Pluripotent and myeloid-committed CD34+ subsets in hematopoietic stem cell allografts

The present study compared the contents of pluripotent and lineage-committed hematopoietic progenitor cells (HPCs) in various types of allografts. Bone marrow (BM) allografts and single leukapheresis products (LPs) collected from G-CSF-mobilized donors contained similar amounts of pluripotent HPCs (CD34(+)CD38(-)) and total CD34(+) cells. However, the content of late-myeloid HPCs (CD34(+)CD33(+)CD15(+)) were significantly higher in BM grafts compared to LPs (P>0.02), whereas the contents of early-myeloid HPCs (CD34(+)CD33(+)CD15-) were 2.5-fold higher in LPs (P<0.03). In comparison to grafts from adult donors, cord blood (CB) grafts contained 26-65-fold lower amounts of early-myeloid HPCs (P<0.001), but only 8-12-fold lower contents of pluripotent HPCs (P<0.04). Additional findings demonstrated that among all tested parameters the numbers of early-myeloid HPCs were the most accurate measure of the total colony-forming cell (CFC) numbers in allografts. Hence, the earlier engraftment observed after transplantation of LPs compared to BM grafts might be explained by the higher content of early-myeloid HPCs/CFCs in LPs. Moreover, the slow engraftment following CB transplantation might not be affected essentially by the low number of myeloid HPCs, but rather by pluripotent HPCs. Finally, this study reports a new gating strategy for the enumeration of pluripotent CD34(+)CD38(-) subsets.     

Flow cytometric assessment of lymphocyte subsets, lymphoid progenitors, and hematopoietic stem cells in allogeneic stem cell grafts.

Currently, bone marrow (BM), cord blood (CB), and G-CSF-mobilized peripheral blood progenitor cells (PBPCs) are the most commonly used sources for allogeneic stem cell transplantation (SCT). The aim of this study was to assess the yields and distribution of lymphocyte subsets, lymphocyte progenitors and hematopoietic stem cells (HSC) in each type of allograft by three-color flow cytometry. The yields of CD34(+)CD38(-) HSCs did not differ significantly between BM grafts (2.80 +/- 0.74 x 10(6)) and leukapheresis products (LPs) (1.82 +/- 0.64 x 10(6)), and were lowest in CB grafts (0.21 +/- 0.05 x 10(6)). For most lymphocyte subsets yields were lowest in CB grafts and significantly higher in LPs than in BM grafts. BM grafts, however, contained the highest yields of CD34(+)CD19(+)CD20(-) B cell progenitors and CD19(+)CD20(-) B cells. The relative frequencies of the naive CD45RA(+)CD45RO(-) phenotype among CD4(+) and CD8(high) T cells were highest in CB grafts (P < or = 0.001), and higher in LPs than in BM grafts (P < or = 0.02). The latter finding was in accordance with a preferential G-CSF mobilization of naive T cells relative to the total lymphocyte population (P < or = 0.014). CD3(+)CD8(low) and CD3(+)CD8(low)CD4(-) subsets, which facilitate engraftment in murine transplantation models, demonstrated a tendency towards lower frequencies among T cells in CB grafts and LPs compared to BM grafts. This observation coincided with a significantly reduced mobilization of subsets potentially enriched for facilitating cells as compared to the total lymphocyte population (P < or = 0.036). The CD34(+) compartment of CB grafts contained a significantly higher percentage (12.1%) of CD34(+)CD7(+)CD3(-) T cell progenitors than those of BM grafts (5.1%) and LPs (3.6%). In addition, CB lymphocytes contained the highest fraction of CD3(-)CD16/56(+) NK cells (P < or = 0.013) and almost no CD3(+)CD16/56(+) NKT cells (P < 0.001) compared to adult cell sources. In summary, LPs, CB allografts and BM allografts differ widely with respect to the cellular composition of their lymphocyte compartments, which is partially affected by a varying mobilization efficiency of G-CSF for distinct lymphocyte subsets.     

A comparative study of CD34+ cells, CD34+ subsets, colony forming cells and cobblestone area forming cells in cord blood and bone marrow allografts

