Immune markers of disease severity and treatment response in pediatric acquired aplastic anemia

Causal role of immune cells in aplastic anemia: Mendelian randomization (MR) study

Prior research has identified associations between immune cells and aplastic anaemia (AA); however, the causal relationships between them have not been conclusively established. A two-sample Mendelian randomisation analysis was conducted to investigate the causal link between 731 immune cell signatures and AA risk using publicly available genetic data. Four types of immune signatures, including relative cell, absolute cell (AC), median fluorescence intensities and morphological parameters, were considered sensitivity analyses were also performed to verify the robustness of the results and assess potential issues such as heterogeneity and horizontal pleiotropy. Following multiple test adjustments using the False Discovery Rate (FDR) method, no statistically significant impact of any immunophenotype on AA was observed. However, twelve immunophenotypes exhibited a significant correlation with AA without FDR correction (p of IVW < 0.01), of which eight were harmful to AA: CD127- CD8br %T cell (Treg panel), CD25 on IgD + CD38dim (B cell panel), CD38 on naive-mature B cell (B cell panel), CD39 + resting Treg % CD4 Treg (Treg panel), CD39 + secreting Treg AC (Treg panel), CD8 on CD28 + CD45RA- CD8br (Treg panel), HLA DR + NK AC (TBNK panel), Naive DN (CD4-CD8-) AC (Maturation stages of T cell panel); and four were protective to AA: CD86 on CD62L + myeloid DC (cDC panel), DC AC (cDC panel), DN (CD4-CD8-) NKT %T cell (TBNK panel), and TD CD4 + AC (Maturation stages of T cell panel). The results of this study demonstrate a close link between immune cells and AA by genetic means, thereby improving the current understanding of the interaction between immune cells and AA risk and providing guidance for future clinical research.

Aplastic anemia and paroxysmal nocturnal hemoglobinuria in children and adults in two centers of Northern Greece

Bone marrow failure (BMF) syndromes are a group of various hematological diseases with cytopenia as a main common characteristic. Given their rarity and continuous progress in the field, we aim to provide data considering the efficiency and safety of the therapeutic methods, focusing on the treatment of aplastic anemia(AA) and paroxysmal nocturnal hemoglobinuria (PNH). We enrolled consecutive patients diagnosed with BMF in two referral centers of Northern Greece from 2008 to 2020. We studied 43 patients with AA (37 adults and 6 children/adolescents) and 6 with classical PNH. Regarding classical PNH, 4 patients have received eculizumab treatment with 1/4 presenting extravascular hemolysis. Among 43 patients with aplastic anemia, PNH clones were detected in 11. Regarding patients that did not receive alloHCT (n=15), 14/15 were treated with ATG and cyclosporine as first line, with the addition of eltrombopag in patients treated after its approval (n=9). With a median follow-up of 16.7 (1.8-56.2) months from diagnosis, 12/14 (85.7%) are alive (4-year OS: 85.1%). AlloHCT was performed in 28 patients. Five patients developed TA-TMA which did not resolve in 3/5 (all with a pre-transplant PNH clone). With the follow-up among survivors reaching 86.3 (6.3-262.4) months, 10-year OS was 56.9%, independently associated with PNH clones after adjusting for age (p=0.024). In conclusion, our real-world experience confirms that novel treatments are changing the field of BMF syndromes. Nevertheless, there is still an unmet need to personalize algorithms in this field.

The Pathophysiology of Acquired Aplastic Anemia: Current Concepts Revisited

Idiopathic acquired aplastic anemia is a rare, life-threatening bone marrow failure syndrome characterized by cytopenias and hypocellular bone marrow. The pathophysiology is unknown; the most favored model is of a dysregulated immune system leading to autoreactive T-cell destruction of hematopoietic stem and progenitor cells in a genetically susceptible host. The authors review the literature and propose that the major driver of acquired aplastic anemia is a combination of hematopoietic stem and progenitor cells intrinsic defects and an inappropriately activated immune response in the setting of a viral infection. Alterations in bone marrow microenvironment may also contribute to the disease process.

