Diazepam-binding inhibitor-related protein 1: a candidate autoantigen in acquired aplastic anemia patients harboring a minor population of paroxysmal nocturnal hemoglobinuria-type cells

Inherited bone marrow failure syndromes and germline predisposition to myeloid neoplasia: A practical approach for the pathologist

The diagnostic work up and surveillance of germline disorders of bone marrow failure and predisposition to myeloid malignancy is complex and involves correlation between clinical findings, laboratory and genetic studies, and bone marrow histopathology. The rarity of these disorders and the overlap of clinical and pathologic features between primary and secondary causes of bone marrow failure, acquired aplastic anemia, and myelodysplastic syndrome may result in diagnostic uncertainty. With an emphasis on the pathologist's perspective, we review diagnostically useful features of germline disorders including Fanconi anemia, Shwachman-Diamond syndrome, telomere biology disorders, severe congenital neutropenia, GATA2 deficiency, SAMD9/SAMD9L diseases, Diamond-Blackfan anemia, and acquired aplastic anemia. We discuss the distinction between baseline morphologic and genetic findings of these disorders and features that raise concern for the development of myelodysplastic syndrome.

Clonal evolution in aplastic anemia: failed tumor surveillance or maladaptive recovery?

Clonal evolution to secondary paroxysmal nocturnal hemoglobinuria (PNH) or myeloid neoplasia (MN) represents one of the long-term complications of patients with aplastic anemia (AA). The recent evidence in the field of immunology and the application of next-generation sequencing have shed light on the molecular underpinnings of these clonal complications, revealing clinical and molecular risk factors as well as potential immunological players. Particularly, whether MN evolution represents a failed tumor surveillance or a maladaptive recovery is still a matter of controversy in the field of bone marrow failure syndromes. However, recent studies have explored the precise dynamics of the immune-molecular forces governing such processes over time, generating knowledge useful for potential early therapeutic strategies. In this review, we will discuss the immune pathophysiology of AA and the emergence of clonal hematopoiesis with regard to the adaptive and maladaptive mechanisms at the basis of secondary evolution trajectories operating under the immune pressure.

Anti-COX-2 autoantibody is a novel biomarker of immune aplastic anemia

In immune aplastic anemia (IAA), severe pancytopenia results from the immune-mediated destruction of hematopoietic stem cells. Several autoantibodies have been reported, but no clinically applicable autoantibody tests are available for IAA. We screened autoantibodies using a microarray containing >9000 proteins and validated the findings in a large international cohort of IAA patients (n = 405) and controls (n = 815). We identified a novel autoantibody that binds to the C-terminal end of cyclooxygenase 2 (COX-2, aCOX-2 Ab). In total, 37% of all adult IAA patients tested positive for aCOX-2 Ab, while only 1.7% of the controls were aCOX-2 Ab positive. Sporadic non-IAA aCOX-2 Ab positive cases were observed among patients with related bone marrow failure diseases, multiple sclerosis, and type I diabetes, whereas no aCOX-2 Ab seropositivity was detected in the healthy controls, in patients with non-autoinflammatory diseases or rheumatoid arthritis. In IAA, anti-COX-2 Ab positivity correlated with age and the HLA-DRB1*15:01 genotype. 83% of the >40 years old IAA patients with HLA-DRB1*15:01 were anti-COX-2 Ab positive, indicating an excellent sensitivity in this group. aCOX-2 Ab positive IAA patients also presented lower platelet counts. Our results suggest that aCOX-2 Ab defines a distinct subgroup of IAA and may serve as a valuable disease biomarker.

Multi-Omics Profiling Identifies Pathways Associated With CD8+ T-Cell Activation in Severe Aplastic Anemia

Severe aplastic anemia (SAA) is an autoimmune disease characterized by immune-mediated destruction of hematopoietic stem and progenitor cells. Autoreactive CD8⁺ T cells have been reported as the effector cells; however, the mechanisms regulating their cell activation in SAA remain largely unknown. Here, we performed proteomics and metabolomics analyses of plasma and bone marrow supernatant, together with transcriptional analysis of CD8⁺ T cells from SAA patients and healthy donors, to find key pathways that are involved in pathogenic CD8⁺ T-cell activation. We identified 21 differential proteins and 50 differential metabolites in SAA patients that were mainly involved in energy metabolism, complement and coagulation cascades, and HIF-1α signaling pathways. Interestingly, we found that these pathways are also enriched in T cells from SAA patients by analyzing available single-cell RNA sequencing data. Moreover, CD8⁺ T cells from SAA patients contain a highly activated CD38⁺ subset, which was increased in the bone marrow of SAA patients and a murine model of SAA. This subset presented enriched genes associated with the glycolysis or gluconeogenesis pathway, HIF-1α signaling pathway, and complement associated pathways, all of which were of importance in T-cell activation. In conclusion, our study reveals new pathways that may regulate CD8⁺ T-cell activation in SAA patients and provides potential therapeutic targets for SAA treatment.

HLA-G-ILT2 interaction contributes to suppression of bone marrow B cell proliferation in acquired aplastic anemia

Acquired aplastic anemia (AA) is an autoimmune disease characterized by hematopoietic stem and progenitor cell destruction in bone marrow. The non-classic human leukocyte class I antigen (HLA-) G interacts with multiple cell subsets, such as T cells and B cells. HLA-G exerts powerful immune suppression by binding with its receptors, immunoglobulin-like transcripts (ILTs). Here, we compared 46 AA patients and 28 healthy controls. Soluble HLA-G levels in bone marrow supernatants from AA patients were higher than controls. The proportion of bone marrow B cells was decreased and the ILT2-expressing cells among CD19⁺ cells were increased in AA patients. In addition, the percentage of mature B cells among marrow B cells was increased in AA patient, while the percentage of pro-B plus pre-B cells was decreased. More immature B cells and pro-B plus pre-B cells expressed ILT2 in AA patients than in controls, while mature B cells expressing ILT2 did not differ significantly. Functional studies demonstrated that high-level soluble HLA-G inhibited bone marrow B cell proliferation by interacting with ILT2 in AA, and was blocked by anti-HLA-G and anti-ILT2 monoclonal antibodies. Together, these results suggest that the abnormal decrease of pro-B plus pre-B cells in AA patients was related to the enhanced suppression by the excess HLA-G and ILT2 proteins. Therapeutic blockade of the HLA-G-ILT2 interaction may help to normalize bone marrow B cell proliferation.

