Immunobiology of allogeneic peripheral blood mononuclear cells mobilized with granulocyte-colony stimulating factor

Decreased circulating myeloid-derived suppressor cell count at the engraftment is one of the risk factors for multiple myeloma relapse after autologous hematopoietic stem cell transplantation

Recent studies demonstrated that myeloid-derived suppressor cells (MDSCs) are involved in the pathogenesis and progression of multiple myeloma (MM). Nevertheless, data on the quantitative and functional changes in MDSCs during standard MM treatment remain poorly understood. Here, we determined that monocytic MDSCs (M-MDSC; CD14+HLA-DRlow/-) and granulocytic MDSCs (PMN-MDSC; Lin-HLA-DR-CD33+CD66b+) in MM patients in remission following induction therapy (IT) were significantly increased, while early MDSCs (E-MDSCs; Lin-HLA-DR-CD33+CD66b-) were decreased compared to the donor group. In progression, MM patients had the most pronounced decrease in E-MDSCs and enhanced levels of PMN-MDSCs. IT was accompanied with a decrease in the expression of arginase-1 (Arg-1). In MM patients with relapse or resistance to IT, Arg-1+ cell frequency in M-MDSCs and E-MDSCs, as well as PD-L1+ M-MDSCs, was increased, which may facilitate tumor immunosuppression. G-CSF administration led to a significant increment in the MDSC subsets. At the engraftment, circulating M-MDSC and PMN-MDSCs were temporarily increased, with a gradual decline to the pre-transplant levels in 12 months. The percentage of E-MDSCs was decreased at the leukocyte recovery. Patients with a higher (>Me) M-MDSC count at the engraftment had a shorter post-transplant leukopenia duration (Me 11 vs. 13 days; pU = 0.0086). The advanced MM stage, depth of response, and lower relative count of circulating E-MDSCs at the engraftment were independent risk factors associated with a lower progression-free survival. The obtained data allow us to hypothesize that MDSCs may play a positive role at the stage of leukocyte recovery by ameliorating the long-term anti-tumor response in MM.

Expert consensus on microtransplant for acute myeloid leukemia in elderly patients -report from the international microtransplant interest group

Recent studies have shown that microtransplant (MST) could improve outcome of patients with elderly acute myeloid leukemia (EAML). To further standardize the MST therapy and improve outcomes in EAML patients, based on analysis of the literature on MST, especially MST with EAML from January 1st, 2011 to November 30th, 2022, the International Microtransplant Interest Group provides recommendations and considerations for MST in the treatment of EAML. Four major issues related to MST for treating EAML were addressed: therapeutic principle of MST (1), candidates for MST (2), induction chemotherapy regimens (3), and post-remission therapy based on MST (4). Others included donor screening, infusion of donor cells, laboratory examinations, and complications of treatment.

Advances in Model Systems for Human Cytomegalovirus Latency and Reactivation

Human cytomegalovirus (HCMV) is a highly prevalent beta-herpesvirus and a significant cause of morbidity and mortality following hematopoietic and solid organ transplant, as well as the leading viral cause of congenital abnormalities. A key feature of the pathogenesis of HCMV is the ability of the virus to establish a latent infection in hematopoietic progenitor and myeloid lineage cells. The study of HCMV latency has been hampered by difficulties in obtaining and culturing primary cells, as well as an inability to quantitatively measure reactivating virus, but recent advances in both in vitro and in vivo models of HCMV latency and reactivation have led to a greater understanding of the interplay between host and virus. Key differences in established model systems have also led to controversy surrounding the role of viral gene products in latency establishment, maintenance, and reactivation. This review will discuss the details and challenges of various models including hematopoietic progenitor cells, monocytes, cell lines, and humanized mice. We highlight the utility and functional differences between these models and the necessary experimental design required to define latency and reactivation, which will help to generate a more complete picture of HCMV infection of myeloid-lineage cells.

Cell Therapy: Types, Regulation, and Clinical Benefits

Cell therapy practices date back to the 19th century and continue to expand on investigational and investment grounds. Cell therapy includes stem cell- and non-stem cell-based, unicellular and multicellular therapies, with different immunophenotypic profiles, isolation techniques, mechanisms of action, and regulatory levels. Following the steps of their predecessor cell therapies that have become established or commercialized, investigational and premarket approval-exempt cell therapies continue to provide patients with promising therapeutic benefits in different disease areas. In this review article, we delineate the vast types of cell therapy, including stem cell-based and non-stem cell-based cell therapies, and create the first-in-literature compilation of the different "multicellular" therapies used in clinical settings. Besides providing the nuts and bolts of FDA policies regulating their use, we discuss the benefits of cell therapies reported in 3 therapeutic areas-regenerative medicine, immune diseases, and cancer. Finally, we contemplate the recent attention shift toward combined therapy approaches, highlighting the factors that render multicellular therapies a more attractive option than their unicellular counterparts.

