Percentage Of Donor Cells Research Articles

Usefulness of antibody-drug conjugate as preconditioning for hematopoietic stem cell-targeted gene therapy in wild-type and Fabry disease mouse models

BackgroundFabry disease (FD) is characterized by deficient activity of α-galactosidase A (GLA). Consequently, globotriaosylceramide (Gb3) accumulates in various organs, causing cardiac, renal, and cerebrovascular damage. Gene therapies for FD have been investigated in humans. Strong conditioning is required for hematopoietic stem cell-targeted gene therapy (HSC-GT). However, strong conditioning leads to various side effects and should be avoided. In this study, we tested antibody-based conditioning for HSC-GT in wild-type and FD model mice. MethodsAfter preconditioning with an antibody-drug conjugate, HSC-GT using a lentiviral vector was performed in wild-type and Fabry model mice. In the wild-type experiment, the EGFP gene was introduced into HSCs and transplanted into preconditioned mice, and donor chimerism and EGFP expression were analyzed. In the FD mouse model, the GLA gene was introduced into HSCs and transplanted into preconditioned Fabry mice. GLA activity and Gb3 accumulation in the organs were analyzed. ResultsIn the wild-type mouse experiment, when anti-CD45 antibody-drug conjugate was used, the percentage of donor cells at 6 months was 64.5%, and 69.6% of engrafted donor peripheral blood expressed EGFP. When anti-CD117 antibody-drug conjugate and ATG were used, the percentage of donor cells at 6 months was 80.7%, and 73.4% of engrafted donor peripheral blood expressed EGFP. Although large variations in GLA activity among mice were observed in the FD mouse experiment for both preconditioning regimens, Gb3 was significantly reduced in many organs. ConclusionsAntibody-based preconditioning may be an alternative preconditioning strategy for HSC-GT for treating FD.

Donor bone marrow–derived macrophage engraftment into the central nervous system of patients following allogeneic transplantation

AbstractHematopoietic stem cell transplantation is a well-known treatment for hematologic malignancies, wherein nascent stem cells provide regenerating marrow and immunotherapy against the tumor. The progeny of hematopoietic stem cells also populate a wide spectrum of tissues, including the brain, as bone marrow–derived macrophages similar to microglial cells. We developed a sensitive and novel combined immunohistochemistry (IHC) and XY fluorescence in situ hybridization assay to detect, quantify, and characterize donor cells in the cerebral cortices of 19 female patients who underwent allogeneic stem cell transplantation. We showed that the number of male donor cells ranged from 0.14% to 3.0% of the total cells or from 1.2% to 25% of microglial cells. Using tyramide-based fluorescent IHC, we found that at least 80% of the donor cells expressed the microglial marker ionized calcium-binding adapter molecule-1, consistent with bone marrow–derived macrophages. The percentage of donor cells was related to pretransplantation conditioning; donor cells from radiation-based myeloablative cases averaged 8.1% of microglial cells, whereas those from nonmyeloablative cases averaged only 1.3%. The number of donor cells in patients conditioned with busulfan- or treosulfan-based myeloablation was similar to that in total body irradiation-based conditioning; donor cells averaged 6.8% of the microglial cells. Notably, patients who received multiple transplantations and those with the longest posttransplantation survival had the highest level of donor engraftment, with donor cells averaging 16.3% of the microglial cells. Our work represents the largest study characterizing bone marrow–derived macrophages in patients after transplantation. The efficiency of engraftment observed in our study warrants future research on microglial replacement as a therapeutic option for disorders of the central nervous system.

Genetic analysis of allogenic donor cells after successful allo-limbal epithelial transplantation in simple and cultivated limbal epithelial transplantation procedures

This non-comparative cohort study investigated long-term donor cell survival after allogenic simple/cultivated limbal epithelial transplantations (allo-SLET/allo-CLET, respectively) by genetic analysis. Transplanted corneal epithelial cells, which underwent impression cytology and/or corneal-button biopsy, were examined for personal identities of autosomal short-tandem repeats; the percentages of donor cells were calculated based on matching recipient or donor buccal-DNA references. Twelve patients were included; 4 underwent allo-CLET, 8 underwent allo-SLET. Eight patients (67%) had total limbal stem cell deficiency (LSCD). Genetic analysis was performed postoperatively (mean, 55.3 months). Donor cells were detected in 4 of 12 patients (25%), all of whom underwent allo-SLET; 1 patient had a donor genotype and 3 patients had a mixed donor/recipient genotype. The longest time of donor cell detection was 30 months. Seven patients (58%) used systemic immunosuppressives at the time of genetic analysis (mean use, 22.5 months). Allogenic donor cells survived in both procedures for the long term postoperatively, which encourages the long-term use of systemic immunosuppressives. Donor cells may not be the only factor in graft survival, in that most successful cases had a recipient profile. Their presence for a specific time may promote niches for the patients’ own cells to repopulate, especially for partial LSCD.

