scholarly journals Dendritic cells pulsed with protein antigens in vitro can prime antigen-specific, MHC-restricted T cells in situ.

1990 ◽  
Vol 172 (2) ◽  
pp. 631-640 ◽  
Author(s):  
K Inaba ◽  
J P Metlay ◽  
M T Crowley ◽  
R M Steinman
Keyword(s):  
T Cells ◽  
Dendritic Cells ◽  
T Cell Response ◽  
Foreign Protein ◽  
Protein Antigens ◽  
Mhc Molecules ◽  
Antigen Presenting ◽  
Vacuolar System

T cells recognize peptides that are bound to MHC molecules on the surface of different types of antigen-presenting cells (APC). Antigen presentation most often is studied using T cells that have undergone priming in situ, or cell lines that have been chronically stimulated in vitro. The use of primed cells provides sufficient numbers of antigen-reactive lymphocytes for experimental study. A more complete understanding of immunogenicity, however, requires that one develop systems for studying the onset of a T cell response from unprimed lymphocytes, especially in situ. Here it is shown that mouse T cells can be reliably primed in situ using dendritic cells as APC. The dendritic cells were isolated from spleen, pulsed with protein antigens, and then administered to naive mice. Antigen-responsive T cells developed in the draining lymphoid tissue, and these T cells only recognized protein when presented on cells bearing the same MHC products as the original priming dendritic cells. In contrast, little or no priming was seen if antigen-pulsed spleen cells or peritoneal cells were injected. Since very small amounts of the foreign protein were visualized within endocytic vacuoles of antigen-pulsed dendritic cells, it is suggested that dendritic cells have a small but relevant vacuolar system for presenting antigens over a several day period in situ.

scholarly journals Response of naive antigen-specific CD4+ T cells in vitro: characteristics and antigen-presenting cell requirements.

1992 ◽  
Vol 176 (5) ◽  
pp. 1431-1437 ◽  
Author(s):  
M Croft ◽  
D D Duncan ◽  
S L Swain
Keyword(s):  
T Cells ◽  
Dendritic Cells ◽  
T Cell ◽  
Cd4 T Cells ◽  
Cd4 Cells ◽  
Peptide Antigen ◽  
Naive T Cells ◽  
Naïve T Cells ◽  
Antigen Presenting

Because of the low frequency of T cells for any particular soluble protein antigen in unprimed animals, the requirements for naive T cell responses in specific antigens have not been clearly delineated and they have been difficult to study in vitro. We have taken advantage of mice transgenic for the V beta 3/V alpha 11 T cell receptor (TCR), which can recognize a peptide of cytochrome c presented by IEk. 85-90% of CD4+ T cells in these mice express the transgenic TCR, and we show that almost all such V beta 3/V alpha 11 receptor-positive cells have a phenotype characteristic of naive T cells, including expression of high levels of CD45RB, high levels of L-selectin (Mel-14), low levels of CD44 (Pgp-1), and secretion of interleukin 2 (IL-2) as the major cytokine. Naive T cells, separated on the basis of CD45RB high expression, gave vigorous responses (proliferation and IL-2 secretion) to peptide antigen presented in vitro by a mixed antigen-presenting cell population. At least 50% of the T cell population appeared to respond, as assessed by blast transformation, entry into G1, and expression of increased levels of CD44 by 24 h. Significant contributions to the response by contaminating memory CD4+ cells were ruled out by demonstrating that the majority of the CD45RB low, L-selectin low, CD44 high cells did not express the V beta 3/V alpha 11 TCR and responded poorly to antigen. We find that proliferation and IL-2 secretion of the naive CD4 cells is minimal when resting B cells present peptide antigen, and that both splenic and bone marrow-derived macrophages are weak stimulators. Naive T cells did respond well to high numbers of activated B cells. However, dendritic cells were the most potent stimulators of proliferation and IL-2 secretion at low cell numbers, and were far superior inducers of IL-2 at higher numbers. These studies establish that naive CD4 T cells can respond vigorously to soluble antigen and indicate that maximal stimulation can be achieved by presentation of antigen on dendritic cells. This model should prove very useful in further investigations of activation requirements and functional characteristics of naive helper T cells.

scholarly journals Development of Stable Chimeric IL-15 for Trans-Presentation by the Antigen Presenting Cells

