Cord Blood Nucleated Cells Induce Delayed Proliferative and Cytotoxic T Cell Alloreactivity.

Blood ◽  
2006 ◽  
Vol 108 (11) ◽  
pp. 5138-5138
Author(s):  
Dolores Mahmud ◽  
Sandeep Chunduri ◽  
Javaneh Abbasian ◽  
John Maciejewski ◽  
Ronak Iqbal ◽  
...  
Keyword(s):  
Cell Proliferation ◽  
T Cells ◽  
T Cell ◽  
Cord Blood ◽  
T Cell Response ◽  
Cytotoxic T Cell ◽  
T Cell Proliferation ◽  
Cd34 Cells ◽  
Ctl Activity

Abstract Transplantation of HLA-mismatched nucleated cells from cord blood (CB) has reduced risks of graft rejection and severe acute graft-versus-host disease. In this study we analyzed the in-vitro alloantigen presenting capacity of cord blood nucleated cells. CB mononuclear cells (MNCs) or immunomagnetically-selected CD34+ cells, or CD14+ monocytes, were irradiated and tested as stimulators of allogeneic blood T cells in primary (stimulator:responder ratio = 1:1) or secondary (stimulator:responder ratio = 1:2) mixed leukocyte culture (MLC), or in cytotoxic T-lymphocytes (CTL) assays. CB-MNCs failed to induce allogeneic T cell proliferation in 6-days primary MLC, whereas CD34+ or CD14+ cells stimulated brisk T cell responses. A suppressive effect of CB-MNCs was ruled out since CD3+ cell-depletion of CB-MNCs did not restore CB immunogenicity and the addition of increasing doses of CB-MNCs did not inhibit T cell alloreactivity to CD34+ cells. Despite allogeneic T cells were unresponsive to CB-MNCs after primary and secondary MLC, T cell anergy was ruled out since T cells that were unresponsive after primary MLC proliferated potently in secondary MLC stimulated with CB CD34+ cells, and even more with CB monocyte-derived dendritic cells (Mo-DC) generated in-vitro with GM-CSF and IL-4. Interestingly, after co-culture with irradiated allogeneic T cells for 6 days, CB-MNCs showed a greater proportion of CD86+ cells and elicited allo- T cell proliferation. In addition, allo-CTL activity was induced by CB-MNCs only after restimulating effector cells for 3–4 weeks (26±7% lysis of antigen-specific PHA-blast at 50:1 E:T ratio), and was comparable to CTL activity induced after 1 week by Mo-DC generated from the same CB. When T cell effectors were stimulated by combining two incompatible cord blood MNCs mixed together, CTL activity was then detected after 4 weeks against both of them regardless of the CB:CB cell ratio. These results show an impaired allo-APC activity of CB-MNCs, without suppressive or tolerogenic activity. These findings might partially explain the initial engraftment of combined HLA mismatched CB grafts in vivo, however they also suggest that a delayed T cell response may occur due to CB-derived APCs activating CTLs.

scholarly journals Naive CD8+ T cells differentiate into protective memory-like cells after IL-2–anti–IL-2 complex treatment in vivo

2007 ◽  
Vol 204 (8) ◽  
pp. 1803-1812 ◽  
Author(s):  
Daisuke Kamimura ◽  
Michael J. Bevan
Keyword(s):  
Cell Proliferation ◽  
T Cells ◽  
T Cell ◽  
Cd8 T Cells ◽  
Cd8 T Cell ◽  
T Cell Response ◽  
T Cell Proliferation ◽  
Memory Phenotype

An optimal CD8+ T cell response requires signals from the T cell receptor (TCR), co-stimulatory molecules, and cytokines. In most cases, the relative contribution of these signals to CD8+ T cell proliferation, accumulation, effector function, and differentiation to memory is unknown. Recent work (Boyman, O., M. Kovar, M.P. Rubinstein, C.D. Surh, and J. Sprent. 2006. Science. 311:1924–1927; Kamimura, D., Y. Sawa, M. Sato, E. Agung, T. Hirano, and M. Murakami. 2006. J. Immunol. 177:306–314) has shown that anti–interleukin (IL) 2 monoclonal antibodies that are neutralizing in vitro enhance the potency of IL-2 in vivo. We investigated the role of IL-2 signals in driving CD8+ T cell proliferation in the absence of TCR stimulation by foreign antigen. IL-2 signals induced rapid activation of signal transducer and activator of transcription 5 in all CD8+ T cells, both naive and memory phenotype, and promoted the differentiation of naive CD8+ T cells into effector cells. IL-2–anti–IL-2 complexes induced proliferation of naive CD8+ T cells in an environment with limited access to self–major histocompatibility complex (MHC) and when competition for self-MHC ligands was severe. After transfer into wild-type animals, IL-2–activated CD8+ T cells attained and maintained a central memory phenotype and protected against lethal bacterial infection. IL-2–anti–IL-2 complex–driven memory-like CD8+ T cells had incomplete cellular fitness compared with antigen-driven memory cells regarding homeostatic turnover and cytokine production. These results suggest that intense IL-2 signals, with limited contribution from the TCR, program the differentiation of protective memory-like CD8+ cells but are insufficient to guarantee overall cellular fitness.

