Telomere length changes in patients undergoing hematopoietic stem cell transplantation.

Telomere length indicates the replicative history of cells, serving as a molecular measure of the replicative potential remaining in cells. To investigate telomere length changes in hematopoietic stem cells, patients undergoing hematopoietic stem cell transplantation (HSCT) were evaluated. Fifteen patients after allogeneic bone marrow transplantation (allo-BMT group), seven patients after autologous peripheral blood stem cell transplantation (auto-PBSCT group), and 39 healthy controls were studied. Telomere length was measured in peripheral mononuclear cells by Southern blot hybridization. There was no significant difference between the allo-BMT and the auto-PBSCT groups. In the allo-BMT group, the mean telomere length of recipients was 2.01 kb shorter than that of their donors (P = 0. 008), and was 1.59 kb shorter than that of age-matched putative normal controls (P = 0.002). Telomere shortening in the allo-BMT group was equivalent to 41.4 years of aging in the donors, and to 52. 4 years of aging in the normal controls. The mean telomere length in the auto-PBSCT group was 2.36 kb shorter than that of the age-matched putative controls (P = 0.043), which was equivalent to 61.5 years of aging in normal controls. The extent of telomere shortening in the allo-BMT group showed a trend to negative correlation with the number of mononuclear cells infused. These findings suggest that hematopoietic stem cells after HSCT lose telomere length and these shortened telomeres may result in a higher incidence of clonal disorders later in life.     

Long-term follow-up of recipients of allogeneic bone marrow grafts reveals no progressive telomere shortening and provides no evidence for haematopoietic stem cell exhaustion

Summary. Accelerated telomere shortening has been proposed as a possible long‐term risk of allogeneic bone marrow transplantation (allo‐BMT). In this study we monitored telomere length in white blood cells (WBC), granulocytes, and naïve and memory CD4⁺ T lymphocytes in recipients of allo‐BMT at long‐term follow‐up. Peripheral blood was collected from 10 allo‐BMT recipients and donors at a median interval of 18 years after allo‐BMT. Telomere length was determined using Southern blot analysis. Similar to results previously reported at short‐term follow‐up, a small difference in telomere length (0·1–0·3 kb) between recipients and donors was detected in WBC, granulocytes and naïve CD4⁺ T cells. Our data therefore provide no evidence for sustained telomere shortening in leucocytes, and render the possibility of long‐term haematopoietic graft failure unlikely. In addition, we observed two phenomena that may be related to involution of the thymus. First, the number of naïve CD4⁺ T cells in the blood was significantly lower in recipients (0·4 × 10⁹/l) than in donors (0·7 × 10⁹/l) (P < 0·05). Second, telomeres in memory CD4⁺ T cells from recipients were on average 0·6 kb shorter than those from donors (P = 0·01). The latter may be related to the reported rapid peripheral expansion of memory T cells immediately after transplantation.     

Telomere shortening in leucocyte subsets of long-term survivors of allogeneic bone marrow transplantation

Recent studies have demonstrated excessive telomeric shortening in peripheral blood leucocytes of bone marrow transplant (BMT) recipients. This finding has raised concerns about accelerated haemopoietic ageing that might predispose to clonal disorders and late graft failure. We studied the peripheral blood neutrophils and T cells of 14 fully engrafted long-term survivors of BMT.
We found that in both neutrophils and T cells there was significant telomere shortening in the recipient (0.6 and 0.5 kb, respectively; P  < 0.001 and < 0.04, respectively). We found no relationship between degree of shortening and the nucleated cell dose given at the time of transplant. We also demonstrated significantly longer telomeres in T cells than neutrophils from the same individual (mean 11.6 kb and 10.6 kb, respectively; P =0.0001).
We propose mechanisms to account for these observations. The replicative stress that causes this telomere shortening does not necessarily occur at the level of the most primitive haemopoietic stem cell.     

A comparison of murine T-cell-depleted adult bone marrow and full-term fetal blood cells in hematopoietic engraftment and immune reconstitution.

