Aplastic anemia: presence in human bone marrow of cells that suppress myelopoiesis

[A case of hepatitis-associated aplastic anemia complicated by hemophagocytic lymphohistiocytosis and literature review]

A 4-year-old boy was admitted to the hospital with a 3-day history of rash and intermittent abdominal pain, during which abnormal results from routine blood tests were discovered. Initially, he presented with acute jaundice hepatitis and pancytopenia. The patient's condition progressed rapidly, with recurrent fever, worsening jaundice of the skin and sclera, and progressively worsening hepatosplenomegaly. Liver function impairment and bone marrow failure continued to deteriorate, while cytokine levels continued to rise. After excluding infections, autoimmune diseases, tumors, genetic metabolic disorders, and toxicities, the patient was diagnosed with hepatitis-associated aplastic anemia (HAAA) complicated by hemophagocytic lymphohistiocytosis (HLH). Following treatment with corticosteroids, plasma exchange, intravenous immunoglobulin, and liver protection therapy, the patient's symptoms partially alleviated. Aplastic anemia complicated by HLH is relatively uncommon, and HAAA complicated by HLH is even rarer, often presenting insidiously and severely. This paper presents a case of HAAA complicated by HLH and summarizes previously reported cases in the literature, providing references for the early diagnosis and treatment of this condition.

Burden, Outcome, and Comorbidities of Extrahepatic Manifestations in Hepatitis B Virus Infections

Hepatitis B virus (HBV) infections affect approximately 296 million people around the world, and the prevalence of any past or present HBV infection during the years 2015-2018 was as high as 4.3%. Acute HBV infection often presents with nonspecific symptoms and is usually self-limited, but 5% of patients can have persistent infections leading to chronic HBV infection and the risk of turning into chronic HBV infection is significantly higher in babies with vertical transmission (95%). Patients with chronic HBV infection are usually asymptomatic, but 15 to 40% of chronic HBV carriers develop cirrhosis and/or hepatocellular carcinoma. In addition to liver-related disorders, HBV is also associated with several extrahepatic complications, including glomerulonephritis, cryoglobulinemia, neurologic disorders, psychological manifestations, polyarthritis, and dermatologic disorders. Making the diagnosis of HBV can be challenging since patients with chronic infections can remain symptom-free for decades before developing cirrhosis or hepatocellular carcinoma, and patients with acute HBV infection may have only mild, nonspecific symptoms. Therefore, understanding how this virus causes extrahepatic complications can help clinicians consider this possibility in patients with diverse symptom presentations. The pathophysiology of these extrahepatic disorders likely involves immune-related tissue injury following immune complex formation and inflammatory cascades. In some cases, direct viral infection of extrahepatic tissue may cause a clinical syndrome. Currently, the American Association for the Study of Liver Diseases recommends treatment of chronic HBV infections with interferon therapy and/or nucleos(t)ide analogs, and this treatment has been reported to improve some extrahepatic disorders in some patients with chronic HBV infection. These extrahepatic complications have a significant role in disease outcomes and increase medical costs, morbidity, and mortality. Therefore, understanding the frequency and pathogenesis of these extrahepatic complications provides important information for both specialists and nonspecialists and may help clinicians identify patients at an earlier stage of their infection.

Clinical Signs and Treatment of New-Onset Bone Marrow Failure Associated SARS-CoV-2 Infection in Children: A Single Institution Prospective Cohort Study

Background

Viral infections can cause direct and indirect damage to hematopoietic stem cells. The objectives of this study were to identify the frequency and severity of aplastic anemia in children infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) as well as recognize the response to treatment.

Methodology

13 children with newly diagnosed severe aplastic anemia were enrolled in this prospective clinical trial. Blood samples were obtained from all patients to detect SARS-CoV-2 antibodies, and nasopharyngeal swabs were collected for reverse-transcription Polymerase Chain Reaction to detect SARS-CoV-2 viruses. According to the laboratory results, patients were classified as having SARS-CoV-2 positive antibodies and SARS-CoV-2 negative antibodies. Both groups received combined cyclosporine (CsA) + Eltrombopag (E-PAG). The hematological response, either complete response (CR) or partial response (PR), no response (NR), and overall response (OR) rates of combined E-PAG + CsA treatment after 6 months were evaluated.

Results

Four children were recognized to have aplastic anemia and SARS-CoV-2 positive antibodies. Two patients fulfilled the hematological criteria for CR and no longer required transfusion of packed red blood cells (PRBCs) or platelets, and one had PR and was still PRBC transfusion-dependent but no longer required platelet transfusion. The remaining patient showed NR, and he had died before reaching the top of the HSCT waiting list. Moreover, six patients in the SARS-CoV-2 negative antibodies group had CR, while three patients had PR. The difference in ANC, Hg, and platelet counts between both groups was not significant.

Conclusion

The SARS-CoV-2 virus is added to several viral infections known to be implicated in the pathogenesis of aplastic anemia. Studies are needed to establish a definitive association and determine whether the response of bone marrow failure to standard therapy differs from that of idiopathic cases.

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.

Hepatitis-associated Aplastic Anemia

Hepatitis-associated aplastic anemia (HAAA) accounts for 4% of autoimmune hepatitis in children. An episode of seronegative autoimmune hepatitis is followed a few days or months later by aplastic anemia or full aplasia. This autoimmune disease could be due to a regulation defect in the immune response to a viral trigger, in a genetically predisposed individual. Other causes of hepatitis or aplastic anemia have to be ruled out. Steroids and azathioprine usually control the liver damage but do not prevent the development of aplastic anemia. Aplastic anemia is treated with either hematopoietic stem cell transplantation in patients with a sibling donor or anti-thymocyte globulins and cyclosporine. We propose guidelines to explore and treat this rare disease. We emphasize on the necessary close collaboration between hepatologists and hematologists.

Interferon-gamma and perforin-positive T cells in acquired aplastic anemia: implication in therapeutic response

Acquired aplastic anemia (aAA) is an autoimmune disease, characterized by infiltration of T lymphocytes in the bone marrow with destruction of hematopoietic stem cells by the effector cells. Interferon-gamma (IFN-γ) and perforin are important mediators of cell destruction. In this flow cytometry-based study, we have investigated the percentage of intracellular IFN-γ+ and perforin+ CD5+ T cells in peripheral blood of newly diagnosed aAA patients before and after immunosuppressive therapy (IST). Patients were categorized as per standard disease severity and response to IST. The median percentage of IFN-γ+ and perforin+ CD5+ T cells was higher in untreated patients compared to healthy controls. The percentage of these cells was also increased in untreated severe and very severe aplastic anemia when compared with non-severe aplastic anemia patients. In patients before and after IST the median percentage of T cells producing IFN-γ and perforin was elevated in non-responders as compared to partial plus complete responders. The higher percentage of IFN-γ+ and perforin+ CD5+ T cells may be useful as an early diagnostic marker for aberrant activation of immune system and predict poor response to IST in aAA patients, who will benefit from alternative therapy.