Disruption of T Cell Suppression in Chronic Lymphocytic Leukemia by CD200 Blockade.

Blood ◽  
2008 ◽  
Vol 112 (11) ◽  
pp. 2072-2072
Author(s):  
Christian P Pallasch ◽  
Susanne Ulbrich ◽  
Reinhild Brinker ◽  
Robert A Uger ◽  
Michael Hallek ◽  
...  
Keyword(s):  
Cell Proliferation ◽  
T Cells ◽  
T Cell ◽  
Regulatory T Cells ◽  
In Vitro Culture ◽  
Mixed Lymphocyte Reaction ◽  
T Cell Response ◽  
T Cell Proliferation ◽  
Therapeutic Benefits

Abstract Suppression of patients’ T-cells is a key event in CLL pathogenesis and was demonstrated to be mediated by direct cell-cell contact of malignant CLL cells with T-cells. CD200 plays a critical role in regulating the immune system and has been shown to be up-regulated on the surface of different tumors including CLL. In this study we addressed the effects of CD200 over-expression on CLL cells on autologous T cells in a mixed lymphocyte reaction system. We used native and CD40 ligand (CD40L)- stimulated CLL cells as antigen-presenting cells (APCs) to expand autologous T cells of 14 patients. T-cell proliferation was analyzed over 3 weeks of in vitro culture. A functional anti- CD200 antibody (1B9) was added to reveal CD200-mediated immunosuppression in the autologous system. Expansion of patient T-cells was assessed by flow cytometry including intracellular staining of FOXP3. Specificity towards CLL-specific antigens was monitored applying fibromodulin derived peptides for detection of specific T-cells by ELISPOT analysis. T-cell proliferation over 3 weeks of in vitro culture was significantly enhanced compared to control cells when using CD40L-stimulated APCs and an anti-CD200 antibody (p=0.0004). CD200 blockade was further shown to stimulate antigen-specific T-cell responses towards the F2 and F4 peptides of the CLL-associated antigen fibromodulin (p=0.04). Finally, the number of CD4+/CD25high/FOXP3+ T cells (Treg) was significantly decreased in CD200 treated mixed lymphocyte reaction (p=0.04). In summary, CD200 blockade may provide therapeutic benefits in CLL by enhancing T-cell expansion, augmenting an antigen-specific T cell response with suppression of regulatory T cells. CD200 seems to be an important immunosuppressive molecule in CLL: by CD200 blockade immune suppression can be overcome by altering tolerance to tumor antigens and deregulation of regulatory T cells. This combination of an immune induction paralleled by a disruption of immunosuppressive factors makes anti-CD200 mAb a powerful tool for future treatment of CLL, possibly in combination with other B cell cytotoxic or immunostimulatory approaches.

scholarly journals Endometrial regenerative cells with galectin-9 high-expression attenuate experimental autoimmune hepatitis

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Hongda Wang ◽  
Yiming Zhao ◽  
Bingbing Ren ◽  
Yafei Qin ◽  
Guangming Li ◽  
...  
Keyword(s):  
Cell Proliferation ◽  
T Cells ◽  
T Cell ◽  
Liver Function ◽  
Cell Response ◽  
T Cell Response ◽  
T Cell Proliferation ◽  
Endometrial Regenerative Cells ◽  
Regenerative Cells