Umbilical cord blood has been increasingly used as a source of hematopoietic stem cells. A major area of concern for the use of cord blood transplantation is the delay in myeloid and lymphoid recovery. To directly compare myeloid and lymphoid recovery using an animal model of bone marrow and cord blood as sources of stem cells, hematopoietic engraftment and immune recovery were studied following infusion of T-cell-depleted adult bone marrow or full-term fetal blood cells, as a model of cord blood in a murine allogeneic transplantation model (C57BL/6 [H-2(b)] --> BALB/c [H-2(d)]). Allogeneic full-term fetal blood has poorer radioprotective capacity but greater long-term engraftment potential on a cell-to-cell basis compared with T-cell-depleted bone marrow. Allogeneic full-term fetal blood recipients had decreased absolute numbers of T, B, and dendritic cells compared with bone marrow recipients. Splenic T cells in allogeneic full-term fetal blood recipients proliferated poorly, were unable to generate cytotoxic effectors against third-party alloantigens in vitro, and failed to generate alloantigen-specific cytotoxic antibodies in vivo. In addition, reconstituting T cells in fetal blood recipients had decreased mouse T-cell receptor delta single-joint excision circles compared with bone marrow recipients. At a per-cell level, B cells from fetal blood recipients did not proliferate as well as those found in bone marrow recipients. These results suggest that full-term fetal blood can engraft allogeneic hosts across the major histocompatibility barrier with slower hematopoietic engraftment and impaired immune reconstitution.     

Comparison of allogeneic T cell-depleted peripheral blood stem cell and bone marrow transplantation: effect of stem cell source on short- and long-term outcome.

We report the results of a retrospective single-center study comparing engraftment, acute and chronic GVHD, relapse and survival in patients with malignant hematological disorders transplanted with allogeneic peripheral blood stem cells (alloPBSCT, n = 40) or bone marrow cells (alloBMT, n = 42). All transplants were T cell depleted by in vitro incubation with the Campath-1 monoclonal antibody. Primary graft failure occurred in none of the patients receiving an alloPBSCT compared with 3/42 of the recipients of an alloBMT. In addition, two patients in the alloBMT group showed no platelet engraftment. Recipients of PBSC had a more rapid recovery of neutrophils (median 14 days) compared to BM transplant recipients (median 32 days). Platelet recovery was also accelerated in PBSC recipients compared to BM recipients (11 vs 38 days). There was an increase in the incidence of grade II acute GVHD and chronic GVHD in patients after alloPBSCT (18% and 23%, respectively) compared to patients receiving alloBMT (5% and 8%, respectively). The 2-year cumulative incidence of relapse was similar in both groups (47%). At 6 months after transplantation, transplant-related mortality (TRM) was lower in PBSCT recipients than in BMT recipients. However, at a follow-up of 3 years TRM was similar in both groups. The disease-free survival rate at 3 years after transplantation did not differ between the groups (42% for PBSCT and 41% for BMT recipients). Our results indicate that T cell-depleted alloPBSCT compared to alloBMT is associated with a more rapid hematopoietic reconstitution and a decreased TRM at 6 months follow-up after transplantation. However, at a follow-up of 3 years, no sustained survival benefits were observed.     

Serum interleukin-3 levels following autologous or allogeneic bone marrow transplantation: effects of T-cell depletion, blood stem cell infusion, and hematopoietic growth factor treatment

