Human hematopoietic progenitor cells in long-term cultures express HLA-DR antigens and lack HLA-DQ antigens.

The expression of HLA-DR antigenic determinants on human hematopoietic progenitor cells (HPC) capable of differentiating into mature blood cells, as determined in semisolid cultures, has been demonstrated previously (3-7). Here, we investigated the expression of class II determinants on HPC responsible for the sustained proliferation of colony-forming units of granulocyte/macrophage (CFU-GM), of multilineage HPC (CFU-GEMM, granulocyte/erythrocyte/macrophage/megakaryocyte), and burst-forming units of erythroid cells (BFU-E) in liquid long-term cultures. Using both fluorescence-activated cell sorting and complement-dependent cytotoxicity assays, HLA-DR determinants could be identified on virtually all these HPC capable of proliferating in long-term cultures. Experiments in which the stromal layer had been irradiated provided evidence that the HPC themselves were truly HLA-DR+, and that the sustained proliferation of HPC was not due to activation of HLA-DR- residual HPC in the stromal layer by reinoculated HLA-DR+ accessory cells. Furthermore, it was shown that all HPC recognized in semisolid and liquid long-term cultures were HLA-DQ-. These results suggest that the human true pluripotential stem cell is HLA-DR+. These results open the possibility of studying class II-dependent regulation of hematopoiesis in liquid long-term cultures.

Colony growth of human hematopoietic progenitor cells in the absence of serum is supported by a proteinase inhibitor identified as antileukoproteinase.

Serum contains many growth factors and nutrients that stimulate colony formation of hematopoietic progenitor cells (HPC) in semisolid cultures. In the absence of serum, no proliferation of HPCs could be obtained in semisolid medium cultures of partially purified bone marrow cells in the presence of multiple hematopoietic growth factors, insulin, cholesterol, and purified clinical-grade human albumin. This appeared to be due to a suppressive activity induced by monocyte- and T lymphocyte-depleted accessory cells on CD34+ HPCs. Serum-free conditioned medium from the bladder carcinoma cellline 5637 could replace serum to support the growth of HPCs in these cultures. After gel filtration and reverse-phase high-performance liquid chromatography of 5637 supernatants, this activity could be attributed to a 15-kD protein that was further identified by NH2-terminal sequence analysis as the serine proteinase inhibitor antileukoproteinase (ALP). The growth-supportive activity from the 5637 conditioned medium and the (partially) purified fractions could be completely neutralized by a polyclonal rabbit IgG antibody against human ALP (huALP). Similar supportive effects on the growth of HPC could be obtained in the presence of recombinant huALP. We demonstrated that the COOH-terminal domain of ALP containing the proteinase inhibitory activity was responsible for this effect. alpha-1 proteinase inhibitor was capable of similar support of in vitro HPC growth. These results illustrate that proteinase inhibitors play an important role in the in vitro growth of hematopoietic cells by the neutralization of proteinases produced by bone marrow accessory cells. This may be of particular relevance for in vitro expansion of human hematopoietic stem cells in serum-free media.

Growth inhibition of clonogenic leukemic precursor cells by minor histocompatibility antigen-specific cytotoxic T lymphocytes.

Minor histocompatibility (mH) antigens appear to play a major role in bone marrow transplantation (BMT) using HLA-identical donors. Previously, we reported the isolation of major histocompatibility complex (MHC)-restricted mH antigen-specific cytotoxic T lymphocytes (CTL) from patients with graft-vs.-host disease or rejection after HLA-identical BMT. We have demonstrated that mH antigens can be recognized on hematopoietic progenitor cells, and residual recipient CTL specific for mH antigens expressed on donor hematopoietic progenitor cells may be responsible for graft rejection in spite of intensive conditioning regimens in HLA-identical BMT. Here, we investigated whether mH antigen-specific CTL directed against the mH antigens HA-1 to HA-5 and the male-specific antigen H-Y were capable of antigen-specific inhibition of in vitro growth of clonogenic leukemic precursor cells. We demonstrate that mH antigen-specific CTL against all mH antigens tested can lyse freshly obtained myeloid leukemic cells, that these mH antigen-specific CTL can inhibit their clonogenic leukemic growth in vitro, and that this recognition is MHC restricted. We illustrate that leukemic (precursor) cells can escape elimination by mH antigen-specific CTL by impaired expression of the relevant MHC restriction molecule. We suggest that mH antigen-specific MHC-restricted CTL may be involved in vivo in the graft-vs.-leukemia reactivity after BMT.

Anti-thymocyte globulin effective in the treatment of aplastic anemia does not stimulate granulocyte precursor cells.

