Human Hematopoietic Stem Cell Transplantation Research Articles

G-CSF Stem Cell Mobilization Is Protective Against Acute Graft-Versus-Host Disease (aGvHD) by Increasing Myeloid-Derived Suppressor Cell (MDSC) Frequencies

AbstractAbstract 1898 Background:In mice, graft-versus-host disease (GvHD) can be abrogated by ex vivo expanded, bone marrow derived myeloid-derived suppressor cells (MDSCs) generated in the presence of GM-CSF, G-CSF and IL-13 (Highfill et al). Whether MDSCs play a role in human allogeneic hematopoietic stem cell transplantation (allo-HSCT) is still unclear. We hypothesized that G-CSF stem cell mobilization may be protective from acute GvHD (aGvHD) by increasing MDSC frequencies. Methods:G-CSF-mobilized peripheral blood (PB) samples were collected from 40 healthy unrelated donors (median age 34, range 20–43, male/female 31/9) who received G-CSF (Filgrastim) at 10 μg/kg/day for 5 days. Donor selection had been performed according to standard criteria, including molecular typing for HLA-A,-B,-C, DRB1, and DQB1. Donors were 10/10 HLA-matched (MUD) in 20 cases, 9/10 in 13 cases and 8/10 in the remaining 7 cases (MMUD). Patients (median age 46, range 18–67) received reduced intensity conditioning based or low-dose total body irradiation (TBI 2Gy) (8), Fludarabine-Rabbit Antithymocyte Globulin (ATG) (9) or Thiotepa-ATG (23). Diagnosis were lymphomas (29), myelomas (8), acute myeloid leukemia (3). GvHD prophylaxis was cyclosporine plus either methotrexate (36) or mycophenolate mofetil (4). As controls, PB samples were collected from 10 healthy adults. Informed consent was obtained from all subjects. Cells were characterized using flow cytometry with Abs against CD3;CD14;CD16;CD19;CD20;CD56;CD11b;HLADR;CD33. The frequencies of MDSCs and T regulatory cells (Tregs, CD4+CD25+CD127-FoxP3+) in the grafts were correlated with the clinical characteristics and outcome of the 40 patients. To verify that G-CSF treatment increases the number of MDSCs that are transferred with the graft and prevent GvHD, a major histocompatibility complex (MHC) mismatched HSCT mouse model was also used. After lethal irradiation, recipient BALB/c mice received spleen and bone marrow (BM) cells from C57BL/6 (B6) donors (GvHD cohort, n=5) or BM cells only (negative control, n=3). To generate MDSC enriched allografts, donor mice were treated with G-CSF (5 μg/d for 5 days) and thereafter BM cells and spleen cells were transferred in recipient mice (MDSC cohort, n=5). Results:Expansion of MDSCs (Lin-/LoHLADR−CD33+CD11b+) in the PB of G-CSF-treated unrelated donors was found with respect to steady state control individuals (p< 0.03, Mann Whitney-U). Acute GvHD occurred in 16 of 40 patients (40%). There was no significant correlation between the incidence of aGvHD and the degree of HLA incompatibility or the presence of donor-recipient sex mismatches. Neither the conditioning regimens nor the GvHD prophylaxis had effect on risk of aGvHD. There was no correlation between the number of Tregs infused and the occurrence of GvHD.Conversely, aGvHD patients received grafts containing significantly lower number of MDSCs when compared to non- aGvHD patients (p < 0.006, Mann Whitney-U). The ability of MDSC levels in the graft to predict the occurrence of aGvHD was determined by the receiver operating characteristic (ROC) curve: sensitivity was 100%, specificity 60%, AUC=0.768. The immunosuppressive activity of the MDSCs on activated T lymphocytes was confirmed in vitro. To confirm these results, we set up a MHC mismatched HSCT mouse model. G-CSF treatment induced a significant increase in MDSCs (up to four fold, p<0.05) whereas the frequencies of CD34+ and CD3+ cells were not affected. The MDSC-enriched BM cells transferred into lethally irradiated recipient mice together with spleen cells, resulted in a less severe aGvHD as confirmed by monitoring the clinical signs of GvHD (weight loss, generalized erythema of the skin, poor fur quality and overall survival) compared to the GvHD cohort not receiving G-CSF. Conclusions:G-CSF mobilization significantly increases circulating MDSC both in Matched Unrelated Donors and in mice. In humans, a significant correlation between the frequencies of MDSC present in the graft and the incidence of aGvHD was found. This result was further confirmed using a MHC mismatched HSCT mouse model. Mice treated with G-CSF received grafts containing higher numbers of MDSCs and developed less severe aGvHD than the untreated mice. Taken together, these findings strongly suggest that G-CSF stem cell mobilization is protective against aGvHD through MDSCs augmentation and might be relevant to modify GvHD prophylaxis. Disclosures:No relevant conflicts of interest to declare.