Engraftment of marrow following autologous or allogeneic bone marrow transplantation (BMT) may be influenced by quantity and function of stem cells. T lymphocytes, supporting microenvironmental cells, and hematopoietic growth factors (HGF). To elucidate the physiologic role of interleukin-3 (IL-3) in the engraftment process, serum IL-3 levels were measured in over 400 samples from 77 transplant recipients before and for up to 3 weeks following transplantation using a novel enzyme- linked immunoabsorbent assay (ELISA) with a sensitivity of > or = 78 pg/mL. Thirty-seven patients received two to three log T-cell-depleted allografts. In the remaining 40 patients (18 autologous marrow, 12 allogeneic marrow, and 10 autologous peripheral blood [PB] stem cell), T cells were not depleted (non-TCD) from the grafts. A burst of IL-3 (peak levels, 1,500 to 6,000 pg/mL) was detected in the immediate posttransplant period between day 0 and day 14 in all non-TCD recipients and in 21 of 37 (57%) of TCD recipients. A strong inverse relationship between IL-3 levels and absolute neutrophil count (ANC) was observed in both non-TCD recipients (r = -.796) and in TCD recipients (r = -.897). However, both peak IL-3 levels and mean IL-3 levels from day 0 through 14 were significantly lower in TCD recipients compared with either autologous or unmodified allogeneic marrow recipients (P < .01). The lowest peak or mean day 0 through 14 IL-3 levels were observed in matched related recipients undergoing the most aggressive (2.5 to 3.0 log) T-cell-depleted BMT. Autografted patients receiving blood stem cell transplants alone or posttransplant granulocyte colony-stimulating factor (G-CSF) or granulocyte-macrophage colony stimulating factor (GM-CSF) also had significantly lower peak IL- 3 levels (P < .01). In patients receiving TCD grafts, administration of antithymocyte globulin (ATG) posttransplant significantly increased peak IL-3 levels compared with patients not treated with ATG (P < .04). This study shows that endogenous release of IL-3 is strongly associated with myeloid engraftment and inversely related to ANC. Removal of T lymphocytes from donor marrow or acceleration of engraftment by use of stem cells or growth factors appears to blunt the endogenous release of IL-3 whereas use of ATG posttransplant increases IL-3 release.     

Bone marrow transplantation for the treatment of immune deficiency states

The first successful allogeneic bone marrow transplants were performed in children with severe combined immune deficiency (SCID). Bone marrow transplants for patients with SCID have been in the forefront of clinical bone marrow transplantation including the first successful use of T lymphocyte-depleted haploidentical bone marrow and matched unrelated donors. Successful bone marrow transplantation for most forms of SCID requires only the engraftment of donor lymphoid stem cells; donor hematopoietic stem cell engraftment is usually not required. The Wiskott-Aldrich syndrome was the first genetic disease involving the hematopoietic stem cell to be completely corrected by allogeneic bone marrow transplantation. The successful transplantation of Wiskott-Aldrich syndrome patients demonstrated that agents with adequate anti-lymphoid and hematopoietic stem cell activity were necessary in order to achieve complete donor lymphoid and hematopoietic stem cell engraftment. Initially, total body irradiation and now busulfan are used to ablate recipient hematopoietic stem cells, while cyclophosphamide is used to ablate recipient lymphoid stem cells. No single agent/drug is capable of eliminating both stem cell populations. Histocompatible bone marrow transplantation has a role in the treatment of patients with immune deficiency due to primary defects of the hematopoietic stem cell. The recent introduction of cytokines (gamma-interferon and granulocyte colony stimulating factor) may reduce the need for bone marrow transplantation for myeloid immune deficiency states. Initial attempts to treat patients with the acquired immune deficiency syndrome by bone marrow transplantation were limited by the lack of effective concomitant anti-viral therapy. Bone marrow transplantation for immune deficiency states continues to be in the forefront of human bone marrow transplantation.     

New strategies in allogeneic stem cell transplantation: immunotherapy using irradiated allogeneic T cells

Recipients of T cell-depleted allogeneic bone marrow transplants have increased risks of relapse and graft rejection. The addition of donor T cells to the TCD allograft will decrease the risk of graft rejection but will increase the risk of graft-versus-host disease (GVHD). Relapse of leukemia or lymphoma following allogeneic bone marrow transplantation can be successfully treated with post-transplant infusions of donor lymphocytes. A relatively small number of donor T cells can have a profound anti-tumor effect and facilitate engraftment, but has an unpredictable potential for severe GVHD. An alternative to using viable immunocompetent donor immune cells to facilitate engraftment and to treat relapsed patients are donor lymphocytes that have been treated to limit their ability to proliferate and cause GVHD. T cells treated with irradiation retain cytotoxic activity against tumor cells and host immune cells. We have tested the hypothesis that allogeneic donor T cells treated with low-dose irradiation will facilitate engraftment and mediate an anti-leukemia effect in a mouse model of bone marrow transplantation. Multiple infusions of irradiated allogeneic donor lymphocytes in the peri-transplant period had graft-enhancing activity without resulting in GVHD. Murine recipients of irradiated allogeneic splenocytes and allogeneic bone marrow had stable donor-derived hematopoiesis without a significant contribution of irradiated donor cells to the T cell compartment. Removing T cells from the allogeneic splenocytes prior to irradiation largely eliminated their graft facilitating activity. Based upon the promising results of the pre-clinical murine studies, we initiated a phase I clinical trial of multiple infusions of irradiated allogeneic lymphocytes in patients who had relapsed after allogeneic BMT. Of 12 patients treated to date on this study, three have shown objective responses of their leukemia or lymphoma to multiple infusions of irradiated donor lymphocytes. We have initiated a new phase I clinical study to test the efficacy of multiple infusions of irradiated allogeneic cytotoxic T cells to facilitate engraftment in allogeneic transplantation. Successive cohorts of patients will be transplanted with allogeneic stem cells alone, or a combination of allogeneic stem cells and increasing numbers of irradiated allogeneic T cells. Irradiated allogeneic lymphocytes that retain short-term allo-specific cytotoxicity and lack the potential for clonal expansion in vivo can be considered as a novel form of immunotherapy with defined pharmacokinetics.     

