Haematopoietic and immunologic abnormalities in severe aplastic anaemia patients treated with anti-thymocyte globulin

Differential Diagnosis and Workup of Monocytosis: A Systematic Approach to a Common Hematologic Finding

Purpose of Review

Monocytosis is a frequently encountered clinical condition that needs appropriate investigation due to a broad range of differential diagnoses. This review is meant to summarize the latest literature in the diagnostic testing and interpretation and offer a stepwise diagnostic approach for a patient presenting with monocytosis.

Recent Findings

Basic studies have highlighted the phenotypic and functional heterogeneity in the monocyte compartment. Studies, both translational and clinical, have provided insights into why monocytosis occurs and how to distinguish the different etiologies. Flow cytometry studies have illustrated that monocyte repartitioning can distinguish chronic myelomonocytic leukemia, a prototypical neoplasm with monocytosis from other reactive or neoplastic causes.

Summary

In summary, we provide an algorithmic approach to the diagnosis of a patient presenting with monocytosis and expect this document to serve as a reference guide for clinicians.

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.

Influence of Polyclonal ATGs on Expression of Adhesion Molecules: An Experimental Study

BACKGROUND

The aim of our study was to assess the influence of polyclonal antithymocyte globulins (ATGs) on the expression of adhesion molecules on lymphocytes, neutrophils, and thrombocytes by means of flow cytometry. ATGs are employed in various regimens for solid organ transplantation. Immunosuppression with ATGs may influence the expression of adhesion molecules on thrombocytes, lymphocytes, and neutrophils due to nonspecific antibodies directed against myeloid and nonmyeloid cells.

MATERIAL AND METHODS

Depletion, activation, and expression of adhesion molecules on thrombocytes (CD41, CD42, CD62p and CD107a), neutrophils, and lymphocytes (CD11, CD18, CD62L) were studied in vitro in whole blood of healthy volunteers by means of flow cytometry after incubation with different dosages of three ATGs.

RESULTS

Our data showed no ATG-mediated cytotoxic activity against platelets. ATGs were able, however, to induce activation of platelets through increased expression of P-selectin and hLAMP-1. ATGs also influenced the expression of adhesion molecules on lymphocytes and neutrophils by reducing the expression of CD62L. Furthermore, the effects of ATG on CD11/CD18 were dependent on the dosage and type of ATG.

CONCLUSION

Polyclonal ATGs induced expression of adhesion molecules and activation of unstimulated thrombocytes as well as reduced the expression of adhesion molecules on lymphocytes and neutrophils. Increased adhesion of thrombocytes may be responsible for the undesirable side effects observed in clinical practice such as thrombocytopenia. However, reduction in the expression of adhesion molecules on lymphocytes and neutrophils may decrease the effects of ischemia/reperfusion injury.

In Vitro Assessment of Dose-Dependent Platelet Activation by Polyclonal Antithymocyte Globulins: A Flow-Cytometric Analysis

Polyclonal antithymocyte globulins (ATGs) are immunosuppressive drugs widely used in transplantation and hematologic disorders. Treatment with ATGs can induce side effects such as neutropenia and thrombocytopenia because of unspecific antibodies directed against nonmyeloid cells present in these preparations. Depletion, activation, and expression of adhesion molecules on platelets in vitro were studied in the whole blood of healthy volunteers by means of flow cytometry after incubation with different doses of three polyclonal ATGs. Our data show no ATG-mediated cytotoxic activity against platelets. ATGs are able to induce activation of platelets through increased expression of P-selectin and hLAMP-1 and higher percentages of gated thrombocytes expressing these molecules. Furthermore, increased expression of hLAMP-1 presented a dose-dependent pattern. ATGs induced activation and enhanced expression of adhesion molecules in unstimulated platelets. Increased adhesion may be responsible for undesirable side effects such as thrombocytopenia and reticulopenia.

Pathophysiology and treatment of aplastic anemia

Aplastic anemia (AA) is a rare hematological disease characterized by peripheral blood pancytopenia and a hypocellular bone marrow in which normal hematopoietic tissue is replaced by fatty marrow. There is strong in vitro and in vivo evidence suggesting an immunologic mechanism for hematopoietic suppression in the majority of patients with AA. Interferon-gamma and tumor necrosis factor-alpha are considered as soluble mediators of bone marrow (BM) suppression in AA. The events triggering the aberrant immune response are less clear but some viruses and drug metabolites may lead to autoimmune destruction of hematopoietic cells. Patients with severe AA who are younger than 35 to 45 years and who have an HLA-identical sibling donor have a 60-80% chance of being cured by allogeneic BM transplantation. In patients surviving more than two years, chronic graftversus-host disease is the major cause of morbidity and mortality and a solid-tumor malignancy may develop in a few patients. Patients without HLA-identical BM donors and patients older than 35 to 45 years are candidates for combined immunosuppressive treatment with antithymocyte globulin, methylpredisolone and cyclosporine, leading to hematological responses in 70-80% of patients. One has to consider, however, that a significant proportion of these patients will develop further clonal hematological disorders such as paroxysmal nocturnal hemoglobinuria and myelodysplastic syndrome.