Efficient control of pandemic 2009 H1N1 virus infection with intravenous zanamivir despite the lack of immune function

A teenager who acquired 2009 H1N1 influenza A lower respiratory tract infection during total bone marrow and lymphoid aplasia, in the setting of human leukocyte antigen-haploidentical hematopoietic stem cell transplantation, was successfully treated with intravenous zanamivir. This case demonstrates efficient control of pandemic influenza infection by intravenous zanamivir in the absence of any functional immune system, thus suggesting profound antiviral activity.

Early posttransplantation donor-derived invariant natural killer T-cell recovery predicts the occurrence of acute graft-versus-host disease and overall survival

AbstractInvariant natural killer T (iNKT) cells can experimentally dissociate GVL from graft-versus-host-disease (GVHD). Their role in human conventional allogeneic hematopoietic stem cell transplantation (HSCT) is unknown. Here, we analyzed the post-HSCT recovery of iNKT cells in 71 adult allografted patients. Results were compared with conventional T- and NK-cell recovery and correlated to the occurrence of GVHD, relapse, and survival. We observed that posttransplantation iNKT cells, likely of donor origin, recovered independently of T and NK cells in the first 90 days after HSCT and reached greater levels in recipient younger than 45 years (P = .003) and after a reduced-intensity conditioning regimen (P = .03). Low posttransplantation iNKT/T ratios (ie, < 10−3) were an independent factor associated with the occurrence of acute GVHD (aGVHD; P = .001). Inversely, reaching iNKT/T ratios > 10−3 before day 90 was associated with reduced nonrelapse mortality (P = .009) without increased risk of relapse and appeared as an independent predictive factor of an improved overall survival (P = .028). Furthermore, an iNKT/T ratio on day 15 > 0.58 × 10−3 was associated with a 94% risk reduction of aGVHD. These findings provide a proof of concept that early postallogeneic HSCT iNKT cell recovery can predict the occurrence of aGVHD and an improved overall survival.

Osteosclerosis and inhibition of human hematopoiesis in NOG mice expressing human Delta-like 1 in osteoblasts

NOD/Shi-scid IL2rγnull (NOG) mice with severe immunodeficiency are excellent recipients to generate "humanized" mice by the transplantation of human CD34(+) hematopoietic stem cells (HSCs). In this study, we developed NOG mice carrying a human Delta-like1 (DLL1) gene, which is a ligand of the Notch receptor and is known to be important in HSC maintenance and self-renewal. We also analyzed the effect of DLL1 signaling on human hematopoiesis and HSC maintenance using humanized DLL1 transgenic NOG mice. To develop DLL1 transgenic NOG (NOG-D1-Tg) mice, a transgenic vector consisting of a human DLL1 complementary DNA fragment placed downstream of the α1(I) collagen (Col1a1) promoter for expression specifically in osteoblasts was constructed. Human CD34(+) HSCs were transplanted into NOG-D1-Tg mice, and differentiation of lymphoid or myeloid lineage cells from human HSCs and maintenance of HSCs in bone marrow were analyzed. Severe osteosclerosis accompanied by increased bone mass and a decreased number of bone marrow cells were observed in NOG-D1-Tg mice. After human HSC transplantation, development of human B lymphocytes, but not T lymphocytes, was significantly suppressed in both bone marrow and the periphery of NOG-D1-Tg mice. Contrary to the initial expectation, retention of human CD34(+) HSCs was inhibited in the bone marrow of NOG-D1-Tg mice. In conclusion, our data suggest that the development of human B lymphocytes and HSC maintenance in osteosclerotic bone may be suppressed by introducing DLL1. These unique humanized mice with sclerotic bone reconstituted by human HSCs are useful models of hematopoiesis in patients with osteosclerosis, such as osteopetrosis, and for investigation of osteogenesis via Notch signaling.

