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

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Abstract
Summary. 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 longterm remission of FHL and that the presence of a small proportion of cells of donor origin can prevent FHL‐related lymphocyte and macrophage activation.