2021 ◽  
Vol 12 ◽  
Author(s):  
Manoj Patidar ◽  
Naveen Yadav ◽  
Sarat K. Dalai
Keyword(s):  
T Cells ◽  
T Cell ◽  
Half Life ◽  
Therapeutic Potential ◽  
Chimeric Protein ◽  
Antigen Presenting Cells ◽  
T Cell Response ◽  
Antigen Presenting

IL-15 is one of the important biologics considered for vaccine adjuvant and treatment of cancer. However, a short half-life and poor bioavailability limit its therapeutic potential. Herein, we have structured IL-15 into a chimeric protein to improve its half-life enabling greater bioavailability for longer periods. We have covalently linked IL-15 with IgG2 base to make the IL-15 a stable chimeric protein, which also increased its serum half-life by 40 fold. The dimeric structure of this kind of IgG based biologics has greater stability, resistance to proteolytic cleavage, and less frequent dosing schedule with minimum dosage for achieving the desired response compared to that of their monomeric forms. The structured chimeric IL-15 naturally forms a dimer, and retains its affinity for binding to its receptor, IL-15Rβ. Moreover, with the focused action of the structured chimeric IL-15, antigen-presenting cells (APC) would transpresent chimeric IL-15 along with antigen to the T cell, that will help the generation of quantitatively and qualitatively better antigen-specific memory T cells. In vitro and in vivo studies demonstrate the biological activity of chimeric IL-15 with respect to its ability to induce IL-15 signaling and modulating CD8+ T cell response in favor of memory generation. Thus, a longer half-life, dimeric nature, and anticipated focused transpresentation by APCs to the T cells will make chimeric IL-15 a super-agonist for memory CD8+ T cell responses.

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 In-VitroDifferentiation of Mature Dendritic Cells From Human Blood Monocytes

1998 ◽  
Vol 6 (1-2) ◽  
pp. 25-39 ◽  
Author(s):  
Robert Gieseler ◽  
Dirk Heise ◽  
Afsaneh Soruri ◽  
Peter Schwartz ◽  
J. Hinrich Peters
Keyword(s):  
Dendritic Cells ◽  
Human Blood ◽  
T Cell Response ◽  
Blood Monocytes ◽  
Gm Csf ◽  
Hla Dr ◽  
Hla Dq ◽  
Specific Stimulation ◽  
Antigen Presenting

Representing the most potent antigen-presenting cells, dendritic cells (DC) can now be generated from human blood monocytes. We recently presented a novel protocol employing GM-CSF, IL-4, and IFN-γto differentiate monocyte-derived DCin vitro. Here, such cells are characterized in detail. Cells in culture exhibited both dendritic and veiled morphologies, the former being adherent and the latter suspended. Phenotypically, they were CD1a-/dim, CD11a+, CD11b++, CD11c+, CD14dim/-, CD16a-/dim, CD18+, CD32dim/-, CD33+, CD40+, CD45R0+, CD50+, CD54+, CD64-/dim, CD68+, CD71+, CD80dim, CD86+/++, MHC class I++/+++HLA-DR++/+++HLA-DP+, and HLA-DQ+. The DC stimulated a strong allogeneic T-cell response, and further evidence for their autologous antigen-specific stimulation is discussed. Although resembling a mature CD 11c+CD45R0+blood DC subset identified earlier, their differentiation in the presence of the Thl and Th2 cytokines IFN-γand IL-4 indicates that these DC may conform to mature mucosal DC.

Mycophenolate Acid Has a Negative Effect on the Maturation and Immune Function of the Murine Bone Marrow-Derived Dendritic Cells.

Blood ◽  
2004 ◽  
Vol 104 (11) ◽  
pp. 3808-3808
Author(s):  
Zhen Cai ◽  
Wenye Huang ◽  
Wenji Sun
Keyword(s):  
Bone Marrow ◽  
T Cells ◽  
Dendritic Cells ◽  
Immune Function ◽  
De Novo ◽  
Th2 Cytokines ◽  
Negative Effect ◽  
Antigen Presenting