Persistent imbalance, anti-apoptotic, and anti-inflammatory signature of circulating C-C chemokines and cytokines in patients with paroxysmal nocturnal hemoglobinuria

OBJECTIVE

Paroxysmal nocturnal hemoglobinuria (PNH) is a clonal non-malignant disease in which hematopoietic cell apoptosis may play an important pathophysiological role. Previous studies of the content of phosphatidylinositol (3,4,5)-trisphosphate (PI(3,4,5)P3) indicated the possibility of remote transmission of anti-apoptotic signals between pathological and normal hematopoietic progenitors.

METHODS

The study determined the plasma levels of beta chemokines and cytokines in N = 19 patients with PNH and 31 healthy controls. The research material was peripheral blood plasma (EDTA) stored at -80 °C until the test. Beta chemokine and cytokine concentrations were tested in duplicate with Bio-Plex Pro Human Cytokine Assay (Bio-Rad, Hercules, CA, USA) using a Luminex 200 flow cytometer and xPONENT software (Luminex Corporation, Austin, TX, USA). In peripheral blood CD34+ cells we tested the proportions of PI(3,4,5)P3+ and Annexin binding apoptotic phenotype using FC and phosflow.

RESULTS

Compared to the control group, the PNH group showed a significant increase in the plasma concentration of some beta chemokines and cytokines, including MIP-1alpha/CCL3, eotaxin/CCL11, MCP1/CCL2, IL4 and G-CSF. In the group of PNH patients, a significant decrease in the concentration of some cytokines was also observed: RANTES/CCL5, MIP-1beta/CCL4, PDGF-BB and IL9. At the same time, the plasma concentrations of the chemokine IP-10/CXCL10 and the cytokines IFN-gamma, TNF, IL6 and IL10 showed no significant deviations from the values for the control group. Anti-apoptotic phenotype and phosphatidylinositol (3,4,5)-trisphosphate content in PNH clone of CD34+ cells were associated with the level of CCL3 and negatively associated with CCL5, CCL4, PDGF-BB and IL9.

CONCLUSIONS

This data suggest the existence of apoptotic and PI(3,4,5)P3 imbalance in PNH CD34+ cells driven by anti-apoptotic cytokine biosignature in PNH. Plasma cytokines and intracellular enzymes that regulate the phosphoinositide pathways may become a therapeutic target in PNH.

Antibodies specific to ferritin light chain polypeptide are frequently detected in patients with immune‑related pancytopenia

Immuno-related pancytopenia (IRP) is characterized by pancytopenia resulting from bone marrow suppression or destruction mediated by auto-antibodies. In our previous study, a K562 cDNA library was established, which was used to screen for seven possible auto-antigens produced by hematopoietic cells in patients with IRP, including ferritin light chain (FTL). In the present study, FTL was expressed and purified, and the levels of the auto-antibodies specific to FTL were measured. Through ELISA, it was shown that the titer of anti-FTL antibodies was higher in patients with IRP without treatment compared with those who had recovered from IRP, those with severe aplastic anemia (SAA), those with myelodysplastic syndrome (MDS) and the healthy controls. Furthermore, the expression levels of FTL-mRNA were upregulated in patients with IRP without treatment compared with those who had recovered from IRP, those with MDS and the normal controls. The results suggest that FTL antibody expression is upregulated in patients with IRP. Detecting FTL antibodies may therefore have certain clinical value in differentiating between IRP, SAA and MDS. Furthermore, in specific patients with IRP, FTL as an auto-antigen may induce immune attack on hematopoietic stem cells.

Roles of immune responses in the pathogenesis of immunorelated pancytopenia

Some patients with pancytopenia do not conform to any diagnostic criteria of known haematological or non-haematological diseases; however, they respond well to corticosteroid, high-dose intravenous immunoglobulin and rituximab treatment. This abnormality is termed immunorelated pancytopenia (IRP). Later studies indicated that IRP might be a kind of autoimmune disease in which T helper (Th) type 2 cell function is enhanced, resulting in the hyperfunction of B lymphocytes, which then produce excess autoantibodies that attack the bone marrow (BM) and cause cytopenia. Hypofunction of regulatory T (Treg) cells and enhanced Th17 cell function, an elevated percentage of plasmacytoid dendritic cells (pDCs) and a decreased percentage of natural killer (NK) cells help to promote the process. Moreover, increased expression of a synergistic stimulator of B lymphocytes, CD70 and the reactive overexpression of the BCR inhibitory coreceptor CD22 also support this claim. Candidate autoantigens targeted by autoantibodies on haematopoietic cell membranes have also been reported in IRP. This review is focused on studies that demonstrate the role of immune responses in the pathogenesis of IRP. Current diagnostic criteria and treatments for IRP are also referenced to provide a thorough understanding. Distinguishing IRP from idiopathic cytopenias of undetermined significance (ICUS) and other haematological disorders, for example myelodysplastic syndrome (MDS), aplastic anaemia (AA), paroxysmal nocturnal hemoglobinuria (PNH) and Evans syndrome, may help patients with pancytopenia benefit from proper treatment. Further studies are required to achieve new insight into the pathophysiology of IRP with regard to the immune system, which will be instrumental for the development of novel therapies for inhibiting disease initiation and/or progression.

Current Concepts of the Pathogenesis of Aplastic Anemia

Abnormal activation of the immune system plays an important role in the pathogenesis of aplastic anemia (AA). Various immune cells and cytokines constitute a complex immune network, leading to bone marrow failure. The known pathogenesis is an increase of the myeloid dendritic cell (mDC)/ plasmacytoid dendritic cell (pDC) ratio, which causes the ratio of T helper (Th)1/Th2 to be skewed in favor of Th1 and eventually leads to an abnormal activation of cytotoxic T lymphocyte (CTL). The antigens that stimulate T cells in the context of AA remain unknown. In this process, regulatory T (Treg), Th17, natural killer (NK) cell, memory T cell and negative hematopoietic regulatory factors are also involved. In addition, genetic background (e.g., chromosomal abnormalities, telomere attrition, somatic cell mutations), abnormal bone marrow hematopoietic microenvironment and viral infection may also contribute to the pathogenesis of AA. This review summarizes the recent studies of the pathogenesis of AA and the current status of AA research.

