Pure red cell aplasia--evidence for an inhibitory action of the bone marrow adherent cell layer

Bone marrow stem cells and stromal cells in autoimmune cytopenias

High-dose immunosuppression followed by autologous haemopoietic stem cell transplantation (ASCT) is a promising practice for the treatment of severe, resistant autoimmune disorders. Patients with refractory autoimmune cytopenias (AIC), primary or secondary to systemic autoimmune diseases (AID) including systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA), have been proposed as potential candidates for such a therapeutic procedure. An abnormal immune milieu, however, may affect the number and functional characteristics of stem cells and/or stromal cells in the bone marrow (BM) and might impact on harvesting and engraftment potential of stem cells or on BM reconstitution following engraftment in patients with AIC undergoing ASCT. Using flow cytometry and in vitro culture assays we have shown that patients with primary AIC display increased number of BM CD34+ cells in response to abnormally high production of granulocyte-colony stimulating factor (G-CSF) by BM stroma. In contrast, patients with AIC secondary to systemic AID display increased apoptosis of BM progenitor cells resulting in low CD34+ cell numbers and abnormal haemopoiesis supporting capacity of BM stroma due to the aberrant, local or systemic, inhibitory cytokine production or to intricate interactions between haemopoietic and immune cells present within the BM microenvironment. In this review we summarize the available knowledge on BM stem cell reserve and function and stromal cell function in patients with primary and secondary AIC with special reference to SLE and RA. The underlying mechanisms possibly involved in the pathogenesis of the observed abnormalities are also discussed.

Assessment of bone marrow stem cell reserve and function and stromal cell function in patients with autoimmune cytopenias

To investigate whether bone marrow (BM) stem cell compartment and/or BM microenvironment are affected by the immune insult in autoimmune cytopenias (AICs), BM stem cell reserve and function and BM stromal function were studied in 15 AIC patients. Stem cells were evaluated by means of flow cytometry, clonogenic progenitor cell assays, long-term BM cultures (LTBMCs), and limiting dilution assay for quantification of long-term–culture initiating cells (LTC-ICs). Stromal cell function was assessed with the use of preformed irradiated LTBMCs from patients and normal controls, recharged with normal CD34+ cells. AIC patients exhibited a high number of CD34+, CD34+/CD38+, and CD34+/CD38− cells; high frequency of granulocyte-macrophage colony forming units in the BM mononuclear cell fraction; high colony recovery in LTBMCs; and normal LTC-IC frequency. Patient BM stromal layers displayed normal hematopoietic-supporting capacity and increased production of granulocyte-colony stimulating factor. Data from this study support the concept that AIC patients with severe, resistant disease might be appropriate candidates for autologous stem cell transplantation.

Assessment of bone marrow stem cell reserve and function and stromal cell function in patients with autoimmune cytopenias

To investigate whether bone marrow (BM) stem cell compartment and/or BM microenvironment are affected by the immune insult in autoimmune cytopenias (AICs), BM stem cell reserve and function and BM stromal function were studied in 15 AIC patients. Stem cells were evaluated by means of flow cytometry, clonogenic progenitor cell assays, long-term BM cultures (LTBMCs), and limiting dilution assay for quantification of long-term–culture initiating cells (LTC-ICs). Stromal cell function was assessed with the use of preformed irradiated LTBMCs from patients and normal controls, recharged with normal CD34+ cells. AIC patients exhibited a high number of CD34+, CD34+/CD38+, and CD34+/CD38− cells; high frequency of granulocyte-macrophage colony forming units in the BM mononuclear cell fraction; high colony recovery in LTBMCs; and normal LTC-IC frequency. Patient BM stromal layers displayed normal hematopoietic-supporting capacity and increased production of granulocyte-colony stimulating factor. Data from this study support the concept that AIC patients with severe, resistant disease might be appropriate candidates for autologous stem cell transplantation.

Pure red cell aplasia associated with malignant thymoma, myasthenia gravis, polyclonal large granular lymphocytosis and clonal thymic T cell expansion

A case with the triad of pure red cell aplasia (PRCA), myasthenia gravis, and malignant thymoma is reported. There was a clonal proliferation of T cells within the thymoma, as demonstrated by a T cell antigen receptor (TCR) delta chain gene rearrangement. However, despite a large granular lymphocytosis, clonality could not be shown in the peripheral blood either before or after thymectomy. There was no evidence of human T cell lymphotrophic virus type 7 (HTLV1) infection. It is postulated that the clonal thymic T cell population secreted cytokine(s), which stimulated the polyclonal proliferation of large granular lymphocytes, which in turn suppressed erythropoiesis. Thymectomy removed the stimulus to the large granular lymphocytes and hence there was a resurgence of erythropoiesis.

Aplastic anemia associated with in vitro inhibition of erythropoiesis by bone marrow-adherent cells

A patient with aplastic anemia that evolved following pure red cell aplasia is described. Cultures of the patient's marrow cells revealed greatly reduced numbers of primitive (BFU-E) and relatively mature (CFU-E) erythroid progenitors, but normal numbers of multipotential (CFU-GEMM) precursors. The BFU-E/CFU-GEMM and CFU-E/BFU-E ratios in the patient's marrow cell cultures were also reduced. T cell- or antibody-mediated inhibition of in vitro erythropoiesis could not be demonstrated in this patient. However, the patient's marrow-adherent cells suppressed the growth of autologous and allogeneic BFU-E and CFU-E, without influencing the growth of CFU-GEMM. Medium conditioned by the patient's adherent cells failed to inhibit the growth of normal erythroid precursors. Our findings suggest a role for marrow-adherent cells in the pathogenesis of aplastic anemia in this patient.