Combination of a CD26 Inhibitor, G-CSF, and Short-term Immunosuppressants Modulates Allotransplant Survival and Immunoregulation in a Rodent Hindlimb Allotransplant Model.

Recent studies have demonstrated that inhibition of CD26 potentiates stromal cell-derived factor-1α (SDF-1α), promotes tissue regeneration, and suppresses the rejection of organ transplants. This study investigated whether the combination of a CD26 inhibitor (CD26i) with granulocyte colony-stimulating factor (G-CSF) and short-term immunosuppressants modulates vascularized composite tissue allotransplant survival in a rodent orthotopic hindlimb allotransplant model. The hindlimb allotransplantation from Brown-Norway to Lewis rats was divided into 4 groups. Group 1 (controls) did not receive any treatment. Group 2 was treated with short-term antilymphocyte serum (ALS) and cyclosporine-A (CsA). Group 3 was administrated CD26i and G-CSF. Group 4 received a combination of CD26i/G-CSF/ALS/CsA. Each subgroup comprised 10 rats. Peripheral blood and sampling of transplanted tissues were collected for immunological and histological analysis. The results revealed that allotransplant survival was found to be significantly prolonged in group 4 with CD26i/G-CSF/ALS/CsA treatment compared with those in the other groups. The interleukin-10 and transforming growth factor-βl levels, the percentage of CD4+/CD25+/FoxP3+ T cells, as well as the levels of SDF-1α expressions were significantly increased in group 4 compared with those in the other groups. Group 4 revealed a statistical increase in the percentage of donor cells (RT1n) expression in the recipient peripheral blood, and the mixed lymphocyte reaction showed hyporesponsiveness of the T cells to donor alloantigens. The combination of CD26i/G-CSF and short-term immunosuppressants prolongs allotransplant survival by inducing immunoregulatory effects and enhancing the percentage of SDF-1α expression. This immunomodulatory approach has great potential as a strategy to increase vascularized composite allotransplantation survival.

OR10 Analysis of engraftment kinetics of donor-type chimerism in lineage-specific cell populations after allogeneic hematopoietic stem cell transplantation

Aim The aim was to monitor the engraftment patterns and outcome of the graft by quantitative lineage chimerism testing based on short tandem repeats (STR), focusing on a longitudinal analysis post allogeneic myeloablative (MA) and nonmyeloablative (NMA) hematopoietic stem cell transplantation (HSCT). Methods The study was conducted on a cohort of 45 patients who received an allogeneic HSCT. All grafts were from a HLA ‘full house’ matched related donor. Post-transplant peripheral blood samples were collected from the recipient at D + 21, D + 30, D + 60, D + 90, D + 120, D + 180 and D + 365. Whole blood mononuclear cells was fractionated into CD3+, CD15 + and CD56 + cells using magnetic beads with sequential positive selection before extracting DNA. Sixteen STR (microsatellite) loci (D8S1179, D21S11, D7S820, CSS1PO, D3S1358, THOI, D13S317, D16S539, D2S1338, D19S433, VWA, TPOX, D18S51, Amelogenin, FGA and D5S818) were amplified by multiplex PCR and the amplicon resolved on DNA sequencer. Results Post-transplant at D + 21 the percentage of donor T-cell chimerism was 100% in 17.9% cases whereas, the myeloid and NK cell donor chimerism was found to be 65% and 47.3% respectively. Overall the NK cell chimerism pattern closely approximated myeloid cell chimerism, while T cell recovery was distinctly different. In the MA category the donor chimerism reached >90% earlier than the NMA group. At D + 21 in the MA cohort, the average percentage of donor cells in CD3+, CD56+, CD15 + lineages was 84.12%, 93.92% and 97.61% whereas in the NMA cohort it was 79.4%, 85.7% and 90.99% respectively. The donor chimerism in MA group at D + 90 was >97% in all lineages, whereas in NMA group the donor cells in the three lineages were CD3 90.5%, CD56 92.8% and CD15 98.9%. The percentage of CD15 cells was higher at all-time points as compared to CD56 and CD3. In relapse the T cell chimerism showed maximum variation while myeloid cells demonstrated a more stable graph. No definite chimerism pattern was detected in the three lineages in ac GVHD. Conclusions This study establishes that, longitudinal chimerism testing is an important parameter for surveillance of engraftment and provides important information on disease recurrence or graft loss in HSCT. As a monitoring approach, it exploits the ability of the STR technique to compare numerical results between samples.

