Partial engraftment of donor bone marrow cells associated with long‐term remission of haemophagocytic lymphohistiocytosis

We used polymerase chain reaction amplification of minisatellite sequences or of a Y chromosome-specific sequence and Southern blotting to analyse long-term engraftment (12-82 months) after bone marrow transplantation (BMT) for familial haemophagocytic lymphohistiocytosis (FHL). Six children aged from 1 to 18 months were transplanted with bone marrow from an HLA-identical sibling in five cases and from an HLA-nonidentical related donor (one mismatched HLA antigen) in one. The conditioning regiment included VP 16-213 (900 mg/m2), busulfan (16 mg/kg), cyclophosphamide (200 mg/kg) and, in one case, aracytine (2 g/m2). Four patients are alive without therapy more than 3 years after BMT; the other two relapsed 1 year after BMT. DNA was extracted from separated polymorphonuclear cells and mononuclear cells, as well as from separated E+ and E- cells in one case and CD16+ (natural killer) and CD16- cells in two cases. Engraftment was partial in the four long-term survivors. Recipient cells were largely predominant in three of them as well as in one of the patients who relapsed (the donor also developed FHL 18 months after BMT). E+, E-, CD16+ and CD16- cells presented the same pattern of chimaerism. Engraftment failed to occur in the patient who received an HLA-nonidentical bone marrow. These results indicate that partial engraftment is compatible with long-term remission of FHL and that the presence of a small proportion of cells of donor origin can prevent FHL-related lymphocyte and macrophage activation.