Abstract Background Autoimmune hepatitis (AIH) is a T cell-mediated immune disease that activates abnormally against hepatic antigens. We have previously reported that endometrial regenerative cells (ERCs) were a novel source of adult stem cells, which exhibiting with powerful immunomodulatory effects. Galectin-9 (Gal-9) is expressed in ERCs and plays an important role in regulating T cell response. This study aims to explore the role of ERCs in attenuation of AIH and to determine the potential mechanism of Gal-9 in ERC-mediated immune regulation. Methods ERCs were obtained from menstrual blood of healthy female volunteers. In vitro, ERCs were transfected with lentivirus vectors carrying LGALS9 gene and encoding green fluoresce protein (GFP-Gal-9-LVs) at a MOI 50, Gal-9 expression in ERCs was detected by ELISA and Q-PCR. CD4+ T cells isolated from C57BL/6 mouse spleen were co-cultured with ERCs. The proliferation of CD4+ T cells was detected by CCK-8 kit and the level of Lck/zap-70/LAT protein was measured by western blot. Furthermore, AIH was induced by ConA in C57BL/6 mice which were randomly assigned to untreated, unmodified ERC-treated and Gal-9 high-expressing ERC-treated groups. Histopathological score, liver function, CD4+/CD8+ cell infiltration in liver tissues, the proportion of immune cells in the spleen and liver, and ERC tracking were performed accordingly to assess the progression degree of AIH. Results After transfecting with GFP-Gal-9-LVs, Gal-9 expression in ERCs was significantly increased. Additionally, Gal-9 high-expressing ERCs effectively inhibited CD4+ T cell proliferation and downregulated CD4+ T cell active related proteins p-Lck/p-ZAP70/p-LAT in vitro. Furthermore, treatment with Gal-9 high-expressing ERCs restored liver function, ameliorated liver pathological damage, inhibit CD4+ and CD8+ T cell proliferation and suppress Th1 and Th17 cell response in the hepatitis mice. In addition, Gal-9 high-expressing ERCs further markedly enhanced the level of IL-10 but reduced the levels of IFN-γ, TNF-α, and IL-4 in mouse sera and liver. Cell tracking also showed that ERCs could migrate to the damaged liver organs. Conclusions The results suggested that Gal-9 was an essential modulator, which was required by ERCs in regulating T cell response and attenuating ConA-induced experimental hepatitis. And also, it provides a novel idea for the clinical treatment of AIH.

scholarly journals Dose-Dependent Changes in Influenza Virus-Infected Dendritic Cells Result in Increased Allogeneic T-Cell Proliferation at Low, but Not High, Doses of Virus

2000 ◽  
Vol 74 (12) ◽  
pp. 5460-5469 ◽  
Author(s):  
SangKon Oh ◽  
J. Michael McCaffery ◽  
Maryna C. Eichelberger
Keyword(s):  
Cell Proliferation ◽  
T Cells ◽  
Influenza Virus ◽  
T Cell ◽  
Influenza Virus Infection ◽  
T Cell Response ◽  
T Cell Proliferation ◽  
High Doses ◽  
Tgf Β1

ABSTRACT During the acute phase of infection with influenza A virus, the degree of lymphopenia correlates with severity of disease. Factors that contribute to T-cell activation during influenza virus infection may contribute to this observation. Since the immune response is initiated when dendritic cells (DC) interact with T cells, we have established an in vitro system to examine the effects of influenza virus infection on DC function. Our results show that allogeneic T-cell proliferation was dependent on the dose of A/PR/8/34 used to infect DC, with enhanced responses at low, but not high, multiplicities of infection. The lack of enhancement at high virus doses was not primarily due to the increased rate of DC apoptosis, but required viral replication and neuraminidase (NA) activity. Clusters that formed between DC or between DC and T cells were also dependent on the viral dose. This change in cellular interaction may oppose T-cell proliferation in response to DC infected with high doses of PR8, since the increased contact between DC resulted in the exclusion of T cells. The enhanced alloreactive T-cell response was restored by neutralization of transforming growth factor β1 (TGF-β1). It is likely that NA present on viral particles released from DC infected with high doses of PR8 activates TGF-β1. Future studies will determine the mechanism by which TGF-β1 modifies the in vitro T-cell response and address the contribution of this cytokine to the lymphopenia observed in severe disease.

scholarly journals Siplizumab, an Anti-CD2 Monoclonal Antibody, Induces a Unique Set of Immune Modulatory Effects Compared to Alemtuzumab and Rabbit Anti-Thymocyte Globulin In Vitro