Late Graft Rejection in Association With T-Large Granular Lymphocyte Expansion of Recipient Origin After Human Leukocyte Antigen–Haploidentical Stem Cell Transplantation: A Case Report

Large granular lymphocyte (LGL) expansion occasionally occurs after allogeneic stem cell transplantation (allo-SCT), and is thought to be a good prognostic sign that is associated with a lower relapse rate. However, there have been no reports of late graft failure (LGF) due to graft rejection in association with oligoclonal LGL expansion. We herein report a case of LGF associated with the transient expansion of recipient-derived T-LGL after allo-SCT. A 65-year-old man underwent peripheral blood stem cell transplantation (PBSCT) from his human leukocyte antigen (HLA)-haploidentical son for the treatment of acute myeloid leukemia, which had evolved from a myelodysplastic syndrome (MDS). Neutrophil engraftment occurred on day 20. A chimerism analysis on day 29 showed both granulocytes and mononuclear cells in the peripheral blood to be completely of donor origin. However, his neutrophil count gradually decreased and a chimerism analysis on day 61 showed that 84% of the patient's T cells were of recipient origin while the granulocytes were 100% donor-derived. His LGLs rapidly increased to 4.01× 109/L on day 113 and decreased thereafter. The percentage of donor cells in his granulocytes gradually decreased, and the patient's leukocytes were completely replaced by recipient cells on day177. The clinical course suggests that the expansion of recipient-derived T-LGLs after allo-SCT can be a sign of graft rejection. Early intervention may be needed if the LGL expansion is recipient-derived.

Effect of PTD-mFoxp3 fusion protein on graft-versus-host disease after allogeneic bone marrow transplantation

This study was aimed to investigate the effect of PTD-mFoxp3 fusion protein on graft-versus-host disease (GVHD) after allogeneic bone marrow transplantation. The 10-weeks-old C57BL/6 mice as recipients were randomly divided into three groups (A,B and C), 10 mice were in each group. The mice on day of transplantation as on day 0 received total body irradiation (TBI) 6.0 Gy, then the bone marrow cells (BMC) from BALB/c mice were injected through tail vein within 4-6 hours. At 2 days before transplantation and 0, 1, 3, 5, 7, 9 and 13 days after transplantation, mice in group A were injected with saline, mice in group B were injected with mFoxp3 protein and mice in group C were injected with PTD-mFoxp3 fusion protein. Symptoms of GVHD, survival time and histopathological changes were observed. The establishment of mixed chimerism was determined by flow cytometry in day 60, and IL-2 and IFN-γ expression profiles in the recipient peripheral blood were assessed by ELISA. The results showed that the mean survival time of recipients in group A,B and C was (32.95 ± 5.48) , (38.00 ± 5.45) and (55.30 ± 3.15) respectively. Graft rejection was observed in the liver and small intestine specimens of group A and group B. The serum levels of IL-2 and IFN-γ significantly decreased in the recipients of group C, as compared with the other groups. The flow cytometry analysis revealed that the survival recipient mice developed high chimerism levels, the percentages of donor cells in group A,B and C were (79.46 ± 1.80) %, (79.13 ± 2.23) % and (85.92 ± 2.82) % respectively. It is concluded that PTD-mFoxp3 fusion protein can reduce the incidence and mortality of GVHD after allogeneic bone marrow transplantation.

The value of donor lymphocyte infusions in thalassemia patients at imminent risk of graft rejection following stem cell transplantation

The aim was to evaluate the feasibility of donor lymphocyte infusion (DLI) in transplanted patients with thalassemia who were at imminent risk of graft rejection (GR). We retrospectively evaluated outcomes in a cohort of 19 patients with thalassemia who received DLI following 21 transplantations. Patients were divided into three groups depending on indication and time of DLI: group I, mixed chimerism-level-3 (MC-level-3) within 2 months and subsequently receiving DLI; group II, MC-level-3 within 2 months and receiving deferred DLI beyond post-transplant 2.5 months; group III, receiving DLI because of a gradual decrease in both donor cells and hemoglobin levels without MC-level-3 within 2 months. Three patients evolved to compete chimerism (16%), 9 patients had MC with transfusion independency (47%) and 7 had GR (37%). Three of 7 patients in group I, 1 of 4 patients in group II and 8 of 10 patients in group III preserved the graft. Although significant increases in the percentage of donor cells were not detected in group III, hemoglobin levels improved (median, 6.8-8.8 g/dl, P = 0.002). The risk of GR is high in patients with thalassemia who have MC-level-3 within 2 months after transplantation. DLI is a feasible method for converting unstable MC towards stable MC or full donor chimerism, but its efficacy is partially related to the percentage of residual host cells at the time of infusion. Serial chimerism studies can identify unstable MC earlier and may guide the proper timing of intervention.

The Value of Donor Lymphocyte Infusions In Unstable Mixed Chimerism In Patients with Beta Thalassemia.