Cord blood (CB) has become an alternative source of hematopoietic progenitor cells (HPCs) for allogeneic transplantation. We have developed a new efficient protocol for CB collection. Using this method an average of 17.7 x 10(8) [range (6.8-29.6) x 10(8), n = 13] total nucleated cells (TNCs) were harvested. Based on recent Eurocord data, which have shown safe engraftment using a threshold dose of 0.37 x 10(8) CB TNCs/kg body weight (BW), we calculated that six out of thirteen CB grafts collected by this method were sufficient to engraft adults. The CB derived CD34+ population contained two-fold higher numbers of committed HPCs (CFU-GM, BFU-E) and six-fold higher numbers of pluripotent HPCs [CD34+/CD38- cells, wk 5 and wk 8 cobblestone area forming cells (CAFCs)] than the CD34+ population of BM. Extrapolation revealed that BM grafts providing the threshold dose for allogeneic transplantation of 2 x 10(8) TNCs/kg BW contained nearly 3 times more pluripotent HPCs than CB grafts providing the Eurocord threshold dose. The assessment of CD34+/CD38(-) cell numbers in CB grafts was highly reproducible and correlated well with the in vitro performance of pluripotent HPCs, i.e. numbers of CAFCs. We conclude that CB grafts providing high numbers of TNCs have the potential to engraft adults and that the enumeration of pluripotent HPCs by flow cytometry may be a useful tool to define the ultimate threshold dose for CB transplantation.     

Characterization of CD34+ peripheral blood cells from healthy adults mobilized by recombinant human granulocyte colony-stimulating factor

Primed peripheral blood hematopoietic stem cells (PBSC) generate and sustain lymphohematopoiesis in myeloablated animals, and recent reports indicate that allogeneic transplantation using PBSC grafts may be feasible in humans. A major concern with the use of PBSC transplants is that permanent engraftment may be limited because of lack of sufficient numbers of primitive progenitor cells in the graft. In the present study, in vitro colony formation and immunophenotype of CD34+ cells in PB of healthy adults during short-term granulocyte colony-stimulating factor (G-CSF) administration were compared with that of CD34+ cells in normal bone marrow (BM). The number of CD34+ cells mobilized to PB peaked at day 4 or 5 of G-CSF administration. The phenotypic profile of CD34+ PB cells showed a substantial increase in the percentage of CD34+CD13+ and CD34+CD33+ cells (myeloid progenitors) and a corresponding decrease in the percentage of CD34+CD10+ and CD34+CD19+ cells (B lymphoid progenitors) compared with CD34+ BM cells. The other subsets studied, including CD34+CD38- and CD34+HLA-DR- cells, were present in both compartments in similar proportions. Furthermore, primed CD34+ PB cells were enriched for colony-forming cells (CFC) and displayed an increased clonogenicity when compared with their counterparts in BM. A comparison between a postulated PBSC graft and an average BM graft is presented, showing that such PBSC grafts will be enriched for CD34+ cells as a whole, CD34+CD33+ cells, and colony- forming cells (CFC), factors which have been shown to correlate to acceleration of hematologic reconstitution and reduction in requirements for supportive care in autografting. Hence, we predict that allogeneic transplantation using G-CSF-primed PBSC grafts will result in a more rapid hematologic reconstitution after myeloablative conditioning than BM grafting. The question of whether PBSC allografting will result in permanent engraftment and clinical benefits as observed in autografting has to be determined in prospective clinical studies.     

Enhanced antileukemic activity of allogeneic peripheral blood progenitor cell transplants following donor treatment with the combination of granulocyte colony-stimulating factor (G-CSF) and stem cell factor (SCF) in a murine transplantation model

Allogeneic peripheral blood progenitor cells (PBPCs) have mostly been mobilized by granulocyte colony-stimulating factor (G-CSF). There is neither clinical nor experimental data available addressing the question if other hematopoietic growth factors or combinations thereof might influence engraftment, graft-versus-host disease (GvHD), and graft-versus-leukemia (GvL) effects after allogeneic peripheral blood progenitor cell transplantation (PBPCT). We used a murine model to investigate these parameters after transplantation of PBPCs mobilized with G-CSF and SCF either alone or in combination. Treatment of splenectomized DBA and Balb/c mice with 250 microg/kg/day G-CSF for 5 days resulted in an increase of CFU-gm from 0 to 53/microl. The highest progenitor cell numbers (147/microl) were observed after treatment with 100 microg/kg/day SCF administered in conjunction with G-SCF. No differences were detected with regard to the number of T cells (CD3+), T cell subsets (CD4+, CD8+), B cells (CD19+) and NK cells (NK1.1+) in PBPC grafts mobilized by G-CSF plus SCF compared to those mobilized with G-CSF alone. The antileukemic activity of syngeneic and MHC-identical allogeneic PBPC grafts was investigated in lethally irradiated Balb/c mice bearing the B-lymphatic leukemia cell line A20. In this model, PBPCs mobilized by G-CSF plus SCF exerted a significantly higher antileukemic activity compared to grafts mobilized by G-CSF alone (94 vs 71% freedom from leukemia at day 100, P<0.05). The antileukemic effect was lowest after BMT (38% freedom from leukemia). Since significant differences in the incidence of lethal GvHD were not observed, improved GVL-activity resulted in superior overall survival. Our data demonstrate that the utilization of specific hematopoietic growth factors not only improve the yield of hematopoietic progenitor cells but can also significantly enhance the immunotherapeutic potential of allografts.     

