الفهرس 
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Abstract
β-thalassemias are a group of recessively inherited hemoglobin disorders characterized by reduced synthesis of β globin chains. Thalassemia constitutes the most common inherited recessive disorder associated with consanguinity, which is a common phenomenon in Egypt. Allo-HSCT is the only established treatment modality that provides a possibility of cure and considered cost effective compared with conventional therapy. Current results of transplantation in pediatrics from matched related donors offer 80% to 87% probability of cure according to risk classes. The thalassemia free survival was respectively 85–90% for class I, 80% for class II, and 70% for class III, while the TRM increased from class I to III. At present, the optimal dose of ATG for GvHD prophylaxis minimizing risk of infections without increasing GvHD remains undefined. Furthermore, dosing of ATG is less clear in pediatric patients than it is in adult patients. Given TM disease specific features, for years, a protocol combining busulfan and cyclophosphamide has been considered the gold standard in patients undergoing HSCT. Studies reported a low incidence of both graft failure and GvHD in children given HLA-matched family donor- HSCT, with the addition of ATG to a Bu/Cy conditioning regimen. The present study aimed to study the impact of using low dose vs. high dose ATG based conditioning regimen on the outcome of peripheral blood stem cell transplantation in children with β-TM. This current study was conducted on 40 patients with β-TM (Pesaro class II, III) were admitted for allogeneic peripheral blood stem cell transplantation from matched related donor including 22 males and 18 females with their age ranged from 2 to 18 years. Our patients were categorized according to the dose of ATG in pretransplant conditioning regimen into two groups; group I included 20 patients who received myeloablative regimen; (Bu/Cy/Low dose ATG-30 mg) and group II with 20 patients who had received myeloablative regimen; (Bu/Cy/High dose ATG-110 mg). All patients included in the study were subjected to the following: Full history taking and complete clinical examination with assessment of Pesaro risk classes. Laboratory investigations including: CBC, blood group, bone marrow aspiration, HLA typing, viral marker screening, renal and liver function tests, electrolytes, random blood glucose, CRP, cultures, serum ferritin level and hemoglobin electrophoresis. Imaging including: ECHO, Chest X ray, ECG and FibroScan/ liver biopsy. All donors – after identification of HLA matched sibling – were subjected to pre-transplantation evaluation including the same hematological, biochemical, virology screen, ECHO, and bone marrow aspiration. Allo-HSCT outcome was assessed with the following parameters: time to engraftment, acute and /or chronic GvHD, incidence and types of infections, regimen related toxicities, TRM, and survival outcomes including OS and DFS. The main findings can be summarized as follows: The majority of cases in both groups aged (2 to 12 years) with majority of patients in both groups were Pesaro II (85% in low dose group and 75% in high dose group). There were no differences in the clinical features between the two groups, including age, sex, Pesaro risk classes, disease status at transplant and diagnosis/transplant lag. No significant difference was found regarding the dose of stem cells infused. No significant difference was observed regarding the duration of hospital stay, transplant related complications and mortality in both groups. No significant difference was observed as regards the time of platelet engraftment in both groups. Patients in low dose group achieved faster neutrophil engraftment. There was a higher risk of mucositis in high dose group. There was no significant difference as regards the total number of platelet transfusions during transplant. Patients in low dose group had lower PRBCs transfusion requirements during transplant. Incidence of infection was significantly higher in high dose group. No significant difference was observed in the incidence of posttransplant viral reactivation in both groups. In multivariate analysis, CMV IgG positive recipients were the only significant risk factor for CMV reactivation. No significant difference in the incidence of acute and chronic GvHD between both groups. The conditioning regimen was non-independent risk factor for acute and chronic GvHD. Older recipient age was the only significant risk factor for acute GvHD. Previous acute GvHD was the only significant risk factor for chronic GvHD. One year survival and DFS were similar in both groups.