THERAPEUTIC GOAL OF HYPOPLASTIC ANEMIA IN PEDIATRICS HOSPITAL IN INDIA

Aleem sarwar,
Pharm.d. Interns.
Dept.of pharmacy practice,
Annamalai University,
Chidambaram,608 002,
Tamil Nadu,India
mob.9962761548.

Abstract
Aplastic anemia is acondition in which the bone marrow does not make enough new blood cells. bone marrow is the soft, fatty tissue in the center of bones.
Most acquired aplastic anemia (AA) is the result of immune-mediated

destruction of hematopoietic stem cells causing pancytopenia and an empty bone marrow, which

can be successfully treated with either immunosuppressive therapy (IST) or hematopoietic stem-

cell transplantation (HSCT).the aplastic anemia is a rare and serious disease.It happens when your bone marrow fails to make enough blood cells (low blood cell counts).

Keywords
aplastic anemia; anti-thymocyte globulin; bone marrow failure; stem cell transplantation;

cyclosporine; pancytopenia

Itroduction

Aplastic anemia (AA) is a life-threatening bone marrow failure disorder

which, if untreated, is associated with very high mortality. Hematopoietic stem cell

transplantation (HSCT) offers an opportunity for cure, but most patients are not suitable

candidates for this procedure due to advanced age, comorbidities, or lack of a

histocompatible donor. For these patients, comparable long term survival is attainable with

immunosuppressive treatment (IST) with anti-thymocyte globulin (ATG) and cyclosporine

(CsA). Although several etiopathogenic triggers have been proposed in AA, the majority of

cases are idiopathic, with a small percentage of cases occurring after an episode of

seronegative hepatitis.

Epidemiology and etiology

Each year, approximately between 800 to 1200 indian learn that they have aplastic anemia.the disease can strike people of any age, race, and gender. But it more common among children, teenagers, and young adults.

About 1 in 4 cases aplastic anemia can be linked to one of sveral causes.

These include.

Toxins, such as pesticides, arsenic, and benzene.
Treatments for other autoimmune disease such as rheumatoid arthritis.
Pregnancy. some times this aplastic anemia improves on its own after the woman give birth. AA was attributed to an idiosyncratic reaction to drug or chemical
exposure. The association of medical drug use to AA is of great importance, as it is

devastating to patients and physicians and presents serious legal consequences and problems

in pharmaceutical drug development. However, the study of idiosyncratic drug reactions,

by definition extremely rare, is difficult and the only clear predisposition to abnormal drug

metabolism underlying susceptibility is one study of a single individual exposed to

carbamazepine published over 20 years ago. Overrepresentation of drug metabolizing

glutathione-S-transferase gene deletions have been observed in some series but no

reasonable mechanism has been developed for chloramphenicol.

Pregnancy and eosinophilic fasciitis are linked to AA. Five to ten percent of cases of AA

follow an episode of seronegative hepatitis, but despite intensive efforts, an infectious

agent has not been identified.

Pathophysiology
In most cases, AA behaves as an immune-mediated disease. An immune response

dominated by oligoclonal expanded cytotoxic T-cells targets hematopoietic stem and

progenitor cells, inducing their death via apoptosis and hematopoietic failure.

T-Cell-mediated destruction of the bone marrow

Recovery of autologous hematopoiesis in patients who failed to engraft after stem cell

transplant and responsiveness to immunosuppressive therapies are the major clinical

evidences supporting an immune pathophysiology underlying acquired AA. Although a

nonimmune pathophysiology has been inferred from a failure to respond to

immunosuppression, refractoriness to therapy is also consistent with very severe stem cell

depletion, a “spent” immune response, or immunological mechanisms resistant to current

therapies.

Removal of lymphocytes from aplastic bone marrows improves colony numbers in tissue

culture, and their addition to normal marrow inhibited hematopoiesis in vitro. The

effector cells within the lymphocyte subset are activated cytotoxic T cells bearing a

profile, expressing and secreting interferon-γ.

T-bet, a transcription factor that binds tothe interferon-γ

promoter region and is critical for Th1 polarization, is up-regulated in T-

cells of patients with AA. Specific CD8+CD28− cell clones are expanded in AA

peripheral blood, as manifest by skewed usage of the Vβ repertoire; and oligoclones

recognize and induce apoptosis of autologous myeloid cells. Regulatory T cells, which

control and suppress auto-reactive T cells, are decreased at presentation in almost all

patients with AA. In a mouse model of immune-mediated marrow failure, addition of T

regulatory cells abrogated pancytopenia induced by the infusion of lymph node cells.