Gene Therapy for Primary Immunodeficiencies

For over 40 years, primary immunodeficiencies (PIDs) have featured prominently in the development and refinement of human allogeneic hematopoietic stem cell transplantation. More recently, ex vivo somatic gene therapy using autologous cells has provided remarkable evidence of clinical efficacy in patients without HLA-matched stem cell donors and in whom toxicity of allogeneic procedures is likely to be high. Together with improved preclinical models, a wealth of information has accumulated that has allowed development of safer, more sophisticated technologies and protocols that are applicable to a much broader range of diseases. In this review we summarize the status of these gene therapy trials and discuss the emerging application of similar strategies to other PIDs.

Extensive Gingival and Respiratory Tract Kaposi Sarcoma in a Child After Allogenic Hematopoietic Stem Cell Transplantation

An 8-year-old, human immune virus-negative boy received full human leukocyte antigen-matched related allogenic hematopoietic stem cell transplantation (HSCT) for relapsed acute myeloid leukemia. While on cyclosporine A and prednisolone therapy for graft versus host disease, he developed extensive gingival, cutaneous, and respiratory tract human herpes virus-8-associated Kaposi sarcoma (KS). Withdrawal of cyclosporine, tapering of prednisolone, recovery of lymphocyte count, and local supportive measures resulted in resolution of his gingival and respiratory tract lesions. To our knowledge this is the first case of gingival and extensive respiratory tract KS to be reported in a child post HSCT.

Current advances in humanized mouse models

Humanized mouse models that have received human cells or tissue transplants are extremely useful in basic and applied human disease research. Highly immunodeficient mice, which do not reject xenografts and support cell and tissue differentiation and growth, are indispensable for generating additional appropriate models. Since the early 2000s, a series of immunodeficient mice appropriate for generating humanized mice has been successively developed by introducing the IL-2Rγ(null) gene (e.g., NOD/SCID/γc(null) and Rag2(null)γc(null) mice). These strains show not only a high rate of human cell engraftment, but also generate well-differentiated multilineage human hematopoietic cells after human hematopoietic stem cell (HSC) transplantation. These humanized mice facilitate the analysis of human hematology and immunology in vivo. However, human hematopoietic cells developed from HSCs are not always phenotypically and functionally identical to those in humans. More recently, a new series of immunodeficient mice compensates for these disadvantages. These mice were generated by genetically introducing human cytokine genes into NOD/SCID/γc(null) and Rag2(null)γc(null) mice. In this review, we describe the current knowledge of human hematopoietic cells developed in these mice. Various human disease mouse models using these humanized mice are summarized.

Maternal administration of busulfan before in utero transplantation of human hematopoietic stem cells enhances engraftments in sheep

In utero transplantation (IUT) of human hematopoietic stem cells has been conducted in sheep, which are used as large animal models of human hematopoietic reconstitution and models for clinical IUT; however, the levels of engraftment have generally been low. Busulfan (BU), a myeloablative agent, is often administered to patients before hematopoietic stem cells transplantation to improve the engraftment. In this study, hematopoietic activity was evaluated in adult sheep after administering BU at different doses. Next, pregnant ewes were administered BU, and dams as well as their fetuses were evaluated, as BU readily crosses the sheep placenta. Then, the BU dose with the desired outcomes was selected and administered to pregnant ewes at 2 or 6 days before performing IUT using human cord blood CD34(+) cells. The engraftment was evaluated in recipients that underwent IUT in the presence or absence of BU. As a result, hematopoietic activity was safely and transiently suppressed in adult sheep treated with 5 to 7.5 mg/kg BU. BU crossed the sheep placenta, and fetal sheep were indeed conditioned by administering 3 mg/kg BU to pregnant ewes. Engraftment of human CD34(+) cells in fetal recipients was enhanced when IUT was carried out 6 days post-BU. Up to 3.3% engraftment levels (in terms of bone marrow colony-forming units) were achieved with the IUT of 0.72 to 2.4 million CD34(+) cells when BU was used. BU can be administered to pregnant ewes to effectively condition the fetal recipient for IUT with enhanced engraftment of donor cells.

