPO), kit-ligand (KL) with or without interleukin-6 (IL6) in serum-replete medium. For clinical use, cell expansion in the absence of serum is a clear advantage. Therefore, stem cell expansion in serum-free (SF) medium with a combination of three (FL, TPO, KL) or four (FL, TPO, KL, IL6) growth factors was compared with the results obtained using fetal calf serum (FCS) or human serum (HS). Human CD34(+) placental blood cells were cultured in the presence of FL, TPO, KL +/- IL6 with SF medium, HS and FCS for up to 8 weeks. CD34(+), CFC, LTC-IC content was measured at intervals. To determine the in vivo repopulating capacity of expanded cells, CD34(+) expanded cells were transplanted in sublethally irradiated NOD/SCID mice. With the three growth factor combination the CD34(+) cell number increased steadily up to the 8 weeks of culture. CD34(+) cells were expanded 67.5-fold with SF, 11.7 with HS and 49.2 with FCS. However, when CFCs and LTC-ICs were considered, a continuous expansion was observed only with HS and FCS, whereas in SF medium after 6 weeks their number started to decline. The addition of IL-6 did not change the expansion significantly. Cells grown ex vivo for 14 days were transplanted into NOD/SCID mice. The engraftment of human cells in mice was higher for serum-replete than for SF expanded cells. Nevertheless, SF cultured cells were also able to engraft both marrow and spleen in all animals. In addition, engrafted human cells still maintained clonogenic ability. With KL, FL, TPO +/- IL6 it is possible to expand haemopoietic progenitor cells in a SF medium. Compared with serum-replete cultures, the absolute number of clonogenic cells and in vivo repopulating cells is lower. Although the degree of expansion remains significant, a clinical trial still needs to be carried out to address the question of whether this expansion might be useful in reducing post-transplant aplasia.

Animals↗

PubMed2000

Very high Q measurements on a fused silica monolithic pendulum for use in enhanced gravity wave detectors

We present for the first time the results of very high Q factor measurements for a 2.8 kg fused silica mass suspended by two fused quartz fibers attached by a novel technique for joining fused silica or quartz. The Q for the pendulum mode at 0.93 Hz was (2.3+/-0. 2)x10(7), the highest value demonstrated to date for a mass of this size. By employing such a new suspension system the sensitivity of the gravitational wave detectors currently under construction can be increased up to 1 order of magnitude.

Journal Article↗

PubMed2000

Negative influence of IL3 on the expansion of human cord blood in vivo long-term repopulating stem cells.

Identification of culture conditions that support expansion or even long-term maintenance of in vivo repopulating human hematopoietic stem cells is still a major challenge. Using a combination of FLT3 ligand (FL), Stem Cell Factor (SCF), Thrombopoietin (TPO) and Interleukin 6 (IL6), we cultured cord blood (CB) CD34+ cells for up to 12 weeks and transplanted their progeny into sublethally irradiated NOD/SCID mice. Bone marrow engraftment was considered successful when recipients contained measurable numbers of human CD45+, CD71+ and Glycophorin A+(GpA) cells 8 weeks after transplantation. Twelve-week expanded cells with FL+SCF+TPO+IL6 successfully engrafted all of the recipients and human CD45(+)+CD71(+)+GpA(+) cells represented 4.3 to 22.4% of bone marrow. Substitution of IL6 with IL3 led to an even better expansion of cells and a similar clonogenic progenitor output in the first 8 weeks of culture; however, LTC-IC output increased up to week 6 and then decreased and disappeared. By contrast, with FL+SCF+TPO+IL6, LTC-IC kept increasing up to week 12. Four-week cultured cells with FL+SCF+TPO+IL3 less efficiently engrafted NOD/SCID mice, both as measured by frequency of positive recipients (4 out of 10) and percentage of engrafted human cells (< or =2%). Six-week expanded cells failed to engraft. This study provides evidence that many, but not all, of the so-called "early acting" cytokines, can sustain long-term maintenance and even expansion of human primitive in vivo repopulating stem cells. In particular, in the culture conditions used in this study, the presence of IL3 greatly reduces the repopulating potential of expanded CD34+ CB cells.