Deep sequencing and flow cytometric characterization of expanded effector memory CD8+CD57+ T cells frequently reveals T-cell receptor Vβ oligoclonality and CDR3 homology in acquired aplastic anemia

Oligoclonal expansion of CD8⁺ CD28⁻ lymphocytes has been considered indirect evidence for a pathogenic immune response in acquired aplastic anemia. A subset of CD8⁺ CD28⁻ cells with CD57 expression, termed effector memory cells, is expanded in several immune-mediated diseases and may have a role in immune surveillance. We hypothesized that effector memory CD8⁺CD28⁻CD57⁺ cells may drive aberrant oligoclonal expansion in aplastic anemia. We found CD8⁺CD57⁺ cells frequently expanded in the blood of aplastic anemia patients, with oligoclonal characteristics by flow cytometric Vβ usage analysis: skewing in 1–5 Vβ families and frequencies of immunodominant clones ranging from 1.98% to 66.5%. Oligoclonal characteristics were also observed in total CD8⁺ cells from aplastic anemia patients with CD8⁺CD57⁺ cell expansion by T-cell receptor deep sequencing, as well as the presence of 1–3 immunodominant clones. Oligoclonality was confirmed by T-cell receptor repertoire deep sequencing of enriched CD8⁺CD57⁺ cells, which also showed decreased diversity compared to total CD4⁺ and CD8⁺ cell pools. From analysis of complementarity-determining region 3 sequences in the CD8⁺ cell pool, a total of 29 sequences were shared between patients and controls, but these sequences were highly expressed in aplastic anemia subjects and also present in their immunodominant clones. In summary, expansion of effector memory CD8⁺ T cells is frequent in aplastic anemia and mirrors Vβ oligoclonal expansion. Flow cytometric Vβ usage analysis combined with deep sequencing technologies allows high resolution characterization of the T-cell receptor repertoire, and might represent a useful tool in the diagnosis and periodic evaluation of aplastic anemia patients. (Registered at clinicaltrials.gov identifiers: 00001620, 01623167, 00001397, 00071045, 00081523, 00961064)

Somatic HLA Mutations Expose the Role of Class I-Mediated Autoimmunity in Aplastic Anemia and its Clonal Complications

Acquired aplastic anemia (aAA) is an acquired deficiency of early hematopoietic cells, characterized by inadequate blood production, and a predisposition to myelodysplastic syndrome (MDS) and leukemia. Although its exact pathogenesis is unknown, aAA is thought to be driven by Human Leukocyte Antigen (HLA)-restricted T cell immunity, with earlier studies favoring HLA class II-mediated pathways. Using whole exome sequencing (WES), we recently identified two aAA patients with somatic mutations in HLA class I genes. We hypothesized that HLA class I mutations are pathognomonic for autoimmunity in aAA, but were previously underappreciated because the Major Histocompatibility Complex (MHC) region is notoriously difficult to analyze by WES. Using a combination of targeted deep sequencing of HLA class I genes and single nucleotide polymorphism array (SNP-A) genotyping we screened 66 aAA patients for somatic HLA class I loss. We found somatic HLA loss in eleven patients (17%), with thirteen loss-of-function mutations in HLA-A*33:03, HLA-A*68:01, HLA-B*14:02 and HLA-B*40:02 alleles. Three patients had more than one mutation targeting the same HLA allele. Interestingly, HLA-B*14:02 and HLA-B*40:02 were significantly overrepresented in aAA patients, compared to ethnicity-matched controls. Patients who inherited the targeted HLA alleles, regardless of HLA mutation status, had a more severe disease course with more frequent clonal complications as assessed by WES, SNP-A, and metaphase cytogenetics, and more frequent secondary MDS. The finding of recurrent HLA class I mutations provides compelling evidence for a predominant HLA class I-driven autoimmunity in aAA, and establishes a novel link between aAA patients' immunogenetics and clonal evolution.

Microbe-Induced Inflammatory Signals Triggering Acquired Bone Marrow Failure Syndromes

Acquired bone marrow failure syndromes encompass a unique set of disorders characterized by a reduction in the effective production of mature cells by the bone marrow (BM). In the majority of cases, these syndromes are the result of the immune-mediated destruction of hematopoietic stem cells or their progenitors at various stages of differentiation. Microbial infection has also been associated with hematopoietic stem cell injury and may lead to associated transient or persistent BM failure, and recent evidence has highlighted the potential impact of commensal microbes and their metabolites on hematopoiesis. We summarize the interactions between microorganisms and the host immune system and emphasize how they may impact the development of acquired BM failure.

The complex pathophysiology of acquired aplastic anaemia

Immune-mediated destruction of haematopoietic stem/progenitor cells (HSPCs) plays a central role in the pathophysiology of acquired aplastic anaemia (aAA). Dysregulated CD8(+) cytotoxic T cells, CD4(+) T cells including T helper type 1 (Th1), Th2, regulatory T cells and Th17 cells, natural killer (NK) cells and NK T cells, along with the abnormal production of cytokines including interferon (IFN)-γ, tumour necrosis factor (TNF)-α and transforming growth factor (TGF)-β, induce apoptosis of HSPCs, constituting a consistent and defining feature of severe aAA. Alterations in the polymorphisms of TGF-β, IFN-γ and TNF-α genes, as well as certain human leucocyte antigen (HLA) alleles, may account for the propensity to immune-mediated killing of HSPCs and/or ineffective haematopoiesis. Although the inciting autoantigens remain elusive, autoantibodies are often detected in the serum. In addition, recent studies provide genetic and molecular evidence that intrinsic and/or secondary deficits in HSPCs and bone marrow mesenchymal stem cells may underlie the development of bone marrow failure.

Severe aplastic anemia associated with eosinophilic fasciitis: report of 4 cases and review of the literature

Diffuse eosinophilic fasciitis (Shulman disease) is a rare sclerodermiform syndrome that, in most cases, resolves spontaneously or after corticosteroid therapy. It has been associated with hematologic disorders, such as aplastic anemia. The clinical features and long-term outcomes of patients with eosinophilic fasciitis and associated aplastic anemia have been poorly described. We report the cases of 4 patients with eosinophilic fasciitis and associated severe aplastic anemia. For 3 of these patients, aplastic anemia was refractory to conventional immunosuppressive therapy with antithymocyte globulin and cyclosporine. One of the patients received rituximab as a second-line therapy with significant efficacy for both the skin and hematologic symptoms. To our knowledge, this report is the first to describe rituximab used to treat eosinophilic fasciitis with associated aplastic anemia. In a literature review, we identified 19 additional cases of eosinophilic fasciitis and aplastic anemia. Compared to patients with isolated eosinophilic fasciitis, patients with eosinophilic fasciitis and associated aplastic anemia were more likely to be men (70%) and older (mean age, 56 yr; range, 18-71 yr). Corticosteroid-containing regimens improved skin symptoms in 5 (42%) of 12 cases but were ineffective in the treatment of associated aplastic anemia in all but 1 case. Aplastic anemia was profound in 13 cases (57%) and was the cause of death in 8 cases (35%). Only 5 patients (22%) achieved long-term remission (allogeneic hematopoietic stem cell transplantation: n = 2; cyclosporine-containing regimen: n = 2; high-dose corticosteroid-based regimen: n = 1).