Peripheral blood progenitor cell (PBPC) counts during steady-state hematopoiesis allow to estimate the yield of mobilized PBPC after filgrastim (R-metHuG-CSF)-supported cytotoxic chemotherapy [see comments]

Peripheral blood progenitor cells (PBPC) can be mobilized using cytotoxic chemotherapy and cytokines. There is a substantial variability in the yield of hematopoietic progenitor cells between patients. We were looking for predictive parameters indicating a patient's response to a given mobilization regimen. Multiparameter flow- cytometry analysis and clonogenic assays were used to examine the hematopoietic progenitor cells in bone marrow (BM) and peripheral blood (PB) before filgrastim (R-metHuG-CSF; Amgen, Thousand Oaks, CA)- supported chemotherapy and in PB and leukapheresis products (LPs) in the recovery phase. Fifteen patients (four with high-grade non- Hodgkin's lymphoma [NHL], two with low-grade NHL, two with Hodgkin's disease, two with multiple myeloma, three with breast cancer, one with ovarian cancer, and one with germ cell tumor) were included in this study. The comparison of immunofluorescence plots showed a homogenous population of strongly CD34+ cells in steady-state and mobilized PB whereas in steady-state BM, the CD34+ cells ranged from strongly positive with continuous transition to the CD34- population. Consistent with the similarity in CD34 antigen expression, a correlation analysis showed steady-state PB CD34+ cells (r = .81, P < .001) and colony- forming cells (CFCs; r = .69, P < .01) to be a measure of a patient's mobilizable CD34+ cell pool. Individual estimates of progenitor cell yields could be calculated. With a probability of 95%, eg, 0.4 steady- state PB CD34+ cells x 10(6)/L allowed to collect in six LPs 2.5 x 10(6) CD34+ cells/kg, the reported threshold-dose of progenitor cells required for rapid and sustained engraftment after high-dose therapy. For the total steady-state BM CD34+ cell population, a weak correlation (r = .57, P < .05) with the mobilized CD34+ cells only became apparent when an outlier was removed from the analysis. Neither the CD34+ immunologic subgroups defined by the coexpression of the myeloid lineage-associated antigens CD33 or CD45-RA or the phenotypically primitive CD34+/HLA-DR- subset nor the BM CFC count had a predictive value for the mobilization outcome. This may be caused by the additional presence of maturing progenitor cells in BM, which express lower levels of the CD34 antigen and do not circulate. Our results permit us to recognize patients who are at risk to collect low numbers of progenitor cells and those who are likely to achieve sufficient or high progenitor cell yields even before mobilization chemotherapy is administered.     

Ex vivo expansion of enriched peripheral blood CD34+ progenitor cells by stem cell factor, interleukin-1 beta (IL-1 beta), IL-6, IL-3, interferon-gamma, and erythropoietin

To provide sufficient numbers of peripheral blood progenitor cells (PBPCs) for repetitive use after high-dose chemotherapy, we investigated the ability of hematopoietic growth factor combinations to expand the number of clonogenic PBPCs ex vivo. Chemotherapy plus granulocyte colony-stimulating factor (G-CSF) mobilized CD34+ cells from 18 patients with metastatic solid tumors or refractory lymphomas were cultured for up to 28 days in a liquid culture system. The effects of interleukin-1 beta (IL-1), IL-3, IL-6, granulocyte-macrophage-CSF (GM-CSF), G-CSF, macrophage-CSF (M-CSF), stem cell factor (SCF), erythropoietin (EPO), leukemia inhibitory factor (LIF), and interferon- gamma, as well as 36 combinations of these factors were tested. A combination of five hematopoietic growth factors, including SCF, EPO, IL-1, IL-3, and IL-6, was identified as the optimal combination of growth factors for both the expansion of total nucleated cells as well as the expansion of clonogenic progenitor cells. Proliferation peaked at days 12 to 14, with a median 190-fold increase (range, 46- to 930- fold) of total clonogenic progenitor cells. Expanded progenitor cells generated myeloid (colony-forming unit-granulocyte-macrophage), erythroid (burst-forming unit-erythroid), as well as multilineage (colony-forming unit-granulocyte, erythrocyte, monocyte, megakaryocyte) colony-forming units. The number of multilineage colonies increased 250- fold (range, 33- to 589-fold) as compared with pre-expansion values. Moreover, the absolute number of early hematopoietic progenitor cells (CD34+/HLA-DR-; CD34+/CD38-), as well as the number of 4-HC-resistant progenitors within expanded cells increased significantly. Interferon- gamma was shown to synergize with the 5-factor combination, whereas the addition of GM-CSF significantly decreased the number of total clonogenic progenitor cells. Large-scale expansion of PB CD34+ cells (starting cell number, 1.5 x 10(6) CD34+ cells) in autologous plasma supplemented with the same 5-factor combination resulted in an equivalent expansion of progenitor cells as compared with the microculture system. In summary, our data indicate that chemotherapy plus G-CSF-mobilized PBPCs from cancer patients can be effectively expanded ex vivo. Moreover, our data suggest the feasibility of large- scale expansion of PBPCs, starting from small numbers of PB CD34+ cells. The number of cells expanded ex vivo might be sufficient for repetitive use after high-dose chemotherapy and might be candidate cells for therapeutic gene transfer.     