Aplastic anemia during pregnancy: a review of obstetric and anesthetic considerations

Aplastic anemia is a hematologic condition occasionally presenting during pregnancy. This pathological process is associated with significant maternal and neonatal morbidity and mortality. Obstetric and anesthetic management is challenging, and treatment requires a coordinated effort by an interdisciplinary team, in order to provide safe care to these patients. In this review, we describe the current state of the literature as it applies to the complexity of aplastic anemia in pregnancy, focusing on pathophysiologic aspects of the disease in pregnancy, as well as relevant obstetric and anesthetic considerations necessary to treat this challenging problem. A multidisciplinary-team approach to the management of aplastic anemia in pregnancy is necessary to coordinate prenatal care, optimize maternofetal outcomes, and plan peripartum interventions. Conservative transfusion management is critical to prevent alloimmunization. Although a safe threshold-platelet count for neuraxial anesthesia has not been established, selection of anesthetic technique must be evaluated on a case-to-case basis.

Standardized high-sensitivity flow cytometry testing for paroxysmal nocturnal hemoglobinuria in children with acquired bone marrow failure disorders: A single center US study

BACKGROUND

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare, acquired hematopoietic stem cell disorder that has not been well-documented in children, particularly those with acquired bone marrow failure disorders (ABMFD)-acquired aplastic anemia (AAA) and myelodysplastic syndrome (MDS). Therefore, we sought to determine the prevalence of PNH populations in children with ABMFD.

METHODS

PNH testing was performed in children with an ABMFD diagnosis using high sensitivity (≥0.01%) fluorescent aerolysin (FLAER)-based assay according to 2010 International Clinical Cytometry Society (ICCS) PNH Consensus Guidelines and 2012 Practical PNH Guidelines. FLAER/CD64/CD15/CD24/CD14/CD45 and CD235a/CD59 panels were used for white blood cell and red blood cell testing, respectively.

RESULTS

Thirty-seven patients with ABMFD (34 AAA, 3 MDS) were included (17M/20F, age 2-18 years, median 9 years). PNH populations were identified in 17 of 37 (46%) patients. Of the 17 patients with PNH populations identified, 7 were PNH clones (>1% PNH population), and 10 had minor PNH population or rare cells with PNH phenotype (≤1% PNH population).

CONCLUSIONS

This is the first study to use a standardized high-sensitivity FLAER-based flow cytometry assay and the recommended cutoff of 0.01% to identify cells with PNH phenotype in pediatric patients with ABMFD in the United States. The identification of a PNH population in 46% of ABMFD supports the recommendation for high sensitivity PNH testing in children with these disorders. As a less sensitive assay using a cutoff of ≥ 1% PNH population would have missed 10 (27%) patients with minor PNH population or rare cells with PNH phenotype. © 2017 International Clinical Cytometry Society.

Frequency of Paroxysmal Nocturnal Hemoglobinuria Clones by Multiparametric Flow Cytometry in Pediatric Aplastic Anemia Patients of Indian Ethnic Origin

BACKGROUND

The literature on paroxysmal nocturnal hemoglobinuria (PNH) in aplastic anemia (AA) is largely focused on adults with few studies in children. Moreover, large studies are conspicuously absent from developing countries. Knowledge of the prevalence and utility of their detection is required before widespread use of PNH screening in pediatric AA in resource-limited settings.

METHODS

We performed a retrospective audit over a period of 9 years to study the prevalence of PNH clones by flow cytometry (FCM) in children ≤12 years of age presenting with AA, and analyzed their response to immunosuppressant therapy.