A comparison of postengraftment infectious morbidity and mortality after allogeneic partially T cell-depleted peripheral blood progenitor cell transplantation versus T cell-depleted bone marrow transplantation

OBJECTIVE: Postengraftment infections are a major cause of transplant-related morbidity and mortality following allogeneic hematopoietic stem cell transplantation (allo-SCT). Allogeneic peripheral blood progenitor cell transplantation (PBPCT) is associated with faster hematopoietic recovery compared to bone marrow transplantation (BMT) and unmanipulated PBPCT may be associated with fewer postengraftment infections. We set out to evaluate and compare the incidence, cause, and outcome of postengraftment infections following HLA-identical sibling T cell-depleted PBPCT vs T cell-depleted BMT between days 30 and 365 posttransplant. PATIENTS: Forty recipients of peripheral blood progenitor cells (PBPC) and 47 recipients of bone marrow (BM) were included. The two groups of patients were comparable with respect to their baseline characteristics. RESULTS: PBPC grafts contained significantly more CD34+ cells and PBPCT was associated with significantly faster neutrophil and lymphocyte recovery as compared to BMT. PBPC recipients experienced more chronic graft-vs-host disease (GVHD; 55% vs 34%; p=0.02). The number of definite and clinical infections per 100 patient days was comparable between recipients of PBPC and BM with similar contribution of causative microorganisms. At one year post SCT, 68% of PBPC recipients had experienced at least one CTC grade 3-4 infection vs 65% of BM recipients. Treatment-related mortality at one year from transplantation was 34% after PBPCT vs 30% after BMT, and no difference in infection-related mortality was observed. CONCLUSION: Postengraftment infectious morbidity and mortality were comparable between recipients of PBPC and BM despite a higher CD34+ cell content of PBPC grafts and faster lymphocyte recovery after PBPCT, which may in part be explained by the higher incidence of chronic GVHD.     

Constitution and telomere dynamics of bone marrow stromal cells in patients undergoing allogeneic bone marrow transplantation

We evaluated the genotypic origin of mesenchymal stem cells (MSC) following sex-mismatched allogeneic bone marrow transplantation (BMT), and investigated the telomere dynamics in MSC in normal individuals and patients after BMT. The study population consisted of 11 patients with hematologic disorders who showed complete chimerism after BMT. Telomere length was measured in MSC using Southern blotting analysis in eight patients and 18 healthy subjects as a control group. Following culture, MSC were identified by the expression of SH2 and SH4, and lack of CD14, CD34, and CD45. All MSC showed the recipient genotype, based on the results of fluorescent in situ hybridization analysis using X-chromosome satellite probes or microsatellite DNA polymorphism analysis. The mean telomere length in MSC from normal controls was 7.2+/-0.53 kb (range, 6.12-7.78), and progressive telomere shortening was seen with age. There was no significant difference in MSC telomere length between the BMT group and age-matched controls. This study confirmed that the MSC isolated from the recipients of allogeneic BMT did not have the donor genotype, despite complete chimerism. Moreover, MSC were demonstrated to show progressive loss of telomere length with age, but the telomeres in MSC were not affected by BMT.     