Engraftment of human hematopoietic precursor cells with secondary transfer potential in SCID-hu mice

Human fetal bone fragments implanted subcutaneously in immunodeficient (SCID) mice maintain active human hematopoiesis. In this study, we show that this human hematopoietic microenvironment supports the engraftment and differentiation of HLA-mismatched, CD34+ primitive hematopoietic progenitor cells isolated from fetal and adult human bone marrow (BM). The BM CD34+ cells were depleted of CD2, CD14, CD15, CD16, glycophorin A, and CD19 lineage-committed cells (CD34+Lin-). Donor cell engraftment was manifested by the presence of B (CD19+) and myeloid (CD33+) cells of donor HLA phenotype. Successful engraftment was observed as early as 4 weeks after fetal BM donor cell injection and sustained for at least 12 weeks, with engraftment success rates of 100% (11/11 grafts) and 92% (11/12 grafts) at 8 and 12 weeks, respectively. Mixed BM chimerism of donor and endogenous cells was consistently observed in SCID-hu bones successfully engrafted with HLA-mismatched CD34+Lin- donor cells. Preconditioning of the SCID-hu bone with a single dose of sublethal (350 rad) whole body irradiation (WBI) immediately before cell injection enhanced the repopulation of the bone grafts with donor cells and, in some instances, resulted in complete repopulation. After WBI, as few as 500 fetal bone marrow CD34+Lin- cells injected in the human bone grafts resulted in donor-derived hematopoiesis. Donor progenitor cells recovered from the SCID-hu bone grafts 8 weeks postinjection had the capacity to repopulate secondary groups of HLA-disparate fetal human bones in SCID-hu mice with B and myeloid cells as well as CD34+ cells in some recipients. In addition, these cells repopulated fetal human thymus fragments in SCID mice with donor thymocytes including immature CD4+CD8+ and mature CD4+CD8- as well as CD4-CD8+ subsets. These results indicate that the fetal human bone implants of SCID-hu mice can support the maintenance of a cell population that has both multilineage potential and repopulating potential for periods of time as long as 16 weeks. The SCID-hu bone model consistently supported the engraftment of both fetal and adult CD34+Lin- cells without the administration of exogenous human cytokines to these animals. This model is currently being used to permit the isolation and characterization of candidate human hematopoietic stem cells (HSCs) and provide important information critical for human HSC therapy in humans.     

Peripheral Blood Progenitor Cell Transplantation

Abstract: Peripheral blood progenitor cells (PBPCs) have become increasingly popular over the last 15 years as the source of hematopoietic stem cells for transplantation. In the early 1990s, PBPCs replaced bone marrow (BM) as the preferred source of autologous stem cells, and recently the same phenomenon is seen in the allogeneic setting. Under steady‐state conditions, the concentration of PBPCs (as defined by CFU‐GM and/or CD34+ cells) is very low, and techniques were developed to increase markedly this concentration. Such mobilization techniques include daily injections of filgrastim (G‐CSF) or a combination of chemotherapy and growth factors. Leukapheresis procedures allow the collection of large numbers of circulating white blood cells (and PBPCs). One or two leukapheresis procedures are often sufficient to obtain the minimum number of CD34+ cells considered necessary for prompt and consistent engraftment (i.e., 2.5–5.0 × 10⁶/kg). As compared to BM, autologous transplants with PBPCs lead to faster hematologic recovery and have few, if any, disadvantages. In the allogeneic arena, PBPCs also result in faster engraftment, but at a somewhat higher cost of chronic graft‐versus‐host disease (GvHD). This may be a double‐edged sword leading to both increased graft‐versus‐tumor effects and increased morbidity. The rapid advances in the study of hematopoietic, and even earlier, stem cells will continue to shape the future of PBPC transplantation.     

