In vitro and in vivo evidence of PNH cell sensitivity to immune attack after nonmyeloablative allogeneic hematopoietic cell transplantation

Successful haploidentical hematopoietic stem cell transplantation for paroxysmal nocturnal hemoglobinuria with severe pancytopenia developed after long-term aplastic anemia treatment

Haploidentical hematopoietic stem cell transplantation (HSCT) with posttransplant cyclophosphamide is an alternative treatment for aplastic anemia-paroxysmal nocturnal hemoglobinuria (PNH) syndrome with poor prognostic factors. Ravulizumab treatment for PNH before HSCT might have a beneficial effect.

Candida krusei pneumonia in graft-versus-host disease after allogeneic hematopoietic stem cell transplant for paroxysmal nocturnal hemoglobinuria: a case report

Introduction and importance

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare disorder caused by a somatic mutation of PIGA (phosphatidylinositol glycan anchor biosynthesis, class A) gene that leads to the destruction of blood cells. Allogeneic haematopoietic stem cell transplant (HSCT) is a treatment option for PHN, but it can cause graft-versus-host disease (GVHD). Long-term immunosuppression as a treatment of GVHD increases the risk for invasive fungal infections such as Candida krusei pneumonia.

Case presentation

We present the case of a 22-year-old male with C. krusei pneumonia in a known case of chronic GVHD following HSCT for PNH undergoing long-term immunosuppressive therapy. The patient presented with progressive shortness of breath, productive cough, palpitations, and difficulty swallowing. On examination, he had skin rashes and oral lesions, along with signs of severe malnutrition. Diagnosis was made on the basis of radiological imaging and fungal culture.

Discussion

The combination of PNH, GVHD, and HSCT created an immunocompromised state, making the patient susceptible to opportunistic infections, including fungal pneumonia. Early recognition of this condition is challenging due to its non-specific symptoms and potential overlap with other post-transplant complications. Timely diagnosis and appropriate treatment, including antifungal therapy and immunosuppression management, are crucial for optimising patient outcomes.

Conclusion

This case highlights the importance of early recognition and timely treatment of fungal infections in patients with severe conditions such as GVHD following HSCT for PNH. Timely treatment with appropriate antifungals is necessary for optimal outcomes. Additionally, more research with long-term follow-up and monitoring is necessary to address the necessary knowledge gaps in this field.

Allogeneic Hematopoietic Stem Cell Transplantation for Paroxysmal Nocturnal Hemoglobinuria: Multicenter Analysis by the Polish Adult Leukemia Group

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is the sole potential cure for paroxysmal nocturnal hemoglobinuria (PNH); however, the data on its utility in PNH are limited. This retrospective analysis of patients with PNH who underwent allo-HSCT in 11 Polish centers between 2002 and 2016 comprised 78 patients with PHN, including 27 with classic PNH (cPNH) and 51 with bone marrow failure-associated PNH (BMF/PNH). The cohort was 59% male, with a median age of 29 years (range, 12 to 65 years). There was a history of thrombosis in 12% and a history of hemolysis in 81%, and 92% required erythrocyte transfusions before undergoing allo-HSCT. No patient received eculizumab, and 26% received immunosuppressive treatment. The median time from diagnosis to allo-HSCT was 12 months (range, 1 to 127 months). Almost all patients (94%) received reduced-toxicity conditioning, 66% with treosulfan. The stem cell source was peripheral blood in 72% and an identical sibling donor in 24%. Engraftment occurred in 96% of the patients. With a median follow-up of 5.1 years in patients with cPNH and 3.2 years in patients with BMF/PNH, 3-year overall survival (OS) was 88.9% in the former and 85.1% in the latter (P = not significant [NS]). The 3-year OS for patients with/without thrombosis was 50%/92% (P = NS) in the cPNH group and 83.3%/85.3% (P = NS) in the BMF/PNH group. The 3-year OS for in the BMF/PNH patients with/without hemolysis was 93.9%/62.9% (hazard ratio, .13; P = .016). No other factors impacted OS. After allo-HSCT, the frequency of the PNH clone was reduced to 0%, <1%, and <2.4% in 48%, 48%, and 4% of cPNH patients and in 84%, 11%, and 5% of BMF/PNH patients, respectively. The frequency of acute graft-versus-host disease (GVHD) grade II-IV was 23%, and the cumulative 1-year incidence of extensive chronic GVHD was 10.8% in the BMF/PNH group and 3.7% in the cPNH group. Allo-HSCT is a valid option for PNH patients, effectively eliminating the PNH clone with satisfactory overall survival and acceptable toxicity. Reduced-toxicity conditioning with treosulfan is effective and safe in patients with cPNH and BMF/PNH.