Changes in bone marrow and peripheral blood lymphocyte subset findings with onset of hepatitis-associated aplastic anemia

RATIONALE

Hepatitis-associated aplastic anemia (HAAA) is a rare illness that results in bone marrow failure following hepatitis development. The etiological agent remains unknown in most HAAA cases. However, clinical features of the disease and immunotherapy response indicate that immune-mediated factors play a central role in the pathogenesis of HAAA. Activation of cytotoxic T cells and increase in CD8 cells could exert cytotoxic effects on the myelopoietic cells in the bone marrow.

PATIENT CONCERNS

A 15-month-old boy was brought to our hospital with complaints of generalized petechiae and purpura observed a week prior to hospitalization. His liver was palpated 3 cm below the costal margin, platelet count was 0 × 104/μL, and alanine aminotransferase level was 1346 IU/L. A blood test indicated cytomegalovirus infection, and 3 bone marrow examinations revealed progressive HAAA. As the disease progressed to the 3rd, 6th, and 9th week after onset, CD4+ T cells were markedly decreased, CD8+ T cells were markedly increased, and the CD4/CD8 ratio was significantly decreased. The number of B cells and natural killer cells decreased with time, eventually reaching 0.0%.

DIAGNOSIS

HAAA.

INTERVENTIONS

Rabbit antithymocyte globulin and eltrombopag olamine (a thrombopoietin receptor agonist) were administered.

OUTCOMES

The patient's platelet count returned to normal, and bone marrow transplantation was avoided. The peripheral blood lymphocytes (PBLs) improved as the patient's general condition recovered.

LESSONS

This case demonstrates that HAAA induced by cytomegalovirus infection features decreasing CD4+ and increasing CD8+ PBLs as the bone marrow hypoplasia progresses. The PBLs return to their normal levels with the recovery from the disease. Our case findings thus support the involvement of immunological abnormality in HAAA.

Immunologic effects on the haematopoietic stem cell in marrow failure

Acquired bone marrow failure (BMF) syndromes comprise a diverse group of diseases with variable clinical manifestations but overlapping features of immune activation, resulting in haematopoietic stem and progenitor cells (HSPC) damage and destruction. This review focuses on clinical presentation, pathophysiology, and treatment of four BMF: acquired aplastic anaemia, large granular lymphocytic leukaemia, paroxysmal nocturnal haemoglobinuria, and hypoplastic myelodysplastic syndrome. Autoantigens are speculated to be the inciting event that result in immune activation in all of these diseases, but specific pathogenic antigens have not been identified. Oligoclonal cytotoxic T cell expansion and an active role of proinflammatory cytokines, primarily interferon gamma (IFN-γ) and tumor necrosis factor alpha (TNF-α), are two main contributors to HSPC growth inhibition and apoptosis in BMF. Emerging evidence also suggests involvement of the innate immune system.

Hepatitis-associated aplastic anemia

Hepatitis-associated aplastic anemia (HAAA) is a rare illness, characterized by onset of pancytopenia with a hypoplastic bone marrow that traditionally occurs within 6 months of an increase in serum aminotransferases. HAAA is observed in 1% to 5% of all newly diagnosed cases of acquired aplastic anemia. Several hepatitis viruses have been linked to the disease, but in many cases no specific virus is detected. The exact pathophysiology is unknown; however, immune destruction of hematopoietic stem cells is believed to be the underlying mechanism. HAAA is a potentially lethal disease if left untreated. Management includes immunosuppression with antithymocyte globulin and cyclosporine and allogeneic hematopoietic stem cell transplantation.

Changes in Different Cytokines (IL-2, TNF-α, and IFN-γ) Profile in Acquired Aplastic Anemia Patients: A Study From Eastern India

Although aplastic anemia has been extensively investigated, little is known about their circulating cytokine pattern. The present study was done to evaluate the severity of the disease with the 3 major anti-hematopoietic cytokines interleukin-2 (IL-2), tumor necrosis factor-alpha (TNF-α), and interferon-gamma (IFN-γ). This study is ethically cleared. A total of 102 bone marrow plasma and peripheral blood plasma paired samples were collected from the confirmed acquired aplastic anemia (AAA) patients and 10 control cases after taking written consent and analyzed by the quantitative enzyme-linked immunosorbent assay. The Mann-Whitney U test was used for statistical analysis. Considerably increased levels of IL-2, TNF-α, and IFN-γ were found in the peripheral blood plasma and bone marrow plasma of AAA patients as compared with controls, that is, 45.76±20.61 versus 1.99±1.25, P<0.00001; 26.51±15.62 versus 11.7±3.67, P=0.00188; 17.04±11.64 versus 5.27±1.92, P=0.00034 and 70.54± 37.57 versus 3.12±1.82, P<0.00001; 251.82±243.80 versus 15.66±6.35, P<0.00001; 39.35±22.58 versus 11.12±2.41, P=0.00012, respectively. The IL-2, TNF-α, and IFN-γ levels were observed to be extraordinarily elevated in AAA, but were very low in the control cases. The results confirm that IL-2, TNF-α, and IFN-γ may have an imperative association with the disaster in the bone marrow compartment of AAA patients. The levels and ranges of the observed cytokines can also be predicted by the severity basis of this study.

Comparative study of bone marrow and blood plasma levels of IL-2 in aplastic anaemia and their relationship with disease severity

OBJECTIVES

Interleukin-2 (alias: IL-2, TCGF, Lymphokine), a type of interleukin, is also a potent signalling molecule in the signalling cascade of the immune-mediated activation of T Lymphocytes leading to the destruction of haematopoietic stem cell (HSC) which is the basis of acquired aplastic anaemia (AAA). The objective was to study the association of IL-2 in the bone marrow plasma (BMP) and peripheral blood plasma (PBP) in AAA patients.

METHODS

A total of 52 BMP and PBP-paired samples (both from the same patients) was collected from the confirmed AAA patients and 10 healthy individuals. The level of IL-2 was measured by the quantitative enzyme-linked immunosorbent assay (ELISA). The Mann-Whitney U test was used for statistical analysis.