Intrahepatic transplantation of CD34+ cord blood stem cells into newborn and adult NOD/SCID mice induce differential organ engraftment

In vivo studies concerning the function of human hematopoietic stem cells (HSC) are limited by relatively low levels of engraftment and the failure of the engrafted HSC preparations to differentiate into functional immune cells after systemic application. In the present paper we describe the effect of intrahepatically transplanted CD34+ cells from cord blood into the liver of newborn or adult NOD/SCID mice on organ engraftment and differentiation.Analyzing the short and long term time dependency of human cell recruitment into mouse organs after cell transplantation in the liver of newborn and adult NOD/SCID mice by RT-PCR and FACS analysis, a significantly high engraftment was found after transplantation into liver of newborn NOD/SCID mice compared to adult mice, with the highest level of 35% human cells in bone marrow and 4.9% human cells in spleen at day 70. These human cells showed CD19 B-cell, CD34 and CD38 hematopoietic and CD33 myeloid cell differentiation, but lacked any T-cell differentiation. HSC transplantation into liver of adult NOD/SCID mice resulted in minor recruitment of human cells from mouse liver to other mouse organs. The results indicate the usefulness of the intrahepatic application route into the liver of newborn NOD/SCID mice for the investigation of hematopoietic differentiation potential of CD34+ cord blood stem cell preparations.

Human peripheral blood CD4 T cell-engrafted non-obese diabetic-scid IL2rγnull H2-Ab1 tm1GruTg (human leucocyte antigen D-related 4) mice: a mouse model of human allogeneic graft-versus-host disease

Graft-versus-host disease (GVHD) is a life-threatening complication of human allogeneic haematopoietic stem cell transplantation. Non-obese diabetic (NOD)-scid IL2rγ(null) (NSG) mice injected with human peripheral blood mononuclear cells (PBMC) engraft at high levels and develop a robust xenogeneic (xeno)-GVHD, which reproduces many aspects of the clinical disease. Here we show that enriched and purified human CD4 T cells engraft readily in NSG mice and mediate xeno-GVHD, although with slower kinetics compared to injection of whole PBMC. Moreover, purified human CD4 T cells engraft but do not induce a GVHD in NSG mice that lack murine MHC class II (NSG-H2-Ab1(tm1Gru), NSG-Ab°), demonstrating the importance of murine major histocompatibility complex (MHC) class II in the CD4-mediated xeno-response. Injection of purified human CD4 T cells from a DR4-negative donor into a newly developed NSG mouse strain that expresses human leucocyte antigen D-related 4 (HLA-DR4) but not murine class II (NSG-Ab° DR4) induces an allogeneic GVHD characterized by weight loss, fur loss, infiltration of human cells in skin, lung and liver and a high level of mortality. The ability of human CD4 T cells to mediate an allo-GVHD in NSG-Ab° DR4 mice suggests that this model will be useful to investigate acute allo-GVHD pathogenesis and to evaluate human specific therapies.

Accumulation of oxidative DNA damage restricts the self-renewal capacity of human hematopoietic stem cells

AbstractStem cells of highly regenerative organs including blood are susceptible to endogenous DNA damage caused by both intrinsic and extrinsic stress. Response mechanisms to such stress equipped in hematopoietic stem cells (HSCs) are crucial in sustaining hematopoietic homeostasis but remain largely unknown. In this study, we demonstrate that serial transplantation of human HSCs into immunodeficient mice triggers replication stress that induces incremental elevation of intracellular reactive oxygen species (ROS) levels and the accumulation of persistent DNA damage within the human HSCs. This accumulation of DNA damage is also detected in HSCs of clinical HSC transplant patients and elderly individuals. A forced increase of intracellular levels of ROS by treatment with a glutathione synthetase inhibitor aggravates the extent of DNA damage, resulting in the functional impairment of HSCs in vivo. The oxidative DNA damage activates the expression of cell-cycle inhibitors in a HSC specific manner, leading to the premature senescence among HSCs, and ultimately to the loss of stem cell function. Importantly, treatment with an antioxidant can antagonize the oxidative DNA damage and eventual HSC dysfunction. The study reveals that ROS play a causative role for DNA damage and the regulation of ROS have a major influence on human HSC aging.

