Outcomes for patients with severe aplastic anemia (SAA) who are refractory to first-line immunosuppressive therapy (IST) and who lack a matched unrelated donor (MUD) remain poor. Recently, the use of eltrombopag (ELT) has shown blood count improvements in 40% of these patients. However, most refractory patients do not respond to ELT or other second-line treatment and are therefore exposed to life-threatening infections, and bleeding. During the past 2 decades, there has been a significant decrease in infection-related mortality in patients with SAA unresponsive to initial IST but clonal evolution including paroxysmal nocturnal hemoglobinuria (PNH), myelodysplastic syndrome (MDS), and acute myeloid leukemia (AML) still occur in the long-term with a grim prognosis. Overall, the overall survival of such patients with acquired refractory SAA to ELT is about 60-70% at 2 years.

Hematopoietic stem cell transplantation (HSCT) using alternative donor sources (i.e., mismatched unrelated donors, cord blood (CBT), and haplo-identical family donors) may be curative in patients with refractory SAA, despite carrying much higher rates of complications than in transplantations from matched related or unrelated donors. Recently, our group showed that CBT is a valuable curative option for young adults with refractory SAA. However, not all patients have available CB and CBT treatment related mortality is high in adult patients. Haploidentical (haplo) related donor Stem Cell Transplantation (haplo-SCT) have improved dramatically outcomes using T-cell replete grafts with administration of post-transplantation cyclophosphamide (PTCy). Preliminary results in a little number of patients with refractory SAA at Kings college (London, UK) and John Hopkins (Baltimore, USA) seem promising. The investigators retrospectively analyzed data from 36 patients (median age 42 years) transplanted between 2010 and 2017 in Europe on behalf of the SAA working party of the European Blood and Marrow Transplantation group. The 1-year overall survival was about 80% suggesting that this approach might be a valid option in this particular poor clinical situation.

The main objective of this study is to demonstrate a benefit in term of the 2-year overall survival rate from 60% (historical rates in patients with acquired refractory idiopathic aplastic anemia) up to 80% using haplo-SCT with PTCy.

Inclusion Criteria:

• Aged from 3 to 35 years old

• Suffering from refractory acquired idiopathic aplastic anemia (at least one course of immunosuppression with anti-thymocyte globulin)

• Absence of geno-identical donor or 10/10 matched donor

• With identification of a haploidentical donor (brother, sister, parents, adult children or cousin)

• Absence of donor specific antibody detected in the patient with a MFI ≥ 1500 (antibodies directed towards the distinct haplotype between donor and recipient)

• With usual criteria for HSCT :

  • ECOG(Eastern Cooperative Oncology Group) ≤ 2
  • No severe and uncontrolled infection
  • Cardiac function compatible with high dose of cyclophosphamide

• Adequate organ function: ASAT(aspartate transaminase) and ALAT (alanine aminotransferase) ≤ 2.5 N (the norm), total bilirubin ≤ 2N, creatinine < 150 μmol/L

• With health insurance coverage

• Contraception methods must be prescribed during all the duration of the research. Women and men of childbearing age must use contraceptive methods within 12 months and 6 months after the last dose of cyclophosphamide, respectively.

• Having signed a written informed consent (2 parents for patients aged less than 18)

Exclusion Criteria :

• With morphologic evidence of clonal evolution (patients with isolated bone marrow cytogenetic abnormalities are also eligible excepted chromosome 7 abnormalities and complex karyotype)
• With uncontrolled infection
• With seropositivity for HIV or HTLV-1 (Human T cell Leukemia) or active hepatitis B or C defined by a positive PCR (polymerase chain reaction) HBV (hepatitis B virus) or HCV (hepatitis C virus) and associated hepatic cytolysis
• Cancer in the last 5 years (except basal cell carcinoma of the skin or "in situ" carcinoma of the cervix)
• Pregnant (βHCG positive) or breast-feeding.
• Who received live attenuated vaccine within 2 months before transplantation and during the research
• Uncontrolled coronary insufficiency, recent myocardial infarction <6 month, current manifestations of heart failure, uncontrolled cardiac rhythm disorders, ventricular ejection fraction <50%
• With heart failure according to NYHA (New York Heart Association) (II or more)
• Preexisting acute hemorrhagic cystitis
• Renal failure with creatinine clearance <30ml / min
• With urinary tract obstruction
• Who receive the following treatments Phenytoin, Pentostatin, inhibitor of adenoside)
• Who have any debilitating medical or psychiatric illness, which preclude understanding the inform consent as well as optimal treatment and follow-up
• Under tutorship or curatorship