Persistent growth impairment of bone marrow stroma after antilymphocyte globulin treatment for severe aplastic anaemia and its association with relapse

Characterization of bone marrow mesenchymal stromal cells in aplastic anaemia

In aplastic anaemia (AA), haemopoietic activity is significantly reduced and generally attributed to failure of haemopoietic stem cells (HSC) within the bone marrow (BM). The regulation of haemopoiesis depends on the interaction between HSC and various cells of the BM microenvironment, including mesenchymal stromal cells (MSC). MSC involvement in the functional restriction of HSC in AA is largely unknown and therefore, the physical and functional properties of AA MSC were studied in vitro. MSC were characterized by their phenotype and ability to form adherent stromal layers. The functional properties of AA MSC were assessed through proliferative, clonogenic and cross-over culture assays. Results indicate that although AA MSC presented typical morphology and distinctive mesenchymal markers, stromal formation was reduced, with 50% of BM samples failing to produce adherent layers. Furthermore, their proliferative and clonogenic capacity was markedly decreased (P = 0·03 and P = 0·04 respectively) and the ability to sustain haemopoiesis was significantly reduced, as assessed by total cell proliferation (P = 0·032 and P = 0·019 at Week 5 and 6, respectively) and clonogenic potential of HSC (P = 0·02 at Week 6). It was concluded that the biological characteristics of AA MSC are different from those of control MSC and their in vitro haemopoiesis-supporting ability is significantly reduced.

Alteration in marrow stromal microenvironment and apoptosis mechanisms involved in aplastic anemia: an animal model to study the possible disease pathology

Aplastic anemia (AA) is a heterogeneous disorder of bone marrow failure syndrome. Suggested mechanisms include a primary stem cell deficiency or defect, a secondary stem cell defect due to abnormal regulation between cell death and differentiation, or a deficient microenvironment. In this study, we have tried to investigate the alterations in hematopoietic microenvironment and underlying mechanisms involved in such alterations in an animal model of drug induced AA. We presented the results of studying long term marrow culture, marrow ultra-structure, marrow adherent and hematopoietic progenitor cell colony formation, flowcytometric analysis of marrow stem and stromal progenitor populations and apoptosis mechanism involved in aplastic anemia. The AA marrow showed impairment in cellular proliferation and maturation and failed to generate a functional stromal microenvironment even after 19 days of culture. Ultra-structural analysis showed a degenerated and deformed marrow cellular association in AA. Colony forming units (CFUs) were also severely reduced in AA. Significantly decreased marrow stem and stromal progenitor population with subsequently increased expression levels of both the extracellular and intracellular apoptosis inducer markers in the AA marrow cells essentially pointed towards the defective hematopoiesis; moreover, a deficient and apoptotic microenvironment and the microenvironmental components might have played the important role in the possible pathogenesis of AA.

Alterations in hematopoietic microenvironment in patients with aplastic anemia

Mechanisms of hematopoietic failure in patients with aplastic anemia (AA) are obscure. We investigate alterations in the hematopoietic microenvironment in AA patients. We present the results of studying mesenchymal stromal cells (MSC), fibroblastic colony-forming units (CFU-F), and adherent cell layers (ACL) of long-term bone marrow cultures (LTBMC) from bone marrow (BM) samples of AA patients. MSC of AA patients proliferated longer than those of donors. In half of the patients' MSC cultures, adipogenesis was impaired. Osteogenic differentiation was not achieved in 36% of AA MSC. CFU-F formed enlarged colonies, and their concentration in the BM of AA patients was significantly increased. Our data suggest that the physiological activation of the stromal microenvironment is characteristic of AA. We detected a decrease in the expression of the angiopoetin-1 (ANG-1) and vascular cell adhesion molecule-1 (VCAM-1) genes, together with an increase in the expression of vascular endothelial growth factor (VEGF) in ACL of AA patients. This indicates abnormal regulatory patterns in both osteoblastic and vascular contexts. Addition of AA patients' serum to donors' LTBMC for 3 weeks induced similar gene expression alterations. The addition of parathyroid hormone (PTH) resulted in the expression levels of analyzed genes returning to normal, in both AA LTBMC and donor cultures treated with AA serum. The physiologic status of the BM stromal microenvironment (MSC, CFU-F, and ACL of LTBMC) of AA patients was altered.

Defective stromal cell function in a mouse model of infusion-induced bone marrow failure

OBJECTIVE

To study bone marrow (BM) stromal damage in a mouse model of infusion-induced BM failure.

MATERIALS AND METHODS

Sublethally irradiated CByB6F1 mice were infused with 5 x 10(6) C57BL/6 (B6) lymph node (LN) cells. Recipient BM cells were taken at 3, 7, 10, and 14 days following LN infusion and were cultured in vitro in alpha-modified Eagle media for 2-3 weeks. Peripheral blood and was analyzed by complete blood counts while BM lymphocyte infiltration/expansion was analyzed by flow cytometry. Marrow cells from affected and control mice were mixed and cultured in vitro to test nonspecific stromal damage.

RESULTS

Donor lymphocytes infiltrated host BM within 3-7 days and expanded significantly between 7 and 10 days, concurrent with the development of leukopenia, thrombocytopenia, and marrow hypoplasia. BM cells from mice at 7, 10, and 14 days after B6-LN cell infusion were progressively defective in forming stromal feeder layers. A 1:1 mixture of BM cells from affected CByB6F1 mice and normal B6 mice failed to form an effective stromal feeder layer that could support cobblestone colony formation, indicating that lymphocytes in the BM of affected CByB6F1 mice were able to damage stromal cells in the normal B6 BM.

