Results of Treatment of Severe Aplastic Anaemia in Children Using Rabbit Antithymocyte Globulin(r-ATG),
Authors: Salamonowicz Malgorzata , Pawelec Katarzyna , Matysiak Michal , Kowalczyk Jerzy , Balwierz Walentyna , Zaleska-Czepko Ewa , Chybicka Alicja , Szmyd Krzysztof , Szczepanski Tomasz , Bubala Halina , Wysocki Mariusz , Kurylak Andrzej , Wachowiak Jacek , Szpecht Dawid , Mlynarski Wojciech , Bulas Monika , Krawczuk-Rybak Maryna , Panasiuk Anna , Leszczynska Elzbieta , Urasinski Tomasz , Peregud-Pogorzelski Jaroslaw , Balcerska Anna , Kaczorowska-Hac Barbara 
Published: October 2019

Abstract
Abstract 3435

Objective:
One of the main patophysiological mechanism of aplastic anemia (AA) is immune-mediated destruction of hematopoietic cells. In children with severe acquired aplastic anemia (SAA) allogenic bone marrow transplantation is the first choice. If there is no matched sibling donor the first line of treatment is immunosuppressive therapy (IST) which consists of ATG combined with cyclosporine A.

Aim.
The aim of this study was to analyze the results of IST containing rabbit anti-thymocyte globulin (r-ATG) performed on children with SAA and vSAA treated between 1996–2009 yr. We wanted to assess the influence of such factors as response to treatment, etiology, sex, age, type of AA, for: event free survival (EFS), and progression free survival (PFS) We analyzed deaths rate, relapses rate, clonality and side effects of IST.

Materials and methods.
We retrospectively analyzed group of 55 children with SAA and vSAA. The group consisted of 23 girls and 32 boys, the median age was 10 years (range 6mth-17,5 years). IST contained antithymocyte globulin,given intravenous at a dose of 3,75 mg/kg/day for 5 days, and cyclosporine A(CSA) at 5 mg/kg/day by mouth in divided doses started on day 1 and continued for at least 6 months(till 24 months). Response rate was assessed on 112, 180 and 360 day and defined as CR, PR, NR. Kaplan–Meier estimator, univariate analysis and multivariate Cox regression models were used to estimate the influence of such factors as response to treatment, etiology, sex, age for EFS, PFS, toxicity and other side effects.

Results.
The 2- year probability of event free survival (EFS) was 71,52%. The 5 and 10 –year EFS was 57,7%. Progression free survival (PFS) was 66,53%, at 2 years and 59,13% at 5- and 10 year
Patients with CR and PR had significantly longer EFS than children with no response(NR) (p<0.0001 Wilcoxon). There was no significant correlation between EFS, PFS and such factors as etiology, sex, age, severity of AA (p > 0,05 Log rank). In all group we observed 15 deaths (27,27%), 5 early and 10 late deaths. Infections were the main causes of death. The relapse rate was 1,81%. The 2-year probability of not having relapse was 87,68%. Relapse free survival was 75,16% at 5 and 10 years. There was one transformation to paroxysmal nocturnal hemoglobinuria (PNH).Non responders (4 patients) received second IST and 11 children underwent MUD-BMT. Infections were the most often side effects of IST (FUO-26,92% of infectious side effects). There was significant association found between EFS and infectious side effects. (p=0,00093 log rank) The most common adverse effects after rabbit immunoglobulin were fever (30,30%) and dyspnoe (24,24%). After CSA treatment we observed mainly gingival hyperplasia (29,16% of side effects of CSA). Most common hemorrhagic side effects were skin petechie. There was significant correlation between hemorrhagic side effects and PFS (p= 0,0144 log rank)

Conclusions.
1. Rabbit-ATG is an effective frontline therapy for children with SAA without familiar bone marrow donor.2.Remission achieved on day 112 seems to be constant. 3.5-year EFS seems to be stable within next 5 years.4.5-year relapse free survival seems to be constant during the next 5 years.5.Etiology, type of SAA, age and sex have no influence on the survival.)6.Infectious and hemorrhagic side effects are a very important factors affecting the survival rate in children with SAA.

Disclosures:
No relevant conflicts of interest to declare.