Effect of high-dose plerixafor on CD34+ cell mobilization in healthy stem cell donors: results of a randomized crossover trial

Hematopoietic stem cells can be mobilized from healthy donors using single-agent plerixafor without granulocyte colony-stimulating factor and, following allogeneic transplantation, can result in sustained donor-derived hematopoiesis. However, when a single dose of plerixafor is administered at a conventional 240 μg/kg dose, approximately one-third of donors will fail to mobilize the minimally acceptable dose of CD34⁺ cells needed for allogeneic transplantation. We conducted an open-label, randomized trial to assess the safety and activity of high-dose (480 μg/kg) plerixafor in CD34⁺ cell mobilization in healthy donors. Subjects were randomly assigned to receive either a high dose or a conventional dose (240 μg/kg) of plerixafor, given as a single subcutaneous injection, in a two-sequence, two-period, crossover design. Each treatment period was separated by a 2-week minimum washout period. The primary endpoint was the peak CD34⁺ count in the blood, with secondary endpoints of CD34⁺ cell area under the curve (AUC), CD34⁺ count at 24 hours, and time to peak CD34⁺ following the administration of plerixafor. We randomized 23 subjects to the two treatment sequences and 20 subjects received both doses of plerixafor. Peak CD34⁺ count in the blood was significantly increased (mean 32.2 versus 27.8 cells/μL, P=0.0009) and CD34⁺ cell AUC over 24 hours was significantly increased (mean 553 versus 446 h cells/μL, P<0.0001) following the administration of the 480 μg/kg dose of plerixafor compared with the 240 μg/kg dose. Remarkably, of seven subjects who mobilized poorly (peak CD34⁺ ≤20 cells/μL) after the 240 μg/kg dose of plerixafor, six achieved higher peak CD34⁺ cell numbers and all achieved higher CD34⁺ AUC over 24 hours after the 480 μg/kg dose. No grade 3 or worse drug-related adverse events were observed. This study establishes that high-dose plerixafor can be safely administered in healthy donors and mobilizes greater numbers of CD34⁺ cells than conventional-dose plerixafor, which may improve CD34⁺ graft yields and reduce the number of apheresis procedures needed to collect sufficient stem cells for allogeneic transplantation. (ClinicalTrials.gov, identifier: NCT00322127)

Accurate measurement of peripheral blood mononuclear cell concentration using image cytometry to eliminate RBC-induced counting error

Peripheral blood mononuclear cells (PBMCs) have been widely researched in the fields of immunology, infectious disease, oncology, transplantation, hematological malignancy, and vaccine development. Specifically, in immunology research, PBMCs have been utilized to monitor concentration, viability, proliferation, and cytokine production from immune cells, which are critical for both clinical trials and biomedical research. The viability and concentration of isolated PBMCs are traditionally measured by manual counting with trypan blue (TB) using a hemacytometer. One of the common issues of PBMC isolation is red blood cell (RBC) contamination. The RBC contamination can be dependent on the donor sample and/or technical skill level of the operator. RBC contamination in a PBMC sample can introduce error to the measured concentration, which can pass down to future experimental assays performed on these cells. To resolve this issue, RBC lysing protocol can be used to eliminate potential error caused by RBC contamination. In the recent years, a rapid fluorescence-based image cytometry system has been utilized for bright-field and fluorescence imaging analysis of cellular characteristics (Nexcelom Bioscience LLC, Lawrence, MA). The Cellometer image cytometry system has demonstrated the capability of automated concentration and viability detection in disposable counting chambers of unpurified mouse splenocytes and PBMCs stained with acridine orange (AO) and propidium iodide (PI) under fluorescence detection. In this work, we demonstrate the ability of Cellometer image cytometry system to accurately measure PBMC concentration, despite RBC contamination, by comparison of five different total PBMC counting methods: (1) manual counting of trypan blue-stained PBMCs in hemacytometer, (2) manual counting of PBMCs in bright-field images, (3) manual counting of acetic acid lysing of RBCs with TB-stained PBMCs, (4) automated counting of acetic acid lysing of RBCs with PI-stained PBMCs, and (5) AO/PI dual staining method. The results show comparable total PBMC counting among all five methods, which validate the AO/PI staining method for PBMC measurement in the image cytometry method.