Adenoviral vector-mediated gene transfer to primitive human hematopoietic progenitor cells: assessment of transduction and toxicity in long-term culture

Adenoviral gene transfer to primitive hematopoietic progenitor cells (HPCs) would be useful in gene therapy applications where transient, high-level transgene expression is required. In the present investigations, we have used an adenoviral vector expressing the green fluorescent protein (AdGFP) to quantify transduction of primitive HPCs and assess adenoviral-associated toxicity in long-term culture. Here we show that a cytokine cocktail protects mass populations of CD34(+) cells and primary colony forming unit-cultures (CFU-Cs) from toxicity, enabling transduction of up to 79% of CD34(+) cells. Transduction of CFU-Cs and more primitive HPCs was quantified following fluorescence activated cell sorting for green flourescence protein expression. Our results demonstrate transduction of 45% of primary CFU-Cs, 33% of week-5 cobblestone area forming cells (CAFCs), and 18% of week-5 CFU-Cs. However, AdGFP infection inhibited proliferation of more primitive cells. Although there was no apparent quantitative change in week-5 CAFCs, the clonogenic capacity of week-5 AdGFP-infected cells was reduced by 40% (P <.01) when compared with mock-infected cells. Adenoviral toxicity specifically affected the transduced subset of primitive HPCs. Transduction of primitive cells is therefore probably underestimated by week-5 CFU-Cs and more accurately indicated by week-5 CAFCs. These studies provide the first functional and quantitative evidence of adenoviral transduction of primitive HPCs. However, further investigations will be necessary to overcome adenoviral toxicity toward primitive HPCs before adenoviral vectors can be considered a safe option for gene therapy.     

Human CD34+AC133+VEGFR-2+ cells are not endothelial progenitor cells but distinct, primitive hematopoietic progenitors

OBJECTIVE: Endothelial progenitor cells (EPCs) are used for angiogenic therapies or as biomarkers to assess cardiovascular disease risk. However, there is no uniform definition of an EPC, which confounds EPC studies. EPCs are widely described as cells that coexpress the cell-surface antigens CD34, AC133, and vascular endothelial growth factor receptor-2 (VEGFR-2). These antigens are also expressed on primitive hematopoietic progenitor cells (HPCs). Remarkably, despite their original identification, CD34+AC133+VEGFR-2+ cells have never been isolated and simultaneously plated in hematopoietic and endothelial cell (EC) clonogenic assays to assess the identity of their clonal progeny, which are presumably the cellular participants in vascular regeneration. METHODS: CD34+AC133+VEGFR-2+ cells were isolated from human umbilical cord blood (CB) or granulocyte colony-stimulating factor-mobilized peripheral blood and assayed for either EPCs or HPCs. RESULTS: CD34+AC133+VEGFR-2+ cells did not form EPCs and were devoid of vessel forming activity. However, CD34+AC133+VEGFR-2+ cells formed HPCs and expressed the hematopoietic lineage-specific antigen, CD45. We next tested whether EPCs could be separated from HPCs by immunoselection for CD34 and CD45. CD34+CD45+ cells formed HPCs but not EPCs, while CD34+CD45- cells formed EPCs but not HPCs. CONCLUSIONS: Therefore, CD34+AC133+VEGFR-2+ cells are HPCs that do not yield EC progeny, and the biological mechanism for their correlation with cardiovascular disease needs to be reexamined.     

Blood-derived autografts collected during granulocyte colony- stimulating factor-enhanced recovery are enriched with early Thy-1+ hematopoietic progenitor cells