AbstractAbstract 4521The only curative option for ß talasemia remains allogeneic hematopoietic stem cell transplantation (HSCT) to correct the genetic defect and provide a normal hemoglobin level in the recipient. Engraftment of donor derived cells is necessary for a success of transplantation. However, it has been shown that complete donor hematopoesis is not essential for sustained engraftment in thalassemia. Donor and recipient cells may coexist and produce a functional graft commonly referred to as donor/recipient mixed chimerism (MC) even with a low amount of engrafted donor cells. We documented our experience in a cohort of 19 beta thalassemia patients receiving DLI (donor lymphocyte infusions) following 21 transplantations with unstable mixed chimerism (MC). Seven patients received DLI with the indication of having more than 25% residual host cells (RHC) (MClevel3(residual host cells>25%)) early after transplantation and assigned as early-DLI group. Four patients although had MClevel3 in the early period, received deferred DLI and assigned as late-DLI group. The difference between these two groups, in respect to preserving functional graft, was not found statistically significant. However the chimerism kinetics of these early and late-DLI groups were also different and a slower decline in percentage of donor cells were observed in patients preserving grafts. Ten patients received DLI in the later period and although a significant increase in percentage of donor cells was not detected, increase in hemoglobin levels was provided. The infusions were safe with acceptable risk for GVHD. We believe that patients with more than 25% of RHC within two months early intervention with DLI seems feasible. Deferring DLI to a later period especially if the decrease in percentage of donor cells is so prompt, seems less effective. In the later period, we propose to consider the hemoglobin level as the main determinative factor for DLI application rather than the percentage of donor cells in line with expectance of better long-term tolerance. A better understanding of the mechanisms underlying the occurrence of persistent MC and strategies for induction and maintenance of tolerance will provide better interventions and outcomes for these patients. Disclosures:No relevant conflicts of interest to declare.

Adult metachromatic leukodystrophy treated by allo-SCT and a review of the literature

Five patients with adult-onset metachromatic leukodystrophy (MLD) underwent allo-SCT. Conditioning was reduced in intensity and grafts were obtained from voluntary unrelated donors. All but one graft were depleted of T-lymphocytes. Patient age at transplantation varied from 18 to 29 (median, 27) years. Two patients rejected their graft and MLD progressed. The recipient of the unmanipulated graft converted to complete donor chimerism with normalization of arylsulphatase A (ARSA) levels. Despite ARSA normalization, he deteriorated. Another patient was a mixed chimera. Following escalated doses of donor lymphocyte infusions he converted to complete donor chimerism. His levels of ARSA correlated positively with the percentage of donor cells and MLD was not progressive. The fifth patient died after 35 days from complications associated with GVHD. We conclude that results of allo-SCT in symptomatic MLD patients are poor. However, allo-SCT may stop progression of MLD in selected patients.

Hepatocyte growth factor mobilizes and recruits hematopoietic progenitor cells into liver through a stem cell factor‐mediated mechanism

Although bone marrow cells are reported to migrate to the liver under circumstances of severe liver injury, the bone marrow cell type and the mechanisms in this process, remain to be clarified. We examined the involvement of hepatocyte growth factor (HGF) in this process and the cell type of migrated hematopoietic cells by HGF. The CD34(+) cells and colony forming cells in the peripheral blood were examined in HGF transgenic, recombinant HGF-administered, and HGF-expressing adenovirus-administered mice. The cell type mobilized by HGF was examined by the percentages of donor cells in the peripheral blood of the recipient mice transplanted with Lin(-)c-kit(+)Sca-1(+)CD34(+) cells and those with Lin(-)c-kit(+)Sca-1(+)CD34(-) cells. Expression of stem cell factor (SCF) was examined after the addition of HGF in MS-5 stromal cells. The numbers of the cells which were mobilized from bone marrow and recruited into liver by HGF were assessed using green fluorescence fluorescent (GFP)-chimera mice. Mobilized CD34+ cells and colony forming cells in the peripheral blood were increased by HGF treatment. The cells mobilized by HGF were mostly Lin(-)c-kit(+)Sca-1(+)CD34(+) cells. Recruitment of bone marrow cells into liver was not suppressed in MMP-9-/- mice. Expression of SCF was induced by HGF in MS-5 stromal cells. However, expression of CXCR4, SDF-1, MMP-9 or VCAM-1 was not changed. The numbers of GFP-positive cells in liver 1 month after treatment by HGF was greater than that by G-CSF. The results of the present study suggest that HGF mobilizes and recruits hematopoietic progenitor cells from bone marrow into the liver through SCF-mediated mechanism.

5–azacitidine Treatment of Imminent Relapse Defined by Decreasing Donor CD34+ Progenitor Subset Chimerism in Patients with CD34+ High-Risk Myelodysplastic Syndromes (MDS) or Acute Myeloid Leukemia (AML) after Allogeneic Stem Cell Transplantation.