The impact of graft composition on clinical outcomes in pediatric patients undergoing unmanipulated HLA-mismatched/haploidentical hematopoietic stem cell transplantation

OBJECTIVE

In pediatric patients, the association of graft composition with clinical outcomes after unmanipulated haploidentical hematopoietic stem cell transplantation has not been well defined. Therefore, the impact of graft composition on transplant outcomes was evaluated.

METHODS

We examined the absolute numbers and relative proportions of CD3+, CD4+, CD8+, CD14+, and CD34+ cells contained in allografts of 103 children who underwent unmanipulated HLA-mismatched/haploidentical hematopoietic stem cell transplantation (HSCT) without in vitro T cell depletion.

RESULTS

Multivariate analysis showed that a high CD34+ cell dose in G-CSF-primed bone marrow and peripheral blood grafts (G-PB) was related to accelerated platelet engraftment (P = 0.004). A higher CD3/CD14 ratio in G-PB (≥ 1.30) was associated with grade II-IV acute graft-versus-host disease (GVHD) (HR = 3.552; 95%CI 1.015-12.428, P = 0.047). In addition, only a heavier donor weight (HR = 5.837; 95%CI 1.841-18.513, P = 0.003) and a higher ratio of CD3/CD14 in the total graft (HR = 9.752; 95%CI 1.834-51.865, P = 0.008) were associated with worse overall survival. No aspect of graft composition affected neutrophil engraftment or disease relapse, though occurrence of chronic GVHD and a higher CD3/CD14 ratio in G-PB and total graft may reflect a lower incidence of relapse without statistical significance.

CONCLUSIONS

The dose of CD34+ cells and the CD3/CD14 ratio in allografts seem to have prognostic value for engraftment and clinical outcomes in pediatric patients undergoing unmanipulated haploidentical hematopoietic stem cell transplantation. A lower CD3/CD14 ratio in allografts demonstrated a survival benefit.

Regulation of granulocyte and macrophage populations of murine bone marrow cells by G-CSF and CD137 protein

Background

Granulocytes and monocytes/macrophages differentiate from common myeloid progenitor cells. Granulocyte colony-stimulating factor (G-CSF) and CD137 (4-1BB, TNFRSF9) are growth and differentiation factors that induce granulocyte and macrophage survival and differentiation, respectively. This study describes the influence of G-CSF and recombinant CD137-Fc protein on myelopoiesis.

Methodology/Principal Findings

Both, G-CSF and CD137 protein support proliferation and survival of murine bone marrow cells. G-CSF enhances granulocyte numbers while CD137 protein enhances macrophage numbers. Both growth factors together give rise to more cells than each factor alone. Titration of G-CSF and CD137 protein dose-dependently changes the granulocyte/macrophage ratio in bone marrow cells. Both factors individually induce proliferation of hematopoietic progenitor cells (lin^-, c-kit⁺) and differentiation to granulocytes and macrophages, respectively. The combination of G-CSF and CD137 protein further increases proliferation, and results in a higher number of macrophages than CD137 protein alone, and a lower number of granulocytes than G-CSF alone demonstrating that CD137 protein-induced monocytic differentiation is dominant over G-CSF-induced granulocytic differentiation. CD137 protein induces monocytic differentiation even in early hematopoietic progenitor cells, the common myeloid progenitors and the granulocyte macrophage progenitors.

Conclusions/Significance

This study confirms earlier data on the regulation of myelopoiesis by CD137 receptor - ligand interaction, and extends them by demonstrating the restriction of this growth promoting influence to the monocytic lineage.

Murine mobilized peripheral blood stem cells have a lower capacity than bone marrow to induce mixed chimerism and tolerance

Allogeneic bone marrow transplantation (BMT) under costimulation blockade allows induction of mixed chimerism and tolerance without global T-cell depletion (TCD). The mildest such protocols without recipient cytoreduction, however, require clinically impracticable bone marrow (BM) doses. The successful use of mobilized peripheral blood stem cells (PBSC) instead of BM in such regimens would provide a substantial advance, allowing transplantation of higher doses of hematopoietic donor cells. We thus transplanted fully allogeneic murine granulocyte colony-stimulating factor (G-CSF) mobilized PBSC under costimulation blockade (anti-CD40L and CTLA4Ig). Unexpectedly, PBSC did not engraft, even when very high cell doses together with nonmyeloablative total body irradiation (TBI) were used. We show that, paradoxically, T cells contained in the donor PBSC triggered rejection of the transplanted donor cells. Rejection of donor BM was also triggered by the cotransplantation of unmanipulated donor T cells isolated from naïve (nonmobilized) donors. Donor-specific transfusion and transient immunosuppression prevented PBSC-triggered rejection and mixed chimerism and tolerance were achieved, but graft-versus-host disease (GVHD) occurred. The combination of in vivo TCD with costimulation blockade prevented rejection and GVHD. Thus, if allogeneic PBSC are transplanted instead of BM, costimulation blockade alone does not induce chimerism and tolerance without unacceptable GVHD-toxicity, and the addition of TCD is required for success.