How we treat paroxysmal nocturnal hemoglobinuria: A consensus statement of the Canadian PNH Network and review of the national registry

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare hematologic disease characterized by intravascular hemolysis, thrombophilia, and marrow failure. Its phenotype is due to absent or reduced expression of GPI-linked complement regulators and subsequent sensitivity of hematopoietic cells to complement-mediated damage and lysis. Introduction of the terminal complement inhibitor eculizumab drastically improved outcomes in PNH patients; however, despite this improvement, there remain several challenges faced by PNH patients and physicians who care for them. One of the most important is increasing awareness of the heterogeneity with which patients can present, which can lead to significant delays in recognition. Data from the Canadian PNH Registry are presented to demonstrate the variety of presenting symptoms. In Canada, geography precludes consolidation of care to just a few centers, so management is distributed across academic hospitals, linked together as the Canadian PNH Network. The Network over the last several years has developed educational programs and clinical checklists and has worked to standardize access to diagnostics across the country. Herein, we address some of the common diagnostic and therapeutic challenges faced by PNH physicians and give our recommendations. Gaps in knowledge are also addressed, and where appropriate, consensus opinion is provided.

Outcomes of allogeneic stem cell transplantation in patients with paroxysmal nocturnal hemoglobinuria with or without aplastic anemia

OBJECTIVE

The aim of this study was to evaluate the long-term outcomes of allogeneic stem cell transplantation (SCT) in patients with paroxysmal nocturnal hemoglobinuria (PNH) with or without aplastic anemia (AA).

METHOD

A total of 33 patients with PNH clones who underwent allogeneic SCT were analyzed.

RESULTS

After a median follow-up of 57 months (range, 6.0-151.3), the 5-year estimated overall survival rate was 87.9±5.7%. Four patients died of transplant-related mortality (TRM). With the exception of one patient with early TRM, 32 patients were engrafted. Two patients who had developed delayed GF received a second transplant and recovered. The cumulative incidences of acute graft-vs-host disease (GVHD) (≥grade II) and chronic GVHD (≥moderate) were 27.3±7.9% and 18.7±7.0%, respectively. Twenty-one patients receiving SCT with reduced-intensity conditioning (RIC) had available follow-up data for PNH cell population for the first 6 months post-transplant. Analysis of these data revealed that the PNH clones disappeared within approximately 2 months.

CONCLUSION

RIC regimen was sufficient to eradicate PNH clones with sustained donor-type engraftment after allogeneic SCT. Therefore, application of allogeneic SCT with RIC should be considered in patients with PNH, in accordance with the severity of the underlying bone marrow failure.

Paroxysmal nocturnal haemoglobinuria

Paroxysmal nocturnal haemoglobinuria (PNH) is a clonal haematopoietic stem cell (HSC) disease that presents with haemolytic anaemia, thrombosis and smooth muscle dystonias, as well as bone marrow failure in some cases. PNH is caused by somatic mutations in PIGA (which encodes phosphatidylinositol N-acetylglucosaminyltransferase subunit A) in one or more HSC clones. The gene product of PIGA is required for the biosynthesis of glycosylphosphatidylinositol (GPI) anchors; thus, PIGA mutations lead to a deficiency of GPI-anchored proteins, such as complement decay-accelerating factor (also known as CD55) and CD59 glycoprotein (CD59), which are both complement inhibitors. Clinical manifestations of PNH occur when a HSC clone carrying somatic PIGA mutations acquires a growth advantage and differentiates, generating mature blood cells that are deficient of GPI-anchored proteins. The loss of CD55 and CD59 renders PNH erythrocytes susceptible to intravascular haemolysis, which can lead to thrombosis and to much of the morbidity and mortality of PNH. The accumulation of anaphylatoxins (such as C5a) from complement activation might also have a role. The natural history of PNH is highly variable, ranging from quiescent to life-threatening. Therapeutic strategies include terminal complement blockade and bone marrow transplantation. Eculizumab, a monoclonal antibody complement inhibitor, is highly effective and the only licensed therapy for PNH.

Effective eculizumab therapy followed by BMT in a boy with paroxysmal nocturnal hemoglobinuria

A 9-year-old boy with paroxysmal nocturnal hemoglobinuria/aplastic anemia syndrome (PNH/AA) developed hemolytic crisis after receiving immunosuppressive therapy. Eculizumab dramatically relieved the signs and symptoms and then he safely underwent unrelated bone marrow transplantation, suggesting the feasibility and effectiveness of eculizumab before stem cell transplantation in children with PNH/AA in hemolytic crisis.

Long-term outcome of fludarabine-based reduced-intensity allogeneic hematopoietic cell transplantation for debilitating paroxysmal nocturnal hemoglobinuria

Paroxysmal nocturnal hemoglobinuria (PNH) is characterized by intravascular hemolysis, venous thrombosis, and bone marrow failure. Seventeen patients with debilitating PNH, including 8 who were HLA-alloimmunized, underwent a reduced-intensity allogeneic hematopoietic cell transplantation (HCT). All received cyclophosphamide/fludarabine +/- antithymocyte globulin followed by a granulocyte colony-stimulating factor-mobilized HCT from an HLA-matched relative. Glycosylphosphatidylinositol-negative neutrophils were detectable after engraftment but disappeared completely at a median 100 days after transplantation. With a median follow-up of nearly 6 years, 15 patients (87.8%) survived, all without any evidence of PNH, transfusion independent, and off anticoagulation. Allogeneic reduced-intensity HCT remains a curative therapeutic option for PNH patients who are not candidates for eculizumab treatment.