RESULTS

Nine (12.9%) out of 70 patients had PNH clones comprising >1% of the target cell population, including five patients (7.14%) with PNH clone size >10%. The clone size in monocytes ranged from 3.7% to 95.2% (median 21.1%) and in neutrophils from 1.6% to 87.6% (median 19.5%). Fluorescent aerolysin (FLAER)-based FCM screening significantly improved the detection of PNH clones compared to non-FLAER based screening techniques (18.4% vs. 6.25%). One child showed chronic intravascular hemolysis and another developed arterial stroke during the course of illness. None of our PNH-positive AA patients tested for chromosome breakage studies (n = 8) showed increased clastrogen-induced breakage.

CONCLUSIONS

A lower frequency but moderate/large-sized PNH clones were seen in our pediatric AA population, compared to western data. FLAER-based FCM screening significantly improved the detection of PNH clones. We recommend routine FLAER-based screening of PNH in pediatric AA patients.

Model-Based Determination of Effective Blood Concentrations of Cyclosporine for Neutrophil Response in the Treatment of Severe Aplastic Anemia in Children

Optimal immunosuppressive therapy in acquired severe aplastic anemia (SAA) remains to be refined, especially cyclosporine (CsA) use. Current recommendations state that CsA trough blood concentrations (TBC) should be maintained between 200 and 400 ng/mL despite the lack of supporting data. This study aimed at quantifying relationships between CsA exposure and neutrophil response and determining an effective range for CsA TBC. Twenty-three SAA patients treated with CsA were retrospectively analyzed. Nonlinear mixed effect modeling approaches were used to develop a pharmacokinetic-pharmacodynamic model. The pharmacokinetic model described the relationships between CsA doses and TBC. The pharmacodynamic model allowed to estimate boundaries for optimal CsA effects, neutrophils being used as biomarker of response. A time-to-event model linked effective concentration to time-to-therapeutic success. CsA TBC were adequately described by a two-compartment model with first-order absorption, a lag time, and a linear elimination. The efficient range of CsA TBC was estimated between 87 and 120 ng/mL. Model-based simulations and external validation in three additional patients confirmed these results. This original modeling approach was successful in describing the relationship between CsA TBC and neutrophil response in SAA patients. Although further evaluation of the model is necessary, this work suggests that an optimal CsA TBC target of 100 ng/mL would be associated with a better neutrophil response in children with SAA.

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.

Paroxysmal nocturnal hemoglobinuria clones in children with acquired aplastic anemia: a multicentre study

A multicentre study evaluating the presence of glycosil phosphatidyl-inositol (GPI)-negative populations was performed in 85 children with acquired aplastic anemia (AA). A GPI-negative population was observed in 41% of patients at diagnosis, 48% during immune-suppressive therapy (IST), and 45% in patients off-therapy. No association was found between the presence of a GPI-negative population at diagnosis and the response to IST. In addition, the response rate to IST did not differ between the patients who were GPI-positive at diagnosis and later developed GPI-negative populations and the 11 patients who remained GPI-positive. Two patients with a GPI-negative population >10%, and laboratory signs of hemolysis without hemoglobinuria were considered affected by paroxysmal nocturnal hemoglobinuria (PNH) secondary to AA; no thrombotic event was reported. Excluding the 2 patients with a GPI-negative population greater than 10%, we did not observe a significant correlation between LDH levels and GPI-negative population size. In this study monitoring for laboratory signs of hemolysis was sufficient to diagnose PNH in AA patients. The presence of minor GPI-negative populations at diagnosis in our series did not influence the therapeutic response. As occasionally the appearance of a GPI-negative population was observed at cyclosporine (CSA) tapering or AA relapse, a possible role of GPI-negative population monitoring during IST modulation may need further investigation.

Acquired aplastic anemia in children

This article provides a practice-based and concise review of the etiology, diagnosis, and management of acquired aplastic anemia in children. Bone marrow transplantation, immunosuppressive therapy, and supportive care are discussed in detail. The aim is to provide the clinician with a better understanding of the disease and to offer guidelines for the management of children with this uncommon yet serious disorder.