RESULTS

Significantly increased level of IL-2 was observed in the BMP than PBP of AAA patients. The level of IL-2 in PBP and BMP was found to be very low in the control cases. Considerably increased levels of IL-2 were found in the PBP and BMP of AAA patients as compared to controls (48.54 ± 21.89 vs. 1.99 ± 1.25 p-value < 0.00001) and (75.33 ± 41.9 vs. 3.12 ± 1.82; p-value < 0.00001) respectively. Among these patients, the IL-2 levels were higher in patients with Very Severe Aplastic Anaemia (VSAA) and Severe Aplastic Anaemia (SAA) than those with Non-severe Aplastic Anaemia (NSAA) in the PBP (65.6 ± 23.61 vs. 31.72 ± 7.64; p-value 0.00338) and (45.37 ± 16.25 vs. 31.72 ± 7.64; p-value 0.01468) respectively. Again the IL-2 levels were higher in patients with VSAA and SAA than those with NSAA in the BMP (115.01 ± 38.91 vs. 38.32 ± 19.49; p-value < 0.00001) and (66.44 ± 23.34 vs. 38.32 ± 19.49; p-value 0.0006). The IL-2 level was higher in VSAA than SAA in PBP (65.6 ± 23.61vs. 45.37 ± 16.25; p-value 0.0114) and BMP (115.01 ± 38.91 vs. 66.44 ± 23.34; p-value 0.00044).

CONCLUSION

This study emphasized on the bone marrow and blood plasma levels of IL-2 in aplastic anaemia and their relationship with disease severity. The results indicate towards the fact that IL-2 may have an important association with the marrow failure of AAA patients and thus can help in disease development. Further study is necessary for better understanding.

Hepatitis-associated Aplastic Anemia Treated Successfully With Antithymocyte Globulin

Hepatitis-associated aplastic anemia (HAAA) is a variant of acquired aplastic anemia in which bone marrow failure follows the development of an acute episode of seronegative hepatitis. HAAA occurs most frequently in male children and is lethal if left untreated. Antilymphocyte globulin, antithymocyte globulin, and allogeneic bone marrow transplantation have been used in the treatment of this disease. In this work, we report the case of a 3-year-old boy with HAAA treated successfully with immunosuppressive therapy.

Cytogenetic study is not essential in patients with aplastic anemia

Depending on contemporary treatment approach of aggressive immunosuppression, Aplastic Anemia (AA) is caused by immunological destruction of otherwise normal hematopoietic stem cells. The aim was to summarize the cytogenetic abnormalities in AA patients and the frequency of Fanconi Anemia (FA) in morphologically normal AA patients in eastern India. Ethical clearances were obtained from both institutions involved in this study. Out of 72800 patients attending the outpatient department, 520 pancytopenia patients were screened for AA after Bone marrow (BM) aspiration and biopsy. Samples were collected from 117 cases in 3 phases. 51 peripheral venous blood (PVB) samples in the first phase, 19 BM & PVB paired samples in the second phase and 47 BM samples in third phase were collected followed by leukocyte and/or BM stem cell culture. Next GTG banding and karyotyping were performed. PVB was collected from 63 (< 50 years) AA patients and stress cytogenetics was done to diagnose FA. In the first phase of the study, out of 51 PVB samples, 1 (1.96%) showed a unique chromosomal abnormality, i.e. 45,XY,rob(14:21)(p10:q10)[20]. In the second phase of study, among 19 BM & PVB paired samples, 1 (5.26%) showed abnormal karyotype i.e. 45,X,-Y[3]/46,XY[47]. In the third phase of the study, 47 BM samples showed normal karyotype. Only 6 (9.52%) cases were found positive for stress cytogenetics. A negligible percentage showing cytogenetic abnormality in such a considerable number of AA cases indicates that routine cytogenetic analysis of AA patient is not essential. A significant percentage was positive for stress cytogenetics; suggestive for FA, even the patients were morphologically normal.

Cytopenia first - hepatitis second: an unusual sequence in aplastic anemia

To the best of our knowledge, this is the first report of aplastic anemia (AA) preceding autoantibody‐negative autoimmune hepatitis (AIH) with successful treatment of both conditions with the same immunosuppressive regimen, resulting in hematopoietic reconstitution and remission of AIH.

Association of aplastic anemia and FoxP3 gene polymorphisms in Koreans

OBJECTIVES

Aplastic anemia (AA) is characterized by pancytopenia and bone marrow failure, and most acquired AA is an immune-mediated disorder. Regulatory T cells (T_regs) suppressing autoreactive T cells were decreased in AA patients. FoxP3 is a major regulator for the development and function of T_regs. Polymorphism in FoxP3 was shown to be associated with various autoimmune diseases, however, has not yet been studied in AA. In this study, we examined the association between FoxP3 polymorphisms and AA in Korean patients.

METHODS

The study population consisted of 94 patients diagnosed by bone marrow examination in Seoul National University Hospital (SNUH) during 1997-2012 and 195 healthy controls. FoxP3 polymorphisms (rs5902434 del/ATT, rs3761548 C/A, rs3761549 C/T, rs2232365 A/G) were analyzed by PCR-sequencing method. We analyzed differences of genotype and allele frequencies between patients and controls. We also compared differences of genotype and allele frequencies between responder and non-responder in patients treated with immunosuppressive therapy (IST). For the statistical analysis, the chi-square test and Fisher's exact test were used and P < 0.05 was regarded as statistically significant.

RESULTS

There was no significant difference in the genotype frequencies of FoxP3 polymorphisms between patients and controls. With regards to the allele frequencies, rs3761548 C allele was significantly higher in AA patients than in controls (87.4% vs. 79.7%, P = 0.047). In patients treated with IST, rs3761549 C allele was significantly higher in non-responder patients than in responders (89.6% vs. 66.7%, P = 0.036) and female rs3761549 C/C genotype carriers were associated with greater risk for non-response to IST (84.2% vs. 16.7%, P = 0.006).

CONCLUSION

Polymorphisms in rs3761548 and rs3761549 of FoxP3 in our population were associated with disease susceptibility and response for IST, respectively. This study suggests an association between FoxP3 polymorphisms and AA in Korean patients and will be useful in further understanding the genetic basis of disease susceptibility and response to IST in AA patients.