Identification of autoantibodies expressed in acquired aplastic anaemia

Acquired aplastic anaemia (aAA) is recognized as an autoimmune disorder; however, the autoantigens and target cells involved remain elusive. Expression of autoantibodies and their target cells were examined using the haematopoietic cell line K562 and bone marrow stromal cell line hTS-5; 43·5% and 21·7% of aAA expressed autoantibody against K562 and hTS-5 cells, respectively. The autoantigens were identified by serological identification of antigens through recombinant cDNA expression cloning. This study indicates that haematopoietic cells are the targets of immune abnormality in aAA. These autoantibodies may be utilized to distinguish patients associated with immune abnormality from bone marrow failure syndrome.

Antibodies against carbonic anhydrase in patients with aplastic anemia

BACKGROUND/AIMS

Antibodies against carbonic anhydrase (CA) have been detected in patients with an aplastic anemia (AA)-like syndrome after autologous stem cell transplantation.

METHODS

We analyzed sera of 53 bona fide AA patients before and after treatment with anti-thymocyte globulin (ATG) or bone marrow transplantation for the presence of anti-CA antibodies.

RESULTS

Anti-CA antibodies were detected in 20 patients (38%) and were associated with older age at diagnosis of AA. Antibody-positive patients showed poor response to ATG treatment (complete response 14%) and inferior long-term survival (36% at 10 years), when compared to antibody-negative patients (complete response and 10-year survival both 64%). Two thirds of patients with antibodies at diagnosis of AA became antibody negative after treatment with ATG. Clearance of the antibody did not appear to be associated with hematological improvement.

CONCLUSION

Antibodies against CA are detected frequently at diagnosis of AA, and their presence identifies a subset of patients with poor response to immunosuppressive treatment.

HLA DR15 antigen status does not impact graft-versus-host disease or survival in HLA-matched sibling transplantation for hematologic malignancies

The HLA class II DRB1 antigen DR15 is an important prognostic marker in immune-mediated marrow failure states. DR15 has also been associated with favorable outcomes (reduced acute graft-versus-host disease [aGVHD] and relapse) after allogeneic hematopoietic cell transplant. To elucidate the impact of DR15 on transplantation outcomes, we conducted a retrospective study of 2891 recipients of first allogeneic stem cell transplant from HLA-matched sibling donors for the treatment of acute leukemia, chronic myeloid leukemia, or myelodysplastic syndrome (MDS) between 1990 and 2007. All patients received conventional myeloablative conditioning, T-replete grafts, and cyclosporine plus methotrexate-based GVHD prophylaxis. DNA-based HLA typing allowed categorization of 732 patients (25.3%) as positive and 2159 patients (74.7%) as negative for DRB1*15:01 or *15:02 (DR15). There were no significant differences in baseline characteristics between the HLA DR15 positive and negative groups. In univariate analysis, HLA-DR15 status had no impact on neutrophil engraftment, aGVHD, chronic GVHD (cGVHD), treatment-related mortality, relapse, disease-free survival, or overall survival (OS). In multivariate analysis, DR15 status showed no significant difference in aGVHD, cGVHD, OS, or relapse. In conclusion, DR15 status had no impact on major HLA-matched sibling donor hematopoietic cell transplant outcomes in this large and homogenous cohort of patients with leukemia and MDS.

HLA-matched sibling transplantation for severe aplastic anemia: impact of HLA DR15 antigen status on engraftment, graft-versus-host disease, and overall survival

The HLA class II DRB1 antigen DR15 (common alleles *1501, *1502) is an important marker in the pathobiology of severe aplastic anemia (SAA). We studied 1204 recipients of HLA-matched sibling bone marrow transplantation for SAA to determine whether HLA DR15 status (as determined by allele-level typing) affected hematopoietic recovery, graft-versus-host disease (GVHD), or overall survival (OS). In multivariate analysis, secondary graft failure rate at 2 years was lower in patients who were HLA DR15+ (hazard ratio = 0.46, P = .01). However, neutrophil recovery at day -28, platelet recovery at day -100, acute GVHD, chronic GVHD, and overall mortality were independent of DR15 status. The 5-year probabilities of OS, after adjusting for age, race, performance score, transplant-conditioning regimen, and year of transplantation, were 78% and 81% for patients who were HLA DR15+ and HLA DR15-, respectively (P = .35). In conclusion, DR15 status is associated with secondary graft failure after HLA-matched sibling bone marrow transplantation for SAA but has no significant impact on survival.

CD34+ gene expression profiling of individual children with very severe aplastic anemia indicates a pathogenic role of integrin receptors and the proapoptotic death ligand TRAIL

BACKGROUND Very severe aplastic anemia is characterized by a hypoplastic bone marrow due to destruction of CD34(+) stem cells by autoreactive T cells. Investigation of the pathomechanism by patient-specific gene expression analysis of the attacked stem cells has previously been impractical because of the scarcity of these cells at diagnosis.

DESIGN AND METHODS

Employing unbiased RNA amplification, patient-specific gene expression profiling was carried out for CD34(+) cells from patients newly diagnosed with very severe aplastic anemia (n=13), refractory anemia (n=8) and healthy controls (n=10). These data were compared to profiles of myelodysplastic disease (n=55), including refractory anemia (n=18). To identify possible targets of autoimmune attack, presence of autoreactive antibodies was tested in pre-therapeutic sera of patients with very severe aplastic anemia (n=19).

RESULTS

CD34(+) gene expression profiling distinguished between healthy controls, children with aplastic or refractory anemia and clonal disease. Interferon stimulated genes such as the apoptosis inducing death ligand TRAIL were strongly up-regulated in CD34(+) cells of patients with aplastic anemia, in particular in patients responding to immunosuppressive treatment. In contrast, mRNA expression of integrin GPVI and the integrin complexes GPIa/IIa, GPIIb/IIIa, GPIB/GPIX/GPV was significantly down-regulated and corresponding antibodies were detected in 7 of 11 profiled patients and in 11 of 19 aplastic anemia patients. CONCLUSIONS As a potential diagnostic tool, patient-specific gene expression profiling of CD34(+) stem cells made it possible to make the difficult differential diagnosis of most patients with aplastic and refractory anemia. Profiling indicated a prognostic correlation of TRAIL expression and patient benefit from immunosuppressive therapy. Downregulation of integrin expression and concurrent presence of autoreactive anti-integrin-antibodies suggested a previously unrecognized pathological role of integrins in aplastic anemia.