Induction of Mixed Chimerism through Transplantation of CD45-Congenic Mobilized Peripheral Blood Stem Cells after Nonmyeloablative Irradiation

Clinical translation of the mixed-chimerism approach for inducing transplantation tolerance would be facilitated if mobilized peripheral blood stem cells (mPBSCs) could be used instead of bone marrow cells (BMCs). Because the use of mPBSCs for this purpose has not been investigated in nonmyeloablative murine protocols, we explored the engraftment potential of mPBSCs in a CD45-congenic model as a first step. After 2, 1.5, or 1 Gy of total body irradiation, CD45.1 B6 hosts received unseparated granulocyte colony-stimulating factor-mobilized CD45.2 B6 PBSCs or unseparated CD45.2 B6 BMCs. The same total cell numbers, or aliquots of mPBSCs and BMCs containing similar numbers of c-kit+ cells, were transplanted both with and without a short course of rapamycin-based immunosuppression (IS). Transplantation of mPBSCs induced long-term multilineage macrochimerism, but chimerism levels were significantly lower than among recipients of the same number of BMCs. Transplanting aliquots containing similar numbers of c-kit+ cells reduced the difference between mPBSCs and BMCs, but lower levels of chimerism were nonetheless observed in mPBSC recipients. Chimerism levels correlated more closely with the number of transplanted progenitor cells as determined by colony-forming unit assays. IS did not affect chimerism levels, indicating that the donor CD45 isoform or other minor disparities do not pose a major barrier to engraftment. Our findings indicate that under nonmyeloablative conditions, progenitor cells contained in mPBSCs have an engraftment capacity similar to progenitor cells from BMCs, allowing induction of lasting mixed chimerism with moderate cell numbers. On a cell-per-cell basis, unseparated BMCs have some advantages that may be minimized if the number of progenitor cells is equalized. These results are expected to facilitate the development of mPBSC-based allogeneic tolerance protocols.

Direct cardiac injection of G-CSF mobilized bone-marrow stem-cells improves ventricular function in old myocardial infarction

Autologous transplant of bone marrow stem cells (BMSC), although extremely useful after acute myocardial events, has not been evaluated in patients with old (>one-year-old) myocardial infarction. Our aim was to determine if CD34(+)-enriched peripheral-blood cells, obtained by apheresis, injected directly into the severely damaged myocardium of five patients with old myocardial infarction could restore depressed myocardial function. We found that 28 weeks after revascularization and peri-infarction injection of the enriched CD34(+) peripheral mononuclear cells, ventricular hemodynamic parameters that included left ventricular ejection fraction, left ventricular diastolic volume, ventricular systolic volume and left ventricular diastolic diameter approximated normal values and there was no restenosis; two patients have been followed for >52 weeks and their parameters are within normal values. In conclusion, intramyocardial injection of easily obtained CD34(+) enriched peripheral blood cells represent an encouraging procedure for patients with severely scarred and dysfunctional myocardium.

rhG-CSF does not affect the phenotype of adult donor peripheral blood NK cells

Considerable evidence in preclinical models as well as in human transplantation now suggests that donor-derived natural killer (NK) cells can contribute to alloimmune recognition of recipient residual tumour cells. This makes the NK cell population an attractive target for in vitro or in vivo manipulations, in order to improve the antitumour effect of allogeneic transplantation. However, conditions in which allogeneic donor cells are collected vary; several reports have emphasised the different phenotypic and functional properties of T cells derived from marrow, cord blood or mobilised peripheral blood grafts; others have demonstrated different clinical outcomes following blood or marrow transplantation after myeloablative conditioning regimens. NK cells have been examined in this setting; the availability of new tools to study the expression of a variety of surface antigens that are involved in the control of NK cell activity offered us an opportunity to extensively characterise the phenotypic properties of NK cells from donors, before and after administration of pharmacological doses of rhG-CSF used for haematopoietic progenitor mobilisation. Our study suggests that rhG-CSF does not reproducibly alter blood NK cell phenotype in normal individuals, and thus that donor-derived cells are fully equipped to exert their potential antitumour effect.

