Pathogenesis of selective expansion of PNH clones

Soluble NKG2D Ligands Are Potential Biomarkers and Sentinels of Immune-Mediated Bone Marrow Injury in Bone Marrow Failure Syndromes

Immune-mediated processes are considered important in the pathogenesis of bone marrow failure syndromes (BFS). We previously reported that natural killer group 2D (NKG2D) ligands were expressed on pathological blood cells of patients with BFS and that NKG2D immunity may be involved in bone marrow failure. In addition to membranous NKG2D ligands on the cell surface, soluble NKG2D ligands can exist in plasma. We therefore examined the relationship between soluble NKG2D ligands and blood cell counts in 86 patients with BFS, including aplastic anemia, myelodysplastic syndrome with single lineage dysplasia, and paroxysmal nocturnal hemoglobinuria. Approximately half of the BFS patients were positive for soluble NKG2D ligands in the plasma by enzyme-linked immunosorbent assay, and soluble NKG2D ligand-positive BFS patients exhibited severe cytopenia regardless of membranous NKG2D ligand expression. In vitroanalyses demonstrated that soluble ULBP1, an NKG2D ligand, down-regulated NKG2D receptors on CD2-positive cells in peripheral blood. Moreover, soluble ULBP1 attenuated the cytotoxic effects of peripheral blood mononuclear cells on K562, which express membranous ULBP1. Our results suggest that soluble NKG2D ligands can be easy-to-measure biomarkers for the prediction of activity of immune-meditated bone marrow injury in BFS and that soluble NKG2D ligands suppress redundant immune-mediated bone marrow injury.

Paroxysmal nocturnal hemoglobinuria: a complement-mediated hemolytic anemia

Paroxysmal nocturnal hemoglobinuria is manifests with a chronic hemolytic anemia from uncontrolled complement activation, a propensity for thrombosis and marrow failure. The hemolysis is largely mediated by the alternative pathway of complement. Clinical manifestations result from the lack of specific cell surface proteins, CD55 and CD59, on PNH cells. Complement inhibition by eculizumab leads to dramatic clinical improvement. While this therapeutic approach is effective, there is residual complement activity resulting from specific clinical scenarios as well as from upstream complement components that can account for suboptimal responses in some patients. Complement inhibition strategies are an area of active research.

Mechanism of paroxysmal nocturnal hemoglobinuria clonal dominance: possible roles of different apoptosis and CD8+ lymphocytes in the selection of paroxysmal nocturnal hemoglobinuria clones

BACKGROUND AND OBJECTIVES

Paroxysmal nocturnal hemoglobinuria (PNH), a clonal hematopoietic stem cell disorder, manifests when the PNH clone populates in the hematopoietic compartment. We explored the roles of different apoptosis of GPI+ and GPI- (glycosylphosphatidylinositol) cells and CD8+ lymphocytes in a selection of PNH clones.

PATIENTS AND METHODS

Granulocytes from PNH patients and normal controls were subjected to an apoptosis assay using annexin V. Hematopoietic cell in semisolid media were cultured with or without CD8+ lymphocytes.

RESULTS

In PNH, CD59+ granulocytes exhibited more apoptosis than their CD59- counterparts, after 0 or 4 hours in liquid growth culture system (mean [standard error of mean]: 2.1 (0.5) vs 1.2 (0.2), P=.01 at 0 hour and 3.4 [0.7] vs 1.8 [0.3], P=.03 at 4 hour, respectively). The presence of mononuclear cells (MNCs) rendered a greater difference in apoptosis. The percentages of apoptotic CD59+ granulocytes measured at 4 hours with or without MNC fraction were correlated with the sizes of PNH clones (r=0.633, P=.011; and r=0.648, P=.009; respectively). The autologous CD8+ lymphocytes inhibited CFU-GM and BFU-E colony formation in PNH patients when compared with normal controls (mean [SEM] of percentages of inhibition: 61.7 (10.4) vs 11.9 (2.0), P=.008 for CFU-GM and 26.1 (6.9) vs 4.9 (1.0), P=.037 for BFU-E).

CONCLUSIONS

Increased apoptosis of GPI+ blood cells is likely to be responsible in selection and expansion of PNH clones. MNCs or possibly CD8+ lymphocytes may play a role in this phenomenon.

NKG2D-mediated immunity underlying paroxysmal nocturnal haemoglobinuria and related bone marrow failure syndromes

It is considered that a similar immune mechanism acts in the pathogenesis of bone marrow (BM) failure in paroxysmal nocturnal haemoglobinuria (PNH) and its related disorders, such as aplastic anaemia (AA) and myelodysplastic syndromes (MDS). However, the molecular events in immune-mediated marrow injury have not been elucidated. We recently reported an abnormal expression of stress-inducible NKG2D (natural-killer group 2, member D) ligands, such as ULBP (UL16-binding protein) and MICA/B (major histocompatibility complex class I chain-related molecules A/B), on granulocytes in some PNH patients and the granulocyte killing by autologous lymphocytes in vitro. The present study found that the expression of NKG2D ligands was common to both granulocytes and BM cells of patients with PNH, AA, and MDS, indicating their exposure to some incitement to induce the ligands. The haematopoietic colony formation in vitro by the patients' marrow cells significantly improved when their BM cells were pretreated with antibodies against NKG2D receptor, suggesting that the antibodies rescued haematopoietic cells expressing NKG2D ligands from damage by autologous lymphocytes with NKG2D. Clinical courses of patients with PNH and AA showed a close association of the expression of NKG2D ligands with BM failure and a favourable response to immunosuppressive therapy. We therefore propose that NKG2D-mediated immunity may underlie the BM failure in PNH and its-related marrow diseases.