Magnetic nanosensor for detection and profiling of erythrocyte-derived microvesicles

During the course of their lifespan, erythrocytes actively shed phospholipid-bound microvesicles (MVs). In stored blood, the number of these erythrocyte-derived MVs has been observed to increase over time, suggesting their potential value as a quality metric for blood products. The lack of sensitive, standardized MV assays, however, poses a significant barrier to implementing MV analyses into clinical settings. Here, we report on a new nanotechnology platform capable of rapid and sensitive MV detection in packed red blood cell (pRBC) units. A filter-assisted microfluidic device was designed to enrich MVs directly from pRBC units, and label them with target-specific magnetic nanoparticles. Subsequent detection using a miniaturized nuclear magnetic resonance system enabled accurate MV quantification as well as the detection of key molecular markers (CD44, CD47, CD55). When the developed platform was applied, MVs in stored blood units could also be monitored longitudinally. Our results showed that MV counts increase over time and, thus, could serve as an effective metric of blood aging. Furthermore, our studies found that MVs have the capacity to generate oxidative stress and consume nitric oxide. By advancing our understanding of MV biology, we expect that the developed platform will lead to improved blood product quality and transfusion safety.

Paroxysmal nocturnal hemoglobinuria and the age of therapeutic complement inhibition

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare disease of hematopoietic stem cells due to a mutation in the PIG-A gene leading to a deficiency of GPI-anchored proteins. Lack of two specific GPI-anchored proteins, CD55 and CD59, leads to uncontrolled complement activation that result in both intravascular and extravascular hemolysis. Free hemoglobin leads to nitric oxide depletion that mediates the pathophysiology of some of the common clinical signs of PNH. Clinical symptoms of PNH include evidence of hemolytic anemia, bone marrow failure, smooth muscle dystonias and thromboses. Treatment options for patients with PNH include bone marrow transplantation, a therapy associated with high morbidity and mortality, or treatment with the complement inhibitor eculizumab. Eculizumab is a first-in-class anti-complement drug that in PNH has been shown to block complement-mediated hemolysis, reduce transfusion dependency, reduce thromboembolic complications and improve the quality of life (QoL) of patients.

Rapid donor T-cell engraftment increases the risk of chronic graft-versus-host disease following salvage allogeneic peripheral blood hematopoietic cell transplantation for bone marrow failure syndromes

The risk of graft-rejection after allogeneic hematopoietic cell transplantation using conventional cyclophosphamide-based conditioning is increased in patients with bone marrow failure syndromes (BMFS) who are heavily transfused and often HLA-alloimmunized. Fifty-six patients with BMFS underwent fludarabine-based reduced-intensity conditioning and allogeneic peripheral blood progenitor cell (PBPC) transplantation at a single institution. The conditioning regimen consisted of intravenous cyclophosphamide, fludarabine, and equine antithymocyte globulin. Graft-versus-host disease (GVHD) prophylaxis included cyclosporine A alone or in combination with either mycophenolate mofetil or methotrexate. To reduce the risk of graft-rejection/failure, unmanipulated G-CSF mobilized PBPCs obtained from an HLA-identical or single HLA-antigen mismatched relative were transplanted rather than donor bone marrow. Despite a high prevalence of pretransplant HLA-alloimmunization (41%) and a heavy prior transfusion burden, graft-failure did not occur with all patients having sustained donor lympho-hematopoietic engraftment. The cumulative incidence of grade II-IV acute-GVHD and chronic-GVHD was 51.8% and 72%, respectively; with 87.1% surviving at a median follow-up of 4.5 years. A multivariate analysis showed pretransplant alloimmunization and rapid donor T-cell engraftment (≥95% donor by day 30) were both significantly (P < 0.05) associated with the development of chronic-GVHD (adjusted HR 2.13 and 2.99, respectively). These data show fludarabine-based PBPC transplantation overcomes the risk of graft-failure in patients with BMFS, although rapid donor T-cell engraftment associated with this approach appears to increase the risk of chronic-GVHD. (Clinicaltrials.gov identifier: NCT00003838).

Allogeneic stem cell transplantation in paroxysmal nocturnal hemoglobinuria

BACKGROUND

In the era of eculizumab, identifying patients with paroxysmal nocturnal hemoglobinuria who may benefit from allogeneic stem cell transplantation is challenging.

DESIGN AND METHODS

We describe the characteristics and overall survival of 211 patients transplanted for paroxysmal nocturnal hemoglobinuria in 83 EBMT centers from 1978 to 2007. Next, we conducted a comparison with a cohort of 402 non-transplanted patients with paroxysmal nocturnal hemoglobinuria diagnosed between 1950 and 2005 in 92 French centers. We compared the occurrence of complications (i.e. thromboembolism and aplastic anemia) using either an individual or a stratum-matching procedure.