Aplastic crisis as primary manifestation of systemic lupus erythematosus

Aplastic crisis is an unusual feature of systemic lupus erythematosus (SLE). We report the case of a 54-year-old woman presenting with both (extravascular) Coombs-positive hemolytic anemia and laboratory findings of bone marrow hyporegeneration with concomitant severe neutropenia. A bone marrow biopsy confirmed aplastic crisis. Diagnostic work-up revealed soaring titers of autoantibodies (anti-nuclear, anti-double-stranded DNA, anti-cardiolipin-IgM, and anti-β2-glykoprotein-IgM antibodies), indicating a connective tissue disease as the most plausible reason for bone marrow insufficiency. As the criteria for SLE were fulfilled, we initiated an immunosuppressive therapy by steroids, which led to a rapid complete hematologic and clinical remission in our patient. In this case, we could report on one of the rare cases of SLE-induced aplastic crisis showing that this condition can be entirely reversed by immunosuppressive treatment and that SLE-induced aplastic crisis yields a good prognosis. In conclusion, in a case of aplastic crisis, physicians should be aware that SLE can be a rare cause that is accessible to specific treatment.

GPI-anchored protein-deficient T cells in patients with aplastic anemia and low-risk myelodysplastic syndrome: implications for the immunopathophysiology of bone marrow failure

Glycosylphosphatidylinositol-anchored protein-deficient (GPI-AP(-) ) T cells can be detected in some patients with bone marrow failure (BMF), but the link between these cells and BMF pathophysiology remains to be elucidated. To clarify the significance of GPI-AP(-) T cells in BMF, peripheral blood from 562 patients was examined for the presence of CD48(-) CD59(-) CD3(+) cells using high-resolution flow cytometry (FCM), and the GPI-AP(-) T cells were characterized with regard to their phenotype and sensitivity to inhibitory molecules, including herpesvirus entry mediator (HVEM) and a myelosuppressive cytokine, TGF-β. A multi-lineage FCM analysis detected CD48(-) CD59(-) CD3(+) T cells in 72 (12.8%) of the patients, together with GPI-AP(-) myeloid cells. Unexpectedly, 12 patients (10 with aplastic anemia and 2 with myelodysplastic syndrome-refractory anemia, 2.1%), who showed clinical features similar to those of other BMF patients with GPI-AP(-) myeloid cells, such as a good response to immunosuppressive therapy, displayed 0.01-0.3% GPI-AP(-) cells exclusively in T cells. The CD48(-) CD59(-) T cells consisted of predominantly effector memory (EM) and terminal effector cells, while CD48(-) CD59(-) T cells from non-BMF patients who had received anti-CD52 antibody only showed EM and central memory phenotypes. TGF-β and HVEM capable of inhibiting T-cell proliferation via its GPI-AP CD160 ligation suppressed the in vitro proliferation of GPI-AP(+) T cells more potently than that of GPI-AP(-) T cells from the same patients. The presence of GPI-AP(-) T cells, as well as GPI-AP(-) myeloid cells, may therefore reflect the immunopathophysiology of BMF in which cytokine-mediated suppression of hematopoietic stem cells via GPI-AP-type receptors takes place.

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.

Autoantibodies specific to hnRNP K: a new diagnostic marker for immune pathophysiology in aplastic anemia

To identify a new diagnostic marker for the immune pathophysiology of aplastic anemia (AA), we screened sera of immune-mediated AA patients for the presence of antibodies (Abs) specific to proteins derived from a leukemia cell line UT-7 using two-dimensional electrophoresis followed by immunoblotting. The target proteins were identified by peptide mass fingerprinting. Heterogeneous nuclear ribonucleoprotein (hnRNP) K was identified as a novel autoantigen. An enzyme-linked immunosorbent assay revealed high titers of anti-hnRNP K Abs in 85 (31%) of 273 patients with AA. Sixty-four patients received antithymocyte globulin and cyclosporine after undergoing screening for anti-hnRNP K Ab, anti-DRS-1 Ab, anti-moesin Ab, and paroxysmal nocturnal hemoglobinuria (PNH)-type cells. Twenty (87%) of 23 patients with the presence of anti-hnRNP K Abs responded to the immunosuppressive therapy (IST), while 19 (46%) of 41 patients without the presence of anti-hnRNP K Abs responded. A multivariate analysis showed only PNH-type cells and anti-hnRNP K Abs to be significant factors for the prediction of a good response to IST. The detection of anti-hnRNP K Abs as well as PNH-type cells may therefore be useful for diagnosing the immune pathophysiology of AA.

Hydroxyurea upregulates NKG2D ligand expression in myeloid leukemia cells synergistically with valproic acid and potentially enhances susceptibility of leukemic cells to natural killer cell-mediated cytolysis

Valproic acid (VPA), a histone deacetylase inhibitor, upregulates NKG2D ligands (NKG2DLs) on some monocytic and lymphoid leukemic cells. However, its effect on myeloid leukemia cells and synergistic agents that can augment the effect of VPA remains unknown. Of the various myeloid cell lines examined, OUN-1, a chronic myelogenous leukemia cell line, showed the most prominent upregulation of MICA/B and ULBP2 in response to VPA. The NKG2DL upregulation was observed only in leukemic cells without apoptosis and the effect was abrogated by pretreatment of cells with caffeine, an inhibitor of ATM/ATR. Several activators of ATM/ATR were screened for their effect on NKG2DL expression, but only hydroxyurea (HU) efficiently upregulated both MICA/B and ULPB2 expression on the cell line. VPA and HU synergistically upregulated the NKG2DLs on OUN-1 cells as well as primary leukemic cells from some patients with acute myeloid leukemia. The upregulation of NKG2DLs by VPA and/or HU was associated with increased transcription of each NKG2DL gene. OUN-1 cells treated with VPA + HU were more susceptible to killing by natural killer (NK) cells than untreated cells and the enhanced cytotoxicity of NK cells was blocked by the treatment of NK cells with anti-NKG2D monoclonal antibodies. The same concentrations of VPA and HU did not affect the cytotoxicity of NK cells against OUN-1 cells. These data suggest that VPA and HU might enhance the NK cell-mediated antileukemia effect by increasing the susceptibility of myeloid leukemic cells to NK cells.

Acyl-coenzyme A binding domain containing 3 (ACBD3; PAP7; GCP60): an emerging signaling molecule

Golgi body-mediated signaling has been linked to its fragmentation and regeneration during the mitotic cycle of the cell. During this process, Golgi-resident proteins are released to the cytosol and interact with other signaling molecules to regulate various cellular processes. Acyl-coenzyme A binding domain containing 3 protein (ACBD3) is a Golgi protein involved in several signaling events. ACBD3 protein was previously known as peripheral-type benzodiazepine receptor and cAMP-dependent protein kinase associated protein 7 (PAP7), Golgi complex-associated protein of 60kDa (GCP60), Golgi complex-associated protein 1 (GOCAP1), and Golgi phosphoprotein 1 (GOLPH1). In this review, we present the gene ontology of ACBD3, its relations to other Acyl-coenzyme A binding domain containing (ACBD) proteins, and its biological function in steroidogenesis, apoptosis, neurogenesis, and embryogenesis. We also discuss the role of ACBD3 in asymmetric cell division and cancer. New findings about ACBD3 may help understand this newly characterized signaling molecule and stimulate further research into its role in molecular endocrinology, neurology, and stem cell biology.