Immunoselection by natural killer cells of PIGA mutant cells missing stress-inducible ULBP

The mechanism by which paroxysmal nocturnal hemoglobinuria (PNH) clones expand is unknown. PNH clones harbor PIGA mutations and do not synthesize glycosylphosphatidylinositol (GPI), resulting in deficiency of GPI-linked membrane proteins. GPI-deficient blood cells often expand in patients with aplastic anemia who sustain immune-mediated marrow injury putatively induced by cytotoxic cells, hence suggesting that the injury allows PNH clones to expand selectively. We previously reported that leukemic K562 cells preferentially survived natural killer (NK) cell-mediated cytotoxicity in vitro when they acquired PIGA mutations. We herein show that the survival is ascribable to the deficiency of stress-inducible GPI-linked membrane proteins ULBP1 and ULBP2, which activate NK and T cells. The ULBPs were detected on GPI-expressing but not on GPI-deficient K562 cells. In the presence of antibodies to either the ULBPs or their receptor NKG2D on NK cells, GPI-expressing cells were as less NK sensitive as GPI-deficient cells. NK cells therefore spared ULBP-deficient cells in vitro. The ULBPs were identified only on GPI-expressing blood cells of a proportion of patients with PNH but none of healthy individuals. Granulocytes of the patients partly underwent killing by autologous cytotoxic cells, implying ULBP-associated blood cell injury. In this setting, the lack of ULBPs may allow immunoselection of PNH clones.

The involvement of adult stem cells originated from bone marrow in the pathogenesis of pterygia

Pterygium is a proliferative disease. Recent research has reported that stem cells are involved in the pathogenesis of various proliferative diseases, including solid tumors and diabetic proliferate vitreoretinopathy. In previous literature, we hypothesized that adult stem cells originated from bone marrow were involved in the pathogenesis of pterygium. We proved this by immunohistochemical staining with various stem cell markers. The staining showed adult stem cells in the pterygium. c-kit positive cells were observed primarily in the stroma, and some cells were also found in the basal epithelium. AC133 and CD34 positive cells were primarily found in the basal epithelium and were ovoid shaped, similar to the c-kit cells. However, some cells were found in vascular endothelium. STRO-1 positive cells were found mainly in the stroma and were spindle shaped. In recurrent pterygium, cells were more scattered and the expression pattern was denser. Therefore, we suggest a new theory of pterygium pathogenesis. Inflammation caused by environmental factors triggers the abnormal production of some growth factors and cytokines in order to recover from cellular damage. If these healing signals are excessive, limbal basal cells will be changed to abnormally-altered pterygial cells. The excessive wound healing process and remnant altered cells result in recurrence using the same mechanism.

Benzene and the hemopoietic stem cell

The emerging understanding of the biology of the hemopoietic stem cell is beginning to shed light on the mechanisms by which benzene gives rise to acute myeloid leukaemia. These mechanisms are complex, affecting not only the DNA, but also the complex intercellular interactions present in the bone marrow microenvironment. The toxic effects of benzene are mediated within the bone marrow and we are beginning to understand the contributions of inter-individual variation in xenobiotic metabolisms and DNA repair to the definition of risk following exposure to benzene in the environment. This process is likely to be accelerated by recent advances in high throughput genotyping. Until now, research has focussed directly on mutation and chromosomal translocations, but we are beginning to understand more how environmental exposures can modify chromatin structure giving rise to heritable changes not affecting DNA. These epigenetic studies are likely to give important further insights into the mode of action of benzene as are studies of its effect on the immune system.

Unusual association between increased bone resorption and presence of paroxysmal nocturnal hemoglobinuria phenotype in multiple myeloma

Paroxysmal nocturnal hemoglobinuria (PNH) clones deficient in glycosylphosphatidylinositol-anchored molecules, including CD55 and CD59, have been previously described in patients with multiple myeloma (MM). The aim of this study was to investigate the possible association between existence of the PNH phenotype and myeloma bone disease. Forty-three patients with newly diagnosed MM were the subjects of the study. Radiographic evaluation of the skeleton was performed in all patients at diagnosis. The following biochemical markers were measured: bone resorption markers (tartrate-resistant acid phosphatase isoform 5b [TRACP-5b]and N-terminal cross-linking telopeptide of type-I collagen [NTX]), bone formation markers (bone alkaline phosphatase [bALP] and osteocalcin [OC]), osteoprotegerin (OPG), soluble receptor activator of nuclear factor KB ligand (sRANKL), and interleukin 6 (IL-6). Detection of CD55- and/or CD59-deficient red cell populations was performed after diagnosis. Patients with MM had elevated mean baseline NTX, TRACP-5b, sRANKL, and IL-6 levels compared with controls, whereas the mean values of bALP, OC, and OPG were significantly decreased. Four patients had no osteolytic lesions, whereas 8 patients had 1 to 3 lytic lesions, and 31 patients had more than 3 lytic lesions and/or pathologic fractures in the skeletal survey. CD55- and/or CD59-deficient red cell populations were observed in 56% of patients with MM. There was a strong correlation between the presence of PNH-like erythrocytes and increased bone resorption, as measured by NTX, TRACP-5b, and sRANKL/OPG ratio (P < .03, P < .02, and P < .02, respectively). There was also a significant correlation between PNH phenotype and severe bone disease (P < .02). These results suggest that there is a possible link between PNH phenotype and increased osteoclastic activity in MM owing to a potential effect of myeloma microenvironment on a preexisting PNH clone. Further studies are required for clarifying this phenomenon and investigating possible mechanisms of this unusual association.