Besides graft versus host disease (GVHD), disease relapse is one of the major challenges in the care of patients with acute myeloid leukemia (AML) or myelodysplastic syndrome (MDS) undergoing allogeneic peripheral blood stem cell transplantation (PBSCT). However, we and others have shown that relapse can be predicted in case of CD34-expression on the malignant clone by a sensitive chimerism analysis in sorted CD34+ peripheral blood cells. If the percentage of donor cells in this compartment drops below 80%, leukemia relapse is inevitable within 4–8 weeks in the absence of clinical interventions like immediate cessation of immunosuppressive drugs or the administration of donor lymphocyte infusions. However, both approaches often result in clinically significant GVHD. Therefore, new strategies are warranted in order to treat imminent relapse in MDS or AML patients. We report results of an ongoing phase II clinical trial evaluating the efficacy of 5-azacitidine (5-aza) to prevent hematological relapse in patients with CD34+ AML or MDS and a decreasing CD34-donor chimerism after allogeneic PBSCT. Therefore, a total of 23 patients with CD34+ MDS (n=3) or AML (n=20) were prospectively screened on day 56, 84, 112, 140, 184, 365 and at later time points after PBSCT for a decreasing chimerism of donor CD34+ cells in the peripheral blood. In case of imminent relapse, defined as a drop of donor CD34+ cells below 80%, 5-aza was given at a dose of 75mg/m2/d s.c. day 1–7. A total of 4 cycles every 28 days were allowed in the absence of hematological relapse or toxicity. A median of 226 days after PBSCT, 9 out of 23 patients screened entered the treatment phase of the study with a median of 31% (range 0–53%) CD34+ donors cells in the peripheral blood (PB). However, a complete overall PB donor chimerism and less than 5% marrow blasts were documented in all patients before 5-aza treatment. Reversible neutropenia and thrombocytopenia grade 3/4 occurred in 50% of the patients. Only three patients still had immunosuppression prior 5-aza, which in two of them was slowly tapered during the period of 5-aza administration. With a median follow-up of 186 days after starting 5-aza all nine patients are eligible for response evaluation. Of these, CD34-chimerism was reverted to complete donor type (>90%) in 6 (66%) patients. Two patients showed a further decrease of donor CD34+ cells and relapsed shortly after having completed the 1st or the 4th cycle of 5-aza, respectively. One patient showed an increase of CD34-chimerism after two cycles, however, died from non-relapse mortality. No hematological relapse occurred in the responders and in the screening cohort without decreasing CD34+ chimerism. Two patients (one without immunosuppression) developed limited cGVHD during 5-aza treatment. Preemptive treatment of minimal residual disease defined by decreasing donor CD34+ subset chimerism with 5-aza seems to be a potent strategy to prevent hematological relapse of CD34+ myeloid malignancies after allogeneic PBSCT.

Alloantigen-Pulsed Host Dendritic Cells Induce T-Cell Regulation and Prolong Allograft Survival in a Rat Model of Hindlimb Allotransplantation

Composite tissue allotransplantation is restricted due to the risks presented by long-term therapeutic immunosuppression. This study is conducted to investigate whether treatment with recipient immature dendritic cells (DCs) pulsed with donor alloantigens can prolong allograft survival and induce T-cell regulation in a rodent model. Orthotopic hindlimb transplants from Brown-Norway (RT1(n)) to Lewis (RT1(1)) rats were performed (day 0). DCs were propagated from the recipient bone marrow and pulsed with the donor alloantigen lysate. Group 1 (control group) did not receive any treatment. Groups 2 and 3 received cyclosporine A (CsA) at a concentration of 10 and 16 mg.kg(-1).day(-1), respectively, on days 0-20 following composite tissue allotransplantation. Group 4 received antilymphocyte serum (i.p. administered 4 d before and 1 d after transplantation) therapy. Group 5 received combined treatment with CsA (10 mg.kg(-1).day(-1), days 0-20) and donor alloantigen-pulsed recipient DCs (i.v. administered on days 7, 14, and 21). Group 6 received combined treatment with CsA (10 mg.kg(-1).day(-1) on days 0-20), antilymphocyte serum (administered i.p. 4 d before and 1 d after transplantation), and DCs (administered i.v. on days 7, 14, and 21). Graft rejection was defined as epidermolysis/desquamation of the donor skin. The mixed lymphocyte reaction was performed to determine the donor T-cell reactivity. Tissue samples were biopsied to analyze the histological changes, and flow cytometry was performed to quantify the donor T-cells. Allograft survival was significantly prolonged (>200 d) in Group 6 when compared with the other groups (P < 0.001). The mixed lymphocyte reaction performed for Group 6 revealed hyporesponsiveness of the T-cells to donor alloantigens. Flow cytometric analysis in Group 6 revealed a significant increase in the percentage of CD4(+)/CD25(+) and CD4(+)/foxP3(+) T-cells expression, and significant increase in the percentage of donor cells (RT1(n)) in the recipient peripheral blood. Immunohistochemical staining of allo-skin revealed a significant increase in the proportion of CD25(+) cells in the subcutaneous and dermis layers in Group 6, as compared to other groups. Treatment with donor alloantigen-pulsed recipient immature DCs in combination with transient immunosuppression prolongs allograft survival and induced tolerance by inducing T-cell hyporesponsiveness to donor alloantigens and increasing the CD4(+)/CD25(+) T-cell population.

