Early Mixed Lymphoid Donor/Host Chimerism is Associated with Improved Transplant Outcome in Patients with Primary or Secondary Myelofibrosis.

ABSTRACT We investigated risk factors for the development of mixed chimerism in 131 patients transplanted for myelofibrosis and determined the impact of lymphoid (CD3+) and myeloid (CD33+) chimerism on transplant outcome. Disease risk included DIPSS plus categories low to high. The median patient age was 58 years. Patients were conditioned with high intensity (myeloablative) or low/reduced intensity (non-myeloablative) regimens and transplanted from related or unrelated donors. Mixed CD3+ chimerism was observed earlier after HCT, while CD33+ chimerism occurred later. Mixed chimerism was more frequent with low intensity than with high intensity regimens. Mixed CD3+ chimerism did not lead to graft failure and was associated with a reduced incidence of acute GVHD, and improved survival overall and relapse-free, while mixed CD33+ chimerism was associated with an increased relapse incidence and reduced overall and relapse-free survival, independent from the CD34+ cell dose transplanted. Thus, mixed CD3+ chimerism in patients with myelofibrosis had a favorable impact on transplant outcome and does not require therapeutic interventions.