RESULTS

After a median follow-up of 5 years, the 5-year overall survival rate ± standard error (%) was 68 ± 3 in the transplanted group (54 ± 7 in the case of thromboembolism, 69 ± 5 in the case of aplastic anemia without thromboembolism and 86 ± 6 in the case of recurrent hemolytic anemia without thromboembolism or aplastic anemia). Only thromboembolism as the indication for transplantation was associated with worse outcome (P=0.03). We identified 24 pairs of transplanted and non-transplanted patients with thromboembolism for the matched comparison, with worse overall survival for the transplanted patients (hazard ratio=10.0; 95% confidence interval, 1.3-78.1; P=0.007). This was confirmed by the global matching procedure (P=0.03). As regards aplastic anemia without thromboembolism, 30 pairs were identified for the matched comparison. It was not observed that transplanted patients had a significantly worse overall survival (hazard ratio=4.0; 95% confidence interval, 0.9-18.9; P=0.06). A global matching procedure was not feasible.

CONCLUSIONS

Allogeneic stem cell transplantation is probably not a suitable treatment option for life-threatening thromboembolism in paroxysmal nocturnal hemoglobinuria.

Strategy for bone marrow transplantation in eculizumab-treated paroxysmal nocturnal hemoglobinuria

Although the recent introduction of eculizumab has had a significant impact on the management of paroxysmal nocturnal hemoglobinuria (PNH), bone marrow transplantation (BMT) remains the only therapeutic option for patients who develop severe aplasia in the clinical course of PNH. However, information regarding BMT for eculizumab-treated PNH patients is scarce, and two major points-the optimal duration of eculizumab therapy, and the optimal BMT conditioning regimen-remain unclear. Here, we describe the clinical course of a PNH patient who was successfully treated with unrelated reduced-intensity BMT. Eculizumab was discontinued 2 weeks prior to the initiation of the conditioning regimen, which consisted of fludarabine 180 mg/m(2), cyclophosphamide 100 mg/kg, rabbit anti-thymocyte globulin 2 mg/kg, and TBI 3 Gy. Complete donor chimerism was rapidly achieved in association with a rapid decrease in the proportion of PNH erythrocytes. The patient became transfusion-free immediately after BMT, and had no recurrence of hemolysis. The present case suggests that discontinuation of eculizumab before BMT and the use of a highly lymphoablative conditioning regimen may act as a successful treatment strategy in BMT for PNH. Further studies are warranted to evaluate the efficacy and safety of this treatment strategy.

Paroxysmal nocturnal hemoglobinuria from bench to bedside

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare hematologic disease that presents with protean manifestations. Clinical and laboratory investigation over the past 25 years has uncovered most of the basic science underpinnings of PNH and has led to the development of a highly effective targeted therapy. PNH originates from a multipotent hematopoietic stem cell (HSC) that acquires a somatic mutation in a gene called phosphatidylinositol glycan anchor biosynthesis, class A (PIG-A). The PIG-A gene is required for the first step in glycosylphosphatidylinositol (GPI) anchor biosynthesis. Failure to synthesize GPI anchors leads to an absence of all proteins that utilize GPI to attach to the plasma membrane. Two GPI-anchor proteins, CD55 and CD59, are complement regulatory proteins; their absence on the surface of PNH cells leads to complement-mediated hemolysis. The release of free hemoglobin leads to scavenging of nitric oxide and contributes to many clinical manifestations, including esophageal spasm, fatigue, and possibly thrombosis. Aerolysin is a pore-forming toxin that binds GPI-anchored proteins and kills normal cells, but not PNH cells. A fluorescinated aerolysin variant (FLAER) binds GPI-anchor and serves as a novel reagent diagnosing PNH. Eculizumab, a humanized monoclonal antibody against C5, is the first effective drug therapy for PNH.

Relapse of leukemia with loss of mismatched HLA resulting from uniparental disomy after haploidentical hematopoietic stem cell transplantation

We investigated human leukocyte antigen (HLA) expression on leukemic cells derived from patients at diagnosis and relapse after hematopoietic stem cell transplantation (HSCT) using flow cytometry with locus-specific antibodies. Two of 3 patients who relapsed after HLA-haploidentical HSCT demonstrated loss of HLA alleles in leukemic cells at relapse; on the other hand, no loss of HLA alleles was seen in 6 patients who relapsed after HLA-identical HSCT. Single-nucleotide polymorphism array analyses of sorted leukemic cells further revealed the copy number-neutral loss of heterozygosity, namely, acquired uniparental disomy on the short arm of chromosome 6, resulting in the total loss of the mismatched HLA haplotype. These results suggest that the escape from immunosurveillance by the loss of mismatched HLA alleles may be a crucial mechanism of relapse after HLA-haploidentical HSCT. Accordingly, the status of mismatched HLA on relapsed leukemic cells should be checked before donor lymphocyte infusion.