G-CSF Disrupts the Stem Cell Niche by Increasing Turnover of Bone Marrow Osteoblasts.

Accumulating evidence suggests that osteoblast-lineage cells play a key role in supporting hematopoiesis, providing signals that maintain the normal function of hematopoietic stem cells (HSC). We and others previously showed that treatment with G-CSF reduces the number and activity of osteoblasts in the bone marrow. Here we confirm these findings using transgenic mice expressing GFP in osteoblast lineage cells under control of a 2.3 kb fragment of the col1a1 promoter. Analysis of these mice confirmed that G-CSF treatment reduced the number of osteoblasts 2.9-fold compared to control mice (n=4, p<.01). Consistent with these findings, expression of several osteoblast genes was sharply reduced during G-CSF treatment; alkaline phosphatase, osteocalcin, stromal-derived factor 1, osteoprotegerin, and bone sialoprotein were all decreased (7.9, 19, 3.8, 14.2, and 4.1-fold decreased; n=5–12 each group, p<.05). These findings are consistent with either a true loss of osteoblasts or induction of osteoblast quiescence. To distinguish between these possibilities, the fate of osteoblasts during G-CSF treatment was assessed by in vivo BrdU labeling. At baseline, 34.9 ± .8% of osteoblasts were labeled after 16 days of BrdU administration. In untreated mice, this percentage decreased to 14.8% ± 0.05% after 9 days. However, in mice harvested 4 days after a 5-day course of G-CSF, the percentage of BrdU positive osteoblasts decreased to 6.5% ± 0.9% (n=2 each group, p<.05). These data suggest that G-CSF treatment increases the turnover of osteoblasts rather than inducing their quiescence. Since apoptosis is one potential mechanism of osteoblast turnover, we measured caspase 3 activation in G-CSF-treated mice. No increased apoptosis was observed [percent activated caspase 3 positive cells + SEM: 8.0% ± 1.5% (untreated),10.5% ± 0.5% (day 3), 5.8% ± 1.2% (day 4); n=2–4 each group, p=ns]. The sharp decrease in osteoblast number suggests that HSC activity might be altered by G-CSF treatment. To address this possibility, competitive repopulation assays were performed with HSC harvested from G-CSF or control mice. In mice competitively reconstituted with control HSC, the percentage of donor cells was 33.7% ± 4.7% at 4 months after transplantation. In contrast, in mice receiving G-CSF treated HSC, the percentage of donor cells was only 10.0% ± 2.6% (n=3–4 each group, p<.05). As this loss in repopulation potential may result from decreased HSC number or function, we estimated HSC number by measuring Kit+ lineage− Sca+ CD34− cells. We found no significant difference in this fraction between treated and untreated mice [number KLS CD34− per femur + SEM: 966 ± 229 (untreated) versus 945 ± 183 (treated); n=6–7 each group, p=ns]. These results suggest that the diminished repopulation potential of G-CSF treated bone marrow results from impaired HSC function rather than reduced HSC number. Finally, we hypothesized that the loss of long-term repopulation potential in HSC from G-CSF treated mice may result from the loss of factors in the bone marrow niche that maintain HSC quiescence. We therefore measured BrdU uptake in the KLS fraction of bone marrow cells. Preliminary results show a trend toward increased BrdU uptake in KLS cells from G-CSF treated mice (48.5% ± 9.2%) compared with untreated mice (26.5% ± 1.4%; n=2 each group, p=.14). In summary, these results suggest a model in which G-CSF induces increased osteoblast turnover, disruption of the stem cell microenvironment, and loss of HSC quiescence.

Effective engraftment but poor mid-term persistence of mononuclear and mesenchymal bone marrow cells in acute and chronic rat myocardial infarction

Bone marrow cells are used with promising results for cell therapy after myocardial infarction (MI). We determined the survival and organ distribution of transplanted mononuclear (MNC) or mesenchymal (MSC) bone marrow cells, and the influence of cell type, cell number and application time. MNC and MSC (male Fischer 344 rats) were injected into the border zone of MI (syngeneic females) immediately or 7 days after LAD ligation (10 5 or 10 6 cells, 50 μl). After 0 h, 48 h, 5 days, 3 weeks and 6 weeks, DNA of heart, lung, liver, spleen, kidney, blood, bone marrow, brain and skeletal muscle was isolated and the number of donor cells determined by quantitative real-time PCR with Y-chromosome specific primers (each n ≥ 4). The percentage of donor-cells in the heart decreased rapidly from 34–80% of injected cells (0 h) to 0.3–3.5% (6 weeks) independent from cell type, number and application time. The absolute number increased after increasing injected cell number (10 6 vs. 10 5). In the lung, MNC and MSC were found at 0 h (126 ± 48 and 140 ± 3 per million organ cells), but in liver and kidney, only few. At 48 h and 6 weeks, an increasing number of MNC, but not MSC, were detected in the spleen (6 weeks, 602 ± 173 per million organ cells vs. 95 ± 50 in the heart, P = 0.02). In all other organs, only few or no grafted cells of either cell type were detected at these times. Organ distribution was independent from injection time. The low survival of grafted cells may limit their therapeutic impact, while their distribution to other organs must be considered in all cell therapy applications.

