Inclusion Criteria: 1. Patient aged from 3 months up to 17 years old. 2. Patient with a FHL caused by mutation of the UNC13D gene. 3. Complete remission is defined by the normalization of clinical and laboratory parameters: 1. Resolution of fever 2. Resolution of splenomegaly or reduced and isolated splenomegaly. 3. Improvement of cytopenia: absolute neutrophil count \> 500/µl AND platelets cout \> 100 000/ µl (unsupported by transfusion) 4. Normalization of serum fibrinogen level (Fibrinogen ≥1.5g/l) 5. Resolution of hyperferritinemia (Ferritin level \< 2000µg/l) 6. Normalization of T-cell activation 4. Patient eligible for an allogeneic HSCT in absence of an HLA geno-identical donor (at diagnostic or 6 months after failure of a previous HSCT (rejection or loss of the graft)) 5. Parental, guardian's patient signed informed consent. 6. For patients of childbearing age : willing to use an effective method of contraception\* during the trial and for at least 12 months post-infusion 7. Affiliation to Social Security Exclusion Criteria: 1. Active CNS encephalitis related to HLH 2. Existence of a matched -sibling donor 3. Unwillingness to return for follow-up during the 2 years study and lifelong for off study review. 4. HIV-1 or 2 or HTLV1 infections. 5. Patient on AME (state medical aid) (unless exemption from affiliation) 6. Pregnancy or breast feeding in a post-partum female 7. Diagnosis of significant psychiatric disorder of the subject that could seriously impeded the ability to participate in the study 8. Known allergies, hypersensitivity, or intolerance to any of busulfan, fludarabine, rituximab, G-CSF, plerixafor or excipients, or similar compounds 9. Unable to tolerate general anesthesia and/or apheresis 10. Participation in another clinical study with an investigational drug within 30 days of inclusion. 11. Uncontrolled HLH manifestation