The diagnosis and treatment of aplastic anemia: a review

Aplastic anemia is a rare disorder characterized by suppression of bone marrow function resulting in progressive pancytopenia. A trigger-related abnormal T cell response facilitated by some genetic predisposition has been postulated as the pathogenetic mechanism leading to the overproduction of bone marrow-inhibiting cytokines. Immuno-mediated pathogenesis is confirmed by the response to immunosuppressive treatment (IST) (cyclosporin A+ATG), which represents the first-choice therapy for patients <40 years when a matched sibling donor (MSD) is not available for transplant. MSD hematopoietic stem cell transplantation (HSCT) is associated with cure in ~90 % of patients. IST up-front provides an overall survival (OS) rate of above 90 %, but a response rate of about 60 %. Front-line matched unrelated donor (MUD) appears to be a viable option in children with similar OS and event-free survival to that in MSD HSCT. MUD HSCT post-IST failure proved to be a very good rescue strategy. Haploidentical donors/cord blood transplants or alternative immunosuppressive therapies, such as alemtuzumab, may represent valid tools for resistant/relapsing cases. New promising strategies, such as eltrombopag, are now under investigation. Patients should be offered an accurate diagnostic work-up in order to rule out other underlying disorders, primarily constitutional marrow failures, which may require different approaches.

Severe Aplastic Anemia following Acute Hepatitis from Toxic Liver Injury: Literature Review and Case Report of a Successful Outcome

Hepatitis associated aplastic anemia (HAAA) is a rare syndrome in which severe aplastic anemia (SAA) complicates the recovery of acute hepatitis (AH). HAAA is described to occur with AH caused by viral infections and also with idiopathic cases of AH and no clear etiology of liver injury. Clinically, AH can be mild to fulminant and transient to persistent and precedes the onset SAA. It is assumed that immunologic dysregulation following AH leads to the development of SAA. Several observations have been made to elucidate the immune mediated injury mechanisms, ensuing from liver injury and progressing to trigger bone marrow failure with the involvement of activated lymphocytes and severe T-cell imbalance. HAAA has a very poor outcome and often requires bone marrow transplant (BMT). The findings of immune related myeloid injury implied the use of immunosuppressive therapy (IST) and led to improved survival from HAAA. We report a case of young male who presented with AH resulting from the intake of muscle building protein supplements and anabolic steroids. The liver injury slowly resolved with supportive care and after 4 months of attack of AH, he developed SAA. He was treated with IST with successful outcome without the need for a BMT.

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.

The optimal immunosuppressive therapy for aplastic anemia

Immunosuppressive treatment (IST) has been the most effective therapeutic modality for patients with aplastic anemia (AA) who are not eligible for allogeneic stem cell transplantation from HLA-matched siblings because of donor unavailability, old age, or comorbidities. The combination of horse anti-thymocyte globulin (ATG) with cyclosporine A (CsA) has shown satisfactory results for these patients, and so it has been regarded as the standard IST regimen. However, treatment failure including unresponsiveness, relapse, and occurrence of clonal evolution remains a major problem, although the results of IST have been improved in the past two decades. Many studies have been conducted to overcome these problems; however, they have yet to show any satisfactory results. This review will discuss immune-mediated pathophysiology of AA, which is associated with therapeutic targets of immunosuppressive agents and clinical outcomes of most commonly used IST regimens. Several trials to improve IST including the addition of other immunosuppressive agents or growth factors to standard IST regimen, comparison between horse ATG/CsA and rabbit ATG/CsA as first-line treatment, and promising alternative agents including alemtuzumab and eltrombopag will also be discussed, focusing on recently published literatures.

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

BACKGROUND

To investigate the immune status among pediatric patients with aplastic anemia (AA) and explore PNH-status, T-regulatory and NK-cell frequency as potential markers of clinical response.

METHODS

Data were retrospectively analyzed from twenty-six patients diagnosed with AA. PNH populations, T- and NK-subsets were determined via flow cytometry.

RESULTS

At diagnosis, 9/23 patients with severe AA (SAA) versus 1/3 with moderate AA (MAA) were PNH(pos) . Among PNH(pos) patients treated with ATG based immunosuppression, 2/6 had a complete response (CR), while 4/6 had a partial response (PR), similarly 2/6 PNH(neg) patients had a CR and 4/6 had a PR. Lymphocyte subset immunophenotyping revealed that T-regulatory cells represented 7.2% of total lymphocytes at diagnosis. Their frequency varied with disease severity (5.5% for SAA and 14.1% for MAA) and response (8.9% for CR and 1.5% for PR), generally increasing following therapy with IST (14.6%). The NK cell frequency was not substantially different based on disease severity or response.

CONCLUSIONS

Neither PNH cell populations, nor NK cell frequency corresponded with disease severity or response. T-regulatory cell frequency, although not statistically significant given the small sample size, corresponded with both severity and response, indicating potential utility as a prognostic tool.

An Ectopic Stromal Implant Model for Hematopoietic Reconstitution and in Vivo Evaluation of Bone Marrow Niches

In adults, hematopoiesis takes places in the bone marrow, where specialized niches containing mesenchymal nonhematopoietic cells (stroma) harbor the hematopoietic stem cell (HSC). These niches are responsible and essential for the maintenance of HSCs. Attempts to expand HSCs fail to keep the general properties of stem cells, which depend on several niche components difficult to reproduce in in vitro culture systems. Here, we describe a methodology for in vivo study of hematopoietic stroma. We use stroma-loaded macroporous microcarriers implanted in the subcutaneous tissue of experimental animals and show that the ectopic stroma implant (ESI) is able to support hematopoiesis. Moreover, lethally irradiated mice can be rescued by ESI preloaded with HSCs, showing that they function as an ectopic bone marrow. ESI is also shown as a good system to study the role of different niche components. As an example, we used stromas lacking connexin 43 (Cx43) and confirm the importance of this molecule in the maintenance of the HSC niche in vivo. We believe ESI can work as an ectopic bone marrow allowing in vivo testing of different niches components and opening new avenues for the treatment of a variety of hematologic conditions particularly when stromal cell defects are the main cause of disease.

Hepatitis associated aplastic anemia: a review

Hepatitis-associated aplastic anemia (HAAA) is an uncommon but distinct variant of aplastic anemia in which pancytopenia appears two to three months after an acute attack of hepatitis. HAAA occurs most frequently in young male children and is lethal if leave untreated. The etiology of this syndrome is proposed to be attributed to various hepatitis and non hepatitis viruses. Several hepatitis viruses such as HAV, HBV, HCV, HDV, HEV and HGV have been associated with this set of symptoms. Viruses other than the hepatitis viruses such as parvovirus B19, Cytomegalovirus, Epstein bar virus, Transfusion Transmitted virus (TTV) and non-A-E hepatitis virus (unknown viruses) has also been documented to develop the syndrome. Considerable evidences including the clinical features, severe imbalance of the T cell immune system and effective response to immunosuppressive therapy strongly present HAAA as an immune mediated mechanism. However, no association of HAAA has been found with blood transfusions, drugs and toxins. Besides hepatitis and non hepatitis viruses and immunopathogenesis phenomenon as causative agents of the disorder, telomerase mutation, a genetic factor has also been predisposed for the development of aplastic anemia. Diagnosis includes clinical manifestations, blood profiling, viral serological markers testing, immune functioning and bone marrow hypocellularity examination. Patients presenting the features of HAAA have been mostly treated with bone marrow or hematopoietic cell transplantation from HLA matched donor, and if not available then by immunosuppressive therapy. New therapeutic approaches involve the administration of steroids especially the glucocorticoids to augment the immunosuppressive therapy response. Pancytopenia following an episode of acute hepatitis response better to hematopoietic cell transplantation than immunosuppressive therapy.