It was the objective of the study to characterize CD34+ hematopoietic progenitor cells from peripheral blood (PB) and bone marrow (BM) in a group of 24 cancer patients. After cytotoxic chemotherapy, R-metHu granulocyte colony-stimulating factor (R-metHuG-CSF; filgrastim, 300 micrograms daily, subcutaneously) was given to shorten the time of neutropenia as well as to increase the rebound of peripheral blood progenitor cells (PBPC) for harvesting. The proportion of CD34+ cells in the leukapheresis products (LPs) was 1.4-fold greater than in BM samples that were obtained at the same day (LP: median, 1.4% v BM: median, 1.0%, P < .01). Two- and three-color immunofluorescence showed that blood-derived CD34+ cells comprised a greater proportion of a particular early progenitor cell than CD34+ cells of bone marrow. Blood- derived progenitor cells tended to have a higher mean fluorescence intensity of CD34 and expressed significantly lower levels of HLA-DR (mean fluorescence intensity of HLA-DR: 442.6 +/- 44.9 [LP] v 661.5 +/- 64.6 [BM], mean +/- SEM, P < .01). Furthermore, the blood-derived CD34+ cells comprised a 1.7-fold greater proportion of Thy-1+ cells (LP: median, 24.4% v BM: median, 14.4%, P < .001) and expressed significantly less c-kit (LP: median, 20.5% v BM: median, 31.0%, P < .01). Three-color analysis showed that high levels of Thy-1 expression were restricted to CD34+/HLA-DRdim or CD34+/HLA-DR- cells confirming the early developmental stage of this progenitor cell subset. The proportion of CD34+/CD45RA(bright) cells representing late colony- forming unit granulocyte-macrophage (CFU-GM) was smaller in LPs compared with BM (P < .05). For an examination of BM CD34+ cells before the mobilization chemotherapy, samples of 16 patients were available. The mean proportion of c-kit expressing CD34+ cells in the bone marrow during G-CSF-stimulated reconstitution decreased 1.8-fold compared with baseline values. There was no difference in the proportion of BM- derived CD34+/Thy-1+ cells and CD34+/CD45RA+ cells between steady-state hematopoiesis and G-CSF-supported recovery. Our data suggest that during G-CSF-enhanced recovery, CD34+ cells in the PB are enriched with more primitive progenitor cells to evenly replenish the BM after the chemotherapy-related cytotoxic damage.     

Primitive hematopoietic cell populations reside in the spleen: Studies in the pig, baboon, and human

OBJECTIVE: We previously observed high levels (>40%) of multilineage hematopoietic cell chimerism following spleen transplantation across full MHC barriers in immunosuppressed miniature swine. We therefore investigated the spleen as a source of hematopoietic progenitor cells (HPCs). MATERIALS AND METHODS: Specific cell-surface markers were used to identify HPCs in the spleen and bone marrow (BM) of young adult (n = 15) and fetal (n = 9) miniature swine by flow cytometry. Hoechst dye-effluxing side population (SP) cells were analyzed in adult spleen, BM, and blood for their expression of c-kit. Functional HPC activity of varying repopulation potential in vitro was investigated by the ability of spleens and BM to give rise to colony-forming units (CFUs) and cobblestone area-forming cells (CAFCs) in long-term stromal cultures. Studies were also carried out on baboon and human spleens and BM. RESULTS: Spleen c-kit+ cells co-expressed more lymphoid markers, but equal myeloid markers, when compared with BM c-kit+ cells. BM and spleen both contained significant percentages of c-kit+ SP cells. Although the frequency of early-forming CFUs in the spleen was only 0.1 to 1.3% of that in the BM, the frequency of CAFCs developing after 8 weeks in culture was comparable to that of BM. Secondary CFUs in long-term culture-initiating cell assays confirmed the presence of long-term repopulating cells at comparable frequencies in spleen and BM. Similar findings were found with regard to baboon and human spleen cells. CONCLUSION: The adult spleen is a relatively rich source of very primitive HPCs, possibly hematopoietic stem cells (HSCs), and may be of therapeutic value.     

Granulocyte colony-stimulating factor mobilizes into peripheral blood the complete clonal repertoire of hematopoietic precursors residing in the bone marrow of mice

We have established the clonal relationships between the hematopoietic precursors residing in the bone marrow (BM) and the peripheral blood (PB) of mice treated with granulocyte colony-stimulating factor (G- CSF). The use of animals whose hematopoiesis was reconstituted with genetically labeled stem cells has allowed us to show that an almost identical repertoire of clones is found in the colony-forming unit (CFU- S) population present in the BM and mobilized PB. Moreover, our data has shown that the frequency of expression of the repopulating clones in both types of CFU-S populations is the same, evidencing that G-CSF mobilized PB progenitor cells (PBPCs) closely reflect the clonal make- up of the hematopoietic precursors residing in the BM. When secondary recipients were transplanted with BM or mobilized PB grafts that had been harvested from the genetically marked mice, the presence of long- term lympho-hematopoietic repopulating clones was showed not only in the BM but also in the PB samples. No new clones were identified in the long-term repopulating cells of the mobilized animals with respect to those found in the CFU-S population. Moreover, the hematopoietic precursors that were capable of long-term reconstitution corresponded to the clones, which were most highly represented in the CFU-S compartment, suggesting, at least in the case of G-CSF treated mice, that the frequency of expression of the repopulating clones in the CFU- S population is prognostic for the clone longevity. Based on our experimental data, new advantages for the use of mobilized PBPCs in place of hematopoietic grafts procured from limited areas of BM are proposed.     