Storage lesion in banked blood due to hemolysis-dependent disruption of nitric oxide homeostasis

PURPOSE OF REVIEW

Whereas blood storage is associated with an increased risk of cardiovascular events and multiorgan failure, the fundamental mechanisms underlying the 'storage lesion' in blood remain uncertain. A major abnormality in aged blood is the reduced red cell life-span after infusion, which is associated with microparticle and free hemoglobin release, and age-related loss of enzymatic functionality. However, the degree of intravascular hemolysis and microparticle formation in humans post-transfusion due to both storage and physiological shear has not been well studied.

RECENT FINDINGS

Our laboratories have discovered that even low levels of intravascular hemolysis severely disrupt nitric oxide bioavailability at the endothelium, via accelerated nitric oxide dioxygenation reactions with free plasma hemoglobin. This process contributes to endothelial dysfunction, adhesion molecule expression, platelet and hemostatic activation, and reactive oxygen species generation. Recent studies also suggest that red cells possess nitric oxide-generating functionality via nitrite reduction and red cell endothelial nitric oxide synthase activity, potentially providing novel pathways to therapeutically alleviate the 'storage lesion'.

SUMMARY

The understanding of the pathological effects of red cell hemolysis on endothelial function suggests that nitric oxide dysregulation may underlie the red cell storage lesion, driven by increased nitric oxide catabolism and loss of nitric oxide-generating functionality.

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.

Glycosylphosphatidylinositol-anchored protein deficiency confers resistance to apoptosis in PNH

OBJECTIVE

Investigate the contribution of PIG-A mutations to clonal expansion in paroxysmal nocturnal hemoglobinuria (PNH).

MATERIALS AND METHODS

Primary CD34+ hematopoietic progenitors from PNH patients were assayed for annexin-V positivity by flow cytometry in a cell-mediated killing assay using autologous effectors from PNH patients or allogeneic effectors from healthy controls. To specifically assess the role of the PIG-A mutation in the development of clonal dominance and address confounders of secondary mutation and differential immune attack that can confound experiments using primary cells, we established an inducible PIG-A CD34+ myeloid cell line, TF-1. Apoptosis resistance was assessed after exposure to allogeneic effectors, NK92 cells (an interleukin-2-dependent cell line with the phenotype and function of activated natural killer [NK] cells), tumor necrosis factor (TNF)-alpha, and gamma-irradiation. Apoptosis was measured by annexin-V staining and caspase 3/7 activity.

RESULTS

In PNH patients, CD34+ hematopoietic progenitors lacking glycosylphosphatidylinositol (GPI)-anchored proteins (GPI-AP(-)) were less susceptible than GPI-AP+ CD34+ precursors to autologous (8% vs 49%; p < 0.05) and allogeneic (28% vs 58%; p < 0.05) cell-mediated killing from the same patients. In the inducible PIG-A model, GPI-AP(-) TF-1 cells exhibited less apoptosis than induced, GPI-AP+ TF-1 cells in response to allogeneic cell-mediated killing, NK92-mediated killing, TNF-alpha, and gamma-irradiation. GPI-AP(-) TF-1 cells maintained resistance to apoptosis when effectors were raised against GPI-AP(-) cells, arguing against a GPI-AP being the target of immune attack in PNH. NK92-mediated killing was partially inhibited with blockade by specific antibodies to the stress-inducible GPI-AP ULBP1 and ULBP2 that activate immune effectors. Clonal competition experiments demonstrate that the mutant clone expands over time under proapoptotic conditions with TNF-alpha.

CONCLUSION

PIG-A mutations contribute to clonal expansion in PNH by conferring a survival advantage to hematopoietic progenitors under proapoptotic stresses.

New insights into paroxysmal nocturnal hemoglobinuria

Paroxysmal nocturnal hemoglobinuria (PNH) is an uncommon acquired hemolytic anemia that manifests with abdominal pain, esophageal spasm, fatigue, and thrombosis. The hallmark of PNH at the cellular level is a deficiency in cell surface glycosylphosphatidylinositol anchored proteins; this deficiency on erythrocytes leads to intravascular hemolysis. Free hemoglobin from hemolysis leads to circulating nitric oxide depletion and is responsible for many of the clinical manifestations of PNH, including fatigue, erectile dysfunction, esophageal spasm, and thrombosis. The recently FDA approved complement inhibitor eculizumab has been shown to decrease hemolysis, decrease erythrocyte transfusion requirements, and improve quality of life for PNH patients.

Reduced intensity HLA-haploidentical BMT with post transplantation cyclophosphamide in nonmalignant hematologic diseases

Allogeneic blood or marrow transplantation (BMT) is potentially curative for a variety of life-threatening nonmalignant hematologic diseases such as paroxysmal nocturnal hemoglobinuria (PNH) and hemoglobinopathies. The application of BMT to treat these disorders is limited by the lack of suitable donors and often end-organ damage from the underlying disease. We treated three patients with thrombotic PNH, one of whom also had sickle cell disease, with a nonmyeloablative, HLA-haploidentical BMT with post-transplant CY. Rapid engraftment without GVHD occurred in two of the patients, including the patient with sickle cell disease. Both patients are disease free with full donor chimerism and require no immunosuppressive therapy, with follow-up of 1 and 4 years, respectively. Nonmyeloablative, HLA-haploidentical BMT with post-transplant CY is a promising approach for patients with life-threatening nonmalignant hematologic disease who lack an HLA-matched sibling donor.

