Quantification of mixed chimerism allows early therapeutic interventions

Hematopoietic stem cell transplantation is the curative option for patients with myelodys-plastic syndrome; however, it requires a long post-transplantation follow-up. A 53-year-oldwoman with a diagnosis of myelodysplastic syndrome underwent related donor allogeneichematopoietic stem cell transplantation in July 2006. Three months after transplanta-tion, a comparative short tandem repeat analysis between donor and recipient revealedfull chimerism, indicating complete, healthy bone marrow reconstitution. Three yearsand ten months after hematopoietic stem cell transplantation, the patient developedleukopenia and thrombocytopenia. Another short tandem repeat analysis was carried outwhich showed mixed chimerism (52.62%), indicating relapsed disease. A donor lymphocyteinfusion was administered. The purpose of donor lymphocyte infusion is to induce a graft-versus-leukemia effect; in fact, this donor’s lymphocyte infusion induced full chimerism.Successive short tandem repeat analyses were performed as part of post-transplantationfollow-up, and in July 2010, one such analysis again showed mixed chimerism (64.25%).Based on this finding, a second donor lymphocyte infusion was administered, but failedto eradicate the disease. In September 2011, the patient presented with relapsed dis-ease, and a second related donor allogeneic hematopoietic stem cell transplantationwas performed. Subsequent short tandem repeat analyses revealed full chimerism, indi-cating complete bone marrow reconstitution. We conclude that quantitative detectionof mixed chimerism is an important diagnostic tool that can guide early therapeuticintervention