A SYBR green‐based real‐time PCR method for detection of haemopoietic chimerism in allogeneic haemopoietic stem cell transplant recipients

To develop a reliable and rapid real-time quantitative polymerase chain reaction (Q-PCR) method using SYBR green to quantify chimerism in allogeneic haemopoietic stem cell transplant recipients. Twelve specific nucleotide polymorphisms (NPs) were selected to identify informative markers for detecting chimerism in transplant donor/recipient pairs. One informative marker was then used in SYBR green Q-PCR to detect chimerism post-transplantation in each patient. The percentage of donor cells was calculated using a standard curve, constructed using artificially mixed donor/recipient chimeric DNA in 12 serial dilutions (0.01-100%). DNA from 37 donor/recipient pairs was screened for informative markers and 18 post-transplant samples were monitored for chimerism with SYBR green Q-PCR method. The Q-PCR was able to discriminate between recipient and donor genetic profiles in all 18 samples, and quantify the chimerism. These results were confirmed by at least one independent method, such as TaqMan Q-PCR, microsatellite and fluorescent in situ hybridisation (FISH) methods. The detection limit of this method was 0.1%, which was more sensitive than the two currently used microsatellite and FISH methods. The new single platform SYBR green Q-PCR method is capable of detecting all haemopoietic chimerism with high accuracy; hence, it may be used to replace the current detection methods.

Partially matched related donor peripheral blood progenitor cell transplantation in paediatric patients adding fludarabine and anti-lymphocyte gamma-globulin.

Twenty-one paediatric patients (11 males and 10 females) received a CD34-selected partially matched related donor transplant for malignant (16 cases) and non-malignant conditions (five cases). The average cell dose was 11.13 x 10(6)/kg. Fifteen of 16 patients with malignant conditions and one with non-malignant disease received total body irradiation plus cyclophosphamide. Three of 5 patients with non-malignant conditions and one with leukaemia, received busulphan plus cyclophosphamide. One patient with Fanconi anaemia received 100 mg/kg of cyclophosphamide. Fludarabine (25 mg/m(2)/day for 5 days) was administered prior to all these regimens. Additionally, anti-lymphocyte gamma-globulin (12.5 mg/kg/day) was administered from day -2 to day +2. Three (15%) patients failed to achieve complete chimaerism (CC). These patients received a second cell infusion. Two of them achieved CC. In the third patient, the percentage of donor cells was increased. The likelihood for engraftment was not related to the cell dose received. Acute graft-versus-host disease (GVHD) occurred in nine patients but only one developed GVHD >grade II. Eight patients developed active viral infections, which resolved after treatment. Patients receiving cell doses higher than our average had a significantly faster CD3 and CD4 cell recovery and experienced a lower incidence of viral infections. After 480 +/- 255 days of median follow-up, 16/21 patients are alive and well and have CC. Three patients died of leukaemic relapse and a fourth from progression of his disease (adreno-leuko-dystrophy). We conclude that partially matched related donors are a feasible source of haemopoietic progenitor cells for transplantation for patients without matched familial or unrelated donors.

Tolerance induction post in utero stem cell transplantation.

The potential advantage of in utero HSC transplantation over a postnatal BMT is that early curative therapy could be given to an affected fetus, thus eliminating standard intensive immunosuppressive, marrow-ablative conditioning. It is apparent from studies in animals and humans that MHC-mismatched donor HSC of either fetal or adult origin can engraft in fetal recipients if the transplants are done sufficiently early in gestation. However, except for SCID, the percentage of donor pluripotent HSC that engraft is unacceptably low. We had hoped that for diseases such as thalassemia there would be a selective survival advantage for committed donor progenitor cells resulting in a high percentage of donor cell engraftment. At least based upon the experience in human fetuses with alpha- or beta-thalassemia, this has not been the case. Furthermore, for the majority of potential recipients of in utero HSC transplants, the marrow is non-defective, and the small percentage of pluripotent donor HSC that engraft would not be expected to selectively expand post-transplant. Our own results suggest that the non-defective fetal mouse and rhesus monkey are excellent models in which to study both stem cell engraftment, rejection, and tolerance induction. In our studies in non-defective mice with normal hematopoiesis, while the percentage of donor cells that are present is quite low, in only a small number of these animals were we able to induce permanent skin graft tolerance. Thus, while we found microchimerism in approximately 75% of recipients, less than 10% became tolerant. Even when we co-injected a large number of DC precursors, similar to what has been shown to induce tolerance to allogeneic liver, most of the animals failed to become tolerant to donor skin grafts. Interestingly, donor c-kit+ cells can be recruited with cytokines into the peripheral blood in engrafted mice, although these cells do not seem to be sufficient to induce tolerance to donor skin grafts, suggesting that the type (and location) of the engrafted donor cell plays a key role in tolerance induction. Our results in the fetal monkey model parallel those in the mouse, i.e., only a small number of donor cells engraft with limited tolerance induction. Interestingly, we found in our study of DC that GVHD was induced in those murine recipients of both allogeneic marrow and DC. It is likely that there were a sufficient number of mature DC in the preparation to facilitate a donor cytotoxic response towards the host. As a consequence there was also a significant increase in the percentage of donor cells that engrafted in the survivors. Future studies will focus on ways of blocking the graft vs host reaction while still maintaining the graft-promoting role of the donor T cell.