Ex Vivo Expanded Hematopoietic Stem Cells Overcome the MHC Barrier in Allogeneic Transplantation

The lack of understanding of the interplay between hematopoietic stem cells (HSCs) and the immune system has severely hampered the stem cell research and practice of transplantation. Major problems for allogeneic transplantation include low levels of donor engraftment and high risks of graft-versus-host disease (GVHD). Transplantation of purified allogeneic HSCs diminishes the risk of GVHD but results in decreased engraftment. Here we show that exvivo expanded mouse HSCs efficiently overcame the major histocompatibility complex barrier and repopulated allogeneic-recipient mice. An 8-day expansion culture led to a 40-fold increase of the allograft ability of HSCs. Both increased numbers of HSCs and culture-induced elevation of expression of the immune inhibitor CD274 (B7-H1 or PD-L1) on the surface of HSCs contributed to the enhancement. Our study indicates the great potential of utilizing exvivo expanded HSCs for allogeneic transplantation and suggests that the immune privilege of HSCs can be modulated.

Growth Factor Independence 1 b (Gfi1b) as a New Regulator of Hematopoietic Stem Cell Fate

AbstractAbstract 837Donor matched transplantation of bone marrow or hematopoietic stem cells (HSCs) are widely used to treat hematological malignancies, but are associated with high mortality. Methods for expansion of HSC numbers and their mobilization into the bloodstream of a donor could significantly improve therapy. We show here that the zinc finger transcriptional repressor Gfi1b is highly expressed in hematopoietic stem cells (defined as CD 150+, CD 48-, Lin-, Sca1+ and c-kit+) cells and is down-regulated more than 10 fold upon differentiation into multipotential progenitors (defined as CD 150+ or CD150-, CD 48+, Lin-, Sca1+ and c-kit+). Constitutive germline deletion of Gfi1b is lethal at midgestation due to impaired development of erythrocytes and megakaryocytes. We have therefore developed a conditional knock-out of Gfi1b to study its role specifically in the adult hematopoietic system. Deletion of Gfi1b leads to a 30-fold increase of HSC numbers in bone marrow and around a100 fold increase in spleen and peripheral blood. This was due to a higher rate of HSCs undergoing cell cycling. Concomitantly, the number of quiescent HSCs was reduced 5–6 times.We then performed an gene expression array of wt and Gfi1b deficient HSCs and observed that loss of Gfi1b leads to an altered RNA expression of integrins and adhesion molecules, for instance CXCR4, VCAM-1 and Tenascin C, which usually retain HSCs in a dormant state in the endosteal niche. These changes were also confirmed on protein level. Finally, we could observe a higher levels of Reactive Oxygen Species (ROS) in the Gfi1b deficient HSCs compared to wt HSCs. We verified whether elevated level of ROS are causative for the expansion of HSCs and noticed that application of N-Acetyl-Cystein, which counteracts the effects of ROS, limits significantly the expansion of HSCs, underscoring the important role of ROS in the expansion of Gfi1b deficient HSCs. Despite markedly increased proliferation, Gfi1b-/- HSCs can reconstitute lymphoid and myeloid lineages to the same extent as wt HSCs when transplanted in competition with wt HSCs. Furthermore, Gfi1b deficient HSCs also feature an expansion after transplantation and expand 5–10 fold more than wt HSC when transplanted initially in equal numbers with wt HSCs. It is possible that lower expression of CXCR4, VCAM-1 and other surface proteins leads to release and egression of Gfi1b deficient HSCs from the hypoxic endosteal stem cell niche and exposes the HSCs to more oxygen which in turn increases ROS levels. Elevated ROS could promote entry of Gfi1b-/- HSCs into cell cycle. In conclusion Gfi1b regulates HSC dormancy, pool size and potentially also the egress and mobilization of HSCs and might offer a new therapeutic approach to improve human HSC transplantation. Disclosures:No relevant conflicts of interest to declare.

CD26 expression in donor stem cell harvest and its correlation with engraftment in human haematopoietic stem cell transplantation: Potential predictor of early engraftment.

6544 Background: The efficiency of Haematopoietic stem and progenitor cells (HSPC) is important when donor cell numbers are limiting. This study evaluates CD26/dipeptidylpeptidase IV expression on ...