To find out whether the preparations of anti-lymphocyte or anti-thymocyte globulin (ATG), successfully used in our center for the treatment of patients with aplastic anemia, were stimulatory for hematopoietic precursor cells, we studied the effect on CFUC in 30 normal bone marrow samples. Although in 2 out of 30 cases stimulation was observed, the overall result for both the horse anti-lymphocyte globulin and the rabbit anti-thymocyte globulin was dose-dependent and complement-dependent inhibition. Neither in the absence, nor in the presence of complement was there any indication of consistent stimulation of CFUC. When bone marrow was depleted of E-rosette forming cells, the incubation of the depleted fraction with ATG did not result in stimulation. The incubation of the E-rosette positive fraction with ATG, followed by the addition of these treated cells to untreated E-rosette depleted cells was equally ineffective in giving any stimulation of CFUC. Our data suggest that the effect of ATG in the treatment of aplastic anemia is not due to direct stimulation of hematopoietic precursor cells.

The impact of the composition of the bone marrow graft on engraftment and graft-versus-host disease.

To study the impact of the composition of the bone-marrow graft on engraftment and graft-versus-host disease (GvHD), we analyzed the data on 29 patients with acute leukemia in remission and 11 patients with aplastic anemia. All of them received bone-marrow grafts from HLA matched, MLC nonreactive, sibling donors, were nursed in laminar down-flow isolators with selective gut decontamination, and received GvHD prophylaxis with methotrexate. The number of nucleated cells in the marrow graft/kg body weight of the recipient had no relation with the rapidity of engraftment or with the occurrence and severity of GvHD. The number of hematopoietic progenitor cells (CFUc)/kg had a weak, but significant, correlation with both the number of neutrophils at day 30 post BMT and with the day at which the reticulocytes passed the 10% level. The number of T cells/kg did not show any correlation with either the occurrence or the severity of GvHD. Our data show that the concentration of hematopoietic progenitor cells in the graft correlates with the rapidity of engraftment. However, within the range of numbers of T cells infused in this study, no correlation is present between T cells in the graft and GvHD. Therefore, nearly complete depletion of marrow grafts of T cells is probably necessary to effectively decrease the incidence of GvHD.

Complement-dependent cytotoxicity in the analysis of antigenic determinants on human hematopoietic progenitor cells with HLA-DR as a model.

Complement-dependent cytotoxicity (CDC) assays using anti-Ia antisera have resulted in controversial conclusions about the expression of HLA-DR determinants on human hematopoietic progenitor cells (HPC). The expression of these antigens on CFU-E in particular could often not be demonstrated. Since this is contradictory to our own results, we decided to study the influence of both the antibody and complement concentrations in CDC assays using murine monoclonal and polyclonal anti-Ia (HLA-DR "backbone") antibodies and human anti-HLA-DR typing sera. We found that with use of the same anti-Ia antibody concentrations, elimination of CFU-E required significantly more complement than CFU-GM and BFU-E. In CDC assays with antipolymorphic HLA-DR antisera, complete kill of both CFU-E and BFU-E required significantly more complement than of CFU-GM. Insufficient complement concentration could be partly overcome by increasing the antibody concentration. Intrinsic insensitivity of CFU-E to low concentrations of complement could be excluded by experiments using monoclonal anti-HLA-A/B/C "backbone" antibodies. Furthermore, FACS experiments demonstrated that the density of HLA-DR determinants on CFU-E is lower than on BFU-E and CFU-GM. These data show that in CDC assays, antigens with low expression on HPC can easily be overlooked.

Recovery of hematopoiesis after blood-group-incompatible bone marrow transplantation with red-blood-cell-depleted grafts.

Severe hemolytic transfusion reactions may complicate major blood-group-incompatible bone marrow transplantations (BMT). Probably the most appropriate way to avoid this complication is removal of the incompatible red blood cells (RBC) from the bone marrow graft. In this report we describe a method to eliminate incompatible RBCs that is based on repeated dilution of the graft with donor-and-recipient--compatible third-party erythrocytes. Four patients with ABO incompatibility and one patient with Rh-C incompatibility were transplanted using this technique. After the procedure 86 +/- 8% (mean +/- SD) of the nucleated cells, 95 +/- 14% of CFU-GM, 88 +/- 14% of BFU-e, and 103 +/- 30% of CFU-e were recovered, but only +/- 1% of the incompatible RBCs was left in the transfusate (1-3 ml). No signs of hemolysis were observed. All patients engrafted promptly. The patients with low titers of antibody had normal reticulocyte recoveries. Maturation of erythropoiesis was suppressed only when high titers of antibody were present. However, despite high antibody titers, erythroid progenitor cells (CFU-GEMM, BFU-e, and CFU-e) could be cultured from the bone marrow of the recipient after BMT. Thus, anti-A and anti-Rh-C antibodies give little, if any, inhibition of stem-cell proliferation. The method described to remove incompatible RBCs appears to be simple, safe, and--in most cases--sufficient.

