Antigen receptor stimulation drives selection against pathogenic mtDNA variants that dysregulate lymphocyte responses

Pathogenic mitochondrial (mt)DNA molecules can exhibit heteroplasmy in single cells and cause a range of clinical phenotypes, although their contribution to immunity is poorly understood. Here, in mice carrying heteroplasmic C5024T in mt-tRNAAla - that impairs oxidative phosphorylation - we found a reduced mutation burden in peripheral T and B memory lymphocyte subsets, compared to their naive counterparts. Furthermore, selection diluting the mutation was induced in vitro by triggering T and B cell antigen receptors. While C5024T dysregulated naive CD8+ T cell respiration and metabolic remodeling post-activation, these phenotypes were partially ameliorated by selection. Analogous to mice, peripheral blood memory T and B lymphocyte subsets from human MELAS (Mitochondrial Encephalomyopathy with Lactic Acidosis and Stroke-like episodes) patients - carrying heteroplasmic A3243G in mt-tRNALeu - displayed a reduced mutation burden, compared to naive cells. In both humans and mice, mtDNA selection was observed in IgG+ antigen-specific B cells after SARS-CoV-2 Spike vaccination, illustrating an on-going process in vivo. Taken together, these data illustrate purifying selection of pathogenic mtDNA variants during the oxidative phosphorylation checkpoints of the naive-memory lymphocyte transition. HighlightsO_LIIn human MELAS patients (A3243G in mt-tRNALeu) and a related mouse model (C5024T in mt-tRNAAla), T and B memory subsets displayed a reduced mtDNA mutation burden compared to their naive counterparts. C_LIO_LISelection was observed in antigen-specific IgG+ B cells after SARS-CoV-2 Spike protein vaccination. C_LIO_LIT and B cell antigen receptor stimulation triggered purifying selection in vitro, facilitating mechanistic studies of mtDNA selection. C_LIO_LIHeteroplasmic pathogenic mutations in mtDNA dysregulated metabolic remodeling after lymphocyte activation and reduced macrophage OXPHOS capacity. C_LI