Miriam Fogli

Mobilization of Bone Marrow-Derived Hematopoietic and Endothelial Stem Cells After Orthotopic Liver Transplantation and Liver Resection

In animals, the bone marrow (BM) is a source of liver‐repopulating cells with therapeutic potential in case of tissue damage. However, the early response of human BM‐derived stem cells (SC) to liver injury is still unknown. Here, we studied 24 patients undergoing orthotopic liver transplantation (OLT) for end‐stage liver disease or hepatocellularcarcinoma, and 13 patients submitted to liver resection. The concentration of circulating BM‐derived SC was determined by phenotypic analysis and clonogenic assays. Moreover, we assessed the serum level of inflammatory and tissue‐specific cytokines. Reverse transcriptase‐polymerase chain reaction and fluorescence‐in situ hybridization were also used to characterize mobilized SC. At baseline, patients showed a significant lower concentration of circulating CD133+, CD34+ SC and clonogenic progenitors (colony‐forming unit cells) than healthy controls. However, the time‐course evaluation of peripheral blood cells after OLT demonstrated the significant early mobilization of multiple subsets of hematopoietic and endothelial stem/progenitor cells. Cytogenetic and molecular analyses of CD34+ cells showed the host origin of mobilized SC and the expression of transcripts for GATA‐4, cytokeratin 19, and α‐fetoprotein hepatocyte markers. In contrast with OLT, only total circulating CD34+ cells significantly increased after liver resection. Mobilization of BM cells after OLT or liver surgery was associated with increased serum levels of granulocyte‐colony stimulating factor, interleukin‐6, stem cell factor, hepatocyte growth factor, and vascular endothelial growth factor. In summary, we demonstrate that tissue damage after OLT and liver resection induces increased serum levels of multiple cytokines but only ischemia/reperfusion injury associated with OLT results in the remarkable mobilization of BM stem/progenitor cells.

In vitro anti-tumour activity of anti-CD80 and anti-CD86 immunotoxins containing type 1 ribosome-inactivating proteins

Immunotoxins specific for the CD80 and CD86 antigens were prepared by linking three type 1 ribosome‐inactivating proteins (RIPs), namely bouganin, gelonin and saporin‐S6, to the monoclonal antibodies M24 (anti‐CD80) and 1G10 (anti‐CD86). These immunotoxins showed a specific cytotoxicity for the CD80/CD86‐expressing cell lines Raji and L428. The immunotoxins inhibited protein synthesis by target cells with IC50s (concentration causing 50% inhibition) ranging from 0·25 to 192 pmol/l as RIPs. The anti‐CD80 immunotoxins appeared 1–2 log more toxic for target cells than the anti‐CD86 ones. Immunotoxins containing saporin and bouganin induced apoptosis of target cells. The toxicity for bone marrow haemopoietic progenitors of these conjugates was also evaluated. Bouganin and related immunotoxins at concentrations up to 100 nmol/l did not significantly affect the recovery of committed progenitors or of more primitive cells. The saporin‐containing immunotoxins at concentrations ≥ 1 nmol/l showed some toxicity on colony‐forming unit cells (CFU‐C). The expression of the CD80 and CD86 molecules is prevalently restricted to antigen‐presenting cells and is also strong on Hodgkin and Reed–Sternberg cells in Hodgkins disease. Present results suggest that immunotoxins targeting type 1 ribosome‐inactivating proteins to these antigens could be considered and further studied for the therapy of Hodgkins disease or other CD80/CD86‐expressing tumours.