The effect of peptide stimulation on haematopoietic stem cell mobilisation including engraftment characteristics and a note on donor side effects

Aplasia or irreversible bone marrow failure and a variety of haematologic malignancies, as well as an increasing number of solid tumours, currently include various forms of marrow or equivalent transplantation in routine management. In both allogeneic and autologous procedures stable recipient immunohaematopoietic reconstitution depends upon infusing the requisite population harvested at a precise time following commencement of a stimulatory peptide. In a first step this prospective study documented the safety of apheresis, defined side effects and enumerated mononuclear, CD34+ and CD3+ cells obtained. In the second stage delivery of the graft, characterised in this way and with the additional measurement of in vitro growth in clonogenic assay, to the suitably conditioned patient was correlated with recovery of neutrophil and platelet numbers appearing in the circulation. In a third and ongoing analysis the influence of passenger T-lymphocytes is being evaluated for impact on infection and a potential anti-tumour effect. The conclusion is that this technology is reliable, has a high degree of patient acceptability without untoward complications, and that local results correspond to international experience thereby providing an important and relevant measure of quality control.

Transplantation of hematopoietic stem cells from the peripheral blood

Hematopoietic stem cells can be collected from the peripheral blood. These hematopoietic stem cells (HSC), or better progenitor cells, are mostly expressed as the percentage of cells than react with CD34 antibodies or that form colonies in semi-solid medium (CFU-GM). Under steady-state conditions the number of HSC is much lower in peripheral blood than in bone marrow. Mobilization with chemotherapy and/or growth factors may lead to a concentration of HSC in the peripheral blood that equals or exceeds the concentration in bone marrow. Transplantation of HSC from the peripheral blood results in faster hematologic recovery than HSC from bone marrow. This decreases the risk of infection and the need for blood-product support. For autologous stem-cell transplantation (SCT), the use of peripheral blood cells has completely replaced the use of bone marrow. For allogeneic SCT, on the other hand, the situation is more complex. Since peripheral blood contains more T-lymphocytes than bone marrow, the use of HSC from the peripheral blood increases the risk of graft-versus-host disease after allogeneic SCT. For patients with goodrisk leukemia, bone marrow is still preferred, but for patients with high-risk disease, peripheral blood SCT has become the therapy of choice.

The effect of hematopoietic growth factors on the risk of graft-vs-host disease after allogeneic hematopoietic stem cell transplantation: a meta-analysis

The effect of hematopoietic growth factors on neutrophil recovery after allogeneic transplantation is well-recognized. Recent laboratory studies demonstrated that these cytokines may also modify T-cell and dendritic cell function, but whether the effect is strong enough to alter the risk of GVHD is unclear. We performed a meta-analysis to determine the effect of G-CSF or GM-CSF on the risk of nonhematopoietic outcomes after allogeneic transplantation. A search of the literature from 1986 to present yielded 18 publications in which data were provided for cohorts receiving growth factor vs either placebo or no therapy. These included nine prospective randomized studies, eight retrospective cohort studies, and one case-control study comprising a total of 1198 patients. The publication types were heterogeneous with regard to demographic and treatment characteristics, although within publications, comparative groups were generally balanced. The pooled risk ratio estimates with use of growth factor was 1.08 (95% CI 0.87-1.33, P=0.48) for grades 2-4 acute GVHD, 1.22 (95% CI 0.80-1.86, P=0.99) for grades 3-4 acute GVHD, and 1.02 (95% CI 0.82-1.26, P=0.87) for chronic GVHD. This analysis did not detect a significant change in the risk of acute or chronic GVHD after allogeneic hematopoietic stem cell transplantation when hematopoietic growth factors were used to shorten the initial period of neutropenia.

Influence of transplanted dose of CD56+ cells on development of graft-versus-host disease in patients receiving G-CSF-mobilized peripheral blood progenitor cells from HLA-identical sibling donors

We investigated effects of variations in the cellular composition of G-CSF-mobilized peripheral blood progenitor cell (G-PBPC) allografts on clinical outcomes of allogeneic PBPC transplantation. We retrospectively analyzed transplanted doses of various immunocompetent cells from 27 HLA-identical sibling donors in relation to engraftment, incidence of graft-versus-host disease (GVHD), and survival. Significant variability was documented in both absolute numbers and relative proportions of CD34+, CD2+, CD3+, CD4(high)+, CD4+25+, CD8(high)+, CD19+, CD56+, and CD56+16+ cells contained in these allografts. Stepwise Cox regression analysis revealed that the CD56+ cell dose was significantly inversely correlated with the incidence of GVHD. Thus, there was a significantly higher incidence of grade II acute GVHD in patients receiving a lower CD56+16+ cell dose (hazard ratio (HR) 0.0090; 95% confidence interval (CI), <0.00001-3.38; P=0.031), a higher incidence of chronic GVHD in those receiving allografts with a lower CD56+16+ to CD34+ ratio (HR <0.00001; 95% CI <0.00001-0.0007; P=0.0035), and a higher incidence of extensive chronic GVHD in those receiving allografts with a lower CD56+ to CD34+ ratio (HR <0.00001; 95% CI <0.00001-0.053; P=0.0083). These results suggest that CD56+ cells in G-PBPC allografts from HLA-identical sibling donors may play an important role in preventing the development of GVHD.