Clinical benefits of granulocyte colony-stimulating factor therapy after hematopoietic stem cell transplant in children: results of a prospective randomized trial

BACKGROUND AND OBJECTIVES: Hematopoietic stem cell transplantation (HSCT) is associated with profound neutropenia and significant morbidity and mortality. To evaluate the safety and efficacy of non-glycosylated recombinant human granulocyte colony-stimulating factor (rHuG-CSF) in accelerating myeloid recovery and its influence on infections, supportive therapy, and transplant-related mortality we carried out a randomized study in pediatric patients receiving HSCT. DESIGN AND METHODS: Two hundred and twenty-one consecutive children, recipients of an allogeneic or autologous bone marrow (BM) or peripheral blood progenitor cell (PBPC) transplant, were randomized to either receive rHuG-CSF 10 mg/kg (n=110) or not (n=111). RESULTS: Myeloid engraftment was faster in the treated arm (14 vs 20 days, p=0.0001). Neutrophil recovery was accelerated both in the BM subgroups (allogeneic and autologous, p=0.002) and in the PBPC group (p=0.0005). All the other evaluated variables showed an advantage in favor of rHuG-CSF treated patients that was significant for platelet transfusion independence and time to discharge (p=0.02 and p=0.04, respectively) only in the BM subgroup. INTERPRETATION AND CONCLUSIONS: We conclude that faster neutrophil recovery in BM recipients receiving rHuG-CSF led to clinical benefits, while, in the PBPC subgroup, it did not translate into clinical advantages.     

Evidence for an immune barrier after in utero hematopoietic-cell transplantation

The competence of the immune system of the developing fetus to act as a barrier to in utero hematopoietic-cell transplantation (IUHCT) has been a source of debate. Until now, comparisons of allogeneic and congenic engraftment have been inconclusive due to methodologic limitations resulting in minimal and inefficient engraftment. In this study, E14 fetal mice received transplants of either allogeneic or congenic bone marrow using a new intravascular technique that allows definitive administration of much higher doses of donor cells. Our results demonstrate that 100% of surviving recipients demonstrate engraftment at 1 week of age, but that 70% of allogeneic recipients lose engraftment by 1 month of age, and 80% ultimately fail to sustain long-term chimerism. In contrast, all congenic recipients maintain stable, long-term, multilineage chimerism. These results strongly support an immune barrier to allogeneic engraftment after IUHCT.     

Homeostasis of telomere length rather than telomere shortening after allogeneic peripheral blood stem cell transplantation

Hematopoietic reconstitution after stem cell transplantation requires excessive replicative activity because of the limited number of stem cells that are used for transplantation. Telomere shortening has been detected in hematopoietic cells after bone marrow transplantation. This has been thought to result from excessive replication of the stem cells, with putative concomitant reduction of their replicative potential. Hematopoietic stem cells from cytokine-mobilized peripheral blood are increasingly used for stem cell transplantation. These grafts contain higher numbers of hematopoietic stem cells, resulting in a faster hematopoietic reconstitution. We have performed a combined prospective and cross-sectional study of hematologic recovery and telomere length dynamics in the immediate reconstitution period after allogeneic T-cell-depleted blood stem cell transplantation. We analyzed hematologic recovery and telomere length of granulocytes, monocytes, B cells, and T-cell subsets in 30 donor/recipient combinations. We found fast recovery in combination with transient telomere shortening in the myeloid lineages. This initial reduction of telomere length was followed by an increase in telomere length to such an extent that 1 year after transplantation the telomere length in recipient cells was similar to the telomere length in donor-derived cells. Therefore, our data indicate telomere length homeostasis after peripheral blood stem cell transplantation, implying no loss of replicative capacity of the stem cells. Our data indicate that fast expansion is accompanied by a reduction of telomere length and that telomere length homeostasis is achieved by de novo generation of hematopoietic cells from stem cells without transplantation-related telomere loss.     