Generation and functional characterization of human dendritic cells derived from CD34 ˛ cells mobilized into peripheral blood: comparison with bone marrow CD34 ˛ cells

Dendritic cells (DCs) are the most powerful professional antigen‐presenting cells (APC), specializing in capturing antigens and stimulating T‐cell‐dependent immunity. In this study we report the generation and characterization of functional DCs derived from both steady‐state bone marrow (BM) and circulating haemopoietic CD34+ cells from 14 individuals undergoing granulocyte colony‐stimulating factor (G‐CSF) treatment for peripheral blood stem cells (PBSC) mobilization and transplantation. Clonogenic assays in methylcellulose showed an increased frequency and proliferation of colony‐forming unit‐dendritic cells (CFU‐DC) in circulating CD34+ cells, compared to that of BM CD34+ precursors in response to GM‐CSF and TNF‐α with or without SCF and FLT‐3L. Moreover, peripheral blood (PB) CD34+ cells generated a significantly higher number of fully functional DCs, as determined by conventional mixed lymphocyte reactions (MLR), than their BM counterparts upon different culture conditions. DCs derived from mobilized stem cells were also capable of processing and presenting soluble antigens to autologous T cells for both primary and secondary immune response. Replacement of the early‐acting growth factors SCF and FLT‐3L with IL‐4 at day 7 of culture of PB CD34+ cells enhanced both the percentage of total CD1a+ cells and CD1a+CD14− cells and the yield of DCs after 14 d of incubation. In addition, the alloreactivity of IL‐4‐stimulated DCs was significantly higher than those generated in the absence of IL‐4. Furthermore, autologous serum collected during G‐CSF treatment was more efficient than fetal calf serum (FCS) or two different serum‐free media for large‐scale production of DCs. Thus, our comparative studies indicate that G‐CSF mobilizes CD34+ DC precursors into PB and circulating CD34+ cells represent the optimal source for the massive generation of DCs. The sequential use of early‐acting and intermediate‐late‐acting colony‐stimulating factors (CSFs) as well as the use of autologous serum greatly enhanced the growth of DCs. These data may provide new insights for manipulating immunocompetent cells for cancer therapy.

Stem Cell Factor and FLT3-Ligand Are Strictly Required to Sustain the Long-Term Expansion of Primitive CD34+DR− Dendritic Cell Precursors

We studied cytokine-driven differentiation of primitive human CD34+HLA-DR− cells to myeloid dendritic cells (DC). Hemopoietic cells were grown in long-term cultures in the presence of various combinations of early acting cytokines such as FLT3-ligand (FLT3-L) and stem cell factor (SCF) and the differentiating growth factors GM-CSF and TNF-α. Two weeks of incubation with GM-CSF and TNF-α generated fully functional DC. However, clonogenic assays demonstrated that CFU-DC did not survive beyond 1 wk in liquid culture regardless of whether FLT3-L and/or SCF were added. FLT3-L or SCF alone did not support DC maturation. However, the combination of the two early acting cytokines allowed a 100-fold expansion of CFU-DC for >1 month. Phenotypic analysis demonstrated the differentiation of CD34+DR− cells into CD34−CD33+DR+CD14+ cells, which were intermediate progenitors capable of differentiating into functionally active DC upon further incubation with GM-CSF and TNF-α. As expected, GM-CSF and TNF-α generated DC from committed CD34+DR+ cells. However, only SCF, with or without FLT3-L, induced the expansion of DC precursors for >4 wk, as documented by secondary clonogenic assays. This demonstrates that although GM-CSF and TNF-α do not require additional cytokines to generate DC from primitive human CD34+DR− progenitor cells, they do force terminal differentiation of DC precursors. Conversely, FLT3-L and SCF do not directly affect DC differentiation, but instead sustain the long-term expansion of CFU-DC, which can be induced to produce mature DC by GM-CSF and TNF-α.