2020 ◽  
Vol 11 ◽  
Author(s):  
Christian Binder ◽  
Felix Sellberg ◽  
Filip Cvetkovski ◽  
Erik Berglund ◽  
David Berglund
Keyword(s):  
Cell Proliferation ◽  
T Cells ◽  
T Cell ◽  
T Cell Activation ◽  
Cell Activation ◽  
Mixed Lymphocyte Reaction ◽  
T Cell Proliferation ◽  
Allogeneic Mixed Lymphocyte Reaction ◽  
Dependent Cell

Antibodies are commonly used in organ transplant induction therapy and to treat autoimmune disorders. The effects of some biologics on the human immune system remain incompletely characterized and a deeper understanding of their mechanisms of action may provide useful insights for their clinical application. The goal of this study was to contrast the mechanistic properties of siplizumab with Alemtuzumab and rabbit Anti-Thymocyte Globulin (rATG). Mechanistic assay systems investigating antibody-dependent cell-mediated cytotoxicity, antibody-dependent cell phagocytosis and complement-dependent cytotoxicity were used to characterize siplizumab. Further, functional effects of siplizumab, Alemtuzumab, and rATG were investigated in allogeneic mixed lymphocyte reaction. Changes in T cell activation, T cell proliferation and frequency of naïve T cells, memory T cells and regulatory T cells induced by siplizumab, Alemtuzumab and rATG in allogeneic mixed lymphocyte reaction were assessed via flow cytometry. Siplizumab depleted T cells, decreased T cell activation, inhibited T cell proliferation and enriched naïve and bona fide regulatory T cells. Neither Alemtuzumab nor rATG induced the same combination of functional effects. The results presented in this study should be used for further in vitro and in vivo investigations that guide the clinical use of immune modulatory biologics.

A combination of anti-CD3 and anti-CD7 ricin A-immunotoxins for the in vivo treatment of acute graft versus host disease

Blood ◽  
2000 ◽  
Vol 95 (12) ◽  
pp. 3693-3701 ◽  
Author(s):  
Ypke V. J. M. van Oosterhout ◽  
Liesbeth van Emst ◽  
Anton V. M. B. Schattenberg ◽  
Wil J. M. Tax ◽  
Dirk J. Ruiter ◽  
...  
Keyword(s):  
T Cells ◽  
T Cell ◽  
Nk Cells ◽  
Graft Versus Host Disease ◽  
T Cell Response ◽  
Cytotoxic T Cell ◽  
Host Disease ◽  
Graft Versus Host ◽  
Ricin A

Abstract This study evaluated the anti-graft versus host disease (GVHD) potential of a combination of immunotoxins (IT), consisting of a murine CD3 (SPV-T3a) and CD7 (WT1) monoclonal antibody both conjugated to deglycosylated ricin A. In vitro efficacy data demonstrated that these IT act synergistically, resulting in an approximately 99% elimination of activated T cells at 10−8 mol/L (about 1.8 μg/mL). Because most natural killer (NK) cells are CD7+, NK activity was inhibited as well. Apart from the killing mediated by ricin A, binding of SPV-T3a by itself impaired in vitro cytotoxic T-cell cytotoxicity. Flow cytometric analysis revealed that this was due to both modulation of the CD3/T-cell receptor complex and activation-induced cell death. These results warranted evaluation of the IT combination in patients with refractory acute GVHD in an ongoing pilot study. So far, 4 patients have been treated with 3 to 4 infusions of 2 or 4 mg/m2 IT combination, administered intravenously at 48-hour intervals. The T1/2 was 6.7 hours, and peak serum levels ranged from 258 to 3210 ng/mL. Drug-associated side effects were restricted to limited edema, fever, and a modest rise of creatine kinase levels. One patient developed low-titer antibodies against ricin A. Infusions were associated with an immediate drop of circulating T cells, followed by a more gradual but continuing elimination of T/NK cells. One patient mounted an extensive CD8 T-cell response directly after treatment, not accompanied with aggravating GVHD. Two patients showed nearly complete remission of GVHD, despite unresponsiveness to the extensive pretreatment. These findings justify further investigation of the IT combination for treatment of diseases mediated by T cells.

