Donor-derived mitochondrial DNA variant peptides elicit allo-specific immune response in transplant patients

Abstract BACKGROUND: Mitochondrial DNA (mtDNA) nonsynonymous single nucleotide variants (SNVs) between transplant donor stem cells and recipient trigger alloimmune responses and transplant rejection. Whether mt SNVs trigger alloimmune responses in solid organ transplantation remains unknown, particularly in the background of immunodominant human leukocyte antigens mismatches. This study characterizes mtDNA SNVs and tests if donor−derived mitochondrial peptides trigger alloimmune responses in solid-organ transplantation. METHODS: To count and compare SNVs between donor and recipient (D−R) lung transplant pairs (n = 163), mtDNA was isolated from pre−transplant D−R blood and sequenced. The number of SNVs was compared for D−R demographic groups. We identified nonsynonymous SNVs, constructed 20mer peptides with donor− or recipient−derived amino acid sequences, and used ELISpot assay to test allo−specific immune response by interferon gamma (IFNγ) release. To test if similar phenomena occur in other solid−organ transplants, we repeated the analyses in 19 heart transplant D−R pairs. RESULTS: We identified a median of 39 mtDNA SNVs (IQR= 32 − 53) per D-R lung transplant pair, of which a median of 6 (IQR = 4 − 9) SNVs were nonsynonymous. SNVs were predominantly located at MT−CYB, MT−ATP6, and MT−ND3 genes. The number of SNVs was higher in D−R race non-concordant pairs than in race−concordant pairs, p = 0.015. Donor-derived mt peptides triggered a 19.8−fold higher IFNγ release compared to recipient−derived peptide, p<0.001. Similar findings were observed in heart transplant patients. CONCLUSIONS: Donor−derived mitochondrial peptides trigger allo−specific immune responses after solid−organ transplantation.