الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Leukemias accounts for about one third of all cancers in children. Acute leukemias constitute 97% of all childhood leukemias, of which 75% are acute lymphoblastic leukemia (ALL). The different subtypes of ALL (B- or T-cell lineages) depend on the stage of lymphoid differentiation at which a leukemogenic event occur.
The improved survival of childhood ALL has focused attention on the late complications of antileukemic therapy. Both short and long-term immunologic effects of chemotherapy have been documented in children treated for leukemia. All arms of the immune system appear to beaffected in those children leaving them at risk for serious bacterial and viral infections.
Partial or complete loss of protective antibody titers against vaccine preventable diseases makes leukemic children more susceptible to infections than general population.
HBV infection occurs worldwide and is an important cause of acute and chronic viral hepatitis. About 2 billion people have been infected by hepatitis B virus and about 350 million people live with a chronic form of the disease. Egypt is considered a country of intermediate endemicity of HBV (2-8% prevalence rate).
Main routes of HBV infections are vertical transmission (perinatal), contact with an infected person (horizontal transmission), transmission through sexual contact and through parenteral, percutaneous and permucosal exposure to blood or other infected body fluids.
Clinically, hepatitis can present in an acute or a chronic form. Infants and children are more susceptible than adults for development of the chronic form of the disease. chronic hepatitis is defined by at least 6 months of persistent HBV disease.
Preventing HBV transmission during infancy and childhood is a high priority because increased risk of chronicity. Immunization with hepatitis B vaccine is the most effective way of preventing HBV infection and its consequences. Integrating HB vaccine into childhood vaccination schedules is hence a crucial step to interrupt HBV transmission.
Recombinant Hepatitis B vaccines are highly immunogenic, inducing a protective anti-HBs antibody titer (≥10 mIU per mL), in more than 95% of healthy children. There is excellent durability of response after a successful primary series. Even if titers of anti-HBs fall to less than the protective level (10 mIU/mL), most of these infants and young children continue to be protected against HBV infection. Long-term immunity has been found to derive from immunological memory. Cellular memory lasts longer than the humoral immune response, and its function remains efficient even after disappearance of anti-HBs from the circulation.
In cancer patients, HBV infection may be community acquired especially in endemic areas, but are also commonly iatrogenic. The course of disease is often severely aggravated. Moreover these patients are at risk of viral reactivation especially after end of treatment.
Immunity against HBV is significantly affected by chemotherapy