Regression of human kidney cancer following allogeneic stem cell transplantation is associated with recognition of an HERV-E antigen by T cells

Transplanted donor lymphocytes infused during hematopoietic stem cell transplantation (HSCT) have been shown to cure patients with hematological malignancies. However, less is known about the effects of HSCT on metastatic solid tumors. Thus, a better understanding of the immune cells and their target antigens that mediate tumor regression is urgently needed to develop more effective HSCT approaches for solid tumors. Here we report regression of metastatic renal cell carcinoma (RCC) in patients following nonmyeloablative HSCT consistent with a graft-versus-tumor effect. We detected RCC-reactive donor-derived CD8(+) T cells in the blood of patients following nonmyeloablative HSCT. Using cDNA expression cloning, we identified a 10-mer peptide (CT-RCC-1) as a target antigen of RCC-specific CD8(+) T cells. The genes encoding this antigen were found to be derived from human endogenous retrovirus (HERV) type E and were expressed in RCC cell lines and fresh RCC tissue but not in normal kidney or other tissues. We believe this to be the first solid tumor antigen identified using allogeneic T cells from a patient undergoing HSCT. These data suggest that HERV-E is activated in RCC and that it encodes an overexpressed immunogenic antigen, therefore providing a potential target for cellular immunity.

Advances in the diagnosis and therapy of paroxysmal nocturnal hemoglobinuria

PNH is an uncommon acquired hemolytic anemia that often manifests with hemoglobinuria, abdominal pain, smooth muscle dystonias, fatigue, and thrombosis. The disease results from the expansion of hematopoietic stem cells harboring a mutation in a gene, PIG-A, that is required for the biosynthesis of a lipid moiety, glycosylphosphatidylinositol (GPI), that attaches dozens of different proteins to the cell surface. Thus, PNH cells are deficient in cell surface GPI anchored proteins; this deficiency on erythrocytes leads to intravascular hemolysis since certain GPI anchored proteins normally function as complement regulators. Free hemoglobin released from intravascular hemolysis leads to circulating nitric oxide depletion and is responsible for many of the clinical manifestations of PNH, including fatigue, erectile dysfunction, esophageal spasm, and thrombosis. Interestingly, rare PIG-A mutations can be found in virtually all healthy control subjects leading to speculation that PIG-A mutations in hematopoietic stem cells are common benign events. However, recent data reveals that most of these mutations in healthy controls are not derived from stem cells. The recently FDA approved complement inhibitor eculizumab has been shown to decrease hemolysis, decrease erythrocyte transfusion requirements, decrease the risk for thrombosis and improve quality of life for PNH patients.

A unique population of effector memory lymphocytes identified by CD146 having a distinct immunophenotypic and genomic profile

Background

CD146 is a well described homotypic adhesion molecule found on endothelial cells and a limited number of other cell types. In cells from the peripheral circulation, CD146 has also been reported to be on activated lymphocytes in vitro and in vivo. The function associated with CD146 expression on lymphoid cells is unknown and very little information is available concerning the nature of CD146+ lymphocytes. In the current study, lymphocytes from healthy donors were characterized based upon the presence or absence of CD146 expression.

Results

CD146 was expressed on a low percentage of circulating T lymphocytes, B lymphocytes, and NK cells in healthy individuals. CD146 expression can be induced and upregulated in vitro on both B cells and T cells, but does not correlate with the expression of other markers of T cell activation. CD146 positive T cells do not represent clonal expansions as determined with the use of anti Vβ reagents. Data suggest that CD146 positive cells have enhanced adherence to endothelial monolayers in vitro. Gene profiling and immunophenotyping studies between CD146+ and CD146- T cells revealed several striking genotypic distinctions such as the upregulation of IL-8 and phenotypic differences including the paucity of CCR7 and CD45RA among CD146 positive T cells, consistent with effector memory function. A number of genes involved in cell adhesion, signal transduction, and cell communication are dramatically upregulated in CD146+ T cells compared to CD146- T cells.

Conclusion

CD146 appears to identify small, unique populations of T as well as B lymphocytes in the circulation. The T cells have immunophenotypic characteristics of effector memory lymphocytes. The characteristics of these CD146+ lymphocytes in the circulation, together with the known functions in cell adhesion of CD146 on endothelial cells, suggests that these lymphocytes may represent a small subpopulation of cells primed to adhere to the endothelium and possibly extravasate to sites of inflammation.