Improved survival and leukocyte reconstitution without detrimental effects on engraftment in murine recipients of human recombinant granulocyte colony-stimulating factor after transplantation of T-cell-depleted histoincompatible bone marrow

In vivo administration of human recombinant granulocyte colony-stimulating factor (rG-CSF) was evaluated for effects on survival, hematologic recovery, and engraftment in an allogeneic murine bone marrow transplantation (BMT) model involving T-cell depletion. Post-BMT recipients of continuous subcutaneous infusions of rG-CSF (n = 62) for 14 days had a significant survival advantage compared with post-BMT controls (n = 60) that received phosphate-buffered saline (PBS) infusions. Moreover, recipients of rG-CSF had significantly increased numbers of circulating leukocytes on days 7 and 14 post-BMT. Engraftment was not adversely affected. Administration of rG-CSF after transplantation of T-cell-depleted histoincompatible bone marrow benefits survival and leukocyte recovery without compromising engraftment.     

Granulocyte-macrophage colony-stimulating factor (GM-CSF) and granulocyte colony-stimulating factor (G-CSF) in serum in bone marrow transplanted patients.

Colony-stimulating factors (CSF) are being increasingly used to accelerate hematopoietic recovery after bone marrow transplantation. To study the endogenous serum levels of CSF in bone marrow transplanted patients we have used immunoassays measuring granulocyte-macrophage colony-stimulating factor (GM-CSF) with a sensitivity of 0.10 ng/ml and granulocyte colony-stimulating factor (G-CSF) with a sensitivity of 0.05 ng/ml. Serum samples, taken from the conditioning treatment until engraftment, were analysed in 13 patients receiving allogeneic transplants and in eight patients receiving autologous transplants. Ten patients had acute myeloid leukemia, seven acute lymphoblastic leukemia, one acute undifferentiated leukemia, two non-Hodgkin's lymphoma and one multiple myeloma. Samples were taken 1-2 times before transplantation and 1-2 times per week after transplantation (median of 46 days in allotransplant recipients and 32 days in autotransplant recipients); 17% of the allogeneic transplanted patients and 35% of the autologous transplanted patients had detectable levels of G-CSF. In both types of transplantation the G-CSF concentrations were low: median 0.06 (range 0.05-0.14) and 0.08 (range 0.05-0.40) ng/ml respectively. GM-CSF was detected only in one analysed sample in all patients. There was no evidence of increased CSF levels related to engraftment or documented infections.     

Augmentation of donor bone marrow engraftment in histoincompatible murine recipients by granulocyte/macrophage colony-stimulating factor

T cell depletion of donor bone marrow can prevent graft v host disease (GVHD) in human and murine marrow graft recipients. However, engraftment in the recipient may be compromised as a consequence of donor marrow T cell depletion. The effect of recombinant murine granulocyte/macrophage colony-stimulating factor (rmu GM-CSF) on engraftment and hematologic reconstitution was evaluated in a murine allogeneic bone marrow transplantation (BMT) model involving T cell depletion of marrow. Before transplantation into irradiated mice differing at major and minor histocompatibility loci, rmu GM-CSF was preincubated with T cell-depleted donor marrow. When low degrees of engraftment were noted in control recipients, treatment of donor marrow with high concentrations of rmu GM-CSF led to enhanced engraftment. Ex vivo donor graft incubation with rmu GM-CSF or a single in vivo injection of rmu GM-CSF were both effective means of promoting engraftment. When the engraftment rate in control recipients was high, rmu GM-CSF did not have an identifiable effect. Only slight increases in hematologic recovery were detected regardless of the rate of engraftment. Neither post-BMT survival nor marrow stem cell capacity was affected by rmu GM-CSF incubation. Furthermore, growth factor administration did not have a significant effect on the incidence of GVHD in recipients of non-T cell-depleted bone marrow splenocyte preparations. In vitro natural killer-mediated target cell lysis was not altered by incubation of effector cells with rmu GM-CSF. These results demonstrate the potential of ex vivo rmu GM-CSF treatment of donor marrow to facilitate engraftment across extensive histo- compatibility barriers.     