Systematic review: hepatitis-associated aplastic anaemia--a syndrome associated with abnormal immunological function

BACKGROUND

Hepatitis-associated aplastic anaemia is a syndrome in which marrow failure follows the development of hepatitis.

AIM

To review systematically the aetiology, immunopathogenesis, clinical presentation, diagnosis and treatment of hepatitis-associated aplastic anaemia.

METHODS

Literature searches were undertaken on the MEDLINE electronic database up to December 2008. Twenty-four relevant studies were identified. The clinical and laboratory characteristics of the patients were analysed and reviewed.

RESULTS

Hepatitis-associated aplastic anemia is a variant of acquired aplastic anemia in which an episode of hepatitis precedes the onset of aplastic anemia. The hepatitis may be acute and severe, even fulminant; it may be self-limiting or chronic. The pathology is often not attributable to a recognized cause of viral hepatitis. The syndrome occurs in 28 percent of young adults after liver transplantation for non-A, non-B, non-C hepatitis. Several features of the syndrome suggest that the marrow aplasia is mediated by immunological mechanisms, possibly mediated by gamma interferon or the cytokine cascade. Survival of patients treated with hematopoietic cell transplantation has been 82%, and the response rate to immunosuppressive therapy 70%.

CONCLUSIONS

Hepatitis-associated bone marrow aplasia is mediated by immunological mechanisms. Treatment options include hematopoietic cell transplantation and immunosuppressive therapy.

Changes in cytokine profile pre- and post-immunosuppression in acquired aplastic anemia

Cytokine expression assessed by flow cytometry in 53 acquired aplastic anemia patients before and after combined immunosuppression (EBMT WPSAA protocols) showed that CD3(+) marrow cells containing TNF-alpha, IFN-gamma and IL4 were similar in subjects with disease at onset (DO) and responsive to treatment who had more CD3(+)/TNF-alpha(+) and CD 3(+)/IFN-gamma(+) cells than normal controls. In vitro block of TNF-alpha and/or IFN-gamma significantly increased BFU-e over baseline in 28 patients. In responsive to treatment patients only TNF-alpha block significantly incremented colonies over normal controls. Absolute marrow CD3(+)/TNF-alpha(+) and CD3(+)/IFN-gamma(+) cells prospectively tested in a group of 21 subjects declined significantly more in Responders than in Non Responders to immunosuppression at Response Evaluation Time respect to Diagnosis. Both in Responders and in Non Responders these cells remained higher than in normal controls. This study suggests that immunosuppression does not fully clear excess TNF-alpha and IFN-gamma from marrow of patients with good outcome and raises the hypothesis that additional cytokine blockade might be useful in immunosuppression for acquired aplastic anemia.

Secondary hematological changes mimicking the preleukemic syndrome. Report of two cases

Two women with hematological and clinical features typical of the preleukemic syndrome, including low marrow myeloid colony and cluster formation in vitro, showed unexplained spontaneous improvement with normalization of both peripheral blood values and in vitro cloning efficiency after 2-4 years. One patient had and the other developed later an autoimmune disorder. It is therefore suggested that secondary hematopoietic changes might have mimicked the preleukemic syndrome.

Immunological abnormalities in massive cutaneous hyalinosis

Immunological studies in a patient with massive cutaneous hyalinosis, a disease characterized by principally dermal and subcutaneous accumulations of monoclonal kappa light chains and a gliadin-binding mannose-rich 90 kD glycoprotein, show that the ratio of helper to suppressor T cells is decreased and the proliferative responses of the peripheral mononuclear cells to T cell and T cell-dependent B cell mitogens are depressed. High levels of circulating immune complexes were demonstrated by C1q-binding and rheumatoid factor enzyme linked immunoassays. IgM and IgA class antibodies against the hyalin components, the mannosyl-90 kD glycoprotein and type I collagen, and against keratin and gluten were present in high titres. The reactivity of mononuclear cells to phytohemagglutinin normalized and the antibody levels to hyalin proteins, keratin and gluten fell during low-dose steroid therapy. However, the concanavalin A response was not reversed, neither did the levels of circulating immune complexes and anti-intercellular substance antibodies decrease. The results demonstrate a very complex dysfunction of the immune system in massive cutaneous hyalinosis.

Immune Pathophysiology of Aplastic Anemia

Acquired aplastic anemia (AA) is considered an immune-mediated disease because approximately 70% of AA patients improve with immunosuppressive therapy. However, little is known about the inciting antigens or the mechanisms responsible for the destruction of hematopoietic stem cells by immune system attack. Recent advances in immunologic techniques have promoted our understanding of the pathogenesis of AA and have provided evidence that AA is an organ-specific T-cell-mediated disease localized in the bone marrow. Moreover, antibody screening of patients' serum with a complementary DNA library derived from hematopoietic cells has identified several proteins as candidate autoantigens in AA.

The polymorphisms -318C>T in the promoter and 49A>G in exon 1 of CTLA4 and the risk of aplastic anemia in a Caucasian population

Aplastic anemia (AA) is a rare disease with a major autoimmune pathogenetic component. CTLA4 is a T-lymphocyte surface molecule involved in the maintenance of immune tolerance. Some polymorphisms associated with a reduced expression of CTLA4, and thus presumably with increased tendency to autoimmunity, have been associated with various autoimmune diseases. In this study, we evaluated the distribution of the low expression polymorphisms -318C > T and 49A > G of CTLA4 in a population of 67 patients with acquired AA and in 100 normal controls. There was no difference in the distribution of the tested polymorphism between patients and controls and, within the patient group, between those who responded to immunosuppression vs those who did not respond. This study indicates that the polymorphisms -318C > T and 49A > G of CTLA4 do not affect the risk of developing AA and do not influence the response to immunosuppression.

