Phased epigenetic fragility and stability accelerate the genetic evolution of B-cells

Non-genetic heterogeneity can provide population robustness when responding to threats or making developmental decisions, but when the biological process rests on specific individuals (tissue-resident macrophages or genetic evolution), non-genetic heterogeneity degrades performance. Vaccine responses depend on the Darwinian evolution of B-cells to generate high-affinity, genetically-encoded antibodies, yet B-cell decision-making is non-genetically variable. In fact, B-cell epigenetic states are fragile during selection but stable during the proliferation burst. Here we report that the iterative dynamics of epigenetic fragility and stability of B-cell fate decisions do not impair but accelerate affinity maturation, by modulating the generation and removal of high-affinity outliers on a fitness landscape that is non-monotonic defined not only by survival/proliferation but plasma cell differentiation. These insights reconcile classical B-cell clonal selection theory with experimentally observed dynamics of epigenetic variability. The resulting model correctly predicts emergent vaccine response properties in alternate mouse strains and may contribute to personalized vaccination strategies.