Animals↗

PubMed2000

Numerical verification of bona fide stochastic resonance

The notion of stochastic resonance as an input/output synchronization mechanism is reestablished quantitatively, based on accurate numerical simulation of a simple two-state model, namely, the Schmitt trigger. The corresponding phenomenological criterion known as bona fide stochastic resonance is thus proven applicable throughout the entire range of the input parameters. Claims to the contrary are briefly discussed.

Journal Article↗

PubMed2000

Intrawell stochastic resonance versus interwell stochastic resonance in underdamped bistable systems

We show that, for periodically driven noisy underdamped bistable systems, an intrawell stochastic resonance can exist, together with the conventional interwell stochastic resonance, resulting in a double maximum in the power spectral amplitude at the forcing frequency as a function of the noise intensity. The locations of the maxima correspond to matchings of deterministic and stochastic time scales in the system. In this paper we present experimental evidence of these phenomena and a phemonological nonadiabatic description in terms of a noise-controlled nonlinear dynamic resonance.

Journal Article↗

PubMed2000

Theory of controlling stochastic resonance

The concept of controlling stochastic resonance has been recently introduced [L. Gammaitoni et al., Phys. Rev. Lett. 82, 4574 (1999)] to enhance or suppress the spectral response to threshold-crossing events triggered by a time-periodic signal in background noise. Here, we develop a general theoretical framework, based on a rate equation approach. This generic two-state theory captures the essential features observed in our experiments and numerical simulations.

Journal Article↗

PubMed1999

Engraftment in nonobese diabetic severe combined immunodeficient mice of human CD34(+) cord blood cells after ex vivo expansion: evidence for the amplification and self-renewal of repopulating stem cells.

Understanding the repopulating characteristics of human hematopoietic stem/progenitor cells is crucial for predicting their performance after transplant into patients receiving high-dose radiochemotherapy. We have previously reported that CD34(+) cord blood (CB) cells can be expanded in vitro for several months in serum containing culture conditions. The use of combinations of recombinant early acting growth factors and the absence of stroma was essential in determining this phenomenon. However, the effect of these manipulations on in vivo repopulating hematopoietic cells is not known. Recently, a new approach has been developed to establish an in vivo model for human primitive hematopoietic precursors by transplanting human hematopoietic cells into sublethally irradiated nonobese diabetic severe combined immunodeficient (NOD/SCID) mice. We have examined here the expansion of cells, CD34(+) and CD34(+)38(-) subpopulations, colony-forming cells (CFC), long-term culture initiating cells (LTC-IC) and the maintenance or the expansion of SCID-repopulating cells (SRC) during stroma-free suspension cultures of human CD34(+) CB cells for up to 12 weeks. Groups of sublethally irradiated NOD/SCID mice were injected with either 35,000, 20,000, and 10,000 unmanipulated CD34(+) CB cells, which were cryopreserved at the start of cultures, or the cryopreserved cells expanded from 35,000, 20,000, or 10,000 CD34(+) cells for 4, 8, and 12 weeks in the presence of a combination of early acting recombinant growth factors (flt 3/flk2 ligand [FL] + megakaryocyte growth and development factor [MGDF] +/- stem cell factor [SCF] +/- interleukin-6 [IL-6]). Mice that had been injected with >/=20,000 fresh or cryopreserved uncultured CD34(+) cells did not show any sign or showed little engraftment in a limited number of animals. Conversely, cells that had been generated by the same number of initial CD34(+) CB cells in 4 to 10 weeks of expansion cultures engrafted the vast majority of NOD/SCID mice. The level of engraftment, well above that usually observed when the same numbers of uncultured cells were injected in the same recipients (even in the presence of irradiated CD34(-) cells) suggested that primitive hematopoietic cells were maintained for up to 10 weeks of cultures. In addition, dilution experiments suggest that SRC are expanded more than 70-fold after 9 to 10 weeks of expansion. These results support and extend our previous findings that CD34(+) CB stem cells (identified as LTC-IC) could indeed be grown and expanded in vitro for an extremely long period of time. Such information may be essential to design efficient stem cell expansion procedures for clinical use.