CONCLUSION

Activated lymphocytes destroy both hematopoietic and stromal cells as innocent bystanders in the infusion-induced BM failure model.

Human mesenchymal stem cells are not of donor origin in patients with severe aplastic anemia who underwent sex-mismatched allogeneic bone marrow transplant

Stromal defects are part of the etiology of severe aplastic anemia (SAA), and hematopoietic engraftment is poor in unrelated and mismatched transplant. Therefore, we wanted to find out whether human mesenchymal stem cells (MSC) are partly of donor origin in patients with SAA years after successful bone marrow transplant (BMT). Three SAA patients 3, 5, and 8 years after BMT (cyclophosphamide, ATG) with bone marrow from an HLA-identical sibling donor of the opposite sex were investigated. MSC were grown from patients' bone marrow aspirates according to Caplan et al. The number of MSC that were isolated from SAA bone marrow post transplant was about 10 times lower than in normal controls. Primary cultures of adherent MSC and passage-one cells were analyzed by dual-color interphase fluorescence in situ hybridization (FISH) analysis using centromere-specific DNA probes for X and Y chromosome. FISH did not show any clear evidence of donor cells in the adherent MSC: In all cases, less than 0.5% of nuclei showed a donor-type signal pattern that is well within assay limits. In a female patient, the absence of male donor cells was confirmed by sensitive and quantitative, Y chromosome-specific TaqMan PCR (QYCS-PCR). In contrast, Ficoll-separated hematopoietic cells from the same aspirates were greater than 90% of donor origin, as expected. In SAA, as previously found in patients with lysosomal and peroxisomal storage disease, bone marrow MSC remain host-derived despite successful hematopoietic engraftment years after allogeneic BMT.

Correction of stromal cell defect after bone marrow transplantation in aplastic anaemia

Defects in stromal cell function have been demonstrated in a number of aplastic anaemia (AA) patients. Here we have studied a patient with severe AA and abnormal stromal cell function who underwent bone marrow transplantation (BMT). The objective of this study was to investigate the timing and the mechanism of correction of the stromal defect after transplantation. The patient, a 25-year-old woman with severe AA, underwent BMT from her brother. BM was obtained from the patient on five occasions: 2 weeks pre BMT, and 3, 8, 16 and 21 months post BMT. Stromal cells were grown to confluence and recharged with purified CD34+ cells from normal donors. The support of such cells, as assessed by weekly colony-forming assay (CFU) of non-adherent cells, was compared with that of stromal layers grown from normal BM. A novel technique of combined fluorescence in situ hybridization (FISH) and immunocytochemistry was used to determine the origin of specific stromal cell types on cytospins of stroma post BMT. Stromal function was defective at 2 weeks pre BMT and at 3 months post BMT, but returned to normal at 8 and 16 months post BMT. At 21 months post BMT, stromal fibroblasts and endothelial cells were shown to be of recipient origin, and macrophages and T cells were of donor origin. We present here evidence in a case of severe AA for defective stromal function before BMT and delayed normalization of function after BMT. This correlated with engraftment of donor macrophages and T cells, but not fibroblasts and endothelial cells.

Chronic overexpression of membrane-bound flt3 ligand by T lymphocytes in severe aplastic anaemia

Aplastic anaemia (AA) is an immune-mediated bone marrow failure associated with high serum levels of flt3 ligand (FL). We examined expression of the membrane-bound isoform of FL in peripheral blood and bone marrow cells from AA patients at diagnosis (n = 16) and after immunosuppressive (IS) treatment (n = 36). Flow cytometry demonstrated strongly increased FL levels on the cell surface of T lymphocytes in AA relative to normal controls (P < 0.0001). T-cell-specific expression of membrane-bound FL was confirmed by confocal microscopy. FL mRNA and total cellular FL protein levels were increased about threefold. Overexpression of FL in AA was observed for up to 20 years after IS treatment. FL levels correlated inversely with CD34+ cell numbers and the colony-forming ability of AA bone marrow (R = -0.68 and -0.85 respectively). Histological examination of spleen specimens and bone marrow biopsies gave no evidence of degeneration or fibrosis due to prolonged exposure to high FL. Levels of membrane-bound FL were not increased in autoimmune diseases (n = 23), including rheumatoid arthritis and lupus erythematosus, nor in graft-versus-host disease (n = 8). Chronic overexpression of FL on the surface of T lymphocytes in AA, but not in other T-cell-mediated disorders, suggests that membrane-bound FL plays a role in cell-cell interactions in bone marrow failure and may be important for long-term haemopoietic recovery.

Hematopoietic growth factors in the pathogenesis and for the treatment of aplastic anemia

The production and release of hematopoietic growth factors from bone marrow stromas established in vitro from patients with aplastic anemia is normal or increased. Addition of hematopoietic growth factors to aplastic anemia bone marrow cells results in only modest increases in colony growth, with the exception of granulocyte colony-stimulating factor (G-CSF), which corrects their impaired cloning efficiency to normal. Most clinical data on the use of hematopoietic growth factors in aplastic anemia have derived from uncontrolled and small single-arm studies or case reports. Sustained trilineage hematologic responses have not been observed when hematopoietic growth factors have been used alone or in combination. Serious side effects have been reported for most of the hematopoietic growth factors in patients with aplastic anemia, with the exception of G-CSF. There is a major concern that they may further increase the risk of clonal disorders such as myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML). Hematopoietic growth factors should not be used alone in newly diagnosed patients as specific treatment for aplastic anemia, and their use in combination with immunosuppressive therapy should be confined to multicenter, prospective randomized studies.