Abstract Mycophenolate mofetil (MMF) is a newly developed immunosuppressor, currently widely used in allogeneic bone marrow transplantation. Its active metabolite, mycophenolic acid (MPA) is a noncompetitive, reversible inhibitor of the enzyme inosine 59-monophosphate dehydrogenase, which plays a major role in the de novo synthesis of guanosine nucleotides. Unlike other cells that also use the salvage pathway for purine biosynthesis, proliferating B and T cells are dependent on the de novo pathway generate guanosine. Thus, MMF exerts its immunosuppressive effects of lymphocyte proliferation. Recently, some studies found that MPA could inhibit the immun immune function of antigen presenting cells. Dendritic cells (DCs), the most potent antigen presenting cells with the unique ability to prime naive T cells, play a central role in antigen processing and presentation to induce T cell response in vitro and in vivo. This study is to evaluate the effects of MPA, the in vivo active metabolite of MMF, on the maturation and immune function of murine bone marrow-derived dendritic cells, and to explore the underlying mechanisms of MMF in graft versus host disease. Bone marrow-derived dendritic cells (DC) were cultured with GM-CSF and IL-4 in the presence of MPA at doses of 0.01 and 0.1μmol/L. The ability of the allostimulatory activities of the DCs on allogeneic T cells was assessed by MLR. IL-12 production in culture supernatant and the Th1/Th2 cytokines such as IL-2, IFN-g, IL-4 and IL-10 levels in mixed lymphocyte reaction (MLR) supernatant were examined by ELISA assays. The activity of NF-κB in DCs was measured with Western blot assays. Our results showed that DCs cultured in the presence of MPA expressed lower levels of CD40, CD80 and CD86, exhibited weaker activity of stimulating the allogeneic T cell proliferation and weaker in antigen presenting function with a concurrent reduction of IL-12 production. MPA-treated DCs stimulated allogeneic T cells to secrete higher levels of Th2 cytokines IL-4 and IL-10 but lower levels of Th1 cytokines IL-2 and IFN-g than did DCs not treated with MPA. The activity of NF-κB was decreased in DCs treated with MPA in a dose-dependent manner. We conclude that MPA, and hence MMF, exerts a negative effect on the maturation and immune function of in vitro cultured DCs, and drives a shift of Th1 cytokines to Th2 cytokines in MLR. This negative effect is associated with a decrease in NF-κB activity. Say something about the significance of this finding regarding GVHD.

scholarly journals Impairments of Antigen-Presenting Cells in Pulmonary Tuberculosis

2015 ◽  
Vol 2015 ◽  
pp. 1-14 ◽  
Author(s):  
Ludmila V. Sakhno ◽  
Ekaterina Ya. Shevela ◽  
Marina A. Tikhonova ◽  
Sergey D. Nikonov ◽  
Alexandr A. Ostanin ◽  
...  
Keyword(s):  
Dendritic Cells ◽  
Pulmonary Tuberculosis ◽  
Peripheral Blood ◽  
Antigen Presenting Cells ◽  
T Cell Response ◽  
Blood Monocytes ◽  
Peripheral Blood Monocytes ◽  
Gm Csf ◽  
Antigen Presenting

The phenotype and functional properties of antigen-presenting cells (APC), that is, circulating monocytes and generatedin vitromacrophages and dendritic cells, were investigated in the patients with pulmonary tuberculosis (TB) differing in lymphocyte reactivity toM. tuberculosisantigens (PPD-reactive versus PPD-anergic patients). We revealed the distinct impairments in patient APC functions. For example, the monocyte dysfunctions were displayed by low CD86 and HLA-DR expression, 2-fold increase in CD14+CD16+expression, the high numbers of IL-10-producing cells, and enhanced IL-10 and IL-6 production upon LPS-stimulation. The macrophages which werein vitrogenerated from peripheral blood monocytes under GM-CSF were characterized by Th1/Th2-balance shifting (downproduction of IFN-γcoupled with upproduction of IL-10) and by reducing of allostimulatory activity in mixed lymphocyte culture. The dendritic cells (generatedin vitrofrom peripheral blood monocytes upon GM-CSF + IFN-α) were characterized by impaired maturation/activation, a lower level of IFN-γproduction in conjunction with an enhanced capacity to produce IL-10 and IL-6, and a profound reduction of allostimulatory activity. The APC dysfunctions were found to be most prominent in PPD-anergic patients. The possible role of APC impairments in reducing the antigen-specific T-cell response toM. tuberculosiswas discussed.

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

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.