Animals↗

PubMed1998

GAS6 inhibits granulocyte adhesion to endothelial cells.

GAS6 is a ligand for the tyrosine kinase receptors Rse, Axl, and Mer, but its function is poorly understood. Previous studies reported that both GAS6 and Axl are expressed by vascular endothelial cells (EC), which play a key role in leukocyte extravasation into tissues during inflammation through adhesive interactions with these cells. The aim of this work was to evaluate the GAS6 effect on the adhesive function of EC. Treatment of EC with GAS6 significantly inhibited adhesion of polymorphonuclear cells (PMN) induced by phorbol 12-myristate 13-acetate (PMA), platelet-activating factor (PAF), thrombin, interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha), but not that induced by FMLP and IL-8. GAS6 did not affect adhesion to resting EC. Titration experiments showed that high concentrations of GAS6 were needed to inhibit PMN adhesion and that inhibition was dose-dependent at the concentration range of 0.1 to 1 microg/mL. One possibility was that high concentrations were needed to overwhelm the effect of endogenous GAS6 produced by EC. In line with this possibility, treatment of resting EC with soluble Axl significantly potentiated PMN adhesion. Analysis of localization of GAS6 by confocal microscopy and cytofluorimetric analysis showed that it is concentrated along the plasma membrane in resting EC and treatment with PAF induces depletion and/or redistribution of the molecule. These data suggest that GAS6 functions as a physiologic antiinflammatory agent produced by resting EC and depleted when proinflammatory stimuli turn on the proadhesive machinery of EC.

Cell Adhesion↗

PubMed1998

The role of c-Mpl ligands in the expansion of cord blood hematopoietic progenitors.

The major limitations to the widespread use of high-dose chemotherapy or radiotherapy followed by autologous or allogeneic transplantation are the scarcity of stem cell donors and the depletion of the autologous stem cell reservoir. Cord blood is a readily available source of stem cells, which, however, might be limited in number. For this reason, up to now, cord blood transplantation has been restricted to children. Therefore, a major goal for experimental and clinical hematology is the identification of mechanisms and conditions that support the expansion of transplantable hematopoietic stem cells. Two systems have been described to identify in vitro these progenitor cell populations in both mice and humans: A) long-term culture-initiating cells (LTC-IC), so named because of their ability to support the growth of hemopoietic colonies (colony-forming cell [CFC]) for five to six weeks when cocultured on stromal layers, and B) the generation of hematopoietic progenitors CFC from stroma-free liquid cultures for extended periods of time, which is another indirect evidence for the presence of primitive stem cells. The two systems detect largely overlapping but not identical cell populations of progenitor cells; thus, the identification of the growth factor requirements for the maintenance and amplification of both systems is relevant. The studies presented here demonstrate that CD34+ cord blood cells can be grown in stroma-free liquid cultures for extremely prolonged periods of time (up to six months). During such a period, hemopoietic precursors and committed progenitors belonging to all of the hematopoietic lineages are continuously and massively generated. Such a massive expansion is sustained by an increasingly larger expansion of primitive stem cells (CFU-BI and LTC-IC). The presence of both FL and thrombopoietin (TPO) was necessary and sufficient to support this phenomenon. The addition of KL +/- interleukin 6 (IL-6) does not appear to substantially modify the extent of LTC-IC expansion. FL and TPO appear to be two unique growth factors that preferentially support the self-renewal of primitive stem cells; the additional presence of KL and IL-6 seems to enhance the proliferative potential of at least a subpopulation of daughter stem cells which can undergo at least three differentiation pathways.

Cell Count↗

PubMed1998

Differential growth factor requirement of primitive cord blood hematopoietic stem cell for self-renewal and amplification vs proliferation and differentiation.