Clonal evolution of aplastic anaemia to myelodysplasia/acute myeloid leukaemia and paroxysmal nocturnal haemoglobinuria

Aplastic anaemia (AA) is a non-malignant haemopoietic disorder characterised by peripheral blood pancytopenia and a hypocellular bone marrow. Successful management of acquired AA including treatment with immunosuppressive agents, mainly antithymocyte globulin (ATG) and cyclosporin or allogeneic haemopoietic stem cell transplantation, has resulted in long-term survival of many patients. The later evolution of complicating clonal disorders such as paroxysmal nocturnal haemoglobinuria, myelodysplasia and acute myeloid leukaemia in patients treated with immunosuppressive therapy may be a manifestation of the natural history of the aplasia, the development of which may or may not be increased by immunosuppressive therapy. A persistent, profound deficiency and/or defect in the stem cell compartment, despite haematological recovery after immunosuppressive therapy, may create an unstable situation which predisposes to later clonal disorders. A review of the progression of AA to clonal disorders is now outlined.

Treatment of familial erythrophagocytic lymphohistiocytosis with cyclosporine A

Familial erythrophagocytic lymphocytosis (FEL) is a rare, nonmalignant class II histiocytosis characterized by fever, irritability, hepatosplenomegaly, pancytopenia, and hemophagocytosis. Various chemotherapeutic regimens have had mixed success, with the only curative therapy being bone marrow transplantation. We report our experience with two children whose therapy with etoposide and steroids failed. They were successfully treated and had durable remissions with cyclosporine A (CSA). We propose that in FEL there may exist abnormal interactions between antigen-presenting cells and T-lymphocyte subsets, and that CSA may down-modulate this aberrant response. The use of a low-dose CSA regimen may represent a treatment option that should be further explored.

Bone marrow transplantation in pediatric patients with severe aplastic anemia: cyclophosphamide and anti-thymocyte globulin conditioning followed by recombinant human granulocyte-macrophage colony stimulating factor

PURPOSE

Graft rejection remains a serious problem in patients transplanted for severe aplastic anemia. Although additional immunosuppression with irradiation may decrease graft failure, significant sequelae may ensue. We evaluated a nonirradiation containing conditioning regimen for children with severe aplastic anemia with matched sibling donors utilizing cyclophosphamide and anti-thymocyte globulin (ATG). To accelerate myeloid recovery, GM-CSF was used posttransplant.

PATIENTS AND METHODS

Twelve patients, with a median age of 3 years underwent BMT from HLA identical sibling (n = 11) or syngeneic (n = 1) donors. Conditioning was cyclophosphamide 50 mg/kg x 4 days and anti-thymocyte globulin 30 mg/kg x 3 days. GM-CSF was administered at 10 micrograms/kg until a neutrophil count of 1,000 was achieved. Cyclosporine alone was used for graft-versus-host disease prophylaxis.

RESULTS

All patients achieved durable engraftment at follow-up of 5-51 + months, with the exception of the identical twin. Median time to neutrophil counts > 200/microliters, 500/microliters, and 1,000/microliters were 12, 13, and 15 days, respectively. Acute GVHD of less than or equal to grade II occurred in four patients; one patient had grade III. This has resolved in all but one.

CONCLUSION

The nonradiation conditioning regimen of cyclophosphamide/ATG appears to achieve durable engraftment in transfused children with matched sibling donors. GM-CSF may accelerate myeloid recovery without exacerbating GVHD, but its contribution to allogeneic transplant required further study.

Relapse of aplastic anaemia after immunosuppressive treatment: a report from the European Bone Marrow Transplantation Group SAA Working Party

This study was designed to determine the incidence of relapse and factors predictive for relapse in 719 patients with severe aplastic anaemia (SAA) after immunosuppressive treatment (IS). Patients developing myelodysplasia or acute leukaemia after IS, and patients receiving a transplant, were excluded from this analysis. Response was defined as reaching complete independence from transfusions, relapse was defined as becoming again transfusion dependent. This criteria was validated by similar figures when using other 'relapse criteria' such as drop in neutrophil or platelet counts. Of 358 patients responding to IS. 74 patients relapsed after a mean time of 778 d after treatment. The actuarial incidence of relapse is 35.2% at 14 years after IS. The risk for relapse was higher in patients responding within 120 d from IS (48%) compared to patients responding between 120 and 360 d (40%) and only 20% for slow responders (> 360 d from IS) (P < 0.00001). In multivariate analysis this factor still proved significant (P < 0.0001). The mean time between diagnosis and treatment was significantly longer in patients relapsing compared to patients who did not relapse (260 v 134 d, P = 0.037). Relapse was not predicted by the severity of the disease, age, and sex. In 39 of the 74 relapsing patients a second response could be achieved. Responses after relapse were associated in univariate analysis with early response to previous IS and early occurrence of relapse. The actuarial survival of patients not relapsing is significantly better than survival of patients relapsing (79.8% v 67.1%, P = 0.0024). However, the actuarial survival of 39 relapsing patients who responded again to IS was similar to patients not relapsing (86%) and significantly better than in 35 patients not reaching a second response after relapse (49.3%, P = 0.0015). This study indicates that relapse is a relevant problem in the treatment of aplastic anaemia, and does have an impact on overall survival. Prospective studies of immunosuppressive regimens, looking at responses, should also address this problem in the future.