Comparison of immunological abnormalities of lymphocytes in bone marrow in myelodysplastic syndrome (MDS) and aplastic anemia (AA)

OBJECTIVE

The subsets and the polarization of lymphocytes in bone marrow from low-risk myelodysplastic syndrome (MDS) were studied and compared with those from patients with aplastic anemia (AA).

METHODS

A total of 34 patients with low-risk MDS (IPSS score< or =1.0) who presented abnormal chromosomes and 16 patients with AA were enrolled in this study. We determined T lymphocyte subsets, T cells polarization status, and the percentages of NK cells and of B lymphocytes in bone marrow and compared these parameters between the two groups of patients. As controls, 24 patients with high-risk MDS (IPSS score>1.0) presenting abnormal chromosomes and 22 healthy/benign hematologic disease subjects were used.

RESULTS

In low-risk MDS/AA patients, the percentage of CD3+ lymphocytes was significantly increased compared to controls (p=0.006 and p=0.001), while the percentage of CD19+ lymphocytes was significantly decreased (p<0.001 and p=0.002); there were no significant differences between MDS/AA and normal controls in other parameters; For low-risk MDS patients, the polarization status of bone marrow CD4+ cells toward Th1 (Th1/Th2) and of CD8+ cells toward Tc1 (Tc1/Tc2) was stronger than that for AA patients (p=0.05 and p<0.001). Other parameters did not show significant differences; Regardless of the predominance of CD4 or CD8 T cells, all patients with low-risk MDS were accompanied with elevated Tc1 polarization (Tc1/Tc2).

CONCLUSION

In both AA and MDS, the number of total T lymphocytes increased. However, polarization towards Th1 and Tc1 was obviously stronger in MDS patients than in AA patients. This might be related to T cell stimulation from the clones of malignant hematopoietic cells.

Abnormal immunity and stem/progenitor cells in acquired aplastic anemia

Acquired aplastic anemia (AA) is considered as an immune-mediated bone marrow failure syndrome, characterized by hypoplasia and pancytopenia with fatty bone marrow. Abnormal immunity is the major factor mediating the pathogenesis of acquired AA. Activated DCs might promote the polarization to Th1 cells, and activate CD8(+) T cells. A variety of immune molecules including IFN-gamma, TNF-alpha, MIP-1alpha and IL-2, 8, 12, 15, 17, 23, produced by them and stromal cells, compose a cytokine network to destruct stem/progenitor cells as well as hematopoietic stem/progenitor cells, mesenchymal stem cells (MSCs) and angioblasts/endothelial progenitor cells. Inversely, deficient MSCs, CD4(+)CD25(+) T cells, NK cells, NKT cells and early hematopoietic growth factors diminish the capacity of immune regulation and the support of hematopoiesis. As a result, stem/progenitor cells are significantly impaired to be disabled cells with markedly deficient proliferation, differentiation, induced apoptosis and dysfunctional response to growth factor stimuli, together with rare normal ones. Although some patients can be ameliorated by stem-cell transplantation or immunosuppressive therapy, more effective and convenient therapies such as patient-specific pluripotent iPS cells based on definite pathogenesis are expected.

Phenotypic and functional characterization of a mouse model of targeted Pig-a deletion in hematopoietic cells

BACKGROUND

Somatic mutation in the X-linked phosphatidylinositol glycan class A gene (PIG-A) causes glycosyl phosphatidylinositol anchor deficiency in human patients with paroxysmal nocturnal hemoglobinuria.

DESIGN AND METHODS

We produced an animal model of paroxysmal nocturnal hemoglobinuria by conditional Pig-a gene inactivation (Pig-a(-/-)) in hematopoietic cells; mice carrying two lox sites flanking exon 6 of the Pig-a gene were bred with mice carrying the transgene Cre-recombinase under the human c-fes promoter. We characterized the phenotypic and functional properties of glycosyl phosphatidylinositol-deficient and glycosyl phosphatidylinositol-normal hematopoietic cells from these Pig-a(-/-) mice using gene expression microarray, flow cytometry, bone marrow transplantation, spectratyping, and immunoblotting.

RESULTS

In comparison to glycosyl phosphatidylinositol-normal bone marrow cells, glycosyl phosphatidylinositol-deficient bone marrow cells from the same Pig-a(-/-) animals showed up-regulation of the expression of immune function genes and contained a significantly higher proportion of CD8 T cells. Both characteristics were maintained when glycosyl phosphatidylinositol-deficient cells were transplanted into lethally-irradiated recipients. Glycosyl phosphatidylinositol-deficient T cells were inactive, showed pronounced Vbeta5.1/5.2 skewing, had fewer gamma-interferon-producing cells after lectin stimulation, and contained fewer CD4(+)CD25(+)FoxP3(+) regulatory T cells. However, the levels of T-cell receptor signaling proteins from glycosyl phosphatidylinositol-deficient cells were normal relative to glycosyl phosphatidylinositol-normal cells from wild type animals, and cells were capable of inducing target cell apoptosis in vitro.

CONCLUSIONS

Deletion of the Pig-a gene in hematopoietic cells does not cause frank marrow failure but leads to the appearance of clonally-restricted, inactive yet functionally competent CD8 T cells.

Anti-moesin antibodies derived from patients with aplastic anemia stimulate monocytic cells to secrete TNF-alpha through an ERK1/2-dependent pathway

Antibodies specific to moesin, which are frequently detectable in the serum of patients with aplastic anemia (AA), can induce tumor necrosis factor-alpha (TNF-alpha) secretion from monocytes and a human monocytic leukemia cell line THP-1. We investigated the mechanisms responsible for TNF-alpha secretion from monocytic cells induced by the auto-antibodies that are purified from the sera of AA patients. TNF-alpha induction by anti-moesin antibodies depended on the amount of cell surface moesin expressed by THP-1 cells. F(ab')(2) fragments prepared from the anti-moesin antibodies were able to stimulate THP-1 cells to secrete TNF-alpha and this stimulatory effect was enhanced by cross-linking of moesins with anti-human IgG F(ab')(2) fragment antibodies. Anti-moesin antibodies as well as their F(ab')(2) fragments induced the phosphorylation of ERK1/2 in monocytic cells and this effect was suppressed by the addition of an ERK1/2 inhibitor. Moreover, anti-moesin antibody treatment induced the phosphorylation of moesin proteins in the monocytes and THP-1 cells within 30 min. These results indicate that anti-moesin antibodies induce TNF-alpha secretion from monocytes through the activation of the ERK1/2 pathway provoked by direct binding to moesin on the cells.