Mobilization of hematopoietic stem cells during homeostasis and after cytokine exposure

We created parabiotic mice, joining ROSA26 and PeP3b animals, to study the trafficking of hematopoietic stem cells (HSCs) from marrow to blood and their return to marrow. The transfer of HSCs was assayed by secondary marrow transplantation and was 1.0% to 2.5% after 3, 6, 8, and 12 weeks. Thus, HSC homeostasis is primarily maintained by the retention of stem cells derived from replication events within the marrow, not the homing and engraftment of HSCs from the circulation. Of interest, the phenotypes of marrow progenitors and granulocytes were similar to those for HSCs, implying that the marrow functions as an intact compartment where differentiating cells derive from endogenous HSC. In contrast, 50% of splenic granulocytes and progenitor cells derived from the parabiotic partner, suggesting splenic progenitor cells were in constant equilibrium with progenitors in blood. In additional studies, animals were exposed to granulocyte-colony-stimulating factor (G-CSF) and stem cell factor at days 17 to 20 of parabiosis and were studied 3 weeks later; 10.1% of marrow HSCs derived from the parabiotic partner. These data imply that HSCs, mobilized to the blood in response to cytokine exposure, are destined to later return to marrow, an observation that supports the concept that the mobilized peripheral blood stem cells used in clinical transplantation function physiologically.

Blood versus marrow hematopoietic allogeneic graft

Allogeneic G-CSF-mobilized blood cell transplantation (BCT), an alternative to allogeneic bone marrow transplantation (BMT), is associated with enhanced engraftment and accelerated hematopoietic recovery. In addition, immune reconstitution and overall alloreactivity after BCT versus BMT differ significantly. Indeed, despite an increased number of donor T cells infused, the incidence of acute graft-versus-host disease (GvHD) after BCT appears to remain identical or lesser than after BMT. On the other hand, a higher risk of chronic GvHD has been reported after BCT. In a SFGM phase III trial, 101 patients with early leukemia and an HLA-matched sibling donor randomly received a BCT or BMT. BCT was associated with a higher number of infused CD34+ cells, accelerated platelet and neutrophil reconstitution, fewer platelet transfusions and similar acute GvHD incidence. However, chronic GvHD occurred more frequently after BCT. With a median follow-up of 20 months, relapse, survival and leukemia-free survival were not different. In the course of this study, immune parameters related to the graft as well as to early reconstitution were prospectively examined. T cells subsets, B cells, NK cells and monocytes numbers were significantly higher in BC grafts (versus BM). T cells in BC grafts were less activated than in BM grafts. Frequency of IFN-gamma, IL-2- and TNF-alpha-secreting cells and single-cell IFN-gamma production potential was reduced in BC graft. One month after BCT, blood T-cell counts were 3-fold higher than after BMT. Moreover, post-BCT T cells were less activated and counts correlated with the number of T cells infused with the graft, which was not the case after BMT. Several acute hemolysis episodes, resulting from anti-A and/or -B donor-derived Ab directed at Ag present on recipient red blood cells (minor ABO mismatch), have been described after BCT. Recipients indeed exhibited significantly increased anti-A and/or -B Ab titers after BCT, particularly in the setting of a "minor" ABO mismatch. Furthermore, the frequency of anti-HLA Ab early after BCT was significantly increased (despite the reduction in platelet transfusion requirements). The higher number of activated B cells and/or CD4 T cells and monocytes in a BCT graft and/or the higher number of circulating CD4 T- and B-cells after BCT could be associated with the enhanced alloAb production. G-CSF-induced TH2 cytokine profile of the T cells present in the graft could also be contributive. Recent studies have determined that BC grafts contained a higher number of type 2 dendritic cells (DC2), themselves associated with high frequencies of TH2 CD4+ cells. Since chronic GvHD is associated with the occurrence of Ab-mediated auto-immune-like syndromes, it is tempting to speculate that a higher incidence of chronic GvHD may result from these findings. In conclusion, BCT results in clinically relevant distinct hematopoietic and immune reconstitution patterns.