Paroxysmal nocturnal hemoglobinuria in children

Paroxysmal nocturnal hemoglobinuria (PNH), an acquired hematologic disorder characterized by intravascular hemolysis, nocturnal hemoglobinuria, thrombotic events, serious infections, and bone marrow failure, is very rare in children. PNH is caused by a somatic mutation of the phosphatidylinositol glycan (GPI) complementation class A (PIGA) gene, followed by a survival advantage of the PNH clone, which results in a deficiency of GPI-anchored proteins on hematopoietic cells. Currently, immunophenotypic GPI-linked anchor protein analysis has replaced the acid Ham and sucrose lysis test, as it provides a reliable diagnostic tool for this disease. The presence of PNH clones should be considered in every child with an acquired bone marrow failure syndrome, for example (hypoplastic) myelodysplastic syndrome and aplastic anemia, and/or unexpected serious thrombosis. Treatment of PNH in children is dependent on the clinical presentation. In cases of severe bone marrow failure, stem cell transplantation should be seriously considered as a therapeutic option even if no matched sibling donor is available. This article reviews the reported cases of PNH in children using the recently published guidelines for classification, diagnostics, and treatment.

Computation of plasma hemoglobin nitric oxide scavenging in hemolytic anemias

Intravascular hemoglobin limits the amount of endothelial-derived nitric oxide (NO) available for vasodilation. Cell-free hemoglobin scavenges NO more efficiently than red blood cell-encapsulated hemoglobin. Hemolysis has recently been suggested to contribute to endothelial dysfunction based on a mechanism of NO scavenging by cell-free hemoglobin. Although experimental evidence for this phenomenon has been presented, support from a theoretical approach has, until now, been missing. Indeed, due to the low amounts of cell-free hemoglobin present in these pathological conditions, the role of cell-free hemoglobin scavenging of NO in disease has been questioned. In this study, we model the effects of cell-free hemoglobin on NO bioavailability, focusing on conditions that closely mimic those under known pathological conditions. We find that as little as 1 microM cell-free intraluminal hemoglobin (heme concentration) can significantly reduce NO bioavailability. In addition, extravasation of hemoglobin out of the lumen has an even greater effect. We also find that low hematocrit associated with anemia increases NO bioavailability but also leads to increased susceptibility to NO scavenging by cell-free hemoglobin. These results support the paradigm that cell-free hemoglobin released into plasma during intravascular hemolysis in human disease contributes to the experimentally observed reduction in NO bioavailability and endothelial dysfunction.

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.

Overcoming graft rejection in heavily transfused and allo-immunised patients with bone marrow failure syndromes using fludarabine-based haematopoietic cell transplantation

Allogeneic haematopoietic cell transplantation (HCT) can cure a variety of non-malignant haematological disorders. Although transplant outcomes for selected patients with severe aplastic anaemia (SAA) and paroxysmal nocturnal haemoglobinuria (PNH) have improved, older age, allo-immunisation from transfusions, prior immunosuppressive therapy and a prolonged time from diagnosis to transplantation are associated with worse outcome. Because of its potent immunosuppressive effects, we investigated a fludarabine-based non-myeloablative conditioning regimen in patients with transfusion-dependent non-malignant haematological disorders at increased risk for graft rejection with conventional transplant conditioning. Twenty-six patients with transfusion dependent/anti-thymocyte globulin (ATG)-refractory SAA, PNH or pure red cell aplasia underwent HCT from a human leucocyte antigen (HLA)-compatible relative. Transplant conditioning consisted of cyclophosphamide (120 mg/kg) and fludarabine (125 mg/m2) with or without ATG. Ciclosporine, alone or combined with mycophenolate mofetil or methotrexate, was used as graft-versus-host disease (GVHD) prophylaxis. All patients achieved durable engraftment and transfusion-independence. Twenty-four of 26 patients are alive at a median of 21 months following transplantation. Although a high cumulative incidence of acute (65% grades II-IV, 54% grades III-IV) and chronic GVHD (56%) was observed, only one patient died from transplant-related causes (cumulative incidence 7%). These data show that HCT following fludarabine-based non-myeloablative conditioning results in durable engraftment and excellent survival in SAA and PNH patients at high risk for graft rejection.

Cell labeling for magnetic resonance imaging with the T1 agent manganese chloride

There is growing interest in using MRI to track cellular migration. To date, most work in this area has been performed using ultra-small particles of iron oxide. Immune cells are difficult to label with iron oxide particles. The ability of adoptively infused tumor specific T cells and N cells to traffic to the tumor microenvironment may be a critical determinant of their therapeutic efficacy. We tested the hypothesis that lymphocytes and B cells would label with MnCl2 to a level that would allow their detection by T1-weighted MRI. Significant signal enhancement was observed in human lymphocytes after a 1 h incubation with 0.05-1.0 mM MnCl2. A flow cytometry-based evaluation using propidium iodide and Annexin V staining showed that lymphocytes did not undergo apoptosis or necrosis immediately after and 24 h following a 1 h incubation with up to 1.0 mM MnCl2. Importantly, NK cells and cytotoxic T cells maintained their in vitro killing capacity after being incubated with up to 0.5 mM MnCl2. This is the first report to describe the use of MnCl2 to label lymphocytes. Our data suggests MnCl2 might be an alternative to iron oxide cell labeling for MRI-based cell migration studies.