Autoantibodies frequently detected in patients with aplastic anemia

Although accumulating evidence strongly suggests that aplastic anemia (AA) is a T cell-mediated autoimmune disease, no target antigens have yet been described for AA. In autoimmune diseases, target autoantigens frequently induce not only cellular T-cell responses but also humoral B-cell responses. We hypothesized that the presence of antigen-specific autoantibodies could be used as a "surrogate marker" for the identification of target T-cell autoantigens in AA patients. We screened a human fetal liver library for serologic reactivity against hematopoietic stem/progenitor cell antigens and isolated 32 genes. In 7 of 18 AA patients, an immunoglobulin G (IgG) antibody response was detected to one of the genes, kinectin, which is expressed in all hematopoietic cell lineages tested including CD34+ cells. No response to kinectin was detected in healthy volunteers, multiply transfused non-AA patients, or patients with other autoimmune diseases. Epitope mapping of IgG autoantibodies against kinectin revealed that the responses to several of the epitopes were shared by different AA patients. Moreover, CD8+ cytotoxic T cells raised against kinectin-derived peptides suppressed the colony formation of granulocyte macrophage colony-forming units (CFU-GMs) in an HLA class I-restricted fashion. These results suggest that kinectin may be a candidate autoantigen that is involved in the pathophysiology of AA.

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.

Acquired pure red cell aplasia associated with lymphoproliferative disease of granular T lymphocytes

Acquired pure red cell aplasia (PRCA) can be associated with lymphoproliferative disease of granular T lymphocytes (T-LDGL), also known as T-cell large granular lymphocyte leukemia. Fifteen adult patients with PRCA associated with T-LDGL comprise this study. Neutropenia and rheumatoid arthritis were uncommon. All patients responded to immunosuppressive therapy. The 2 most commonly used treatments were prednisone and cyclophosphamide +/- corticosteroids, producing overall response rates of 50% and 60%, respectively. Treatment with cyclophosphamide was associated with a more durable remission (median, 60 versus 7.5 months). After a median follow-up of 67 months, 2 patients died of treatment-related complications, one from myelodysplasia and another from cyclosporine-induced renal failure. The clinical course and treatment responses of PRCA associated with T-LDGL in this series were similar to the general group of PRCA. Because T-LDGL is frequently underdiagnosed, it is likely that a significant proportion of idiopathic or primary PRCA is in fact secondary to T-LDGL.

Sequential Variations in the Content of Bone Marrow Colony-forming Cells in Individual Patients with Aplastic Anemia Before and After Immunosuppressive Therapy; Hematopoiesis

Previous studies have shown that the levels of hematopoietic progenitor cells (colony-forming cells; CFC) are drastically reduced in the vast majority of patients with aplastic anemia (AA). This has been observed both in patients before and after immunosuppressive therapy. In those studies, however, both groups of patients were usually formed by different individuals, thus it was not possible to follow the kinetics of such cells in each particular patient. In the present study, we have determined the content of myeloid and erythroid CFC in individual AA patients before and after therapy. Treated patients were studied at two different times (8-18 months apart) to detect any possible variations due to the ongoing treatment. At diagnosis, the levels of both myeloid and erythroid CFC were drastically reduced, as compared to normal bone marrow, in all the patients studied. This correlated with very low levels of leukocytes and hemoglobin in circulation. After the patients entered an immunosuppressive treatment, all of them showed significant increments in their CFC levels, and this correlated with increments in their hematological parameters in peripheral blood. However, in most patients CFC levels were still below the normal range. When the second sample after treatment was obtained, great variations in CFC numbers were observed. In terms of erythroid CFC levels, a further increase was seen in most patients, and this correlated with a further increase in hemoglobin levels. In contrasts, the levels of myeloid CFC were increased in only some of the patients, whereas in others, significant reductions were evident. Interestingly, in this latter group of patients, CFC never reached the levels observed before treatment. Our results indicate that, in a significant proportion of patients, a common pattern seems to exist. That is to say, low CFC numbers are present before treatment; an increase in the numbers of such cells results as an effect of the immunosuppressive therapy and further variations in CFC numbers (within individual limits that may differ significantly from one patient to another) take place as long as the treatment continues. Finally, we observed a correlation between CFC levels and the clinical status of the patients, i.e., those patients that showed a complete or a partial response to treatment showed higher levels of both myeloid and erythroid CFC than those patients that did not respond to therapy.

Lack of known hepatitis virus in hepatitis-associated aplastic anemia and outcome after bone marrow transplantation

Viral infection has been shown to induce aplastic anemia, unidentified types of hepatitis being the most common cause for aplastic anemia-associated viral hepatitis. The survival rate for this group of patients after bone marrow transplantation with stem cells from an HLA-matched sibling is not well known. The aim of this study was to determine the prevalence of hepatitis G virus (HGV) and transfusion transmitted virus (TTV) infection in non-A, non-B, non-C hepatitis associated-aplastic anemia (HAAA) patients, and to define the role of bone marrow transplantation (BMT) as a therapeutic modality for this disease. Sixty-eight patients (43 males and 25 females) with aplastic anemia, underwent allogeneic BMT at the Hadassah University Hospital between 1981 and 1997. Onset of hepatitis was defined as jaundice and elevated alanine aminotransaminase (ALT) levels. Onset of aplastic anemia was defined as the first date on which varying degrees of pancytopenia occurred: hemoglobin level below 10 g/dl, WBC below 2 x 10(9)/l and low platelet count 10 x 10(10)/l. Serial serum samples from HAAA patients were assayed for virological and/or serological markers of hepatitis A, B, C, D, E, G viruses, TTV and parvovirus B19. Seventeen of the 68 patients with aplastic anemia (25%) suffered from hepatitis, 12 males and five females, ages 5 to 36 years. The mean interval between onset of hepatitis and first indication of aplastic anemia was 62 days (range 14-225 days). The development of aplastic anemia was unrelated to age, sex or severity of hepatitis. Ten of the 17 patients (59%) achieved complete ALT recovery prior to the diagnosis of aplastic anemia. Serum samples were available for 15 patients; none had evidence of acute or active hepatitis A, B, C, D, E, G and TTV virus infection at the time of diagnosis. Parvovirus B19 DNA sequences were not detectable in 10 of 12 tested cases; two positive results were detected in serum samples obtained after blood transfusion, making the analysis of these positive results difficult. All 17 patients underwent BMT. The mean post-BMT follow-up period was 38 months (range 1 day-123 months), five patients (30%) died 1 to 160 days post BMT, and 12 (70%) are alive 31 to 123 months after BMT. Relapsing hepatitis was not observed in any of the patients. In conclusion, HAAA is a disease of the young and the etiologic agent associated with HAAA remains unknown. HGV, TTV and parvovirus B19 sequences were not detected in any of the HAAA cases. The survival rate after BMT with stem cells from an HLA-matched sibling is similar to that for patients with non-hepatitis-associated aplastic anemia.

