Neither Donor nor Recipient Mitochondrial Haplotypes Are Associated with Unrelated Donor Transplant Outcomes: A Validation Study from the CIBMTR

Abstract

Graft-versus-host-disease (GVHD) is a multistep process that involves T-cell recognition and priming toward alloantigen, expansion, acquisition of effector function, and repeated tissue injury, resulting in clinical manifestations of the disease. All of these processes have considerable metabolic demands and understanding the key role of mitochondria in cellular metabolism as it relates to GVHD has increased significantly. Mitochondrial DNA (mtDNA) haplotypes have been linked to functional differences in vitro, suggesting they have functional differences at an organismal level. We previously used mtDNA typing to assess the impact of mtDNA haplotypes on outcomes of ~400 allo-HCT patients. This pilot study identified uncommon mtDNA haplotypes potentially associated with inferior outcomes. We sought to validate pilot findings of associations between donor and recipient mitochondrial haplotypes and transplant outcome. We examined a cohort of 4143 donor-recipient pairs obtained from the Center for International Blood and Marrow Transplant Research. MtDNA was extracted from whole blood or peripheral blood mononuclear cells from donors and recipients and sequenced to discern haplotype. We used multiple regression analysis to examine the independent association of mtDNA haplotype with overall survival and grade III-IV acute GVHD (aGVHD) adjusting for known risk factors for poor transplant outcome. Neither recipient nor donor mtDNA haplotype reached groupwise significance for overall survival (P =.26 and .39, respectively) or grade III-IV aGVHD (P = .68 and.57, respectively). Adjustment for genomically determined ancestry in the subset of donor-recipient pairs for which this was available did not materially change results. We conclude that our original finding was due to chance in a small sample size and that there is essentially no evidence that mtDNA haplotype or haplotype mismatch contributes to risk of serious outcomes after allogeneic transplantation.