Page 102 - 2020_01-Haematologica-web

F. Bernaudin et al.
Introduction
Methods
Sickle cell anemia (SCA) represents a growing global health problem. Over 300,000 children are born each year with SCA worldwide, with 85% of these births occurring in sub-Saharan Africa.1 SCA is a severe recessive genetic disorder, resulting from a single nucleotide substitution in codon 6 of the beta-globin gene, producing abnormal hemoglobin (HbS) that is prone to polymer formation under deoxygenated conditions. Polymerized HbS leads to decreased red blood cell deformability and sickling within end arterioles, resulting in vaso-occlusive crisis and pain.
Despite significant progress in the management of SCA, such as the prevention of pneumococcal infection,2,3 the introduction of hydroxyurea therapy (HU),4-10 and early detection of cerebral vasculopathy with transcranial Doppler,11,12 followed by rapid establishment of transfu- sion programs for patients at risk of stroke,13,14 SCA remains a disease with a high risk of morbidity and early death.15-18
Allogeneic hematopoietic stem cell transplantation (SCT) is the only curative therapy for SCD19-26 as it can pre- vent SCA-related organ damage if the erythroid compart- ment is adequately replaced by donor erythropoiesis. However, barriers to SCT use include the risks of rejec- tion, transplant-related mortality (TRM), chronic graft-versus-host disease (cGvHD), infertility, and the lack of matched-sibling donors (MSD). While at least 1,000 MSD-SCT have been performed so far worldwide, the number of transplanted SCA patients remains very low,23 especially in developing countries that have a large SCA population. We have previously reported studies in 87 consecutive myeloablative MSD-SCT for SCA patients performed in France between 1988 and December 2004.22 We showed that the addition of antithymocyte globulin (ATG) to the conditioning regimen (CR) allowed a signif- icant reduction in the risk of rejection despite a higher prevalence of mixed chimerism. The myeloablative CR (MAC), consisting of busulfan, cyclophosphamide and rabbit ATG was well tolerated by these young patients (aged 2.2-22 years), as only one death occurred during aplasia and limited early toxicity was noted. Moreover, the outcome significantly improved with time, as event- free survival (EFS) was 95.3% at five years for the 44 patients transplanted between January 2000 and December 2004.22 These results led us to use the same MAC in SCA adults under the age of 30 years without major organ dysfunction and children with less severe cerebral vasculopathy.
Since that initial report, extremely interesting results have been obtained in adults using non-myeloablative (NMA) CR, resulting in 87% EFS with 13% rejection risk, but with preserved fertility and no GvHD with mixed chimerism.27-29 It is thus timely and warranted to report the long-term outcome of chimerism, cGvHD and fertility after MAC-MSD-SCT in order to provide evidence for making an informed decision about the use of MAC or NMA CR for SCA children and young adults. For this rea- son, we analyzed the results of MAC-MSD-SCT per- formed in France between 1988 and December 2012 in 234 SCA patients, ranging in age from 2.2 to 28.9 years with a minimum 5-year follow up for surviving patients, to evaluate long-term outcomes, especially in the context of incidence of cGvHD and chimerism.
Considering the better cure rate observed with MSD-SCT after MAC for SCA patients transplanted after 2000 (95.3%), the Société Française de Greffe de Moelle et de Thérapie Cellulaire (SFGM-TC) decided to continue the previously described proto- col,22 and 151 new consecutive patients were transplanted between January 2005 and December 2012 for severe SCA. Thus, a total of 234 SCA patients had received MSD-SCT following MAC between November 1988 and December 2012. Informed consent was obtained from recipients, donors and their parents or guardians before transplantation. The data were obtained in the context of consensual treatment guidelines among French trans- plant centers in accordance with the Declaration of Helsinki, and the French laws and regulations protecting human subjects. To complement the data from the European Group for Blood and Marrow Transplantation (EBMT) registry, clinical and biological data including chimerism, eventual carcinogenic issues and fertili- ty were recorded in a French database, and its use for this project was approved by the Créteil Institutional Review Board.
Patients’ characteristics are presented in Table 1. The overall median age at transplant was 8.4 years (range: 2.2-28.9) with 32 patients (13.7%) older than 15 years (Figure 1A). All donors were MSD and genotype, available in 208 of 234 patients, was het- erozygous AS (n=127), AThal (n=2), AC (n=1), A/DPunjab (n=1), and homozygous AA (n=77). Median age of donors was 9.6 years (range 0-33.7), counting the donor’s age for isolated CBT as 0. The stem cell sources are shown in Table 2. All 234 consecutive patients were transplanted with an MSD following myeloablative CR using busulfan, cyclophosphamide at 200 mg/kg and rabbit ATG at different doses (Table 2 and Figure 1B).
Chimerism was studied by analyzing various polymorphisms after polymerase chain reaction (PCR) amplification of DNA obtained from whole blood at 1, 3, 6, 9 and 12 months after trans- plantation and every year thereafter. Real-time (RT) quantitative PCR of insertion/deletion polymorphisms was used when the minority chimeric fraction was below 10% and short-tandem- repeat (STR)-PCR was performed when the minority fraction was over 10%. In both cases, analyses were performed according to the kit manufacturer’s recommendations (Promega; PowerPlex 16S assay for STR-PCR) and GenDex for Indel RT-PCR (KMRDX Chimerism Assay). When possible, peripheral-blood CD3+ T cells and CD3– cells were selected for analysis.
Exact Fisher tests were used to compare proportions and Wilcoxon rank sum tests for continuous distributions. Patients were censored on the date of death or last visit for Kaplan-Meier (KM) estimates of survival and on the date of event (death, non- engraftment or rejection) or last visit for KM estimates of EFS. Cumulative incidences of rejections, deaths, acute GvHD (aGvHD) grade ≥II and cGvHD were also estimated by the KM method because of the small number of deaths and rejections. Failure time data curves were compared by the Log rank test. Risk factors for EFS, acGvHD and cGvHD, were analyzed by Cox regression with estimated hazards ratio (HR) and 95% Confidence Interval (CI). Type 1 error was fixed at the 5% level. All tests were two-tailed. Univariate models were fitted and all variables associated with the outcome at the 10% level were retained for introduction into a multivariate model. Statistical analyses were performed on SPSS version 22, and MedCalc (Belgium).
Results
The median (range) follow up was of 7.9 years (0.1-27.6
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haematologica | 2020; 105(1)