Serum inhibitors in aplastic anaemia.

To study the frequency and clinical importance of serum factors inhibiting CFU-c in patients with aplastic anaemia, sera from 21 patients were analysed. The sera of eight patients showed inhibition of at least one normal bone marrow, but strong and consistent inhibition of two or more normal bone-marrow samples was found in only two cases. In both of these two patients the inhibition disappeared after successful therapy. Fair, but not complete, correlation was found between serum inhibitors and HLA-antibodies, suggesting that at least part of these inhibitors are antibodies directed against HLA-antigens present on myeloid progenitor cells. Serum inhibitors appear to be infrequent in the population of patients with aplastic anaemia seen in our hospital and appear to have no major implications for therapy or outcome of the disease.

The in vitro growth pattern of human bone marrow in methylcellulose stimulated by different concentrations of conditioned medium.

The proliferation of human bone marrow in methylcellulose stimulated by various concentrations of conditioned medium (CM) and observed at various intervals was studied. The growth kinetics of granulocytic aggregates was found to differ from monocytic clusters and colonies. Granulocytic aggregates showed a consistent and reproducible dose-response relationship; at day 7, the maximum number of granulocytic aggregates was found at 4% CM. At higher levels, the total number of aggregates decreased, while the number of cells per aggregate increased. The number of macrophage aggregates was far less, depending on the CM concentration. Photographic interval studies showed that at high concentrations of CM, clusters and colonies were formed earlier, but also coalesce to form one colony. Our results suggest that the proliferation kinetics of granulocytic aggregates are complex and preclude simple statements about sensitivity to colony-stimulating activity.

Acquired aplastic anemia in adults. IV. Histological and CFU studies in transplanted and non-transplanted patients.

A follow-up study of 10 patients suffering from acquired aplastic anaemia, comprising methocrylate-embedded bone marrow biopsies and CFU cultures, is presented. The haematopoietic recovery patterns and changes in the inflammatory infiltration after permanent engraftment could be distinguished from those in non-transplanted patients. After anti-thymocyte globulin treatment followed by allogeneic bone marrow infusion, the recovery pattern resembled that in non-transplanted patients. The persistently low colony-forming capacity in some patients could be explained by the existence of lymphoid inhibitory cells, which suggests an immunologic auto-destructive mechanism.

Proliferation of myeloid progenitor cells in human long-term bone marrow cultures is stimulated by interleukin-1 beta.

To study the effect of interleukin-1 (IL-1) beta on the proliferation of hematopoietic progenitor cells (HPC) in long-term bone marrow cultures (LTBMC), stromal cell layers were established from normal human bone marrow. Autologous cryopreserved mononuclear phagocyte- and T-lymphocyte-depleted bone marrow cells were reinoculated on the stromal layers in fresh culture medium, with or without the addition of human IL-1 beta (30 U/mL). Once a week, half of the culture supernatant was replaced with fresh culture medium with or without IL-1, and all nonadherent cells were returned to the flasks. At weekly intervals during a period of 5 weeks, one culture was sacrificed to determine the total number of cells and hematopoietic progenitor cells, present in the adherent and the nonadherent cell fractions. In IL-1-stimulated cultures, the number of cells recovered during a period of 5 weeks exceeded the number of cells in unstimulated control cultures by 1.5 times. This difference was attributed to a twofold increase in the number of adherent cells. The number of HPC recovered from IL-1-stimulated cultures was not different from that recovered from controls. The levels of colony-stimulating activity (CSA) in supernatants from IL-1-stimulated cultures were significantly higher than those in supernatants from control cultures. These results indicate that IL-1 enhances the recovery of cells in LTBMC by stimulating the proliferation of HPC with the concurrent release of CSA from stromal cells, without diminishing the number of HPC.

Interleukin 1 induces human marrow stromal cells in long-term culture to produce granulocyte colony-stimulating factor and macrophage colony-stimulating factor.

Pure interleukin 1 (IL 1) was found to stimulate established human bone marrow stromal layers in long-term culture to produce colony-stimulating activity (CSA). Maximal concentrations in the culture medium were reached 24 hours after a single IL 1 pulse. The effect could be neutralized by a specific rabbit anti-IL 1 antiserum. Stromal layers, once stimulated by IL 1, continued to release CSA into the culture medium in the absence of exogenous IL 1. A second IL 1 pulse induced CSA release in an identical manner, as did the primary stimulation, indicating that the CSA released was actively produced. Using specific immunologic assays, both granulocyte colony-stimulating factor (G-CSF) and macrophage CSF (M-CSF) could be identified in the culture supernatants, and production of both factors was inducible by IL 1. Shortly after initiation of the long-term marrow cultures "spontaneous" G-CSF and M-CSF release occurred. The release of G-CSF diminished following addition of the anti-IL 1 antiserum, indicating that endogenous production of IL 1 by stromal cells had contributed to this effect. These results further support the role of IL 1 as an important modulator of CSF production by cells of the hematopoietic microenvironment.