Development and aging of primitive hematopoietic stem cells in BALB/cBy mice

Evaluating the function of an individual hematopoietic stem cell (HSC) is a difficult and important problem. The functional ability per HSC, as well as the HSC concentration, was measured with minimal disruption to the cells in vivo using the new competitive dilution assay. Distribution of HSC into recipients was modeled based on Poisson probabilities. Predictions of donor contributions from models assuming different levels of donor HSC functional ability and concentration were compared to actual observations. The model with the least difference between predictions and observations was accepted. In BALB/cBy (BALB) mice, models assuming equal functional ability of HSC from the same donor fit extremely well with actual observations, suggesting that all HSC are functionally homogeneous at any particular time point during development or aging. Relative HSC functional ability per cell declined during development, so that a fetal HSC had 1.6 to 3.0 times the functional ability of a young adult HSC. The decline continued with age, so that a young adult HSC had 1.6 to 2.0 times the functional ability of an old HSC. Concentrations of HSC that engrafted and functioned were similar among 16-day fetal liver cells and bone marrow cells (BMC) from 3-month and 25 to 28-month-old adult mice. They were either 10 or 4 HSC per million cells when tested in BALB or CByB6F1 recipients, respectively. All HSC were pluripotent and produced lymphoid and myeloid descendants proportionally (r = 0.80 to 0.98, p < 0.01). Fetal and young HSC in both types of recipients maintained clonal stability long term so that percentages of donor cells at 6 and 9 months were strongly correlated (r = 0.72 to 0.93, p < 0.01). Although HSC from aged donors in BALB recipients maintained clonal stability, HSC from the same aged donors failed to show clonal stability in CByB6F1 recipients, perhaps due to the less suitable host environment. All HSC from BALB mice seemed to have equal functional levels at a given stage of life and were gradually exhausted simultaneously through development and aging.

Delaying transplantation after total body irradiation is a simple and effective way to reduce acute graft-versus-host disease mortality after major H2 incompatible transplantation.

We have previously reported that delaying histoincompatible transplantation after total body irradiation (TBI) conditioning markedly decreased the mortality of acute graft-versus-host disease (GVHD) in severe combined immunodeficiency mice. However, it was not clear whether the delayed transplantation would affect the final engraftment and acute GVHD mortality in normal hosts. BALB/c mice (H2d) were lethally irradiated with 8.5 Gy TBI and transplanted with C57BL/6 (H2d) bone marrow plus spleen cells on the same day (TBI+day 0) or 4 days after TBI conditioning (TBI+day 4). We again demonstrated that delaying transplantation by 4 days after TBI conditioning markedly reduced acute GVHD mortality in normal hosts after major histoincompatible transplantation. The survival rates were 66% in TBI+day 4 vs. 0% in TBI+day 0 allogeneic transplanted animals by day +60 (P<0.001). Further analysis demonstrated that the 4-day rest between the TBI and allogeneic transplantation broke the interaction of cell/inflammatory tumor necrosis factor-alpha, interleukin (IL)-1beta, and IL-6 cytokine reactions stimulated by TBI and incompatible transplantation. Flow cytometry revealed 97% donor cells in host marrow by 2 weeks in TBI+day 0 transplantation versus 57% in TBI+day 4 transplantation. There was no difference in percentage of donor CD3+ T-cell engraftment between the TBI+day 0 and TBI+day 4 allogeneic transplanted animals. In TBI+day 4 transplantation, the percentage of donor cells in host marrow steadily increased to 74% by day +60 and 93% by day +100. This 2- to 3-month early mixed chimerism in TBI+day 4 transplanted animals might be related to lower levels of tumor necrosis factor-alpha and IL-6 both of which have been shown to stimulate lymphohematopoiesis and was associated with lower acute GVHD mortality. The data again demonstrated in immunologically normal BALB/c mice that delaying allogeneic transplantation after TBI is a simple and effective way to reduce acute GVHD mortality, achieve satisfactory engraftment and significantly increase overall survival.