Generation of dendritic cells from CD14+ monocytes positively selected by immunomagnetic adsorption for multiple myeloma patients enrolled in a clinical trial of anti‐idiotype vaccination

Summary. Circulating monocytes from multiple myeloma patients enrolled in a clinical study of anti‐idiotype vaccination were labelled with clinical‐grade anti‐CD14 microbeads and positively selected with the CliniMACS instrument. Cells were then grown, according to good manufacturing practice guidelines, in fetal‐calf‐serum‐free medium in cell culture bags and differentiated to dendritic cells (DC) with granulocyte–macrophage colony stimulating factor plus interleukin 4 (IL‐4), followed by either tumour necrosis factor‐α (TNF‐α) or a cocktail of IL‐1β, IL‐6, TNF‐α and prostaglandin‐E2. The CD14+ cell yield was increased from 17·6 ± 6·5% to 93·8 ± 6·3% (recovery 64·4 ± 15·4%, viability > 97%). After cell culture, phenotypic analysis showed that 86·7 ± 6·8% of the cells were DC: 2·27 ± 0·9 × 108 DC/leukapheresis were obtained, which represented 20·7 ± 4·6% of the initial number of CD14+ cells. Notably, the cytokine cocktail induced a significantly higher percentage and yield (28·6 ± 3% of initial CD14+ cells) of DC than TNF‐α alone, with secretion of larger amounts of IL‐12, potent stimulatory activity on allogeneic T cells and efficient presentation of tumour idiotype to autologous T cells. Storage in liquid nitrogen did not modify the phenotype or functional characteristics of preloaded DC. The recovery of thawed, viable DC was 78 ± 10%. Finally, interferon‐α‐2b was at least as efficient as IL‐4 in inducing the differentiation of mature, functional DC from monocytes.

Expression and functional role of c-kit ligand (SCF) in human multiple myeloma cells.

Summary. In this study we investigated the proliferation of three well‐documented MM lines and 10 bone marrow samples from myeloma patients in response to rh‐SCF alone and combined with Interleukin‐6 (IL‐6), IL‐3 and IL‐3/GMCSF fusion protein PIXY 321. Neoplastic plasma cells were highly purified (>90%) by immunomagnetic depletion of T, myeloid. monocytoid and NK cells. The number of S‐phase cells was evaluated after 3 and 7d of liquid culture by the bromodeoxyuridine (BRDU) incorporation assay. The proliferation of RPMI 8226 and U266 cell lines was also assessed by a clonogenic assay. All the experiments were performed in serum‐free conditions. RPMI 8226 cell line was not stimulated by SCF which also did not augment the proliferative activity of IL‐6, IL‐3 and PIXY‐321. Conversely, SCF addition resulted in 2.4‐fold increase of the number of U266 colonies and in a higher number of U266 and MT3 cells in S‐phase (24.5 ± 2% SEM v 14.5 ± 1% SEM and 32 ± 3% SEM v 21 ± 4% SEM, respectively; P < 0.05). The c‐kit ligand also enhanced the proliferation of MT3 and U266 cells mediated by the other cytokines. Anti‐SCF polyclonal antibodies completely abrogated the proliferative response of MT3 cells to exogenous SCF and markedly reduced the spontaneous growth of the same cell line. Reverse transcriptase‐polymerase chain reaction amplification (RT‐PCR) did detect SCF mRNA in MT3 and RPMI 8226 cells. Moreover, secreted SCF was found, in a biologically active form, in the supernatant of the two cell lines by the M07e proliferation assay.

The Kinetic Status of Hematopoietic Stem Cell Subpopulations Underlies a Differential Expression of Genes Involved in Self‐Renewal, Commitment, and Engraftment

