Abstract 600: Lower T-lymphocyte mitochondrial DNA copy number is associated with graft versus host disease in patients undergoing hematopoietic cell transplantation
Authors: Thyagarajan Bharat , Shanley Ryan , Prakash Pallavi , Barcelo Helene , Ross Julie A. , Verneris Michael R. , Arora Mukta 
Published: August 2015

Background: Graft-versus-host disease (GvHD) continues to be a major cause of transplant related mortality, morbidity and decreased quality of life post allogeneic hematopoietic cell transplant (HCT). Despite extensive use of histocompatibility antigen (HLA) matching between patients and donors and a variety of prophylactic regimens, the rates of GvHD have not declined substantially over the last decade. Recent studies have shown mitochondrial reactive oxygen species (ROS) plays an important role in T lymphocyte activation and initiation of the inflammatory response and represents a novel biological pathway that influences GvHD risk. We hypothesized that lower mitochondrial DNA (mtDNA) copy number that increases ROS related oxidative damage will be associated with acute and chronic GvHD.

Methods: In a cohort of 201 patients who underwent allogeneic HCT for treatment of hematologic malignancies at the University of Minnesota between 2009 and 2012, we evaluated the association between donor post HCT mtDNA copy number at 7 time points (days 21, 28, 60, 100, 180, 365 and 730) and acute and chronic GvHD. Recipient blood was separated into CD3+ (T-lymphocytes) and CD15+ (neutrophil) fractions at each time point using magnetic bead separation. All recipients had 100% donor engraftment at the various time points for inclusion in the study. We used a quantitative real time PCR method, comparing the number of copies of the mitochondria- specific gene (ND1) to the number of copies of a nuclear gene (18s) to estimate mtDNA copy number. We used a linear mixed model adjusting for fixed effects of donor type (sibling, unrelated and cord blood donors), donor age, the interaction of GVHD status with time, and random effects for subject and assay run number. The outcome (CD3+/CD15+ mtDNA copy number) was log-transformed to improve model fit and normalize residual variance.

Results: Overall CD3+ mtDNA copy number was lower among patients with grade II-IV acute GvHD (n = 90) as compared to those without acute GvHD (n = 79) (2.03 vs. 2.18, respectively; p = 0.02), while there were no significant differences in CD15+ mtDNA copy number between the two groups (p = 0.49). Similarly, CD3+ mtDNA copy number was lower among patients with chronic GvHD (n = 43) as compared to those without chronic GvHD (n = 79) (1.82 vs. 2.24, respectively; p = 0.01) while there were no significant differences in CD15+ mtDNA copy number between the two groups (p = 0.47).

Conclusion: Our study shows that mtDNA is decreased in acute and chronic GVHD compared to transplant recipients without this complication, providing preliminary evidence that mtDNA copy number may serve as a biomarker for early detection and monitoring of GvHD. Future studies that evaluate the significance of altered mtDNA copy number on T lymphocyte function and ROS are needed to evaluate the utility of novel mt-based interventions for treatment of GvHD.

Citation Format: Bharat Thyagarajan, Ryan Shanley, Pallavi Prakash, Helene Barcelo, Julie A. Ross, Michael R. Verneris, Mukta Arora. Lower T-lymphocyte mitochondrial DNA copy number is associated with graft versus host disease in patients undergoing hematopoietic cell transplantation. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 600. doi:10.1158/1538-7445.AM2015-600