A Nanobody Against Cytotoxic T-Lymphocyte Associated Antigen-4 Increases the Anti-Tumor Effects of Specific CD8+ T Cells

2019 ◽  
Vol 15 (11) ◽  
pp. 2229-2239 ◽  
Author(s):  
Zhuoran Tang ◽  
Fengzhen Mo ◽  
Aiqun Liu ◽  
Siliang Duan ◽  
Xiaomei Yang ◽  
...  
Keyword(s):  
Cell Proliferation ◽  
T Cells ◽  
T Cell ◽  
Tumor Cells ◽  
Cytotoxic T Lymphocyte ◽  
Ex Vivo ◽  
T Cell Proliferation ◽  
Tumor Cell Apoptosis ◽  
Xenograft Models

Adoptive cell-based immunotherapy typically utilizes cytotoxic T lymphocytes (CTLs), expanding these cells ex vivo. Such expansion is traditionally accomplished through the use of autologous APCs that are capable of interactions with T cells. However, incidental inhibitory program such as CTLA-4 pathway can impair T cell proliferation. We therefore designed a nanobody which is specific for CTLA-4 (CTLA-4 Nb 16), and we then used this molecule to assess its ability to disrupt CTLA-4 signaling and thereby overcome negative costimulation of T cells. With CTLA-4 Nb16 stimulation, dendritic cell/hepatocellular carcinoma fusion cells (DC/HepG2-FCs) enhanced autologous CD8+ T cell proliferation and production of IFN-γ in vitro, thereby leading to enhanced killing of tumor cells. Using this approach in the context of adoptive CD8+ immunotherapy led to a marked suppression of tumor growth in murine NOD/SCID hepatocarcinoma or breast cancer xenograft models. We also observed significantly increased tumor cell apoptosis, and corresponding increases in murine survival. These findings thus demonstrate that in response to nanobody stimulation, DC/tumor cells-FC-induced specific CTLs exhibit superior anti-tumor efficacy, making this a potentially valuable means of achieving better adoptive immunotherapy outcomes in cancer patients.

scholarly journals Dendritic cells transduced by multiply deleted HIV-1 vectors exhibit normal phenotypes and functions and elicit an HIV-specific cytotoxic T-lymphocyte response in vitro

Blood ◽  
2000 ◽  
Vol 96 (4) ◽  
pp. 1327-1333 ◽  
Author(s):  
Andreas Gruber ◽  
June Kan-Mitchell ◽  
Kelli L. Kuhen ◽  
Tetsu Mukai ◽  
Flossie Wong-Staal
Keyword(s):  
T Cells ◽  
Dendritic Cells ◽  
T Cell ◽  
Ex Vivo ◽  
T Cell Response ◽  
Adoptive T Cell Therapy ◽  
Cytotoxic T Cell ◽  
T Cell Therapy ◽  
Hiv 1

Abstract Dendritic cells (DCs) genetically modified to continually express and present antigens may be potent physiologic adjuvants for induction of prophylactic or therapeutic immunity. We have previously shown that an env and nef deleted HIV-1 vector (HIV-1ΔEN) pseudotyped with VSV-G transduced monocyte-derived macrophages as well as CD34+ precursors of DCs. Here we extended these findings with HIV-1ΔEN to highly differentiated human DCs derived in culture from circulating monocytes (DCs). In addition, a new vector derived from HIV-1ΔEN but further deleted in its remaining accessory genes vif, vpr, and vpu(HIV-1ΔEN V3) was also tested. Both vectors efficiently transduced DCs. Transduction of DCs did not significantly alter their viability or their immunophenotype when compared with untransduced DCs. Furthermore, the phagocytic potential of immature DCs, as well as their ability to differentiate into mature DCs capable of stimulating T-cell proliferation, was not affected. Finally, DCs transduced by the HIV-1ΔEN vector were able to elicit a primary antiviral cytotoxic T-cell response in autologous CD8 T cells. These results suggest that HIV-1–based vectors expressing viral antigens may be useful for in vivo active immunization as well as ex vivo priming of cytotoxic T cells for adoptive T-cell therapy.

scholarly journals Allergen-Induced C5a/C5aR1 Axis Activation in Pulmonary CD11b+ cDCs Promotes Pulmonary Tolerance through Downregulation of CD40

Cells ◽  
2020 ◽  
Vol 9 (2) ◽  
pp. 300 ◽  
Author(s):  
Konstantina Antoniou ◽  
Fanny Ender ◽  
Tillman Vollbrandt ◽  
Yves Laumonnier ◽  
Franziska Rathmann ◽  
...  
Keyword(s):  
Cell Proliferation ◽  
T Cells ◽  
T Cell ◽  
T Cell Activation ◽  
Cd4 T Cells ◽  
Cell Activation ◽  
T Cell Proliferation ◽  
C5a Receptor ◽  
The Impact