CD26 expression in donor stem cell harvest and its correlation with engraftment in human haematopoietic stem cell transplantation: potential predictor of early engraftment

BackgroundThe efficiency of haematopoietic stem and progenitor cells (HSPCs) is important when donor cell numbers are limiting. Stable white blood cell (WBC) and platelet engraftment is crucial for the outcome of haematopoietic stem cell transplantation (HSCT). DesignThis article evaluates CD26/dipeptidyl peptidase-IV expression on mobilised peripheral blood stem cell (PBSC) harvest of donors and its correlation with engraftment in HSCT. We have analysed CD26 expression on cells in various gates, that is, lymphocytes, monocytes, neutrophils and all populations using flow cytometry tool. ResultsOurs is the first study on human mobilised PBSC harvest from cancer patients or allogeneic related donors (n = 28) to demonstrate that increased CD26 expression leads to early engraftment in transplanted cancer patients. Correlation of CD26 expression with WBC engraftment was statistically significant (lymphocyte gate: P < 0.00001; monocyte gate: P < 0.00001; neutrophil gate: P < 0.00001; all populations: P < 0.00001). CD34 expression is a known predictor of engraftment. Nevertheless, there was no correlation between CD34 and CD26 expression in these cases. ConclusionsThis study has given important leads indicating that CD26 expression may be an independent predictor of engraftment. Further study with large number of patients as well as study on circulatory CD26 may add valuable information towards improving current knowledge on CD26.

Irradiated Third Party Peripheral Blood Mononuclear Cells Enhance Umbilical Cord Blood Engraftment.

Abstract 3533Poster Board III-470Umbilical Cord Blood (UCB) is a readily available, alternate donor source for allogeneic Hematopoietic Stem Cell (HSC) transplantation and can be used with lower stringency HLA-matching between donor and host. However, only limited numbers of cells are available and non-engraftment or delayed engraftment occurs often when recipients receive single UCB units that contain < 2.5 × 107 TNC/kg recipient body weight. This excludes single UCB as a donor source for many adult patients who might otherwise benefit from an UCB transplant. Both immunologic and non-immunologic mechanisms may contribute to UCB HSC engraftment failure. UCB T-cells are phenotypically and functionally immature with a high percentage of CD45RA+ T cells and T cells are known to facilitate engraftment in human HSC transplantation. Co-transplantation of irradiated T-cells supported engraftment in an immunocompetent mouse transplant model without increasing GvHD (Waller et al. Blood94: 3222,1999).The working hypothesis for his study is that the irradiated third party peripheral blood mononuclear cells (PBMNCs) induce a cytokine or cellular response that facilitates hematopoietic engraftment. Long-term culture initiating cell (LTC-IC) frequencies determined with limiting dilution assays were statistically higher when either purified UCB derived CD34+ cells or CB MNCs cells were plated with irradiated PBMNCs (Figure 1). [Display omitted] To assess the impact of irradiated third party PBMCs on UCB engraftment we utilized sub-lethally irradiated NOD/SCID-IL2Rgnull mice in the presence and absence of irradiated third-party human PBMNCs. After sublethal irradiation (240 cGy) female 8 week-old animals were transplanted with either UCB MNCs corresponding to 8×103 (n=5) or 2.66×103 (n=9), or 8.88×102 CD34+ cells (n=9) with or without co-transplantation of 1×106 irradiated (2500 cGy) PBMNCs, and 4 animals received only irradiated PBMNCs as the control group. Engraftment levels are compared by calculating SCID repopulating cell (SRC) frequency. Co-transplantation of PB MNCs with UCB MNCs provided a steady, statistically significant increase in both short-term and long term hematopoietic engraftment (Figure 2). [Display omitted] In these pre-clinical studies, we have confirmed in vitro effects on LTIC formation and in vivo UCB graft-enhancing effects of irradiated PBMNCs. If applied in clinic, this cellular therapy option might overcome a major barrier to successful allogeneic UCB HSC transplantation: engraftment failure, making the procedure more applicable and safer. Disclosures:No relevant conflicts of interest to declare.

Conjunctival Epithelial Cells With Donor-Derived Genome After Human Haematopoietic Stem-Cell Transplantation

To detect conjunctival epithelial cells with donor derived genome following human haematopoietic stem cell transplantation. Conjunctival biopsies from allotransplanted females were stained for the Y-chromosome, cytokeratin, and CD45 followed by a DAPI counterstain and CD68 staining and were then evaluated by laser-scanning confocal microscopy and 3D analysis. In 5 patients donor derived epithelial cells identified as Y+/DAPI+/CK+/CD45-/CD68-/epithelial morphology could be found (57%) with a mean incidence of 5.4% (range 2.42% - 7.94%). Our study demonstrates that besides the already published results in liver, colon, lung, skin and oral mucosa, epithelial cells with donor-derived genome also emerge in the conjunctiva following human HSCT. The biological significance and the underlying mechanism of these findings need further clarification.