Characterization of T-Cell Repertoire of the Bone Marrow in Immune-Mediated Aplastic Anemia: Evidence for the Involvement of Antigen-Driven T-Cell Response in Cyclosporine-Dependent Aplastic Anemia

To determine whether the antigen-driven T-cell response is involved in the pathogenesis of aplastic anemia (AA), we examined the complementarity-determining region 3 (CDR3) size distribution of T-cell receptor (TCR) β-chain (BV) subfamilies in the bone marrow (BM) of untreated AA patients. AA patients who did not respond to immunosuppressive therapy and those who obtained unmaintained remission early after cyclosporine (CyA) or antithymocyte globulin (ATG) therapy exhibited essentially a normal CDR3 size pattern. In contrast, five patients who needed continuous administration of CyA to maintain remission exhibited a skewed CDR3 size pattern in a number (>40%) of BV subfamilies suggestive of clonal predominance. The skewing of CDR3 size distribution became less pronounced in one of the CyA-dependent patients when the patient achieved unmaintained remission after a 4-year therapy with CyA, whereas it persisted longer than 7 years in the other patient requiring maintenance therapy. Sequencing of BV15 cDNA for which the CDR3 size pattern exhibited apparent clonal predominance in all CyA-dependent patients showed high homology of the amino acid sequence of the CDR3 between two different patients. These findings indicate that antigen-driven expansion of T cells is involved in the pathogenesis of AA characterized by CyA-dependent recovery of hematopoiesis.

Characterization of T-Cell Repertoire of the Bone Marrow in Immune-Mediated Aplastic Anemia: Evidence for the Involvement of Antigen-Driven T-Cell Response in Cyclosporine-Dependent Aplastic Anemia

To determine whether the antigen-driven T-cell response is involved in the pathogenesis of aplastic anemia (AA), we examined the complementarity-determining region 3 (CDR3) size distribution of T-cell receptor (TCR) β-chain (BV) subfamilies in the bone marrow (BM) of untreated AA patients. AA patients who did not respond to immunosuppressive therapy and those who obtained unmaintained remission early after cyclosporine (CyA) or antithymocyte globulin (ATG) therapy exhibited essentially a normal CDR3 size pattern. In contrast, five patients who needed continuous administration of CyA to maintain remission exhibited a skewed CDR3 size pattern in a number (&gt;40%) of BV subfamilies suggestive of clonal predominance. The skewing of CDR3 size distribution became less pronounced in one of the CyA-dependent patients when the patient achieved unmaintained remission after a 4-year therapy with CyA, whereas it persisted longer than 7 years in the other patient requiring maintenance therapy. Sequencing of BV15 cDNA for which the CDR3 size pattern exhibited apparent clonal predominance in all CyA-dependent patients showed high homology of the amino acid sequence of the CDR3 between two different patients. These findings indicate that antigen-driven expansion of T cells is involved in the pathogenesis of AA characterized by CyA-dependent recovery of hematopoiesis.

Aplastic anemia rescued by exhaustion of cytokine-secreting CD8+ T cells in persistent infection with lymphocytic choriomeningitis virus

Aplastic anemia may be associated with persistent viral infections that result from failure of the immune system to control virus. To evaluate the effects on hematopoiesis exerted by sustained viral replication in the presence of activated T cells, blood values and bone marrow (BM) function were analyzed in chronic infection with lymphocytic choriomeningitis virus (LCMV) in perforin-deficient (P0/0) mice. These mice exhibit a vigorous T cell response, but are unable to eliminate the virus. Within 14 d after infection, a progressive pancytopenia developed that eventually was lethal due to agranulocytosis and thrombocytopenia correlating with an increasing loss of morphologically differentiated, pluripotent, and committed progenitors in the BM. This hematopoietic disease caused by a noncytopathic chronic virus infection was prevented by depletion of CD8+, but not of CD4+, T cells and accelerated by increasing the frequency of LCMV-specific CD8+ T cells in T cell receptor (TCR) transgenic (tg) mice. LCMV and CD8+ T cells were found only transiently in the BM of infected wild-type mice. In contrast, increased numbers of CD8+ T cells and LCMV persisted at high levels in antigen-presenting cells of infected P0/0 and P0/0 x TCR tg mice. No cognate interaction between the TCR and hematopoietic progenitors presenting either LCMV-derived or self-antigens on the major histocompatibility complex was found, but damage to hematopoiesis was due to excessive secretion and action of tumor necrosis factor (TNF)/lymphotoxin (LT)-alpha and interferon (IFN)-gamma produced by CD8+ T cells. This was studied in double-knockout mice that were genetically deficient in perforin and TNF receptor type 1. Compared with P0/0 mice, these mice had identical T cell compartments and T cell responses to LCMV, yet they survived LCMV infection and became life-long virus carriers. The numbers of hematopoietic precursors in the BM were increased compared with P0/0 mice after LCMV infection, although transient blood disease was still noticed. This residual disease activity was found to depend on IFN-gamma-producing LCMV-specific T cells and the time point of hematopoietic recovery paralleled disappearance of these virus-specific, IFN-gamma-producing CD8+ T cells. Thus, in the absence of IFN-gamma and/or TNF/LT-alpha, exhaustion of virus-specific T cells was not hampered.

The Assessment of the Hematopoietic Reservoir After Immunosuppressive Therapy or Bone Marrow Transplantation in Severe Aplastic Anemia

We investigated the hematopoietic reservoir in 43 severe aplastic anemia (SAA) patients following immunosuppression (IS) (n = 15) or bone marrow transplantation (BMT) (n = 28), at a median interval of 5 years (range, 2-20) from treatment. All patients had normal blood counts, good marrow cellularity, and normal numbers of colony forming unit-granulocyte macrophages (CFU-GM). Burst forming unit-erythroid (BFU-E) and colony forming unit-granulocyte erythroid megakaryocyte macrophages (CFU-GEMM) numbers were reduced when compared with normal controls. However, the most pronounced defect was observed at the level of long-term culture-initiating cells (LTC-IC), which significantly differed from controls (P < .00001) both for IS and BMT patients. Their number did not improve with time and was not affected by transplant or treatment-related variables. When IS patients were compared with BMT we found comparable numbers of CFU-GEMM (P = .8) and LTC-IC (P = .9), but lower numbers of BFU-E and CFU-GM (P = .05 and P = .004, respectively), suggestive of a persistent suppressive mechanism. These data indicate that LTC-IC numbers are severely reduced in BMT and IS patients, contradicting the common belief that the former are fully reconstituted as compared with the latter. In addition, the number of mature cells and committed progenitors does not seem to reflect the real size of the hematopoietic reservoir and few stem cells may be sufficient to guarantee normal hematopoiesis long term.