Activation of the C5/C5a/C5a receptor 1 (C5aR1) axis during allergen sensitization protects from maladaptive T cell activation. To explore the underlying regulatory mechanisms, we analyzed the impact of C5aR1 activation on pulmonary CD11b+ conventional dendritic cells (cDCs) in the context of house-dust-mite (HDM) exposure. BALB/c mice were intratracheally immunized with an HDM/ovalbumin (OVA) mixture. After 24 h, we detected two CD11b+ cDC populations that could be distinguished on the basis of C5aR1 expression. C5aR1− but not C5aR1+ cDCs strongly induced T cell proliferation of OVA-reactive transgenic CD4+ T cells after re-exposure to antigen in vitro. C5aR1− cDCs expressed higher levels of MHC-II and CD40 than their C5aR1+ counterparts, which correlated directly with a higher frequency of interactions with cognate CD4+ T cells. Priming of OVA-specific T cells by C5aR1+ cDCs could be markedly increased by in vitro blockade of C5aR1 and this was associated with increased CD40 expression. Simultaneous blockade of C5aR1 and CD40L on C5aR1+ cDCs decreased T cell proliferation. Finally, pulsing with OVA-induced C5 production and its cleavage into C5a by both populations of CD11b+ cDCs. Thus, we propose a model in which allergen-induced autocrine C5a generation and subsequent C5aR1 activation in pulmonary CD11b+ cDCs promotes tolerance towards aeroallergens through downregulation of CD40.

Impaired Alloantigen Presenting Activity of Cord Blood Nucleated Cells.

Blood ◽  
2005 ◽  
Vol 106 (11) ◽  
pp. 2203-2203
Author(s):  
Sandeep Chunduri ◽  
Dolores Mahmud ◽  
Javaneh Abbasian ◽  
Damiano Rondelli
Keyword(s):  
T Cells ◽  
Stem Cell ◽  
T Cell ◽  
Cord Blood ◽  
Mononuclear Cells ◽  
Ex Vivo ◽  
Solid Organ Transplantation ◽  
T Cell Response ◽  
Solid Organ ◽  
Cd34 Cells

Abstract Transplantation of HLA-mismatched cord blood (CB) nucleated cells has limited risk of severe acute graft-versus-host disease and graft rejection. This may depend on naïve T cells not yet exposed to many antigens and on immature antigen-presenting cells (APC) not delivering appropriate signals to allogeneic T cells. In order to test the APC activity of human circulating CB cells in-vitro, we initially used irradiated CB mononuclear cells (MNC) or immunomagnetically selected CD34+ cells, CD133+ cells, or CD14+ monocytes to stimulate the proliferative response of incompatible blood T cells in mixed leukocyte culture (MLC). CB MNC failed to induce allogeneic T cell proliferation, while CD34+ and CD133+ progenitors or CD14+ monocytes induced potent T cell alloresponses. Nevertheless, since allogeneic T cell response was not restored after depletion of CD3+ cells in the CB, nor the add-back of irradiated CB MNC to CD34+ or CD14+ stimulators inhibited allo-T cells, a direct suppressive effect of CB MNC was excluded. Allogeneic peripheral blood cytotoxic T-lymphocyte (CTL) responses were not induced after 7 days of stimulation with irradiated CB MNC, although after 4 weekly rechallenges with CB MNC, on average a 23% lysis of antigen-specific CB PHA-blasts was observed at the highest effector:target ratio (50:1). To test the tolerogenic potential of CB MNC, T cells initially exposed to CB MNC were rechallenged in secondary MLC with CB MNC, or CD34+ cells, or monocyte-derived dendritic cells (Mo-DC) generated in liquid culture with GM-CSF and IL-4. Allogeneic T cells were still unresponsive upon rechallenge with CB MNC, but proliferated upon 3 days of restimulation with CD34+ cells or Mo-DC from the same CB. Surprisingly, the supernatant of these latter MLCs did inhibit completely a 3rd party MLC. Instead, the supernatant of blood T cells that had been activated by CB CD34+ cells or Mo-DC both in primary and secondary MLC did not. These results show an impaired allo-APC activity of CB MNC but not CB CD34+ cells, and suggest that T cells releasing immunosuppressive cytokines may be activated by CB MNC and then expanded by a second more potent stimulation with professional APC. This hypothesis could explain the sustained engraftment of HLA-mismatched CB stem cell transplants in humans. Based on these results, the in-vivo or ex-vivo downregulation of T cell alloreactivity induced by CB MNC will be tested in experimental models of stem cell, as well as solid organ transplantation.

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