Development and characterization of a novel CD34 monoclonal antibody that identifies sheep hematopoietic stem/progenitor cells

We and many others have long used sheep as a predictive model system in which to explore stem cell transplantation. Unfortunately, while numerous markers are available to identify and isolate human hematopoietic stem cells (HSC), no reagents exist that allow HSC/progenitors from sheep to be identified or purified, greatly impeding the application of this well-established large animal model to the study of autologous or allogeneic HSC transplantation. The current studies were undertaken to create a monoclonal antibody to sheep CD34 that would enable isolation and study of sheep HSC/progenitors. A partial cDNA to the extracellular domain of the sheep CD34 antigen was polymerase chain reaction cloned, characterized, and used to genetically immunize mice and create hybridomas. The resultant monoclonal antibody to sheep CD34 allows flow cytometric detection of sheep HSC/progenitors present within bone marrow, cord blood, and mobilized peripheral blood. Moreover, this antibody can be used to enrich for HSC/progenitors with enhanced in vitro colony-forming potential, and also identifies endothelial cells in situ within paraffin-embedded tissue sections, similarly to antibodies to human CD34. The availability of this monoclonal antibody recognizing the stem cell antigen CD34 in sheep will greatly facilitate the study of autologous and allogeneic HSC transplantation using this clinically relevant large animal model.

Expanded CD34+ human umbilical cord blood cells generate multiple lymphohematopoietic lineages in NOD-scid IL2rgamma(null) mice.

Umbilical cord blood (UCB) is increasingly being used for human hematopoietic stem cell (HSC) transplantation in children but often requires pooling multiple cords to obtain sufficient numbers for transplantation in adults. To overcome this limitation, we have used an ex vivo two-week culture system to expand the number of hematopoietic CD34(+) cells in cord blood. To assess the in vivo function of these expanded CD34(+) cells, cultured human UCB containing 1 x 10(6) CD34(+) cells were transplanted into conditioned NOD-scid IL2rgamma(null) mice. The expanded CD34(+) cells displayed short- and long-term repopulating cell activity. The cultured human cells differentiated into myeloid, B-lymphoid, and erythroid lineages, but not T lymphocytes. Administration of human recombinant TNFalpha to recipient mice immediately prior to transplantation promoted human thymocyte and T-cell development. These T cells proliferated vigorously in response to TCR cross-linking by anti-CD3 antibody. Engrafted TNFalpha-treated mice generated antibodies in response to T-dependent and T-independent immunization, which was enhanced when mice were co-treated with the B cell cytokine BLyS. Ex vivo expanded CD34(+) human UCB cells have the capacity to generate multiple hematopoietic lineages and a functional human immune system upon transplantation into TNFalpha-treated NOD-scid IL2rgamma(null) mice.

Regulatory CD4 +CD25 hi T cells conserve their function and phenotype after granulocyte colony-stimulating factor treatment in human hematopoietic stem cell transplantation

Acute graft-versus-host disease (aGVHD), mediated by CD4(+) and CD8(+) effector T cells, is a life-threatening complication in hematopoietic stem cell transplantation. CD4(+)CD25(hi) regulatory T cells (T(reg)) have been shown to modulate tolerance to aGVHD in murine models. Based on these observations, we examined their role in the prevention of aGVHD in patients who underwent transplantation with peripheral blood-mobilized hematopoietic stem cells after administration of granulocyte colony-stimulating factor. The effects of the G-CSF on the phenotype, frequency, and function of CD4(+)CD25(hi) T cells were analyzed in grafts and after transplantation to determine whether these cells were regulatory T cells. CD4(+)CD25(hi) T cells could be detected at the same frequency before and after granulocyte colony-stimulating factor administration in the donors' peripheral blood. The isolation of these cells from the grafts or from the recipients' peripheral blood after transplantation revealed that they were suppressive to the same extent as T(reg) isolated from healthy volunteers. Their number and frequency were estimated in the grafts and the results indicated that protection against aGVHD was not dependent on the T(reg) amount transferred to the recipients. Similarly there was no correlation between the number of circulating CD4(+)CD25(hi) T cells in the recipients' peripheral blood during the early period after transplantation and the outcome of aGVHD.