Aplastic anaemia: pathogenetic mechanisms and treatment with special reference to immunomodulation

Aplastic anaemia (AA) has been defined as a syndrome in which the presence of pancytopenia is accompanied by marrow hypocellularity. Ample laboratory data and clinical observations continue to make immune mediation of bone-marrow failure an attractive hypothesis. Recent progress in the practice of bone-marrow transplantation has led to a survival rate of approximately 80% in the best cases, but such a treatment is only amenable in young patients (less than 45-50 years) with HLA-identical bone-marrow donors. Anti-lymphocyte and thymocyte globulin treatment has been surprisingly effective for AA, resulting in transfusion independence in 40-80% of patients. The mechanism of action is unknown, although effects on immunosuppression appear to be the most likely candidates. Long-term results for patients receiving cyclosporin A treatment will soon be available, and preliminary data show an effect similar to that of antithymocyte globulin. In contrast to successful bone-marrow transplantation, improvement following immunomodulation leaves quantitative abnormalities in all haematopoietic cell lines, and patients are prone to develop clonal (malignant) disease.

Severe aplastic anemia (SAA): response to cyclosporin A (CyA) in vivo and in vitro

The aim of the present study was to test the effect of cyclosporin A (CyA) in vitro on CFU-GM growth from patients with severe aplastic anemia (SAA). For this purpose, bone marrow (BM) cells from 9 SAA patients and 5 healthy individuals were incubated with or without CyA and then cultured for CFU-GM growth in the presence of exogenous recombinant human GM-CSF (30 ng/ml). SAA patients were tested before or after treatment with CyA, or after treatment with antilymphocyte globulin (ALG). In 3 patients responding to CyA, the addition of CyA in vitro enhanced colony growth from 13 +/- 10 to 40 +/- 20/10(5) BM cells (p = 0.01) - the median increment of colony formation was 2.4-fold. In 5 ALG responders, CyA produced no increment of CFU-GM growth (from 14 +/- 26 to 15 +/- 16/10(5) BM cells, p = 0.1). CyA did not enhance significantly CFU-GM growth in normal controls (from 57 +/- 45 to 58 +/- 81/10(5) BM cells, p = 0.9). In conclusion, it would appear that some patients with SAA can respond to CyA in vivo and in vitro, and ALG responders are not necessarily among these. This is in keeping with different mechanisms of action of CyA and ALG and possibly with the existence of distinct pathogenetic pathways in SAA.

Effect of antilymphocyte globulin (ALG) on bone marrow T/non-T cells from aplastic anaemia patients and normal controls

The aim of this study was twofold: (a) to test the effect of antilymphocyte globulin (ALG) on bone marrow (BM) T/non-T cells, and (b) to look for a possible differential response of cells from severe aplastic anaemia (SAA) patients and controls. For this purpose bone marrow T/non-T cells from normal individuals (n = 7) or aplastic patients (SAA, n = 13) were kept in liquid culture with or without ALG. Supernatants were then tested for enhancement/suppression on colony forming unit, granulocyte-macrophage (CFU-GM) growth (in the presence of exogenous recombinant granulocyte-macrophage colony stimulating factor (rGM-CSF)), or for their ability to support CFU-GM growth (in the absence of exogenous rGM-CSF). Supernatants from SAA T cells suppressed CFU-GM growth of normal bone marrow cells in 5/12 patients (mean expected growth (EG) 71 +/- 16%), but not after incubation with ALG (mean 110 +/- 29% EG, P = 0.03). No inhibition could be obtained with the supernatants from untreated normal T cells. Significant enhancement was seen with ALG treated versus untreated SAA T cells (142 +/- 28% EG v. 105 +/- 61% EG, P = 0.01) and with ALG treated versus untreated SAA non-T cells (165 +/- 26% EG v. 105 +/- 23% EG, P = 0.01), but not in controls. Supernatants from SAA and control T/non-T cells were capable of promoting colony formation in the absence of rGM-CSF (colony-stimulating activity (CSA) production): 16 +/- 14% for SAA-T cells and 19 +/- 18% EG for non-T cells (100% = 30 ng rGM-CSF/ml). The addition of ALG increased CSA production in T cells to 37 +/- 23% EG (P = 0.04) and in non-T cells to 40 +/- 13% EG (P = 0.04). Similar results could be obtained in controls.

IN CONCLUSION

(a) ALG interacts in vitro with bone marrow T and non-T cells from SAA patients, down-regulating the production of negative lymphokines and enhancing the release of haemopoietins; (b) the latter, but not the former effect, can be shown also with cells from normal controls. The two effects are not mutually exclusive, and are likely to provide maximal benefit in vivo.