Identification of annexin 1 as a novel autoantigen in acute exacerbation of idiopathic pulmonary fibrosis

Consistent with the hypothesis that pulmonary epithelial apoptosis is the key to the acute exacerbation of idiopathic pulmonary fibrosis (IPF), we conducted serological identification of Ags by recombinant expression cloning (SEREX) analysis using type II alveolar cell carcinoma (A549) cell lines to identify disease-related Abs. In a survey of Abs to the recombinant autoantigens identified by SEREX analysis, five Abs were identified as novel candidates for the acute exacerbation of IPF. Abs to annexin 1 were detected in 47 and 53% of the sera and bronchoalveolar lavage materials from patients with acute exacerbation of IPF. Some identical TCR Vbeta genes were identified in sequential materials obtained at 1-3 mo in all 10 acute exacerbation IPF cases, suggesting that some infiltrating CD4-positive T cells sharing limited epitopes expand by Ag-driven stimulation during disease extension. The CDR3 region of these identical TCR Vbeta genes showed high homology with the N-terminal portion of annexin 1, including in the HLA-DR ligand epitopes predicted by TEPITOPE analysis. By Western blotting analysis and observation of the CD4-positive T cell responses in bronchoalveolar lavage samples, the N-terminal portion of annexin 1 was cleaved and found to induce marked proliferative responses of CD4-positive T cells in three patients. Our study demonstrates that annexin 1 is an autoantigen that raises both Ab production and T cell response in patients with acute exacerbation of IPF, and that the N-terminal portion of annexin 1 plays some role in the pathogenesis of acute exacerbation in IPF patients.

Clinical impact of HLA-DR15, a minor population of paroxysmal nocturnal haemoglobinuria-type cells, and an aplastic anaemia-associated autoantibody in children with acquired aplastic anaemia

Aplastic anaemia (AA) is defined as a pancytopenia caused by bone marrow failure, and its pathogenesis is thought to involve autoimmune processes. Several predictive markers of the response to immunosuppressive therapy (IST) have been proposed, which appear to reflect the immune pathophysiology. We prospectively investigated the presence of human leucocyte antigen (HLA)-DR15, a minor population of paroxysmal nocturnal haemoglobinuria (PNH)-type cells, and antibodies to the recently identified autoantigen postmeiotic segregation increased 1 (PMS1) in 103 children with AA enrolled in a multicentre study. In contrast to adults, children with AA did not show an increased frequency of HLA-DR15. In addition, a sensitive flow cytometric assay revealed that children with AA have a much lower prevalence of PNH-type cells (21.4%) than reported for adults with this disease. An immunoblotting assay detected anti-PMS1 antibody in 15 of 103 (14.6%) of the children. Finally, the response rate to IST was not significantly different between patients with and without DR15 (45.5% vs. 54.0%), PNH-type cells (68.2% vs. 53.1%) or anti-PMS1 antibody (40.0% vs. 59.1%). The current study did not confirm a correlation between these markers and the response to IST, suggesting that there is a difference in the pathophysiologies of adult and paediatric AA.

Autoimmunity and malignancy in hematology—More than an association

Several associations between hematological malignancies and autoimmunity directed against hematopoietic cells exist. Antibody mediated elimination of mature blood cells such as autoimmune hemolytic anemia (AIHA) and immune thrombocytopenia (ITP) are frequent complications of non-Hodgkin lymphomas, most prominently chronic lymphocytic leukemia. Autoimmunity directed against hematopoietic precursor cells is the hallmark of aplastic anemia, but many features of this disease are shared by two related disorders, paroxysmal nocturnal hemoglobinuria (PNH) and myelodysplastic syndrome (MDS). While the clinical associations between hematological malignancy and autoimmunity have been described many decades ago, only in the last several years have the common pathogenetic mechanisms been elucidated. We summarize the recent progress made in understanding how hematological malignancy gives rise to autoimmunity directed against blood cells and vice versa, and illustrate parallels in the etiology of malignant and autoimmune hematological disorders. Specifically, recent progress in the recognition of the association of lymphoproliferative disorders and autoimmunity against mature blood cells, and common pathogenetic background of aplastic anemia, paroxysmal nocturnal hemoglobinuria, and myelodysplastic syndrome are discussed.

PTPN22 620W allele is not associated with aplastic anemia

The 1858C/T variant in PTPN22 imparts a gain of function mutation dysregulating T-cell stimulation and is associated with an array of autoimmune diseases. Using a case-control design, we compared the frequency of this polymorphism in 91 patients with acquired aplastic anemia to 132 ethnically matched controls. Representation of the PTPN22 variant was not significantly different between the two populations, suggesting that this gene polymorphism does not contribute to the etiology of aplastic anemia. Aplastic anemia thus joins a list of autoimmune diseases that commonly lack a major humoral disease component and do not associate with the PTPN22 variant.

Specific antibodies to moesin, a membrane-cytoskeleton linker protein, are frequently detected in patients with acquired aplastic anemia

To identify novel autoantibodies in acquired aplastic anemia (AA), we screened the sera of patients with AA possessing small populations of paroxysmal nocturnal hemoglobinuria (PNH)–type cells for the presence of antibodies (Abs) which recognize proteins derived from a leukemia cell line, UT-7. Immunoblotting using proteins derived from lysates or culture supernatants of UT-7 cells revealed the presence of IgG Abs specific to an 80-kDa protein. Peptide mass fingerprinting identified this 80-kDa protein as moesin. Enzyme-linked immunosorbent assay (ELISA) using recombinant moesin showed high titers of antimoesin Abs in 25 (37%) of 67 patients with AA. Moesin was secreted from several myeloid leukemia cell lines other than UT-7, such as OUN-1 and K562, as an exosomal protein. The presence of antimoesin Abs was significantly correlated with the presence of PNH-type cells and antidiazepam-binding inhibitor-related protein-1 (DRS-1) Abs. Patients with AA that did not show any of these 3 markers tended to respond poorly to immunosuppressive therapy. These findings suggest that a B-cell response to moesin, possibly derived from hematopoietic cells, frequently occurs in patients with AA and that detection of antimoesin Abs in combination with other markers may be useful in diagnosing immune pathophysiology in patients with AA.