Hepatitis B virus reactivation with clinical flare in allogeneic stem cell transplants with chronic graft-versus-host disease

We conducted a retrospective study with the aim of identifying risk factors and clinical characteristics associated with HBV reactivation and clinical flare after allogeneic stem cell transplantation (aSCT). We reviewed the King Faisal Specialist Hospital and Research Center International Bone Marrow Transplant Registry database from January 1998 to June 2000. Complete serological screening for HBV was available in 128 of 131 patients transplanted during that period. Fifty-four (42%) had evidence of prior infection and recovery from HBV before transplant (hepatitis B core antibody positive, B surface antigen negative). Forty-two were evaluable for HBV reactivation and clinical flare. Six (14%) reactivated with clinical flare as documented by seroconversion and/or positive HBV DNA in the serum with biochemical hepatitis at 5.5, 18, 18, 19, 21 and 23 months post-transplant. Five of fifteen patients with chronic graft-versus-host disease (cGVHD) reactivated with clinical flare in contrast to 1/27 without cGVHD (RR: 9.0, 95% CI: 1.2-70.1 P < 0.02). HBV reactivation with clinical flare occurred during immunosuppressive therapy tapering or withdrawal in all patients. In conclusion, hepatitis B core antibody positive allogeneic stem cell recipients with cGVHD are at significant risk of HBV reactivation with clinical flare.

Serum soluble IL-6 receptor levels during the mobilization of stem cells to peripheral blood

Serum soluble interleukin-6 receptors (sIL-6R) have been demonstrated to play an important role in hematopoiesis. We report here that serum sIL-6R levels reflect proliferative kinetics of the progenitors after stimulation by chemotherapy plus granulocyte colony-stimulating factor. Serum sIL-6R were serially evaluated in 26 courses of peripheral blood (PB) stem cell collections in 16 patients using enzyme-linked immunosorbent assay. Expressions of IL-6R and CD34 on PB mononuclear cells were examined by flow cytometric analysis and expressions of IL-6R mRNA were examined by reverse transcriptase polymerase chain reaction. There were no significant differences between the serum sIL-6R levels on day 0 in patients (27.8+/-2.1 ng/ml, mean +/- SEM) and those in controls (27.5+/-1.5 ng/ml). Following chemotherapy the serum sIL-6R levels were significantly decreased, reaching a minimal level on day 14 (22.3+/-1.2 ng/ml, p < 0.01) and then significantly increased to above the baseline levels on day 21 (32.0+/-2.1 ng/ml, p < 0.01). Similar oscillations in the number of white blood cells, IL6R+ cells, CD34+ cells and colony-forming unit-granulocyte/macrophage (CFU-GM) in PB could be observed and the peak expression of mRNA was compatible with the expression of antigen. Serum sIL-6R levels on day 17 and 19 were positively correlated with the number of CD34+ cells, IL-6R+ cells, CFU-GM in PB and the number of collected CD34+ cells in leukapheresis products. In addition, when comparing the 2 groups divided by the number of prior chemotherapies, the status of disease or dose of the mobilizing regimen, the serum sIL-6R levels were significantly increased after day 17 in the group that received fewer courses of prior chemotherapy, the group in complete remission and the group of high-dose chemotherapy. These findings indicated that sIL-6R levels do not reflect the hematopoietic ability in the steady state, or the capability of the hematopoiesis after stimulation. Thus, sIL-6R levels may be a marker for the timing of PBSC collection or the prediction of the number of collected CD34+ cells.

Peripheral blood progenitor cell transplantation

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 x 10(6)/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.

Optimizing engraftment--source and dose of stem cells

In recent years, the use of antibodies to measure CD34(+) cells and the availability of peripheral blood (PB) and umbilical cord blood (CB) as additional stem cell sources other than bone marrow (BM) has increased interest in determining the impact of stem cell source and dose on the outcome of allogeneic stem cell transplantation. In addition to differences in their stem cell content, transplants from the three sources differ in the composition and state of activation of immune cells. As a consequence, BM, CB, and PB transplants have different kinetics of hematological recovery, the most rapid engraftment being observed with PB and the slowest with CB. Stem cell source also incurs different risks for developing graft-versus-host disease (GVHD): PB transplants show a possible increase in acute and a definite increase in chronic GVHD compared with BM. CB transplants have a favorably low risk of GVHD even in mismatched transplants. Stem cell dose in an independent factor in transplants from any source, determining engraftment, transplant-related mortality and risk of leukemic relapse. These findings are of clinical importance-an understanding of the impact of stem cell source and dose is essential to obtain optimum conditions for a successful outcome after transplant.