Why T-cells are activated in AA is unclear. HLA-DR2 is over-represented among patients,

suggesting a role for antigen recognition, and its presence is predictive of a better response

to cyclosporine. Polymorphisms in cytokine genes, associated with an increased

immune response, also are more prevalent, such as for tumor necrosis factor-α(TNF2)

promoter at −308, interferon-γ, and interleukin 6 genes. These alterations in

nucleotide sequence and in gene regulation suggest a genetic basis for aberrant T cell

activation in bone marrow failure.

Hematopoiesis

Immune attack leads to marrow failure. The targets, mainly CD34+ cells, are very few or

absent in the aplastic bone marrow, and minimal numbers of colonies derive from

committed progenitors in semisolid media, all reflecting the severe reduction in

hematopoietic progenitor cells that defines the disease. The reduced number and function of

the marrow is secondary to cell destruction, and apoptosis is prevalent among the few

remaining elements. Microarray analysis of the remaining CD34+ cells shows a

transcriptome shifted towards apoptosis, cell death, and immune regulation.

A minority of AA cases may share pathophysiologic basis with inherited marrow failure

syndromes. One peculiar feature of white blood cells in AA is short telomeres, observed in

approximately a third of cases. Although initially blamed on excessive stem cell

turnover, telomere shortening in some cases of acquired AA and in dyskeratosis congenita, a

constitutional marrow failure syndrome is due to mutations in components of the telomerase

complex, causing low telomerase activity, progressive telomere erosion, and a deficient

proliferative capacity of hematopoietic stem cells. Family members who share the

mutation, despite normal or near normal blood counts, have hypocellular marrows, reduced

CD34+ cell counts and poor hematopoietic colony formation, increased hematopoietic

growth factor levels, and of course short telomeres; some affected relatives may present with

pulmonary fibrosis or liver cirrhosis in isolation. A few adult AA patients also have

heterozygous mutations in the Shwachman-Bodian-Diamond syndrome (SBDS) gene

(Shwachman-Diamond syndrome occurs when patient carries biallelic mutations).

Clonal evaluation

AA may coexist or evolve to clonal disorders, as paroxysmal nocturnal hemoglobinuria

(PNH), myelodysplasia (MDS), or acute myeloid leukemia (AML).

Paroxysmal nocturnal hemoglobinuria (PNH)

About 40–50% of patients with acquired AA have expanded populations of PNH cells,

easily detected by flow cytometry due to the absence of glycosylphosphatidylinositol-linked

membrane proteins, the result of somatic PIG-A gene mutations arising in hematopoietic

stem cells. Most clones are small and do not lead to clinical manifestations of

hemolysis or thrombosis, but classic PNH can evolve to marrow failure (the AA/PNH

syndrome) and all PNH patients show evidence of underlying hematopoietic deficiency. The

global absence of large number of cell surface proteins in PNH has been hypothesized to

allow escape and survival of a pre-existing mutant clone.

Myelodysplasia (MDS)

Aneuploidy develops in a minority of patients treated with immunosuppression over time,

usually monosomy 7 and trisomy 8. AA patients who develop trisomy 8 usually respond

to IST. T-cell oligoclones appear to recognize the aneuploid cells and specifically WT1

as an antigen, but target cells are not killed due to their expression of anti-apoptotic genes.

Immunosuppressive therapy

Horse anti-thymocyte globulin (ATGAM (R); h-ATG) is the only drug approved by the

Food and Drug Administration for the treatment of AA. While it is generally believed that h-ATG administration leads to depletion of immune competent cells, its exact mechanism of

action remains unclear. H-ATG preparations contain a variety of antibodies recognizing

human T-cell epitopes, many directed against activated T-cells or activation antigens.

Both refractory and relapsed patients are frequently treated with further courses of ATG. In

these settings, rabbit ATG (r-ATG) + CsA has been frequently used. R-ATG is similar to h-ATG except that gamma immune globulin is obtained by immunization of rabbits with

human thymocytes. Clinically, r-ATG appears to be more immunosuppressive as a more

prolonged lymphopenia is observed with this agent compared to h-ATG. This enhanced

lymphocytotoxicity of r-ATG may be explained by higher affinity IgG subtype to human

lymphocytes, less batch-to-batch variability, longer half-life, and more efficient lymphocyte

depletion. In addition, r-ATG may promote immune regulation as suggested by an in

vitro assay where CD4+CD25− were converted to CD4+CD25+ regulatory T cells in the

presence of r-ATG but not h-ATG. For the 1/3 of patients who are refractory to h-ATG/CsA, repeated courses of immunosuppression have yielded response rates varying from 30 –70%. For relapsed patients, re-introduction of CsA commonly result in

improvement in blood counts, however, CsA-dependence is frequent and the dose of CsA

usually is tapered slowly with hematologic monitoring. Re-treatment with ATG/CsA in

relapsed AA has resulted in response rates of 50–60%. In our experience, relapse

does not correlate to a poor prognosis, as patients often respond to re-introduction of CsA and/or re-treatment with ATG

In moderate AA, the clinical course is variable: some patients progress to severe disease,

others remain stable and may not require intervention; regular transfusions may not be

required. Very few clinical trials have specifically addressed moderate disease.

