The use of locus-specific minisatellite probes to check engraftment following allogeneic bone marrow transplantation for severe combined immunodeficiency disease.

The graft status of 14 patients, 13 of whom had received an allogeneic bone marrow transplant (BMT) for severe combined immunodeficiency disease (SCID) and one patient with SCID in whom intrauterine maternal engraftment was suspected, was examined using bone marrow or peripheral blood DNA and a combination of locus-specific minisatellite probes for the sex-matched and locus-specific and a Y specific probe for the sex-mismatched patients. The sensitivity of the assay systems was such that less than 0.1% recipient DNA was detectable in a background of donor DNA. Graft status could be satisfactorily documented by 2.5 weeks post-transplant and in one case was of particular value as immunological parameters were misleading. In the six long-term survivors of allogeneic BMT for SCID, the use of the locus-specific probes showed total donor lymphoid and myeloid haemopoietic engraftment in five cases and mixed host/donor populations in one case. The diagnosis in approximately 10% of cases of SCID may prove difficult due to engraftment of the fetus by maternal cells. Diagnosis may be facilitated by the use of the locus specific minisatellite probes and indeed we found specific evidence for such maternal engraftment in one patient at presentation. The combination of these probes together with a Y specific probe thus provides a rapid and accurate method of assessing graft take following allogeneic BMT for SCID. The simple pattern of inheritance obtained and the high level of sensitivity of detection of low numbers of allogeneic cells make the techniques amenable for use in any routine DNA diagnostic laboratory.