A comparative study of the phenotype and proliferative capacity of peripheral blood (PB) CD34+ cells mobilized by four different protocols and those of steady-phase PB and bone marrow CD34+ cells

Peripheral blood (PB) CD34+ cells from four commonly used mobilization protocols were studied to compare their phenotype and proliferative capacity with steady-state PB or bone marrow (BM) CD34+ cells. Mobilized PB CD34+ cells were collected during hematopoietic recovery after myelosuppressive chemotherapy with or without granulocyte- macrophage colony-stimulating factor (GM-CSF) or granulocyte colony- stimulating factor (G-CSF) or during G-CSF administration alone. The expression of activation and lineage-associated markers and c-kit gene product were studied by flow cytometry. Proliferative capacity was measured by generation of nascent myeloid progenitor cells (granulocyte- macrophage colony-stimulating factor; CFU-GM) and nucleated cells in a stroma-free liquid culture stimulated by a combination of six hematopoietic growth factors (interleukin-1 (IL-1), IL-3, IL-6, GM-CSF, G-CSF, and stem cell factor). G-CSF-mobilized CD34+ cells have the highest percentage of CD38- cells (P < .0081), but otherwise, CD34+ cells from different mobilization protocols were similar to one another in their phenotype and proliferative capacity. The spectrum of primitive and mature myeloid progenitors in mobilized PB CD34+ cells was similar to their steady-state counterparts, but the percentages of CD34+ cells expressing CD10 or CD19 were lower (P < .0028). Although steady-state PB and chemotherapy-mobilized CD34+ cells generated fewer CFU-GM at day 21 than G-CSF-mobilized and steady-state BM CD34+ cells (P < .0449), the generation of nucleated cells and CFU-GM were otherwise comparable. The presence of increased or comparable numbers of hematopoietic progenitors within PB collections with equivalent proliferative capacity to BM CD34+ cells is not unexpected given the rapid and complete hematopoietic reconstitution observed with mobilized PB. However, all four types of mobilized PB CD34+ cells are different from steady-state BM CD34+ cells in that they express less c-kit (P < .0002) and CD71 (P < .04) and retain less rhodamine 123 (P < .0001). These observations are novel and suggest that different mobilization protocols may act via similar pathways involving the down-regulation of c-kit and may be independent of cell-cycle status.     

The impact of graft composition on clinical outcomes in unmanipulated HLA-mismatched/haploidentical hematopoietic SCT

This study examines the absolute numbers and relative proportions of CD4+, CD8+, CD14+ and CD34+ cells contained in allografts and their impact on early engraftment and later clinical outcomes in 141 patients with hematological malignancies who underwent unmanipulated HLA-mismatched/haploidentical hematopoietic SCT without in vitro T-cell depletion. These patients received G-CSF-primed BM grafts (G-BM) and peripheral blood grafts (G-PB) following a modified regimen of BU/CY 2 plus antithymocyte globulin. Multivariate analysis showed that high CD34+ cell numbers were associated with accelerated plt engraftment (P=0.001). Meanwhile, patients with a higher CD4/CD8 ratio in G-BM (> or =1.16) had a survival disadvantage (P<0.01) and a trend towards relapse (P=0.086) after controlling for disease status. A higher CD4/CD8 was also associated with a significantly increased risk of acute GVHD grades II-IV (P=0.013), even after adjusting for an ABO major mismatch. No aspect of graft composition affected neutrophil engraftment or chronic GVHD. In conclusion, the differences in CD34+ cell dose and the CD4/CD8 ratio in grafts seem to affect engraftment and clinical outcomes; in particular, a lower CD4/CD8 ratio in primed BM graft is associated with a survival benefit.     

Engraftment potential of different sources of human hematopoietic progenitor cells in BNX Mice

Human hematopoietic progenitor cells (HPCs) from mobilized peripheral blood mononuclear cells (PBMCs), adult bone marrow (ABM), and fetal bone marrow (FBM) were evaluated for their ability to produce multilineage human hematopoietic engraftment in vivo. Sublethally irradiated BNX (beige/nude/xid) mice were injected with either unfractionated cells or CD34+ cells purified from these sources. The presence of human cells in the mouse PB, BM, and spleen was evaluated by flow cytometry at either 6 to 8 weeks or 6 months postinjection. Recipients with > or = 1% human cells in any of these tissues were considered chimeric. Of 26 mice injected with FBM, 4 showed up to 73% human cells in the BM or spleen at 6 months. The phenotypes of these cells included CD13/33+ myelomonocytic cells (38%), CD19+ B cells (67%), and CD34+ progenitor cells (28%). In contrast, ABM gave rise to a mean of 5% human cells in the PB in 2 of 42 (4%) recipients at 6 to 8 weeks. These circulating human cells were predominantly CD3+, whereas CD13/33+ and CD34+ cells were detected in the BM for up to 6 months. A total of 18% of mice injected with PBMCs showed a mean of 36% human cells in the PB. Both the BM and spleens of PBMC-injected mice contained CD3+ cells in a proportion similar to that observed in the PB. These CD3+ cells were phenotypically mature CD4+,CD8- or CD4-,CD8+ T cells and coexpressed a variety of Vbeta T-cell receptor (TCR) genes. The percentage of CD3+ cells in the circulation of chimeric recipients injected with either FBM, ABM, or PBMCs correlated well with the input CD3+ cell dose for each of these HPC sources (r = .99). The high levels of engraftment of CD3+ cells in recipients of PBMCs and the long-term multilineage engraftment of FBM recipients have important implications for developing strategies to study the regulation of these human cells in vivo.     

