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Dataset ID
Description
Technology
Samples
EGAD00001007851
Age-related loss of function in the human haematopoietic system is well documented, manifesting as reduced regenerative capacity, age-related cytopenias and immune dysfunction. However, the cellular and population level changes that underpin both this functional decline and the increased risk of clonal haematopoiesis and blood cancer in the elderly remain elusive. Here we performed whole genome sequencing on >3350 single haematopoietic stem cell / multipotent progenitors (HSC/MPP) derived colonies across 10 haematologically normal subjects aged 0 to 81. We found that HSC/MPPs accumulated 17 single nucleotide variants per year post birth and had a reduction in telomere length of 50bp per year throughout young adult life. We reconstructed phylogenies of the sampled HSC/MPPs to interrogate changes in clonal dynamics through life. Haematopoiesis in adults aged less than 65 was predominantly polyclonal, with few known driver mutations. In contrast, individuals aged over 75 displayed a profound change in clonal structure, with frequent clonal expansions, many unexplained by known driver mutations. The ratio of non-synonymous to synonymous mutations revealed widespread positive selection, estimating around 1000 driver mutations in the dataset (10-fold more than the number of known drivers). We identified novel genes ZNF318 and HIST2H3D as being under positive selection, despite not being enriched in myeloid malignancies. Our data show that HSC clonal dynamics is more complex than previously thought. One implication is that by old age, the majority of HSCs carry at least one of a number of largely undescribed driver mutations, which may underlie aspects of their functional decline.
HiSeq X Ten
Illumina NovaSeq 6000
3601
EGAD00001008107
A lymphocyte suffers many threats to its genome, including programmed mutation during differentiation, antigen-driven proliferation and residency in diverse microenvironments. After developing protocols for single-cell lymphocyte expansions, we sequenced whole genomes from 717 normal naive and memory B and T lymphocytes and hematopoietic stem cells. All lymphocyte subsets carried more point mutations and structural variants than haematopoietic stem cells – the extra mutations were mostly acquired during differentiation, with burdens higher in memory than naive lymphocytes, although T cells also had a higher rate of mutation accumulation throughout life. Off-target effects of immunological diversification accounted for most of the additional differentiation-associated mutations in lymphocytes. Memory B cells acquired, on average, 18 off-target mutations genome-wide for every one on-target IGV mutation during the germinal centre reaction. Structural variation was 16-fold higher in lymphocytes than stem cells, with ~15% of deletions being attributable to off-target RAG activity. Mutational processes associated with ultraviolet light exposure and other sporadic mutational processes generated hundreds to thousands of mutations in some memory lymphocytes. The mutation burden and signatures of normal B lymphocytes were broadly comparable to those seen in many B-cell cancers, suggesting that malignant transformation of lymphocytes arises from the same mutational processes active across normal ontogeny. The mutational landscape of normal lymphocytes chronicles the off-target effects of programmed genome engineering during immunological diversification and the consequences of differentiation, proliferation and residency in diverse microenvironments.
HiSeq X Ten
717