The gene expression profile of CD34− hematopoietic stem cells (HSCs) and the correlations with their biological properties are still poorly understood. To address this issue, we used the DNA microarray technology to compare the expression profiles of different peripheral blood hemopoietic stem/progenitor cell subsets, lineage‐negative (Lin−) CD34−, Lin−CD34+, and Lin+CD34+ cells. The analysis of gene categories differentially expressed shows that the expression of CD34 is associated with cell cycle entry and metabolic activation, such as DNA, RNA, and protein synthesis. Moreover, the significant upregulation in CD34− cells of pathways inhibiting HSC proliferation induces a strong differential expression of cyclins, cyclin‐dependent kinases (CDKs), CDK inhibitors, and growth‐arrest genes. According to the expression of their receptors and transducers, interleukin (IL)‐10 and IL‐17 showed an inhibitory effect on the clonogenic activity of CD34− cells. Conversely, CD34+ cells were sensitive to the mitogenic stimulus of thrombopoietin. Furthermore, CD34− cells express preferentially genes related to neural, epithelial, and muscle differentiation. The analysis of transcription factor expression shows that the CD34 induction results in the upregulation of genes related to self‐renewal and lineage commitment. The preferential expression in CD34+ cells of genes supporting the HSC mobilization and homing to the bone marrow, such as chemokine receptors and integrins, gives the molecular basis for the higher engraftment capacity of CD34+ cells. Thus, the different kinetic status of CD34− and CD34+ cells, detailed by molecular and functional analysis, significantly influences their biological behavior.

Molecular and functional analysis of the stem cell compartment of chronic myelogenous leukemia reveals the presence of a CD34- cell population with intrinsic resistance to imatinib

We show the molecular and functional characterization of a novel population of lineage-negative CD34-negative (Lin(-)CD34(-)) hematopoietic stem cells from chronic myelogenous leukemia (CML) patients at diagnosis. Molecular karyotyping and quantitative analysis of BCR-ABL transcript demonstrated that approximately one-third of CD34(-) cells are leukemic. CML Lin(-)CD34(-) cells showed kinetic quiescence and limited clonogenic capacity. However, stroma-dependent cultures induced CD34 expression on some cells and cell cycling, and increased clonogenic activity and expression of BCR-ABL transcript. Lin(-)CD34(-) cells showed hematopoietic cell engraftment rate in 2 immunodeficient mouse strains similar to Lin-CD34(+) cells, whereas endothelial cell engraftment was significantly higher. Gene expression profiling revealed the down-regulation of cell-cycle arrest genes and genes involved in antigen presentation and processing, while the expression of genes related to tumor progression, such as angiogenic factors, was strongly up-regulated compared with normal counterparts. Phenotypic analysis confirmed the significant down-regulation of HLA class I and II molecules in CML Lin(-)CD34(-) cells. Imatinib mesylate did not reduce fusion transcript levels, BCR-ABL kinase activity, and clonogenic efficiency of CML Lin(-)CD34(-) cells in vitro. Moreover, leukemic CD34(-) cells survived exposure to BCR-ABL inhibitors in vivo. Thus, we identified a novel CD34(-) leukemic stem cell subset in CML with peculiar molecular and functional characteristics.

Efficient presentation of tumor idiotype to autologous T cells by CD83(+) dendritic cells derived from highly purified circulating CD14(+) monocytes in multiple myeloma patients.