Transduction of donor hematopoietic stem-progenitor cells with Fas ligand enhanced short-term engraftment in a murine model of allogeneic bone marrow transplantation

Fas-mediated apoptosis is a major physiologic mechanism by which activated T cells are eliminated after antigen-stimulated clonal expansion generates a specific cellular immune response. Because activated T cells are the major effectors of allograft rejection, we hypothesized that genetically modifying allogeneic bone marrow (BM) cells prior to transplantation could provide some protection from host T-cell attack, thus enhancing donor cell engraftment in bone marrow transplantation (BMT). We undertook studies to determine the outcome of lentiviral vector-mediated transduction of Fas ligand (FasL) into lineage antigen-negative (lin(-)) mouse BM cells (lin(-) BMs), in an allogeneic BMT model. FasL-modified lin(-) BMs killed Fas-expressing T cells in vitro. Mice that received transplants of allogeneic FasL(+) lin(-) BMs had enhanced short-term engraftment, after nonmyeloablative conditioning, as compared to controls. We observed no major hepatic toxicity or hematopoietic or immune impairment in recipient mice at these time points. These results suggest potential therapeutic approaches by manipulating lymphohematopoietic stem-progenitor cells to express FasL or other immune-modulating genes in the context of BMT.     

Shortening of telomeres in recipients of both autologous and allogeneic hematopoietic stem cell transplantation

Telomere length of peripheral blood mononuclear cells (PBMCs) from 23 autologous HSCT patients ranging from 4 to 61 years old, and 46 allogeneic HSCT recipients from 6 to 52 years old were studied to confirm whether excessive shortening of telomeres is associated with HSCT. After autologous HSCT, telomere length of PBMCs ranged from 6.8 to 12.0 kb. The comparison between transplanted PBMCs and PBMCs after autologous HSCT showed shortening by up to 1.9 kb (mean +/- s.d.: 0.64 +/- 0.50 kb). There was a difference between autologous HSCT patients and normal volunteers in the slopes of regression lines. After allogeneic HSCT, telomere length of PBMCs ranged from 6.8 to 12.0 kb. Telomeres of recipients were up to 2.1 kb (0.60 +/- 0.468 kb) shorter than those of donors. The slope of regression lines for allogeneic HSCT patients and normal volunteers were parallel. Although all patients were transplanted with more than 2.0 x 10(8) cells/kg, telomere length did not correlate with the number of transplanted cells. There was no significant correlation between telomere length and recovery of hematological parameters. However, three patients with an average telomere length of 6.8 kb after HSCT took a longer period to reach the normal hematological state. Taken together, these data suggest that most HSCTs are performed within the biological safety range of telomeres, while the patients who have telomeres shorter than 7.0 kb after HSCT should be observed carefully for long-term hematopoiesis and the occurrence of hematopoietic disorders.     

Allogenic fetal liver cells have a distinct competitive engraftment advantage over adult bone marrow cells when infused into fetal as compared with adult severe combined immunodeficient recipients

In utero transplantation (IUT) is becoming a viable option for the treatment of various immune and metabolic disorders diagnosed early in gestation. In this study, donor fetal liver cells had a 10-fold competitive engraftment advantage relative to adult bone marrow in allogeneic fetal severe combined immunodeficient (SCID) recipients compared with adult recipients. In contrast, adult bone marrow cells engrafted slightly better than fetal liver cells in allogeneic adult SCID transplant recipients. By using different ratios of fetal and adult cell mixtures, fetal liver cells repopulated 8.2 times better than adult bone marrow cells in fetal recipients, but only 0.8 times as well in adult recipients. Fetal SCID recipients were more permissive to an allogeneic donor graft than adult recipients. These data indicate that the recipient microenvironment may regulate the engraftment efficiency of a given stem cell source and suggest that the use of cord blood should be tested in clinical IUT.     

Graft-versus-leukemia following bone marrow transplantation

Considerable data in animals suggest an anti-leukemia reaction associated with transplantation of allogeneic bone marrow cells. In some instances, this graft-versus leukemia (GVL) reaction may be distinct from graft-versus-host-disease (GVHD). Data in humans also support the concept of a GVL effect associated with bone marrow transplantation. These observations include an increased risk of leukemia relapse in identical twin transplants and in recipients of T cell-depleted allogeneic transplants, and a decreased risk-of leukemia relapse in individuals who develop acute or chronic GVHD. These findings are among the most convincing evidence that the immune system plays a role against cancer in man.