Regulation of alveolar macrophage-T cell interactions during Th1-type sarcoid inflammatory process

1999 ◽  
Vol 277 (2) ◽  
pp. L240-L250 ◽  
Author(s):  
Carlo Agostini ◽  
Livio Trentin ◽  
Alessandra Perin ◽  
Monica Facco ◽  
Marta Siviero ◽  
...  
Keyword(s):  
T Cells ◽  
T Cell ◽  
Costimulatory Molecules ◽  
T Cell Response ◽  
Accessory Function ◽  
B7 Family ◽  
Ifn Γ ◽  
Low Levels ◽  
Antigen Presenting

The accessory function of antigen-presenting cells depends on the presence of a number of costimulatory molecules, including members of the B7 family (CD80 and CD86) and the CD5 coligand CD72. The aim of this study was to evaluate the regulation of T cell-antigen-presenting cell costimulatory pathways in the lung of patients with a typical Th1-type reaction, i.e., sarcoidosis. Although normal alveolar macrophages (AMs) did not bear or bore low levels of costimulatory molecules, AMs from sarcoid patients with CD4 T-cell alveolitis upmodulated CD80, CD86, and CD72 and expressed high levels of interleukin (IL)-15; lymphocytes accounting for T-cell alveolitis expressed Th1-type cytokines [interferon (IFN)-γ and/or IL-2] and bore high levels of CD5 and CD28 but not of CD152 molecules. In vitro stimulation of AMs with Th1-related cytokines (IL-15 and IFN-γ) upregulated the expression of CD80 and CD86 molecules. However, stimulation with IL-15 induced the expression of Th1-type cytokines (IFN-γ) and CD28 on sarcoid T cells, suggesting a role for this macrophage-derived cytokine in the activation of the sarcoid T-cell pool. The hypothesis that CD80 and CD86 molecules regulate the sarcoid T-cell response was confirmed by the evidence that AMs induced a strong proliferation of T cells that was inhibited by pretreatment with CD80 and CD86 monoclonal antibodies. To account for these data, it is proposed that locally released cytokines provide AMs with accessory properties that contribute to the development of sarcoid T-cell alveolitis.

Transfection of Dendritic Cells with In Vitro Transcribed RNA Induces Polyclonal CMV-Specific CD8+ and CD4+ Mediated T Cell Responses.

Blood ◽  
2004 ◽  
Vol 104 (11) ◽  
pp. 1354-1354
Author(s):  
Annkristin Heine ◽  
Tobias Holderried ◽  
Frank Grünebach ◽  
Silke Appel ◽  
Markus M. Weck ◽  
...  
Keyword(s):  
T Cells ◽  
Dendritic Cells ◽  
T Cell ◽  
Cell Response ◽  
Cytotoxic T Cells ◽  
T Cell Responses ◽  
T Cell Response ◽  
Cell Responses ◽  
Rna Transfection

Abstract Transfection of dendritic cells (DC) with in vitro transcribed RNA was shown to be a highly efficient method to generate antigen specific T cells, probably due to the induction of a polyclonal T cell response directed against multiple antigens presented on different HLA allels. However, the experimental evidence of this assumption remains to be demonstrated. To accomplish this, we used monocyte derived DC that were electroporated with RNA coding for the CMV pp65 antigen. The induction and expansion of antigen specific CD8+ and CD4+ T cells was assessed using a pannel of peptides derived from this antigen and presented on HLA-A2, -A1, -A11, -A24, -B35 and -B7 in IFN-g ELISPOT, 51Cr-release and proliferation assays. Autologous DC generated from CMV positive healthy donors were pulsed with peptides or transfected with pp65 RNA and utilized as stimulators. Autologous purified CD8+ and CD4+ lymphocytes were used as effector cells. By applying this approach we found that transfection of DC with pp65 RNA induces an expansion of polyclonal CD8+ mediated T cell responses that recognized peptide antigens presented on different HLA molecules. These in vitro generated cytotoxic T cells were able to efficiently lyse DC pulsed with pp65 derived peptides or transfected with the cognate RNA in an antigen specific manner after several in vitro restimulations. Furthermore, this experimental approach allowed the identification of the immunodominace of T cell epitopes presented upon RNA transfection. The HLA-2 directed responses were more pronounced as compared to the HLA-A1, -A11, -A24 or -B35 allels. In contrast, in 7 out of 7 HLA-A2 and HLA-B7 positive donors B7-peptides elicited a stronger T cell response than the A2-peptide, indicating the immunodominance of HLA-B7 epitopes. Interestingly, transfection of DC with pp65 RNA resulted in the induction of CD4+ antigen specific T cells that produced IFN-g and proliferated upon stimulation with transfected DC. In the next set of experiments we analyzed the possible induction of CMV specific T cells that recognize epitopes deduced from different antigens. Co-transfection of DC with a mixture of RNAs coding for the CMV pp65 and IE1 antigens elicited polyclonal T lymphocytes specific for peptides derived from both antigens. More importantly, polyclonal cytotoxic T cells could be elicited in peripheral blood of 2 out of 3 CMV negative donors demonstrating the efficiency of this approach. Our results demonstrate that DC transfected with RNA can elicit polyclonal T cell responses and have implications for the development of immunotherapeutic strategies to target viral or tumor associated antigens.