Human Leukocyte Antigen DR15 Is Associated with Reduced Relapse Rate and Improved Survival after Human Leukocyte Antigen-Identical Sibling Hematopoietic Stem Cell Transplantation

Human leukocyte antigen (HLA) DR15 is associated with autoimmune cytopenia in patients with aplastic anemia, myelodysplastic syndrome, and paroxysmal nocturnal hemoglobinuria. Presence of this antigen also predicts response to immunosuppressive treatment. If DR15 expression on hematopoietic cells also favors induction of immune responses in an allogeneic setting, a lower relapse rate after hematopoietic stem cell transplantation (HSCT) might result through an enhanced graft-versus-leukemia effect. We retrospectively analyzed outcome of HLA-identical sibling HSCT in 192 consecutive patients with acute or chronic leukemia or non-Hodgkin lymphoma. Patients carrying the DR15 antigen had a higher estimated 5-year overall survival (76%) than did DR15-negative patients (55%; P = .04). Improved survival for DR15 patients was due to a significant decrease in death from relapse (5% for DR15(+) versus 24% for DR15(-); P = .02), whereas no difference was seen for rates of transplant-related mortality (19% and 21%, respectively; P = .76). Findings were confirmed by multivariate analyses. Our results show an association of DR15 with a decreased risk of disease relapse and improved survival after HSCT for leukemia or non-Hodgkin lymphoma. This adds to the growing list of links between DR15 and immune reactions in hematopoiesis.

Current concepts in the pathophysiology and treatment of aplastic anemia

Aplastic anemia, an unusual hematologic disease, is the paradigm of the human bone marrow failure syndromes. Almost universally fatal just a few decades ago, aplastic anemia can now be cured or ameliorated by stem-cell transplantation or immunosuppressive drug therapy. The pathophysiology is immune mediated in most cases, with activated type 1 cytotoxic T cells implicated. The molecular basis of the aberrant immune response and deficiencies in hematopoietic cells is now being defined genetically; examples are telomere repair gene mutations in the target cells and dysregulated T-cell activation pathways. Immunosuppression with antithymocyte globulins and cyclosporine is effective at restoring blood-cell production in the majority of patients, but relapse and especially evolution of clonal hematologic diseases remain problematic. Allogeneic stem-cell transplant from histocompatible sibling donors is curative in the great majority of young patients with severe aplastic anemia; the major challenges are extending the benefits of transplantation to patients who are older or who lack family donors. Recent results with alternative sources of stem cells and a variety of conditioning regimens to achieve their engraftment have been promising, with survival in small pediatric case series rivaling conventional transplantation results.

Paroxysmal nocturnal hemoglobinuria: an acquired X-linked genetic disease with somatic-cell mosaicism

Paroxysmal nocturnal hemoglobinuria (PNH) is a severe hemolytic anemia caused by an intrinsic abnormality of the red blood cells that makes them exceedingly susceptible to the lytic action of activated complement (C). This abnormality results from a mutation in the PIG-A gene on Xp22. Given that the mutation is not inherited but is somatically acquired by a hematopoietic stem cell, it creates two populations of blood cells: normal cells and PNH cells. The clinical expression of PNH depends on the relative and absolute expansion of the PNH cell population, which probably depends, in turn, on a paradoxical growth advantage conferred to it by the existence in the patients of an autoimmune process that exerts negative selection against the 'normal' hematopoietic stem cells.

Human leukocyte antigen (HLA) DR15 is associated with reduced incidence of acute GVHD in HLA-matched allogeneic transplantation but does not impact chronic GVHD incidence

The DR15 allele at the HLA DRB1 locus is a marker for immune-mediated bone marrow failure syndromes. We hypothesized that HLA DR15 plays a role in T-cell interactions with hematopoiesis and investigated the role of HLA DR15 on graft-versus-host disease (GVHD) and graft-versus-leukemia effects in HLA-matched allogeneic blood or marrow transplantation (BMT) performed for myeloid malignancies. We performed a retrospective analysis of 119 consecutive related and 48 consecutive unrelated allogeneic BMT for myeloid malignancies treated between 1991 and 2005 to investigate the influence of HLA DR15 on overall survival (OS), progression-free survival (PFS), and incidence of grades II to IV acute GVHD. HLA DR15 was determined by either molecular (n = 108) or serologic (n = 59) methods. The incidence of HLA DR15 was similar to the general white population (35/167 = 21%). There were no significant differences in transplantation characteristics between the HLA DR15–positive and –negative groups. There was no significant difference in chronic GVHD, OS, or PFS between the HLA DR15–positive versus–negative groups in any disease or donor relation subgroups. The HLA DR15–positive group experienced a significantly lower incidence of acute GVHD grades II to IV: 23% versus 42% (P = .041). These results suggest that HLA DR15 reduces the risk of acute GVHD.

Minor population of CD55-CD59- blood cells predicts response to immunosuppressive therapy and prognosis in patients with aplastic anemia

We investigated the clinical significance of a minor population of paroxysmal nocturnal hemoglobinuria (PNH)-type blood cells in patients with acquired aplastic anemia (AA). We quantified CD55-CD59- granulocytes and red blood cells (RBCs) in peripheral blood from 122 patients with recently diagnosed AA and correlated numbers of PNH-type cells and responses to immunosuppressive therapy (IST). Flow cytometry detected 0.005% to 23.1% of GPI-AP- cells in 68% of patients with AA. Sixty-eight of 83 (91%) patients with an increased proportion of PNH-type cells (PNH+) responded to antithymocyte globulin (ATG) + cyclosporin (CsA) therapy, whereas 18 of 39 (48%) without such an increase (PNH-) responded. Failure-free survival rates were significantly higher (64%) among patients with PNH+ than patients with PNH- (12%) at 5 years, although overall survival rates were comparable between the groups. Numbers of PNH-type and normal-type cells increased in parallel among most patients with PNH+ who responded to IST, suggesting that these cells are equally sensitive to immune attack. These results indicate that a minor population of PNH-type cells represents a reliable marker of a positive IST response and a favorable prognosis among patients with AA. Furthermore, immune attack against hematopoietic stem cells that allows PNH clonal expansion might occur only at the onset of AA.

Pathophysiologic mechanisms in acquired aplastic anemia

Aplastic anemia, an unusual hematologic disease, is the paradigm of the human bone marrow failure syndromes. Absence of hematopoietic cells has been recognized from the characteristic morphology for a century; an immune pathophysiology has been inferred from improvement in blood counts with immunosuppressive therapy in the majority of patients. Molecular mechanisms underlying both T cell effector cells and the target marrow stem and progenitor cells are now being identified. Activated type 1 cytotoxic T cells and type 1 cytokines have been implicated in cell culture experiments; clues to the molecular basis of the aberrant immune response include cytokine gene polymorphisms and abnormalities in the regulatory pathways for gamma-interferon. For stem cell depletion, mutations in genes of the telomere repair complex are present in some patients with apparently acquired aplastic anemia. Telomerase deficiency is associated with short telomeres and a quantitative reduction in marrow progenitors and likely also a qualitative deficiency in the repair capacity of hematopoietic tissue.