Assessment of graft status following allogeneic bone marrow transplantation for haematological disorders in children using locus-specific minisatellite probes.

We have examined peripheral blood or bone marrow DNA following allogeneic bone marrow transplantation (BMT) in children suffering from a variety of haematological disorders. Using either locus-specific minisatellite probes separately or in combination with a Y specific probe for sex-mismatched transplants, complete haematological chimaerism, autologous reconstitution, or mixed chimaeric states have been defined immediately post-BMT. We have also been able to identify emerging autologous cells or relapse prior to morphological diagnosis. Forty-two children, mean age 6.4 years (range 9 months to 15 years), received an allogeneic BMT for: acute lymphoblastic leukaemia (ALL), n = 17; acute myeloid leukaemia (AML), n = 5; biphenotypic leukaemia, n = 1; myelodysplastic syndrome (MDS), n = 5; chronic granulocytic leukaemia (CGL), n = 1; severe aplastic anaemia (SAA), n = 7; familial erythrophagocytic lymphohistiocytosis (FEL), n = 2; beta thalassaemia major (beta thal), n = 1; and juvenile chronic myeloid leukaemia (JCML), n = 3. Immediately post-transplant, 78% had achieved complete haematological chimaerism, 12% had failed to engraft (DNA analysis confirmed autologous reconstitution) and 10% had mixed chimaerism. SAA was the underlying disease in two of the chimaeric cases, the third case having had a matched unrelated donor (MUD) BMT for MDS. In 3/4 cases which subsequently relapsed, DNA analysis showed re-emergence of autologous cells (indicative of relapse), prior to their morphological identification. We conclude that DNA analysis using minisatellite probes to assess graft status provides a useful contribution to patient management following allogeneic BMT.