Aplastic Anemia: Management of Adult Patients

The primary therapeutic approach to acquired aplastic anemia (AA) in older adults differs from the primary approach used in children and younger adults because in the former group, the results of allogeneic bone marrow transplantation (BMT) are less favorable. With increasing age of the patients, immunosuppressive therapy with antithymocyte globulin (ATG) and cyclosporine (CsA) constitutes the primary treatment option and may be better than BMT. There are very few clinical clues as to the selection of patients likely to respond to immunosuppression. Repeated ATG/CsA cycles are often used as salvage regimens, but in refractory patients BMT may be the best treatment option, as the prognosis for non-responders is poor without definitive treatment. Conservative therapy such as intense immunosuppression is associated with a high relapse rate but does not impact the survival and overall prognosis. The inability to eliminate autoimmune T cell clones using current therapeutic strategies suggests that prolonged immunosuppressive maintenance therapy may be needed for a substantial proportion of patients. Late clonal complications of conservatively treated patients include evolution to myelodysplasia and paroxysmal nocturnal hemoglobinuria and may develop in 20% of the patients. However, BMT also has several sequelae including an increased frequency of solid tumors. Novel immunosuppressive and immunomodulatory agents and constantly improving results of allogeneic BMT will further improve the survival rate of adult patients with AA.

Enhanced cytotoxicity of allogeneic NK cells with killer immunoglobulin-like receptor ligand incompatibility against melanoma and renal cell carcinoma cells

Cellular inactivation through killer immunoglobulin-like receptors (KIRs) may allow neoplastic cells to evade host natural killer (NK) cell–mediated immunity. Recently, alloreactive NK cells were shown to mediate antileukemic effects against acute myelogenous leukemia (AML) after mismatched transplantation, when KIR ligand incompatibility existed in the direction of graft-versus-host disease (GVHD). Therefore, we investigated whether solid tumor cells would have similar enhanced susceptibility to allogeneic KIR-incompatible NK cells compared with their KIR-matched autologous or allogeneic counterparts. NK populations enriched and cloned from the blood of cancer patients or healthy donors homozygous for HLA-C alleles in group 1 (C-G1) or group 2 (C-G2) were tested in vitro for cytotoxicity against Epstein-Barr virus–transformed lymphoblastic cell lines (EBV-LCLs), renal cell carcinoma (RCC), and melanoma (MEL) cells with or without a matching KIR-inhibitory HLA-C ligand. Allogeneic NK cells were more cytotoxic to tumor targets mismatched for KIR ligands than their KIR ligand–matched counterparts. Bulk NK populations (CD3–/CD2+/CD56+) expanded 104-fold from patients homozygous for C-G1 or C-G2 had enhanced cytotoxicity against KIR ligand–mismatched tumor cells but only minimal cytotoxicity against KIR ligand–matched targets. Further, NK cell lines from C-G1 or C-G2 homozygous cancer patients or healthy donors expanded but failed to kill autologous or KIR-matched MEL and RCC cells yet had significant cytotoxicity (more than 50% lysis at 20:1 effector-target [E/T] ratio) against allogeneic KIR-mismatched tumor lines. These data suggest immunotherapeutic strategies that use KIR-incompatible allogeneic NK cells might have superior antineoplastic effects against solid tumors compared with approaches using autologous NK cells.

Improved survival in steroid-refractory acute graft versus host disease after non-myeloablative allogeneic transplantation using a daclizumab-based strategy with comprehensive infection prophylaxis

Approximately 15% of patients undergoing non-myeloablative allogeneic haematopoietical cell transplantation (NMHCT) develop steroid-refractory acute-graft versus host disease (aGVHD), a usually fatal complication. We encountered 18 cases of steroid-refractory aGVHD in 146 patients, undergoing NMHCT from a related human leucocyte antigen-compatible donor following cyclophosphamide/fludarabine-based conditioning. Our initial cohort of steroid-refractory aGVHD patients treated with antithymocyte globulin (ATG) and mycophenolate mofetil (regimen-1: n = 6) had high GVHD-related mortality. Therefore, we investigated an alternative strategy for subsequent patients developing this complication (regimen-2: n = 12), consisting of daclizumab (alone or combined with infliximab/ATG) and targeted broad spectrum antibacterial and aspergillus prophylaxis in conjunction with rapid tapering of steroids to minimize opportunistic infections. In a retrospective analysis, patients receiving regimen-2 were significantly more likely to have complete resolution of GVHD compared with those receiving regimen-1 [12/12 (100%) vs. 1/6 (17%); P < 0.001]. When compared with those receiving regimen-1, regimen-2 patients also had a higher probability of survival at day 100 (100% vs. 50%) and day 200 (73% vs. 17%) post-transplant, and improved overall survival (median 453 d vs. 42 d from aGVHD onset; P < 0.0001). GVHD-related mortality was 89% for regimen-1 patients vs. 17% for regimen-2 patients (P < 0.0001). These data suggest that a co-ordinated approach using immunoregulatory monoclonal antibodies, pre-emptive antimicrobial therapy and judicious steroid withdrawal can dramatically improve outcome in steroid-refractory aGVHD.