Cord blood (CB) is an attractive alternative to bone marrow or peripheral blood as a source of transplantable hematopoietic tissue. However, because of the reduced volume, the stem cell content is limited; therefore its use as a graft for adult patients might require ex vivo manipulations. Two systems have been described that identify these stem cell populations in vitro in both mice and humans: (1) the long-term culture-initiating cells (LTC-IC), thus named because of their ability to support the growth of hematopoietic colonies (colony-forming cell (CFC)) for 5-6 weeks when co-cultured on stromal layers; (2) the generation of hematopoietic progenitors (CFC) from stroma-free liquid cultures for extended periods of time, which provides further indirect evidence of the presence of primitive stem cells. Both systems detect largely overlapping but not identical populations of stem cells. Thus the identification of the growth factor requirements for the maintenance and amplification of both systems is relevant. On this basis, analysis of the effects of 18 cytokine combinations on stroma-free liquid cultures of CB CD34+ cells, showed that: (1) after 7- and 14 day-incubation periods, several growth factor combinations expanded the LTC-IC pool to a similar extent; as compared to the LTC-IC, the generation of CFC was not impressive; (2) time-course analysis of the LTC-IC expansion demonstrated that, by extending the incubation period, only a few growth factor combinations, containing FL, TPO, KL and IL6, could support a further, increasingly greater LTC-IC expansion (up to 270000-fold of the initial value). In similar culture conditions, CFC production underwent continuous expansion, which persisted for over 7 months and reached values of one million-fold of the initial value. The simultaneous presence of FL and TPO was both necessary and sufficient to support this phenomenon. The addition of KL+/-IL6 did not appear to substantially modify the extent of LTC-IC expansion; nevertheless, it played an important role in sustaining an even more massive and prolonged output of CFU-GM, CFU-Mk and BFU/CFU-GEMM (up to 100 million-fold); (3) the presence of IL3 was found to be negative, in that it inhibited both the extent of LTC-IC expansion and the long-term generation of CFC. Thus, FL and TPO appear as two unique growth factors that preferentially support the self-renewal of primitive stem cells; the additional presence of KL and IL6 seems to enhance the proliferative potential of at least one subpopulation of daughter stem cells, which may follow three differentiation pathways. Far from being definitive, our data demonstrated that massive stem cell expansion, in cord blood, can be obtained in reasonably well-defined culture conditions. This could represent an initial step towards larger scale cultures for transplantation and gene therapy protocols.

Adult↗

PubMed1998

Ex vivo expansion of cord blood progenitors.

Human umbilical cord blood contains abundant primitive and committed hematopoietic progenitors; in addition, the general availability and the ease of procurement make cord blood a very attractive alternative source of transplantable hematopoietic tissue. However, the major limitation to a widespread use of cord blood for transplantation lays in its limited volume. For such a reason, until now, cord blood transplant has been mainly restricted to children and small size adults. Ex vivo expansion of cord blood stem cells could make the use of cord blood transplant feasible also for adult patients. Recently we developed a stroma-free culture system in which a progressive, increasingly greater production of hemopoietic progenitors belonging to all the hematopoietic lineages was sustained for over six months. A similar sustained and prolonged expansion of the most primitive stem cells that can be detected in vitro (LTC-IC), was also documented. The extremely prolonged maintenance and the massive expansions suggest that extensive self-renewal and little differentiation can be triggered in vitro by FLT3/FLK2 ligand (FL) plus c-mpl ligand (Thrombopoietin) and this could represent a first step towards the implementation of clinical expansion-transplantation strategies.

Adult↗

PubMed1997

GAS6, the ligand of Axl and Rse receptors, is expressed in hematopoietic tissue but lacks mitogenic activity.

GAS6, a gene previously identified as growth arrest specific, has been demonstrated to be the ligand of Axl, a novel tyrosine kinase receptor widely expressed in both normal and neoplastic hematopoietic tissue. We have observed previously that GAS6 mRNA was present in whole bone marrow. This preliminary finding prompted us to investigate the presence of GAS6 in hematopoietic tissue and the possible role of this molecule in controlling the proliferation of hematopoietic precursors. We report here that the protein GAS6 is diffusely present in hematopoietic tissue, both in stromal and in hematopoietic cells, and that, among these cells, positivity is observed in megakaryocytes and myelomonocytic precursors. Furthermore, our data suggest that GAS6 is not a growth factor for hematopoietic progenitors or stromal fibroblasts. Despite the fact that both the Axl receptor and its ligand, GAS6, are expressed in hematopoietic tissue, the biological role of their interactions remains to be determined.

Biopsy↗

PubMed1996