To generate mature and fully functional CD83(+) dendritic cells derived from circulating CD14(+) cells highly purified from the leukapheresis products of multiple myeloma patients.CD14(+) monocytes were selected by high-gradient magnetic separation and differentiated to immature dendritic cells with granulocyte-macrophage colony-stimulating factor and interleukin-4 for 6-7 days and then induced to terminal maturation by the addition of tumor necrosis factor-alpha or stimulation with CD40 ligand. Dendritic cells were characterized by immunophenotyping, evaluation of soluble antigens uptake, cytokine secretion, capacity of stimulating allogeneic T cells, and ability of presenting nominal antigens, including tumor idiotype, to autologous T lymphocytes. Phenotypic analysis showed that 90% +/- 6% of cells recovered after granulocyte-macrophage colony-stimulating factor and interleukin-4 stimulation expressed all surface markers typical of immature dendritic cells and demonstrated a high capacity of uptaking soluble antigens as shown by the FITC-dextran assay. Subsequent exposure to maturation stimuli induced the downregulation of CD1a and upregulation of CD83, HLA-DR, costimulatory molecules and induced the secretion of large amounts of interleukin-12. Mature CD83(+) cells showed a diminished ability of antigen uptake whereas they proved to be potent stimulators of allogeneic T cells in a mixed lymphocyte reaction. Monocyte-derived dendritic cells, pulsed before the addition of maturation stimuli, were capable of presenting soluble proteins such as keyhole limpet hemocyanin and tetanus toxoid to autologous T cells for primary and secondary immune response, respectively. Conversely, pulsing of mature (CD83(+)) dendritic cells was less efficient for the induction of T-cell proliferation. More importantly, CD14(+) cells-derived dendritic cells stimulated autologous T-cell proliferation in response to a tumor antigen such as the patient-specific idiotype. Moreover, idiotype-pulsed dendritic cells induced the secretion of interleukin-2 and gamma-interferon by purified CD4(+) cells. T-cell activation was better achieved when Fab immunoglobulin fragments were used as compared with the whole protein. When dendritic cells derived from CD14(+) cells from healthy volunteers were analyzed, we did not find any difference with samples from myeloma patients as for cell yield, phenotypic profile, and functional characteristics. These studies demonstrate that mobilized purified CD14(+) cells represent the optimal source for the production of a homogeneous cell population of mature CD83(+) dendritic cells suitable for clinical trials in multiple myeloma.

THROMBOPOIETIN AND INTERLEUKIN 11 HAVE DIFFERENT MODULATORY EFFECTS ON CELL CYCLE AND PROGRAMMED CELL DEATH IN PRIMARY ACUTE MYELOID LEUKEMIA CELLS

The c-mpl ligand, thrombopoietin (TPO), is a physiologic regulator of platelet and megakaryocytic production, acting synergistically on thrombopoiesis with the growth factors interleukin 11 (IL-11), stem cell factor, interleukin 3 (IL-3), interleukin 6 (IL-6), and granulocyte-macrophage colony-stimulating factor. Because some of these growth factors, especially TPO and IL-11, are now being evaluated clinically to reduce chemotherapy-associated thrombocytopenia in cancer patients, we evaluated 25 acute myeloid leukemia (AML) samples to test whether TPO, IL-11, and other early-acting megakaryocyte growth factors can affect leukemic cell proliferation, cell cycle activation, and programmed cell death (PCD) protection. TPO induced proliferation in the majority of AML samples from an overall mean proportion of S-phase cells of 7.8% +/-1.5% to 14.5% +/- 2.1% (p = 0.0006). Concurrent G0 cell depletion was found in 47.3% of AML samples. TPO-supported leukemic cell precursor (CFU-L) proliferation was reported in 5 of 17 (29.4%) of the samples with a mean colony number of 21.4 +/- 9.6 x 10(5) cells plated. In 13 of 19 samples, a significant protection from PCD (from an overall mean value of 13% +/-0.7% to 8.8% +/- 1.8%;p = 0.05) was detected after TPO exposure. Conversely, IL-11-induced cell cycle changes (recruitment from G0 to S phase) were detected in only 2 of 14 samples (14.2%). In addition, IL-11 showed little, if any, effect on CFU-L growth (mean colony number = 17.5 9.5) or apoptosis. Combination of TPO with IL-11 resulted in only a slight increase in the number of CFU-L, whereas IL-3 and stem cell factor significantly raised the mean colony numbers up to 119.2 +/- 68.3 and 52.9 +/- 22.1 x 10(5) cells plated, respectively. We conclude that TPO induces cell cycle activation in a significant proportion of cases and generally protects the majority of AML blast cells from PCD. On the other hand, IL-11 has little effect on the cell cycle or PCD. Combination of both TPO and IL-11 is rarely synergistic in stimulating AML clonogenic growth. These findings may be useful for designing clinical studies aimed at reducing chemotherapy-associated thrombocytopenia in AML patients.