The evolution of polyclonal competition in aging hematopoiesis.

Abstract

Clonal hematopoiesis (CH) - the expansion of genetic variants in blood - is a prime example of somatic evolution. Although it often precedes malignant transformation, many aspects of this process remain unknown. We show that a model of polyclonal competition, in which selectively-advantaged clones continually appear and compete, explains observed CH dynamics throughout human life. We quantify the fitness distribution and occurrence rate of clonal expansions using either variant trajectories or HSC genetic heterogeneity. Inferences on both data converge. Approximately three fit clones enter the HSC pool per year, yet rarely more than five achieve >1.5% frequency throughout life. The fittest clones emerge predominantly later in life in accordance with a multistep evolutionary process. DNMT3A-variants were enriched for single-hit clones, whereas TET2, ASXL1, JAK2, SF3B1, and SRSF2 showed enrichment for multi-hit evolution. These findings suggest precursors of hematological malignancies are identifiable prior to transformation and may facilitate early intervention strategies.