Immunosuppression can reverse moderate pancytopenia and alleviate transfusion

requirements; ATG and cyclosporine are more effective in combination. Daclizumab, a

humanized monoclonal antibody to the interleukin-2 receptor, improved blood counts and

relieved transfusion requirements in 6 of 16 evaluable patients; the outpatient regimen had

little toxicity.

Allogeneic Hematopoietic Stem Cell Transplantation

Allogeneic bone marrow transplantation from a histocompatible matched sibling is curative

therapy in the majority of SAA patients who undergo this procedure . The most recent

cohort reported to the IBMTR showed 77% 5-year survival, and in children and patients

who were minimally transfused, survival of 80–90% may be routinely achieved. Acute

grade II–IV graft-versus-host-disease (GVHD) occurs in about 20–30% of patients and

chronic GVHD in 30–40%. Chronic GVHD has been a major cause of morbidity

and mortality in patients who survived more than 2 years post graft, with the necessity of

long term immunosuppressive therapy common. Graft rejection, a historic problem in

the application of transplant to SAA is now infrequent, likely a benefit of less immunogenic

blood products (leukocyte-depleted erythrocytes, for example) from fewer donors (platelets

collected by cytoapheresis). Also, better radiation-free conditioning regimens have

improved the tolerability of HSCT and allowed for engraftment in heavily transfused (and in

some cases alloimmunized) patients who were refractory to IST. The frequently

employed conditioning regimen of cyclophosphamide + ATG was compared to

cyclophosphamide in a prospective randomized study no differences in engraftment,

GVHD, and survival rates were observed between the two groups, suggesting that the better

outcome with HSCT over time relates to advances in supportive care. The main source of

stem cells up to 2000 has been bone marrow cells; in recent years, G-CSF peripheral blood

(PB) mobilized CD34+ have become more widely used. In a retrospective analysis, the use

of PB progenitor cell graft has been correlated to a worse outcome and more chronic GVHD

in younger patients (less than 20) compared to those who receive a bone marrow graft in

HLA-matched sibling donor transplants. This difference was not observed in older

patients.

Matched unrelated donor transplant

A matched sibling donor is available in only 20–30% of cases. As the outcome in aplastic

patients who have failed a single round of ATG has been poor, alternative sources of

hematopoietic stem cells have been sought, usually from now very large donor registries.

Data from large retrospective studies suggest that the outcome for an unrelated donor HSCT

remains less favorable compared to a matched-related transplant, due to more GVHD, a

mortality rate that is about twice that observed in matched sibling transplants, and long term

survival of about 50% Older patients with poor performance status have the

worst outcome and better results are obtained in children than for adults. Progress in donor

selection through high-resolution HLA typing technology has likely contributed to

decreased graft rejection and better survival and recently reported outcomes for MUD

rival those for an HLA-matched sibling transplant in children and young adults.

Conclusion

In recent years, further evidence has accumulated to strengthen the hypothesis that bone

marrow failure in AA results from immunologic destruction of hematopoietic stem and

progenitor cells. In a minority of patients with shortened telomeres, a qualitative disorder

may accompany the numerical diminution of CD34+ cells in the bone marrow. Current

research is aimed at investigating the mechanisms that lead to T cell activation and, whether

it is antigen driven or a result of immunological disarray. The clinical implication of

telomere shortening in AA is being investigated for prognostic significance. Most patients

with AA are now expected to survive regardless of the treatment modality employed.

Advances in supportive care and better salvage therapies have produced significantly

increased survival among initial non-responders to ATG+ CsA; the decrease in allo-

sensitization (through routine leucodepletion of blood products) and better donor selection

(through high molecular HLA-typing) have improved the outcomes of both related and

unrelated HSCT; long term survival in pediatric patients who respond to IST is excellent and

ATG based regimen should be offered as initial therapy to those who lack a matched sibling

donor. Our practice has been to consider an alternative donor HSCT in suitable pediatric

patients who have failed an initial course of ATG + CSA or in adults who have failed two

courses of IST. Refractory patients who are not suitable candidates for alternative donor

HSCT can be supported through a combination of transfusions, androgens and/or

administration of hematopoietic growth factors. In chronically transfused patients, iron

overload can now be managed with more convenient oral agents (deferasirox, Exjade) and,

the prospect of approval of newer oral thrombopoietic drugs is likely to ease platelet

transfusion requirements especially in AA patients who are refractory to IST.