CD34 cell dose in granulocyte colony-stimulating factor-mobilized peripheral blood mononuclear cell grafts affects engraftment kinetics and development of extensive chronic graft-versus-host disease after human leukocyte antigen-identical sibling transplantation

A retrospective analysis of granulocyte colony-stimulating factor (G-CSF)-mobilized peripheral blood mononuclear cell (G-PBMC) products harvested from healthy donors indicates significant variability in both the absolute number and relative proportion of CD34, CD3, and CD14 cells obtained. This report examined whether variations in the cellular composition of G-PBMC products correlated with clinical outcomes after myeloablative allogeneic transplantation. The numbers of CD34, CD3, and CD14 cells infused into 181 human leukocyte antigen (HLA)-identical sibling recipients were analyzed with respect to tempo of engraftment, acute graft-versus-host-disease (GVHD), clinical extensive chronic GVHD, overall survival, and disease relapse. Neither acute GVHD, overall survival, nor disease relapse was statistically significantly associated with CD34, CD3, or CD14 cell doses or the CD14 to CD3 ratio. CD3 and CD14 cell doses and CD14 to CD3 ratios did not correlate with the tempo of neutrophil and platelet engraftment. However, increasing CD34 cell numbers were significantly associated with accelerated neutrophil (P =.03) and platelet (P =.01) engraftment. Higher doses of CD34 cells (> 8.0 x 10(6)/kg) were also associated with a significantly increased hazard of clinical extensive chronic GVHD (HR = 2.3, 95% confidence interval [CI] 1.4-3.7, P =.001), but neither CD3 nor CD14 doses were statistically significantly associated with chronic GVHD. It was concluded that CD34 cell dose in G-PBMC grafts appears to affect both the engraftment kinetics and the development of clinical extensive chronic GVHD in HLA-identical sibling recipients but without a demonstrable impact on survival, relapse, and acute GVHD. Given the morbidity associated with extensive chronic GVHD, efforts to further accelerate engraftment in HLA-matched sibling transplants by increasing CD34 cell number in G-PBMC products may be counterproductive.

Peripheral blood stem cells for allogeneic transplantation: a review

Peripheral blood stem cells (PBSCs) have become increasingly popular for use in hematopoietic stem cell transplantation. PBSCs are readily collected by continuous-flow apheresis from patients and healthy donors after the administration of s.c. recombinant colony-stimulating factors with only minimal morbidity and discomfort. Although the precise identification of PBSCs remains elusive, they can be phenotypically identified as a subset of all circulating CD34(+) cells. There are important phenotypic and biologic distinctions between PBSCs and bone marrow (BM)-derived progenitor cells. PBSCs express more lineage-specific antigens but are less metabolically active than their BM-derived counterparts. The use of PBSCs for allogeneic transplantation has been compared to BM in several randomized trials and cohort studies. The use of PBSCs in leukemia, myeloma, non-Hodgkin's lymphoma, and myelodysplasia has resulted in shorter times to neutrophil and platelet engraftment at the expense of increased rates of chronic graft-versus-host disease. The increase in graft-versus-host disease is mainly due to a log-fold increase in donor T cells transferred with the graft. Relapse rates after transplantation may be lower after PBSC transplantation but a convincing survival advantage has not been demonstrated overall. It is possible that a stronger graft-versus-tumor effect may exist with PBSCs when compared with BM although the mechanisms leading to this effect are not clear.

Allogeneic peripheral blood stem cell transplantation

Granulocyte colony stimulating factor (G-CSF)-mobilized peripheral blood stem cells (PBSC) are now widely used instead of bone marrow for autologous transplantation due to earlier hematopoietic recovery after transplant. The low toxicity of G-CSF has prompted phase I and II studies to evaluate PBSC for allogeneic transplantation; these studies have demonstrated that engraftment of neutrophils, red blood cells and platelets is faster with peripheral blood cells compared to marrow. In randomized studies comparing mobilized PBSC and marrow for allogeneic transplantation, most trials have confirmed significantly earlier engraftment with PBSC and similar risks of acute graft-vs.-host disease (GVHD). In some trials, an increase of 10-15% in grade II-IV GVHD has been noted with PBSC. All studies showed a trend towards more chronic GVHD with PBSC. Some randomized studies have shown improved survival and disease-free survival with the use of PBSC due to lowered transplant-related mortality and fewer relapses in recipients of PBSC as a result of improved immune reconstitution and a graft-vs.-leukemia (GVL) effect. This survival benefit is most apparent in patients with more advanced hematologic malignancies, but further studies are needed to define the relative benefits of PBSC for patients with less advanced disease. The GVL effect of PBSC is currently being exploited with the use of non-ablative allografts.