Generation of Leukemia-Derived Dendritic Cells (DCleu) as a Basis for Specific Immunotherapy in Acute Myeloid Leukemia (AML) and Myelodysplastic Syndrome (MDS).

Blood ◽  
2004 ◽  
Vol 104 (11) ◽  
pp. 2547-2547
Author(s):  
Helga Schmetzer ◽  
Christoph Schmid ◽  
Susanne Kufner ◽  
Renate Pelka-Fleischer ◽  
Tanja Kroell ◽  
...  
Keyword(s):  
T Cells ◽  
Dendritic Cells ◽  
T Cell ◽  
Cell Response ◽  
T Cell Response ◽  
Aberrant Expression ◽  
Immune Phenotype ◽  
Cytogenetic Aberrations ◽  
Stimulation Of

Abstract The presentation of leukemic antigens can be improved in AML and MDS by in vitro generation of dendritic cells of leukemic origin (DCleu), thereby creating a platform for the generation of leukemia-specific cytotoxic lymphocytes (CTL). To further investigate this approach, we developed a serum-free culture system using MCM-Mimic medium (X-vivo + GM-GSF + IL-4 + FL + IL1β + IL-6 + TNFα + PGE2) for differentiation of malignant myeloid blasts to DCleu. Periperal blood mononuclear cells (PB-MNC) were obtained from 100 AML and 55 MDS-patients. Samples contained a mean of 59%/and 6% of blasts, respectively. After 14 days, cultures contained on average 34% (AML) and 20%(MDS) DC. DC yields were best in monocytic subtypes (AML M4, M5 and CMML). Cytogenetic aberrations of the leukemia had no influence. The leukemic origin of cultured DC was demonstrated using a acombined FISH/immune phenotyping assay (FISH/IPA): In cells showing a characteristic DC morphology and immune phenotype, FISH was used to detect specific cytogenetic aberrations identified in the leukemic population at time of diagnosis. Alternativly, DCleu were identified by detecting coexpression of DC markers and a leukemia-specific immune phenotype (as defined by aberrant expression of lineage markers or a characteristic CD34+/CD117+ phenotype in MDS). However, in most cases not all leukemic blasts in a given sample could be differentiated, since on average 47% of clonal cells did not acquire a DC-like immunophenotype. Vice versa, not all DC identified at the end of the culture period were DCleu. The capacity of DCleu to elicit a specific T-cell response was demonstrated by upregulation of contact-molecules, responsible for DC/T-cell contact, by DC-activated T-cell proliferation and by the capacity of DC-activated T-cells to specifically lyse naive blasts. In 6%/31% of AML/MDS-cases, <10% DC could be generated. Therefore, other DC-culture-assays were compared with respect to DC harvest, to identify the best method for DC-generation in each individual patient. Compared to `MCM-Mimic`, harvest of DC could be improved by `CA-Ionophore-media`(A23187 + Il4) in 4 of 7 cases, whereas in 3 cases, MCM led to higher DC-yields. In conclusion, DCleu can be generated in the majority of patients with AML and MDS. To optimize DC harvest for in vitro and in vivo use, different culture assays should be compared in each individual case. DCleu are able to elicit a specific T-cell response in vitro. Nevertheless, cultures containing DCleu also contain relevant numbers of undifferentiated blasts and DC of non-leukemic origin. These cells may represent an obstacle for the clinical use of DCleu, since they may cause specific anergy or unspecific stimulation of effector T-cells. Improvement of culture conditions for generation of DCleu, and methods to separate DCleu before stimulation of effector cells will be required, before clinical trials are feasible.

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