Positively selected autologous blood CD34+ cells and unseparated peripheral blood progenitor cells mediate identical hematopoietic engraftment after high-dose VP16, ifosfamide, carboplatin, and epirubicin

To investigate the feasibility of peripheral blood CD34+ cell selection and to analyze CD34+ cell-mediated engraftment after high-dose chemotherapy, we performed a phase I/II trial in 21 patients with advanced malignancies. The rationale for the selection of CD34+ cells from peripheral blood progenitor cell (PBPC) collections is based on the observation that contaminating tumor cells can be depleted approximately 3 logs using this procedure. CD34+ cells from chemotherapy+granulocyte colony-stimulating factor-mobilized PBPCs were positively selected with an avidin-biotin immunoadsorption column (CEPRATE SC system). One leukapheresis product with a median number of 2.8 x 10(6) CD34+ cells/kg was labeled with a biotinylated anti-CD34 monoclonal antibody and subsequently processed over the column. The yield of selected CD34+ cells was 73% +/- 24.6%. The purity of the CD34+ cell fraction was 61.4% +/- 19.7%. CD34+ cells were shown to represent predominantly committed progenitors coexpressing CD33, CD38, and HLA-DR molecules (lin+). They gave rise to myeloid as well as erythroid and multilineage colonies in vitro. In addition, positively selected CD34+ cells also comprised early hematopoietic progenitor cells, as shown by the presence of CD34+/lin- cells. Transfusion of positively selected CD34+ cells (2.5 x 10(6) CD34+/kg; range, 0.45 to 5.1) after high-dose VP16 (1,500 mg/m2), ifosfamide (12 g/m2), carboplatin (750 mg/m2), and epirubicin (150 mg/m2) (VIC-E) in 15 patients resulted in a rapid and stable engraftment of hematopoiesis without any adverse events. As compared with 13 historical control patients reconstituted with a comparable number of unseparated PBPCs, time to neutrophil and platelet recovery was identical in both groups (absolute neutrophil count > 500/microL, day + 12; platelet count > 50,000/microL, day + 15). These data indicate that autologous peripheral blood CD34+ cells and unseparated PBPCs mediate identical reconstitution of hematopoiesis after high-dose VIC-E chemotherapy. Because positive selection of CD34+ cells from mobilized blood results in a median 403-fold depletion of T cells, allogeneic CD34+ cells from mobilized blood should be investigated as an alternative to bone marrow cells for allotransplantation.     

Progenitor content of autologous grafts: mobilized bone marrow vs mobilized blood

The progenitor content of autologous peripheral blood progenitor and stem cell collections is a major determinant of prompt hematopoietic recovery following autologous stem cell transplantation. We analyzed unstimulated bone marrow (BM) and peripheral blood (PB) apheresis products in comparison to those collected following G-CSF or GM-CSF stimulation. We quantitated their committed (CFU-GM) and primitive (long-term culture-initiating cells, LTC-IC) progenitors in relation to hematologic recovery in 63 patients undergoing autografting for lymphoid malignancies. G-CSF, but not GM-CSF, substantially enriched the committed progenitor content (2.5-3.6-fold) of both PB and BM grafts. G-CSF also enriched the LTC-IC content of BM and PB compared to control grafts. GM-CSF augmented (11.5-fold) the LTC-IC content of stimulated BM, but not GM-CSF-mobilized PB. Neutrophil recovery was substantially quicker in recipients of BM or PB mobilized with G-CSF or GM-CSF. In contrast, red cell and platelet recovery was accelerated in recipients of GM-CSF-stimulated BM (but not PB) and G-CSF-stimulated PB (but not BM). No direct correlation between progenitor dose and hematopoietic recovery for neutrophils, platelets or red cells was observed. Cytokine stimulation can augment the committed and more primitive multilineage progenitor content of BM and PB grafts, to a differing extent. The uncertain relationship with multilineage myeloid recovery emphasizes the limitations in using clonogenic progenitor analyses to assess the adequacy of an autologous graft prior to transplantation.