The Assessment of the Hematopoietic Reservoir After Immunosuppressive Therapy or Bone Marrow Transplantation in Severe Aplastic Anemia

We investigated the hematopoietic reservoir in 43 severe aplastic anemia (SAA) patients following immunosuppression (IS) (n = 15) or bone marrow transplantation (BMT) (n = 28), at a median interval of 5 years (range, 2-20) from treatment. All patients had normal blood counts, good marrow cellularity, and normal numbers of colony forming unit-granulocyte macrophages (CFU-GM). Burst forming unit-erythroid (BFU-E) and colony forming unit-granulocyte erythroid megakaryocyte macrophages (CFU-GEMM) numbers were reduced when compared with normal controls. However, the most pronounced defect was observed at the level of long-term culture-initiating cells (LTC-IC), which significantly differed from controls (P < .00001) both for IS and BMT patients. Their number did not improve with time and was not affected by transplant or treatment-related variables. When IS patients were compared with BMT we found comparable numbers of CFU-GEMM (P = .8) and LTC-IC (P = .9), but lower numbers of BFU-E and CFU-GM (P = .05 and P = .004, respectively), suggestive of a persistent suppressive mechanism. These data indicate that LTC-IC numbers are severely reduced in BMT and IS patients, contradicting the common belief that the former are fully reconstituted as compared with the latter. In addition, the number of mature cells and committed progenitors does not seem to reflect the real size of the hematopoietic reservoir and few stem cells may be sufficient to guarantee normal hematopoiesis long term.

Isolation of a T-Cell Clone Showing HLA-DRB1*0405-Restricted Cytotoxicity for Hematopoietic Cells in a Patient With Aplastic Anemia

The existence of T cells capable of inhibiting in vitro hematopoiesis has been shown in aplastic anemia (AA), although whether such inhibition is mediated by a specific immune reaction involving an HLA allele remained unknown. We isolated a CD4+ Vβ21+ T-cell clone that was most dominant among Vβ21+ T cells in the bone marrow (BM) of an AA patient whose HLA-DRB1 alleles included 1501 and 0405. The T-cell clone named NT4.2 lysed an autologous Epstein-Barr virus-transformed lymphoblastoid cell line (LCL) and phytohemagglutinin-stimulated lymphocytes (PHA-blasts) as well as allogeneic LCLs sharing HLA-DRB1*0405. Cytotoxicity against LCL cells and PHA-blasts by NT4.2 was blocked by anti–HLA-DR monoclonal antibody (MoAb) or anti-CD3 MoAb. NT4.2 also lysed autologous BM mononuclear cells enriched with CD34+ cells that had been cultured for one week in the presence of colony-stimulating factors as well as allogeneic CD34+ cells of a normal individual carrying HLA-DRB1*0405, cultured in the same way. Moreover, NT4.2 strongly inhibited colony formation by hematopoietic progenitor cells derived from cultured CD34+ cells sharing HLA-DRB1*0405. These results indicate that the AA patient has T cells capable of killing hematopoietic cells in an HLA-DRB1*0405-restricted manner and that such cytotoxic T cells may contribute to the pathogenesis of AA.

Isolation of a T-Cell Clone Showing HLA-DRB1*0405-Restricted Cytotoxicity for Hematopoietic Cells in a Patient With Aplastic Anemia

The existence of T cells capable of inhibiting in vitro hematopoiesis has been shown in aplastic anemia (AA), although whether such inhibition is mediated by a specific immune reaction involving an HLA allele remained unknown. We isolated a CD4+ Vβ21+ T-cell clone that was most dominant among Vβ21+ T cells in the bone marrow (BM) of an AA patient whose HLA-DRB1 alleles included 1501 and 0405. The T-cell clone named NT4.2 lysed an autologous Epstein-Barr virus-transformed lymphoblastoid cell line (LCL) and phytohemagglutinin-stimulated lymphocytes (PHA-blasts) as well as allogeneic LCLs sharing HLA-DRB1*0405. Cytotoxicity against LCL cells and PHA-blasts by NT4.2 was blocked by anti–HLA-DR monoclonal antibody (MoAb) or anti-CD3 MoAb. NT4.2 also lysed autologous BM mononuclear cells enriched with CD34+ cells that had been cultured for one week in the presence of colony-stimulating factors as well as allogeneic CD34+ cells of a normal individual carrying HLA-DRB1*0405, cultured in the same way. Moreover, NT4.2 strongly inhibited colony formation by hematopoietic progenitor cells derived from cultured CD34+ cells sharing HLA-DRB1*0405. These results indicate that the AA patient has T cells capable of killing hematopoietic cells in an HLA-DRB1*0405-restricted manner and that such cytotoxic T cells may contribute to the pathogenesis of AA.

Hepatitis-associated aplastic anemia

BACKGROUND

Hepatitis-associated aplastic anemia is a variant of aplastic anemia in which aplastic anemia follows an acute attack of hepatitis. The aplastic anemia, however, is often fatal if untreated. To characterize the illness, investigate the role of hepatitis viruses, and assess the response to immunosuppressive treatment, we studied patients with the syndrome who were referred to the National Institutes of Health (NIH).

METHODS

Standard hematologic and biochemical tests and measurements of bone marrow cellularity were used to monitor the patients' response to treatment. Serum was assayed for antibodies and antigens related to hepatitis A, B, and C viruses and for the RNA of hepatitis C and GB virus C by the polymerase chain reaction. All patients were treated with antithymocyte globulin and cyclosporine.

RESULTS

Ten patients with hepatitis-associated aplastic anemia were referred to the NIH between 1990 and 1996; all had the typical features of this syndrome. There was evidence of activated CD8 T lymphocytes in the blood. Serologic tests for hepatitis A, B, and C viruses were negative; RNA of hepatitis C virus was undetectable in all patients, but RNA of GB virus C was detected in three patients. Seven of the patients responded to intensive immunosuppressive treatment; the three who did not respond all died within one year of treatment, two from complications of stem-cell or marrow transplantation.

CONCLUSIONS

The hepatitis of the hepatitis-associated aplastic anemia does not appear to be caused by any of the known hepatitis viruses. We recommend immunosuppressive treatment for patients who do not have an HLA-matched related donor available for bone marrow transplantation. Several features of the syndrome suggest that it is mediated by immunopathologic mechanism.