P015 Bone marrow donor selection in the presence of both allogeneic and syngeneic donors

Syngeneic transplants provide an interesting dilemma with respect to donor selection. The risk of relapse is higher for patients with AML undergoing syngeneic transplant vs. HLA-matched sibling transplant, however, rates of graft versus host disease and transplant related mortality have historically been lower with syngeneic transplants. Thus, HLA -matched sibling donors are preferred to identical twin donors for patients undergoing transplant for malignant diseases (ie. AML) to optimize the impact of graft vs. leukemia (GvL) whereas identical twin donors are ideal for non-malignant disorders. We present a patient with AML who had both an HLA matched sibling donor as well as an identical twin. He was initially transplanted with the HLA matched sibling donor successfully however, at 6 months post transplant he developed severe neutropenia (ANC = 0). Chimerism studies revealed 95% DNA from the related donor T cells at this time. The cause of his neutropenia was autoimmune in nature and refractory to multiple immunosuppressive medications and therefore he underwent a second transplant this time using his identical twin as the donor. The patient’s neutrophils engrafted and he has undergone a complete recovery post transplant. Chimerism studies after the second transplant reveal that 85% of the DNA is from the second donor’s T cells. Typically, chimerism studies with syngeneic transplant are not helpful as the patient and donor are identical. However in this case, chimerism studies were possible to determine the engraftment of the initial related donor to the patient/twin. This case illustrates that optimal donor selection depends on disease when an identical twin and an HLA matched sibling donor are available. It also showcases the interesting results of chimerism testing in a patient who has received both an allogeneic and a syngeneic transplant.