Effect of mast cell growth factor (c-kit ligand) on clonogenic leukemic precursor cells.

Mast cell growth factor (MGF), the ligand for the c-kit receptor, has been shown to be a hematopoietic growth factor that preferentially stimulates the proliferation of immature hematopoietic progenitor cells (HPC). We studied the effect of MGF on the in vitro growth of clonogenic leukemic precursor cells in the presence or absence of interleukin-3 (IL-3), granulocyte-macrophage colony-stimulating factor (GM-CSF), and/or erythropoietin (EPO). Leukemic blood and bone marrow cells from patients with various types of acute myeloid leukemia (AML), chronic myeloid leukemia (CML) in chronic phase, as well as bone marrow samples from patients with myelodysplastic syndromes (MDS) were studied. MGF as a single factor did not induce significant colony formation by clonogenic leukemic precursor cells. In the presence of IL-3 and/or GM-CSF, MGF weakly stimulated the colony formation by clonogenic precursor cells from patients with AML. In contrast, in the presence of IL-3 and/or GM-CSF, MGF strongly induced both size and number of leukemic colonies from patients with CML in chronic phase. Furthermore, in the presence of EPO, MGF strongly stimulated erythroid colony formation by CML precursor cells. Cytogenetic analysis of the colonies showed that all metaphases after 1 week of culture were derived from the leukemic clone. In patients with MDS, MGF strongly stimulated myeloid colony formation in the presence of IL-3 and/or GM-CSF (up to fourfold), and erythroid colony formation in the presence of EPO (up to eightfold). Not only the number, but also the size of the colonies increased. In the presence of MGF, the percentage of normal metaphases increased in three patients tested after 1 week of culture compared with the initial suspension, suggesting that the normal HPC were preferentially stimulated compared with the preleukemic precursor cells. In the absence of exogenous EPO and in the presence of 10% human AB serum, MGF in the presence of IL-3 and/or GM-CSF induced erythroid colony formation from normal bone marrow and patients with MDS or CML, illustrating that MGF greatly diminished the EPO requirement for erythroid differentiation. These results indicate that MGF may be a candidate as a hematopoietic growth factor to stimulate normal hematopoiesis in patients with acute myeloid leukemia, or with myelodysplastic syndromes.

Recognition of minor histocompatibility antigens on lymphocytic and myeloid leukemic cells by cytotoxic T-cell clones.

Clinical studies indicated an enhanced antileukemic effect of allogeneic bone marrow transplantation (BMT), as compared with autologous BMT. After allogeneic HLA-identical BMT, donor-derived cytotoxic T lymphocytes (CTLs) directed at minor histocompatibility (mH) antigens on the recipients, tissues can be shown. To evaluate the antileukemic reactivity of mH antigen-specific CTLs, we analyzed the expression of mH antigens on circulating lymphocytic and myeloid leukemic cells. We show that the defined mH specificities HA-1 through HA-5 and H-Y are present on leukemic cells, indicating that mH antigen-specific CTLs are capable of HLA class I-restricted antigen-specific lysis of leukemic cells. Compared with interleukin-2-stimulated normal lymphocytes, leukemic cells of lymphocytic origin are less susceptible to T-cell-mediated cytotoxicity by the HA-2 mH antigen-specific CTL and the anti-HLA-A2 CTL clone. A possible explanation for this phenomenon is impaired expression of the LFA-1 adhesion molecule. Our study suggests that mH antigen-specific HLA class I-restricted CD8+ CTLs may be involved in the graft-versus-leukemia reactivity after allogeneic BMT.

Polymorphic and monomorphic HLA-DR determinants on human hematopoietic progenitor cells.

The expression of monomorphic Ia-like antigens and polymorphic (allotypic) HLA-DR determinants on CFU-GM, BFU-E, CFU-E, and CFU-GEMM was studied in bone marrow and peripheral blood cells from normal healthy individuals. Using various polyclonal and monoclonal anti-Ia-like antibodies, the presence of HLA-DR backbone antigens was shown on all hematopoietic progenitor cells (HPC) studied, both in complement-dependent cytotoxicity assays and in fluorescence-activated cell sorting (FACS). The expression of allotypic determinants was demonstrated on all HPCs, using the HLA-DR typing sera anti-HLA-DR1, 2, 3, 4, 5, and 7. The Class II antigen MT-2 was also shown on all HPCs, using both monoclonal and alloantisera, whereas the MB-1 (DC-1) determinant could not be demonstrated on HPCs. This might open the possibility of removing MB-1-positive malignant cells from the graft in autologous bone marrow transplantation.